compiler, runtime: replace hashmap code with Go 1.7 hashmap

[official-gcc.git] / gcc / go / gofrontend / gogo.cc

// gogo.cc -- Go frontend parsed representation.

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "go-system.h"

#include <fstream>

#include "filenames.h"

#include "go-c.h"
#include "go-dump.h"
#include "go-optimize.h"
#include "lex.h"
#include "types.h"
#include "statements.h"
#include "expressions.h"
#include "runtime.h"
#include "import.h"
#include "export.h"
#include "backend.h"
#include "gogo.h"

// Class Gogo.

Gogo::Gogo(Backend* backend, Linemap* linemap, int, int pointer_size)
  : backend_(backend),
    linemap_(linemap),
    package_(NULL),
    functions_(),
    globals_(new Bindings(NULL)),
    file_block_names_(),
    imports_(),
    imported_unsafe_(false),
    current_file_imported_unsafe_(false),
    packages_(),
    init_functions_(),
    var_deps_(),
    need_init_fn_(false),
    init_fn_name_(),
    imported_init_fns_(),
    pkgpath_(),
    pkgpath_symbol_(),
    prefix_(),
    pkgpath_set_(false),
    pkgpath_from_option_(false),
    prefix_from_option_(false),
    relative_import_path_(),
    verify_types_(),
    interface_types_(),
    specific_type_functions_(),
    specific_type_functions_are_written_(false),
    named_types_are_converted_(false)
{
  const Location loc = Linemap::predeclared_location();

  Named_type* uint8_type = Type::make_integer_type("uint8", true, 8,
                                                   RUNTIME_TYPE_KIND_UINT8);
  this->add_named_type(uint8_type);
  this->add_named_type(Type::make_integer_type("uint16", true,  16,
                                               RUNTIME_TYPE_KIND_UINT16));
  this->add_named_type(Type::make_integer_type("uint32", true,  32,
                                               RUNTIME_TYPE_KIND_UINT32));
  this->add_named_type(Type::make_integer_type("uint64", true,  64,
                                               RUNTIME_TYPE_KIND_UINT64));

  this->add_named_type(Type::make_integer_type("int8",  false,   8,
                                               RUNTIME_TYPE_KIND_INT8));
  this->add_named_type(Type::make_integer_type("int16", false,  16,
                                               RUNTIME_TYPE_KIND_INT16));
  Named_type* int32_type = Type::make_integer_type("int32", false,  32,
                                                   RUNTIME_TYPE_KIND_INT32);
  this->add_named_type(int32_type);
  this->add_named_type(Type::make_integer_type("int64", false,  64,
                                               RUNTIME_TYPE_KIND_INT64));

  this->add_named_type(Type::make_float_type("float32", 32,
                                             RUNTIME_TYPE_KIND_FLOAT32));
  this->add_named_type(Type::make_float_type("float64", 64,
                                             RUNTIME_TYPE_KIND_FLOAT64));

  this->add_named_type(Type::make_complex_type("complex64", 64,
                                               RUNTIME_TYPE_KIND_COMPLEX64));
  this->add_named_type(Type::make_complex_type("complex128", 128,
                                               RUNTIME_TYPE_KIND_COMPLEX128));

  int int_type_size = pointer_size;
  if (int_type_size < 32)
    int_type_size = 32;
  this->add_named_type(Type::make_integer_type("uint", true,
                                               int_type_size,
                                               RUNTIME_TYPE_KIND_UINT));
  Named_type* int_type = Type::make_integer_type("int", false, int_type_size,
                                                 RUNTIME_TYPE_KIND_INT);
  this->add_named_type(int_type);

  this->add_named_type(Type::make_integer_type("uintptr", true,
                                               pointer_size,
                                               RUNTIME_TYPE_KIND_UINTPTR));

  // "byte" is an alias for "uint8".
  uint8_type->integer_type()->set_is_byte();
  Named_object* byte_type = Named_object::make_type("byte", NULL, uint8_type,
                                                    loc);
  this->add_named_type(byte_type->type_value());

  // "rune" is an alias for "int32".
  int32_type->integer_type()->set_is_rune();
  Named_object* rune_type = Named_object::make_type("rune", NULL, int32_type,
                                                    loc);
  this->add_named_type(rune_type->type_value());

  this->add_named_type(Type::make_named_bool_type());

  this->add_named_type(Type::make_named_string_type());

  // "error" is interface { Error() string }.
  {
    Typed_identifier_list *methods = new Typed_identifier_list;
    Typed_identifier_list *results = new Typed_identifier_list;
    results->push_back(Typed_identifier("", Type::lookup_string_type(), loc));
    Type *method_type = Type::make_function_type(NULL, NULL, results, loc);
    methods->push_back(Typed_identifier("Error", method_type, loc));
    Interface_type *error_iface = Type::make_interface_type(methods, loc);
    error_iface->finalize_methods();
    Named_type *error_type = Named_object::make_type("error", NULL, error_iface, loc)->type_value();
    this->add_named_type(error_type);
  }

  this->globals_->add_constant(Typed_identifier("true",
                                                Type::make_boolean_type(),
                                                loc),
                               NULL,
                               Expression::make_boolean(true, loc),
                               0);
  this->globals_->add_constant(Typed_identifier("false",
                                                Type::make_boolean_type(),
                                                loc),
                               NULL,
                               Expression::make_boolean(false, loc),
                               0);

  this->globals_->add_constant(Typed_identifier("nil", Type::make_nil_type(),
                                                loc),
                               NULL,
                               Expression::make_nil(loc),
                               0);

  Type* abstract_int_type = Type::make_abstract_integer_type();
  this->globals_->add_constant(Typed_identifier("iota", abstract_int_type,
                                                loc),
                               NULL,
                               Expression::make_iota(),
                               0);

  Function_type* new_type = Type::make_function_type(NULL, NULL, NULL, loc);
  new_type->set_is_varargs();
  new_type->set_is_builtin();
  this->globals_->add_function_declaration("new", NULL, new_type, loc);

  Function_type* make_type = Type::make_function_type(NULL, NULL, NULL, loc);
  make_type->set_is_varargs();
  make_type->set_is_builtin();
  this->globals_->add_function_declaration("make", NULL, make_type, loc);

  Typed_identifier_list* len_result = new Typed_identifier_list();
  len_result->push_back(Typed_identifier("", int_type, loc));
  Function_type* len_type = Type::make_function_type(NULL, NULL, len_result,
                                                     loc);
  len_type->set_is_builtin();
  this->globals_->add_function_declaration("len", NULL, len_type, loc);

  Typed_identifier_list* cap_result = new Typed_identifier_list();
  cap_result->push_back(Typed_identifier("", int_type, loc));
  Function_type* cap_type = Type::make_function_type(NULL, NULL, len_result,
                                                     loc);
  cap_type->set_is_builtin();
  this->globals_->add_function_declaration("cap", NULL, cap_type, loc);

  Function_type* print_type = Type::make_function_type(NULL, NULL, NULL, loc);
  print_type->set_is_varargs();
  print_type->set_is_builtin();
  this->globals_->add_function_declaration("print", NULL, print_type, loc);

  print_type = Type::make_function_type(NULL, NULL, NULL, loc);
  print_type->set_is_varargs();
  print_type->set_is_builtin();
  this->globals_->add_function_declaration("println", NULL, print_type, loc);

  Type *empty = Type::make_empty_interface_type(loc);
  Typed_identifier_list* panic_parms = new Typed_identifier_list();
  panic_parms->push_back(Typed_identifier("e", empty, loc));
  Function_type *panic_type = Type::make_function_type(NULL, panic_parms,
                                                       NULL, loc);
  panic_type->set_is_builtin();
  this->globals_->add_function_declaration("panic", NULL, panic_type, loc);

  Typed_identifier_list* recover_result = new Typed_identifier_list();
  recover_result->push_back(Typed_identifier("", empty, loc));
  Function_type* recover_type = Type::make_function_type(NULL, NULL,
                                                         recover_result,
                                                         loc);
  recover_type->set_is_builtin();
  this->globals_->add_function_declaration("recover", NULL, recover_type, loc);

  Function_type* close_type = Type::make_function_type(NULL, NULL, NULL, loc);
  close_type->set_is_varargs();
  close_type->set_is_builtin();
  this->globals_->add_function_declaration("close", NULL, close_type, loc);

  Typed_identifier_list* copy_result = new Typed_identifier_list();
  copy_result->push_back(Typed_identifier("", int_type, loc));
  Function_type* copy_type = Type::make_function_type(NULL, NULL,
                                                      copy_result, loc);
  copy_type->set_is_varargs();
  copy_type->set_is_builtin();
  this->globals_->add_function_declaration("copy", NULL, copy_type, loc);

  Function_type* append_type = Type::make_function_type(NULL, NULL, NULL, loc);
  append_type->set_is_varargs();
  append_type->set_is_builtin();
  this->globals_->add_function_declaration("append", NULL, append_type, loc);

  Function_type* complex_type = Type::make_function_type(NULL, NULL, NULL, loc);
  complex_type->set_is_varargs();
  complex_type->set_is_builtin();
  this->globals_->add_function_declaration("complex", NULL, complex_type, loc);

  Function_type* real_type = Type::make_function_type(NULL, NULL, NULL, loc);
  real_type->set_is_varargs();
  real_type->set_is_builtin();
  this->globals_->add_function_declaration("real", NULL, real_type, loc);

  Function_type* imag_type = Type::make_function_type(NULL, NULL, NULL, loc);
  imag_type->set_is_varargs();
  imag_type->set_is_builtin();
  this->globals_->add_function_declaration("imag", NULL, imag_type, loc);

  Function_type* delete_type = Type::make_function_type(NULL, NULL, NULL, loc);
  delete_type->set_is_varargs();
  delete_type->set_is_builtin();
  this->globals_->add_function_declaration("delete", NULL, delete_type, loc);
}

// Convert a pkgpath into a string suitable for a symbol.  Note that
// this transformation is convenient but imperfect.  A -fgo-pkgpath
// option of a/b_c will conflict with a -fgo-pkgpath option of a_b/c,
// possibly leading to link time errors.

std::string
Gogo::pkgpath_for_symbol(const std::string& pkgpath)
{
  std::string s = pkgpath;
  for (size_t i = 0; i < s.length(); ++i)
    {
      char c = s[i];
      if ((c >= 'a' && c <= 'z')
          || (c >= 'A' && c <= 'Z')
          || (c >= '0' && c <= '9'))
        ;
      else
        s[i] = '_';
    }
  return s;
}

// Get the package path to use for type reflection data.  This should
// ideally be unique across the entire link.

const std::string&
Gogo::pkgpath() const
{
  go_assert(this->pkgpath_set_);
  return this->pkgpath_;
}

// Set the package path from the -fgo-pkgpath command line option.

void
Gogo::set_pkgpath(const std::string& arg)
{
  go_assert(!this->pkgpath_set_);
  this->pkgpath_ = arg;
  this->pkgpath_set_ = true;
  this->pkgpath_from_option_ = true;
}

// Get the package path to use for symbol names.

const std::string&
Gogo::pkgpath_symbol() const
{
  go_assert(this->pkgpath_set_);
  return this->pkgpath_symbol_;
}

// Set the unique prefix to use to determine the package path, from
// the -fgo-prefix command line option.

void
Gogo::set_prefix(const std::string& arg)
{
  go_assert(!this->prefix_from_option_);
  this->prefix_ = arg;
  this->prefix_from_option_ = true;
}

// Munge name for use in an error message.

std::string
Gogo::message_name(const std::string& name)
{
  return go_localize_identifier(Gogo::unpack_hidden_name(name).c_str());
}

// Get the package name.

const std::string&
Gogo::package_name() const
{
  go_assert(this->package_ != NULL);
  return this->package_->package_name();
}

// Set the package name.

void
Gogo::set_package_name(const std::string& package_name,
                       Location location)
{
  if (this->package_ != NULL)
    {
      if (this->package_->package_name() != package_name)
        error_at(location, "expected package %<%s%>",
                 Gogo::message_name(this->package_->package_name()).c_str());
      return;
    }

  // Now that we know the name of the package we are compiling, set
  // the package path to use for reflect.Type.PkgPath and global
  // symbol names.
  if (this->pkgpath_set_)
    this->pkgpath_symbol_ = Gogo::pkgpath_for_symbol(this->pkgpath_);
  else
    {
      if (!this->prefix_from_option_ && package_name == "main")
        {
          this->pkgpath_ = package_name;
          this->pkgpath_symbol_ = Gogo::pkgpath_for_symbol(package_name);
        }
      else
        {
          if (!this->prefix_from_option_)
            this->prefix_ = "go";
          this->pkgpath_ = this->prefix_ + '.' + package_name;
          this->pkgpath_symbol_ = (Gogo::pkgpath_for_symbol(this->prefix_) + '.'
                                   + Gogo::pkgpath_for_symbol(package_name));
        }
      this->pkgpath_set_ = true;
    }

  this->package_ = this->register_package(this->pkgpath_,
                                          this->pkgpath_symbol_, location);
  this->package_->set_package_name(package_name, location);

  if (this->is_main_package())
    {
      // Declare "main" as a function which takes no parameters and
      // returns no value.
      Location uloc = Linemap::unknown_location();
      this->declare_function(Gogo::pack_hidden_name("main", false),
                             Type::make_function_type (NULL, NULL, NULL, uloc),
                             uloc);
    }
}

// Return whether this is the "main" package.  This is not true if
// -fgo-pkgpath or -fgo-prefix was used.

bool
Gogo::is_main_package() const
{
  return (this->package_name() == "main"
          && !this->pkgpath_from_option_
          && !this->prefix_from_option_);
}

// Import a package.

void
Gogo::import_package(const std::string& filename,
                     const std::string& local_name,
                     bool is_local_name_exported,
                     Location location)
{
  if (filename.empty())
    {
      error_at(location, "import path is empty");
      return;
    }

  const char *pf = filename.data();
  const char *pend = pf + filename.length();
  while (pf < pend)
    {
      unsigned int c;
      int adv = Lex::fetch_char(pf, &c);
      if (adv == 0)
        {
          error_at(location, "import path contains invalid UTF-8 sequence");
          return;
        }
      if (c == '\0')
        {
          error_at(location, "import path contains NUL");
          return;
        }
      if (c < 0x20 || c == 0x7f)
        {
          error_at(location, "import path contains control character");
          return;
        }
      if (c == '\\')
        {
          error_at(location, "import path contains backslash; use slash");
          return;
        }
      if (Lex::is_unicode_space(c))
        {
          error_at(location, "import path contains space character");
          return;
        }
      if (c < 0x7f && strchr("!\"#$%&'()*,:;<=>?[]^`{|}", c) != NULL)
        {
          error_at(location, "import path contains invalid character '%c'", c);
          return;
        }
      pf += adv;
    }

  if (IS_ABSOLUTE_PATH(filename.c_str()))
    {
      error_at(location, "import path cannot be absolute path");
      return;
    }

  if (local_name == "init")
    error_at(location, "cannot import package as init");

  if (filename == "unsafe")
    {
      this->import_unsafe(local_name, is_local_name_exported, location);
      this->current_file_imported_unsafe_ = true;
      return;
    }

  Imports::const_iterator p = this->imports_.find(filename);
  if (p != this->imports_.end())
    {
      Package* package = p->second;
      package->set_location(location);
      std::string ln = local_name;
      bool is_ln_exported = is_local_name_exported;
      if (ln.empty())
        {
          ln = package->package_name();
          go_assert(!ln.empty());
          is_ln_exported = Lex::is_exported_name(ln);
        }
      if (ln == "_")
        ;
      else if (ln == ".")
        {
          Bindings* bindings = package->bindings();
          for (Bindings::const_declarations_iterator p =
                 bindings->begin_declarations();
               p != bindings->end_declarations();
               ++p)
            this->add_dot_import_object(p->second);
          std::string dot_alias = "." + package->package_name();
          package->add_alias(dot_alias, location);
        }
      else
        {
          package->add_alias(ln, location);
          ln = this->pack_hidden_name(ln, is_ln_exported);
          this->package_->bindings()->add_package(ln, package);
        }
      return;
    }

  Import::Stream* stream = Import::open_package(filename, location,
                                                this->relative_import_path_);
  if (stream == NULL)
    {
      error_at(location, "import file %qs not found", filename.c_str());
      return;
    }

  Import imp(stream, location);
  imp.register_builtin_types(this);
  Package* package = imp.import(this, local_name, is_local_name_exported);
  if (package != NULL)
    {
      if (package->pkgpath() == this->pkgpath())
        error_at(location,
                 ("imported package uses same package path as package "
                  "being compiled (see -fgo-pkgpath option)"));

      this->imports_.insert(std::make_pair(filename, package));
    }

  delete stream;
}

Import_init *
Gogo::lookup_init(const std::string& init_name)
{
  Import_init tmp("", init_name, -1);
  Import_init_set::iterator it = this->imported_init_fns_.find(&tmp);
  return (it != this->imported_init_fns_.end()) ? *it : NULL;
}

// Add an import control function for an imported package to the list.

void
Gogo::add_import_init_fn(const std::string& package_name,
                         const std::string& init_name, int prio)
{
  for (Import_init_set::iterator p =
         this->imported_init_fns_.begin();
       p != this->imported_init_fns_.end();
       ++p)
    {
      Import_init *ii = (*p);
      if (ii->init_name() == init_name)
        {
          // If a test of package P1, built as part of package P1,
          // imports package P2, and P2 imports P1 (perhaps
          // indirectly), then we will see the same import name with
          // different import priorities.  That is OK, so don't give
          // an error about it.
          if (ii->package_name() != package_name)
            {
              error("duplicate package initialization name %qs",
                    Gogo::message_name(init_name).c_str());
              inform(UNKNOWN_LOCATION, "used by package %qs",
                     Gogo::message_name(ii->package_name()).c_str());
              inform(UNKNOWN_LOCATION, " and by package %qs",
                     Gogo::message_name(package_name).c_str());
            }
          ii->set_priority(prio);
          return;
        }
    }

  Import_init* nii = new Import_init(package_name, init_name, prio);
  this->imported_init_fns_.insert(nii);
}

// Return whether we are at the global binding level.

bool
Gogo::in_global_scope() const
{
  return this->functions_.empty();
}

// Return the current binding contour.

Bindings*
Gogo::current_bindings()
{
  if (!this->functions_.empty())
    return this->functions_.back().blocks.back()->bindings();
  else if (this->package_ != NULL)
    return this->package_->bindings();
  else
    return this->globals_;
}

const Bindings*
Gogo::current_bindings() const
{
  if (!this->functions_.empty())
    return this->functions_.back().blocks.back()->bindings();
  else if (this->package_ != NULL)
    return this->package_->bindings();
  else
    return this->globals_;
}

void
Gogo::update_init_priority(Import_init* ii,
                           std::set<const Import_init *>* visited)
{
  visited->insert(ii);
  int succ_prior = -1;

  for (std::set<std::string>::const_iterator pci =
           ii->precursors().begin();
       pci != ii->precursors().end();
       ++pci)
    {
      Import_init* succ = this->lookup_init(*pci);
      if (visited->find(succ) == visited->end())
        update_init_priority(succ, visited);
      succ_prior = std::max(succ_prior, succ->priority());
    }
  if (ii->priority() <= succ_prior)
    ii->set_priority(succ_prior + 1);
}

void
Gogo::recompute_init_priorities()
{
  std::set<Import_init *> nonroots;

  for (Import_init_set::const_iterator p =
           this->imported_init_fns_.begin();
       p != this->imported_init_fns_.end();
       ++p)
    {
      const Import_init *ii = *p;
      for (std::set<std::string>::const_iterator pci =
               ii->precursors().begin();
           pci != ii->precursors().end();
           ++pci)
        {
          Import_init* ii = this->lookup_init(*pci);
          nonroots.insert(ii);
        }
    }

  // Recursively update priorities starting at roots.
  std::set<const Import_init*> visited;
  for (Import_init_set::iterator p =
           this->imported_init_fns_.begin();
       p != this->imported_init_fns_.end();
       ++p)
    {
      Import_init* ii = *p;
      if (nonroots.find(ii) != nonroots.end())
        continue;
      update_init_priority(ii, &visited);
    }
}

// Add statements to INIT_STMTS which run the initialization
// functions for imported packages.  This is only used for the "main"
// package.

void
Gogo::init_imports(std::vector<Bstatement*>& init_stmts)
{
  go_assert(this->is_main_package());

  if (this->imported_init_fns_.empty())
    return;

  Location unknown_loc = Linemap::unknown_location();
  Function_type* func_type =
      Type::make_function_type(NULL, NULL, NULL, unknown_loc);
  Btype* fntype = func_type->get_backend_fntype(this);

  // Recompute init priorities based on a walk of the init graph.
  recompute_init_priorities();

  // We must call them in increasing priority order.
  std::vector<const Import_init*> v;
  for (Import_init_set::const_iterator p =
         this->imported_init_fns_.begin();
       p != this->imported_init_fns_.end();
       ++p)
    v.push_back(*p);
  std::sort(v.begin(), v.end(), priority_compare);

  // We build calls to the init functions, which take no arguments.
  std::vector<Bexpression*> empty_args;
  for (std::vector<const Import_init*>::const_iterator p = v.begin();
       p != v.end();
       ++p)
    {
      const Import_init* ii = *p;
      std::string user_name = ii->package_name() + ".init";
      const std::string& init_name(ii->init_name());

      Bfunction* pfunc = this->backend()->function(fntype, user_name, init_name,
                                                   true, true, true, false,
                                                   false, unknown_loc);
      Bexpression* pfunc_code =
          this->backend()->function_code_expression(pfunc, unknown_loc);
      Bexpression* pfunc_call =
        this->backend()->call_expression(pfunc_code, empty_args,
                                         NULL, unknown_loc);
      init_stmts.push_back(this->backend()->expression_statement(pfunc_call));
    }
}

// Register global variables with the garbage collector.  We need to
// register all variables which can hold a pointer value.  They become
// roots during the mark phase.  We build a struct that is easy to
// hook into a list of roots.

// struct __go_gc_root_list
// {
//   struct __go_gc_root_list* __next;
//   struct __go_gc_root
//   {
//     void* __decl;
//     size_t __size;
//   } __roots[];
// };

// The last entry in the roots array has a NULL decl field.

void
Gogo::register_gc_vars(const std::vector<Named_object*>& var_gc,
                       std::vector<Bstatement*>& init_stmts)
{
  if (var_gc.empty())
    return;

  Type* pvt = Type::make_pointer_type(Type::make_void_type());
  Type* uint_type = Type::lookup_integer_type("uint");
  Struct_type* root_type = Type::make_builtin_struct_type(2,
                                                          "__decl", pvt,
                                                          "__size", uint_type);

  Location builtin_loc = Linemap::predeclared_location();
  Expression* length = Expression::make_integer_ul(var_gc.size(), NULL,
                                                   builtin_loc);

  Array_type* root_array_type = Type::make_array_type(root_type, length);
  Type* ptdt = Type::make_type_descriptor_ptr_type();
  Struct_type* root_list_type =
      Type::make_builtin_struct_type(2,
                                     "__next", ptdt,
                                     "__roots", root_array_type);

  // Build an initializer for the __roots array.

  Expression_list* roots_init = new Expression_list();

  size_t i = 0;
  for (std::vector<Named_object*>::const_iterator p = var_gc.begin();
       p != var_gc.end();
       ++p, ++i)
    {
      Expression_list* init = new Expression_list();

      Location no_loc = (*p)->location();
      Expression* decl = Expression::make_var_reference(*p, no_loc);
      Expression* decl_addr =
          Expression::make_unary(OPERATOR_AND, decl, no_loc);
      init->push_back(decl_addr);

      Expression* decl_size =
          Expression::make_type_info(decl->type(), Expression::TYPE_INFO_SIZE);
      init->push_back(decl_size);

      Expression* root_ctor =
          Expression::make_struct_composite_literal(root_type, init, no_loc);
      roots_init->push_back(root_ctor);
    }

  // The list ends with a NULL entry.

  Expression_list* null_init = new Expression_list();
  Expression* nil = Expression::make_nil(builtin_loc);
  null_init->push_back(nil);

  Expression *zero = Expression::make_integer_ul(0, NULL, builtin_loc);
  null_init->push_back(zero);

  Expression* null_root_ctor =
      Expression::make_struct_composite_literal(root_type, null_init,
                                                builtin_loc);
  roots_init->push_back(null_root_ctor);

  // Build a constructor for the struct.

  Expression_list* root_list_init = new Expression_list();
  root_list_init->push_back(nil);

  Expression* roots_ctor =
      Expression::make_array_composite_literal(root_array_type, roots_init,
                                               builtin_loc);
  root_list_init->push_back(roots_ctor);

  Expression* root_list_ctor =
      Expression::make_struct_composite_literal(root_list_type, root_list_init,
                                                builtin_loc);

  Expression* root_addr = Expression::make_unary(OPERATOR_AND, root_list_ctor,
                                                 builtin_loc);
  root_addr->unary_expression()->set_is_gc_root();
  Expression* register_roots = Runtime::make_call(Runtime::REGISTER_GC_ROOTS,
                                                  builtin_loc, 1, root_addr);

  Translate_context context(this, NULL, NULL, NULL);
  Bexpression* bcall = register_roots->get_backend(&context);
  init_stmts.push_back(this->backend()->expression_statement(bcall));
}

// Get the name to use for the import control function.  If there is a
// global function or variable, then we know that that name must be
// unique in the link, and we use it as the basis for our name.

const std::string&
Gogo::get_init_fn_name()
{
  if (this->init_fn_name_.empty())
    {
      go_assert(this->package_ != NULL);
      if (this->is_main_package())
        {
          // Use a name which the runtime knows.
          this->init_fn_name_ = "__go_init_main";
        }
      else
        {
          std::string s = this->pkgpath_symbol();
          s.append("..import");
          this->init_fn_name_ = s;
        }
    }

  return this->init_fn_name_;
}

// Build the decl for the initialization function.

Named_object*
Gogo::initialization_function_decl()
{
  std::string name = this->get_init_fn_name();
  Location loc = this->package_->location();

  Function_type* fntype = Type::make_function_type(NULL, NULL, NULL, loc);
  Function* initfn = new Function(fntype, NULL, NULL, loc);
  return Named_object::make_function(name, NULL, initfn);
}

// Create the magic initialization function.  CODE_STMT is the
// code that it needs to run.

Named_object*
Gogo::create_initialization_function(Named_object* initfn,
                                     Bstatement* code_stmt)
{
  // Make sure that we thought we needed an initialization function,
  // as otherwise we will not have reported it in the export data.
  go_assert(this->is_main_package() || this->need_init_fn_);

  if (initfn == NULL)
    initfn = this->initialization_function_decl();

  // Bind the initialization function code to a block.
  Bfunction* fndecl = initfn->func_value()->get_or_make_decl(this, initfn);
  Location pkg_loc = this->package_->location();
  std::vector<Bvariable*> vars;
  this->backend()->block(fndecl, NULL, vars, pkg_loc, pkg_loc);

  if (!this->backend()->function_set_body(fndecl, code_stmt))
    {
      go_assert(saw_errors());
      return NULL;
    }
  return initfn;
}

// Search for references to VAR in any statements or called functions.

class Find_var : public Traverse
{
 public:
  // A hash table we use to avoid looping.  The index is the name of a
  // named object.  We only look through objects defined in this
  // package.
  typedef Unordered_set(const void*) Seen_objects;

  Find_var(Named_object* var, Seen_objects* seen_objects)
    : Traverse(traverse_expressions),
      var_(var), seen_objects_(seen_objects), found_(false)
  { }

  // Whether the variable was found.
  bool
  found() const
  { return this->found_; }

  int
  expression(Expression**);

 private:
  // The variable we are looking for.
  Named_object* var_;
  // Names of objects we have already seen.
  Seen_objects* seen_objects_;
  // True if the variable was found.
  bool found_;
};

// See if EXPR refers to VAR, looking through function calls and
// variable initializations.

int
Find_var::expression(Expression** pexpr)
{
  Expression* e = *pexpr;

  Var_expression* ve = e->var_expression();
  if (ve != NULL)
    {
      Named_object* v = ve->named_object();
      if (v == this->var_)
        {
          this->found_ = true;
          return TRAVERSE_EXIT;
        }

      if (v->is_variable() && v->package() == NULL)
        {
          Expression* init = v->var_value()->init();
          if (init != NULL)
            {
              std::pair<Seen_objects::iterator, bool> ins =
                this->seen_objects_->insert(v);
              if (ins.second)
                {
                  // This is the first time we have seen this name.
                  if (Expression::traverse(&init, this) == TRAVERSE_EXIT)
                    return TRAVERSE_EXIT;
                }
            }
        }
    }

  // We traverse the code of any function or bound method we see.  Note that
  // this means that we will traverse the code of a function or bound method
  // whose address is taken even if it is not called.
  Func_expression* fe = e->func_expression();
  Bound_method_expression* bme = e->bound_method_expression();
  if (fe != NULL || bme != NULL)
    {
      const Named_object* f = fe != NULL ? fe->named_object() : bme->function();
      if (f->is_function() && f->package() == NULL)
        {
          std::pair<Seen_objects::iterator, bool> ins =
            this->seen_objects_->insert(f);
          if (ins.second)
            {
              // This is the first time we have seen this name.
              if (f->func_value()->block()->traverse(this) == TRAVERSE_EXIT)
                return TRAVERSE_EXIT;
            }
        }
    }

  Temporary_reference_expression* tre = e->temporary_reference_expression();
  if (tre != NULL)
    {
      Temporary_statement* ts = tre->statement();
      Expression* init = ts->init();
      if (init != NULL)
        {
          std::pair<Seen_objects::iterator, bool> ins =
            this->seen_objects_->insert(ts);
          if (ins.second)
            {
              // This is the first time we have seen this temporary
              // statement.
              if (Expression::traverse(&init, this) == TRAVERSE_EXIT)
                return TRAVERSE_EXIT;
            }
        }
    }

  return TRAVERSE_CONTINUE;
}

// Return true if EXPR, PREINIT, or DEP refers to VAR.

static bool
expression_requires(Expression* expr, Block* preinit, Named_object* dep,
                    Named_object* var)
{
  Find_var::Seen_objects seen_objects;
  Find_var find_var(var, &seen_objects);
  if (expr != NULL)
    Expression::traverse(&expr, &find_var);
  if (preinit != NULL)
    preinit->traverse(&find_var);
  if (dep != NULL)
    {
      Expression* init = dep->var_value()->init();
      if (init != NULL)
        Expression::traverse(&init, &find_var);
      if (dep->var_value()->has_pre_init())
        dep->var_value()->preinit()->traverse(&find_var);
    }

  return find_var.found();
}

// Sort variable initializations.  If the initialization expression
// for variable A refers directly or indirectly to the initialization
// expression for variable B, then we must initialize B before A.

class Var_init
{
 public:
  Var_init()
    : var_(NULL), init_(NULL), dep_count_(0)
  { }

  Var_init(Named_object* var, Bstatement* init)
    : var_(var), init_(init), dep_count_(0)
  { }

  // Return the variable.
  Named_object*
  var() const
  { return this->var_; }

  // Return the initialization expression.
  Bstatement*
  init() const
  { return this->init_; }

  // Return the number of remaining dependencies.
  size_t
  dep_count() const
  { return this->dep_count_; }

  // Increment the number of dependencies.
  void
  add_dependency()
  { ++this->dep_count_; }

  // Decrement the number of dependencies.
  void
  remove_dependency()
  { --this->dep_count_; }

 private:
  // The variable being initialized.
  Named_object* var_;
  // The initialization statement.
  Bstatement* init_;
  // The number of initializations this is dependent on.  A variable
  // initialization should not be emitted if any of its dependencies
  // have not yet been resolved.
  size_t dep_count_;
};

// For comparing Var_init keys in a map.

inline bool
operator<(const Var_init& v1, const Var_init& v2)
{ return v1.var()->name() < v2.var()->name(); }

typedef std::list<Var_init> Var_inits;

// Sort the variable initializations.  The rule we follow is that we
// emit them in the order they appear in the array, except that if the
// initialization expression for a variable V1 depends upon another
// variable V2 then we initialize V1 after V2.

static void
sort_var_inits(Gogo* gogo, Var_inits* var_inits)
{
  if (var_inits->empty())
    return;

  typedef std::pair<Named_object*, Named_object*> No_no;
  typedef std::map<No_no, bool> Cache;
  Cache cache;

  // A mapping from a variable initialization to a set of
  // variable initializations that depend on it.
  typedef std::map<Var_init, std::set<Var_init*> > Init_deps;
  Init_deps init_deps;
  bool init_loop = false;
  for (Var_inits::iterator p1 = var_inits->begin();
       p1 != var_inits->end();
       ++p1)
    {
      Named_object* var = p1->var();
      Expression* init = var->var_value()->init();
      Block* preinit = var->var_value()->preinit();
      Named_object* dep = gogo->var_depends_on(var->var_value());

      // Start walking through the list to see which variables VAR
      // needs to wait for.
      for (Var_inits::iterator p2 = var_inits->begin();
           p2 != var_inits->end();
           ++p2)
        {
          if (var == p2->var())
            continue;

          Named_object* p2var = p2->var();
          No_no key(var, p2var);
          std::pair<Cache::iterator, bool> ins =
            cache.insert(std::make_pair(key, false));
          if (ins.second)
            ins.first->second = expression_requires(init, preinit, dep, p2var);
          if (ins.first->second)
            {
              // VAR depends on P2VAR.
              init_deps[*p2].insert(&(*p1));
              p1->add_dependency();

              // Check for cycles.
              key = std::make_pair(p2var, var);
              ins = cache.insert(std::make_pair(key, false));
              if (ins.second)
                ins.first->second =
                  expression_requires(p2var->var_value()->init(),
                                      p2var->var_value()->preinit(),
                                      gogo->var_depends_on(p2var->var_value()),
                                      var);
              if (ins.first->second)
                {
                  error_at(var->location(),
                           ("initialization expressions for %qs and "
                            "%qs depend upon each other"),
                           var->message_name().c_str(),
                           p2var->message_name().c_str());
                  inform(p2->var()->location(), "%qs defined here",
                         p2var->message_name().c_str());
                  init_loop = true;
                  break;
                }
            }
        }
    }

  // If there are no dependencies then the declaration order is sorted.
  if (!init_deps.empty() && !init_loop)
    {
      // Otherwise, sort variable initializations by emitting all variables with
      // no dependencies in declaration order. VAR_INITS is already in
      // declaration order.
      Var_inits ready;
      while (!var_inits->empty())
        {
          Var_inits::iterator v1;;
          for (v1 = var_inits->begin(); v1 != var_inits->end(); ++v1)
            {
              if (v1->dep_count() == 0)
                break;
            }
          go_assert(v1 != var_inits->end());

          // V1 either has no dependencies or its dependencies have already
          // been emitted, add it to READY next.  When V1 is emitted, remove
          // a dependency from each V that depends on V1.
          ready.splice(ready.end(), *var_inits, v1);

          Init_deps::iterator p1 = init_deps.find(*v1);
          if (p1 != init_deps.end())
            {
              std::set<Var_init*> resolved = p1->second;
              for (std::set<Var_init*>::iterator pv = resolved.begin();
                   pv != resolved.end();
                   ++pv)
                (*pv)->remove_dependency();
              init_deps.erase(p1);
            }
        }
      var_inits->swap(ready);
      go_assert(init_deps.empty());
    }

  // VAR_INITS is in the correct order.  For each VAR in VAR_INITS,
  // check for a loop of VAR on itself.  We only do this if
  // INIT is not NULL and there is no dependency; when INIT is
  // NULL, it means that PREINIT sets VAR, which we will
  // interpret as a loop.
  for (Var_inits::const_iterator p = var_inits->begin();
       p != var_inits->end();
       ++p)
    {
      Named_object* var = p->var();
      Expression* init = var->var_value()->init();
      Block* preinit = var->var_value()->preinit();
      Named_object* dep = gogo->var_depends_on(var->var_value());
      if (init != NULL && dep == NULL
          && expression_requires(init, preinit, NULL, var))
        error_at(var->location(),
                 "initialization expression for %qs depends upon itself",
                 var->message_name().c_str());
    }
}

// Write out the global definitions.

void
Gogo::write_globals()
{
  this->build_interface_method_tables();

  Bindings* bindings = this->current_bindings();

  for (Bindings::const_declarations_iterator p = bindings->begin_declarations();
       p != bindings->end_declarations();
       ++p)
    {
      // If any function declarations needed a descriptor, make sure
      // we build it.
      Named_object* no = p->second;
      if (no->is_function_declaration())
        no->func_declaration_value()->build_backend_descriptor(this);
    }

  // Lists of globally declared types, variables, constants, and functions
  // that must be defined.
  std::vector<Btype*> type_decls;
  std::vector<Bvariable*> var_decls;
  std::vector<Bexpression*> const_decls;
  std::vector<Bfunction*> func_decls;

  // The init function declaration, if necessary.
  Named_object* init_fndecl = NULL;

  std::vector<Bstatement*> init_stmts;
  std::vector<Bstatement*> var_init_stmts;

  if (this->is_main_package())
    this->init_imports(init_stmts);

  // A list of variable initializations.
  Var_inits var_inits;

  // A list of variables which need to be registered with the garbage
  // collector.
  size_t count_definitions = bindings->size_definitions();
  std::vector<Named_object*> var_gc;
  var_gc.reserve(count_definitions);

  for (Bindings::const_definitions_iterator p = bindings->begin_definitions();
       p != bindings->end_definitions();
       ++p)
    {
      Named_object* no = *p;
      go_assert(!no->is_type_declaration() && !no->is_function_declaration());

      // There is nothing to do for a package.
      if (no->is_package())
        continue;

      // There is nothing to do for an object which was imported from
      // a different package into the global scope.
      if (no->package() != NULL)
        continue;

      // Skip blank named functions and constants.
      if ((no->is_function() && no->func_value()->is_sink())
          || (no->is_const() && no->const_value()->is_sink()))
        continue;

      // There is nothing useful we can output for constants which
      // have ideal or non-integral type.
      if (no->is_const())
        {
          Type* type = no->const_value()->type();
          if (type == NULL)
            type = no->const_value()->expr()->type();
          if (type->is_abstract() || !type->is_numeric_type())
            continue;
        }

      if (!no->is_variable())
        no->get_backend(this, const_decls, type_decls, func_decls);
      else
        {
          Variable* var = no->var_value();
          Bvariable* bvar = no->get_backend_variable(this, NULL);
          var_decls.push_back(bvar);

          // Check for a sink variable, which may be used to run an
          // initializer purely for its side effects.
          bool is_sink = no->name()[0] == '_' && no->name()[1] == '.';

          Bstatement* var_init_stmt = NULL;
          if (!var->has_pre_init())
            {
              // If the backend representation of the variable initializer is
              // constant, we can just set the initial value using
              // global_var_set_init instead of during the init() function.
              // The initializer is constant if it is the zero-value of the
              // variable's type or if the initial value is an immutable value
              // that is not copied to the heap.
              bool is_constant_initializer = false;
              if (var->init() == NULL)
                is_constant_initializer = true;
              else
                {
                  Type* var_type = var->type();
                  Expression* init = var->init();
                  Expression* init_cast =
                      Expression::make_cast(var_type, init, var->location());
                  is_constant_initializer =
                      init_cast->is_immutable() && !var_type->has_pointer();
                }

              // Non-constant variable initializations might need to create
              // temporary variables, which will need the initialization
              // function as context.
              if (!is_constant_initializer && init_fndecl == NULL)
                init_fndecl = this->initialization_function_decl();
              Bexpression* var_binit = var->get_init(this, init_fndecl);

              if (var_binit == NULL)
                ;
              else if (is_constant_initializer)
                {
                  if (expression_requires(var->init(), NULL,
                                          this->var_depends_on(var), no))
                    error_at(no->location(),
                             "initialization expression for %qs depends "
                             "upon itself",
                             no->message_name().c_str());
                  this->backend()->global_variable_set_init(bvar, var_binit);
                }
              else if (is_sink)
                var_init_stmt =
                    this->backend()->expression_statement(var_binit);
              else
                {
                  Location loc = var->location();
                  Bexpression* var_expr =
                      this->backend()->var_expression(bvar, loc);
                  var_init_stmt =
                      this->backend()->assignment_statement(var_expr, var_binit,
                                                            loc);
                }
            }
          else
            {
              // We are going to create temporary variables which
              // means that we need an fndecl.
              if (init_fndecl == NULL)
                init_fndecl = this->initialization_function_decl();

              Bvariable* var_decl = is_sink ? NULL : bvar;
              var_init_stmt = var->get_init_block(this, init_fndecl, var_decl);
            }

          if (var_init_stmt != NULL)
            {
              if (var->init() == NULL && !var->has_pre_init())
                var_init_stmts.push_back(var_init_stmt);
              else
                var_inits.push_back(Var_init(no, var_init_stmt));
            }
          else if (this->var_depends_on(var) != NULL)
            {
              // This variable is initialized from something that is
              // not in its init or preinit.  This variable needs to
              // participate in dependency analysis sorting, in case
              // some other variable depends on this one.
              Btype* btype = no->var_value()->type()->get_backend(this);
              Bexpression* zero = this->backend()->zero_expression(btype);
              Bstatement* zero_stmt =
                  this->backend()->expression_statement(zero);
              var_inits.push_back(Var_init(no, zero_stmt));
            }

          if (!is_sink && var->type()->has_pointer())
            var_gc.push_back(no);
        }
    }

  // Register global variables with the garbage collector.
  this->register_gc_vars(var_gc, init_stmts);

  // Simple variable initializations, after all variables are
  // registered.
  init_stmts.push_back(this->backend()->statement_list(var_init_stmts));

  // Complete variable initializations, first sorting them into a
  // workable order.
  if (!var_inits.empty())
    {
      sort_var_inits(this, &var_inits);
      for (Var_inits::const_iterator p = var_inits.begin();
           p != var_inits.end();
           ++p)
        init_stmts.push_back(p->init());
    }

  // After all the variables are initialized, call the init
  // functions if there are any.  Init functions take no arguments, so
  // we pass in EMPTY_ARGS to call them.
  std::vector<Bexpression*> empty_args;
  for (std::vector<Named_object*>::const_iterator p =
           this->init_functions_.begin();
       p != this->init_functions_.end();
       ++p)
    {
      Location func_loc = (*p)->location();
      Function* func = (*p)->func_value();
      Bfunction* initfn = func->get_or_make_decl(this, *p);
      Bexpression* func_code =
          this->backend()->function_code_expression(initfn, func_loc);
      Bexpression* call = this->backend()->call_expression(func_code,
                                                           empty_args,
                                                           NULL, func_loc);
      init_stmts.push_back(this->backend()->expression_statement(call));
    }

  // Set up a magic function to do all the initialization actions.
  // This will be called if this package is imported.
  Bstatement* init_fncode = this->backend()->statement_list(init_stmts);
  if (this->need_init_fn_ || this->is_main_package())
    {
      init_fndecl =
        this->create_initialization_function(init_fndecl, init_fncode);
      if (init_fndecl != NULL)
        func_decls.push_back(init_fndecl->func_value()->get_decl());
    }

  // We should not have seen any new bindings created during the conversion.
  go_assert(count_definitions == this->current_bindings()->size_definitions());

  // Define all globally declared values.
  if (!saw_errors())
    this->backend()->write_global_definitions(type_decls, const_decls,
                                              func_decls, var_decls);
}

// Return the current block.

Block*
Gogo::current_block()
{
  if (this->functions_.empty())
    return NULL;
  else
    return this->functions_.back().blocks.back();
}

// Look up a name in the current binding contour.  If PFUNCTION is not
// NULL, set it to the function in which the name is defined, or NULL
// if the name is defined in global scope.

Named_object*
Gogo::lookup(const std::string& name, Named_object** pfunction) const
{
  if (pfunction != NULL)
    *pfunction = NULL;

  if (Gogo::is_sink_name(name))
    return Named_object::make_sink();

  for (Open_functions::const_reverse_iterator p = this->functions_.rbegin();
       p != this->functions_.rend();
       ++p)
    {
      Named_object* ret = p->blocks.back()->bindings()->lookup(name);
      if (ret != NULL)
        {
          if (pfunction != NULL)
            *pfunction = p->function;
          return ret;
        }
    }

  if (this->package_ != NULL)
    {
      Named_object* ret = this->package_->bindings()->lookup(name);
      if (ret != NULL)
        {
          if (ret->package() != NULL)
            {
              std::string dot_alias = "." + ret->package()->package_name();
              ret->package()->note_usage(dot_alias);
            }
          return ret;
        }
    }

  // We do not look in the global namespace.  If we did, the global
  // namespace would effectively hide names which were defined in
  // package scope which we have not yet seen.  Instead,
  // define_global_names is called after parsing is over to connect
  // undefined names at package scope with names defined at global
  // scope.

  return NULL;
}

// Look up a name in the current block, without searching enclosing
// blocks.

Named_object*
Gogo::lookup_in_block(const std::string& name) const
{
  go_assert(!this->functions_.empty());
  go_assert(!this->functions_.back().blocks.empty());
  return this->functions_.back().blocks.back()->bindings()->lookup_local(name);
}

// Look up a name in the global namespace.

Named_object*
Gogo::lookup_global(const char* name) const
{
  return this->globals_->lookup(name);
}

// Add an imported package.

Package*
Gogo::add_imported_package(const std::string& real_name,
                           const std::string& alias_arg,
                           bool is_alias_exported,
                           const std::string& pkgpath,
                           const std::string& pkgpath_symbol,
                           Location location,
                           bool* padd_to_globals)
{
  Package* ret = this->register_package(pkgpath, pkgpath_symbol, location);
  ret->set_package_name(real_name, location);

  *padd_to_globals = false;

  if (alias_arg == "_")
    ;
  else if (alias_arg == ".")
    {
      *padd_to_globals = true;
      std::string dot_alias = "." + real_name;
      ret->add_alias(dot_alias, location);
    }
  else
    {
      std::string alias = alias_arg;
      if (alias.empty())
        {
          alias = real_name;
          is_alias_exported = Lex::is_exported_name(alias);
        }
      ret->add_alias(alias, location);
      alias = this->pack_hidden_name(alias, is_alias_exported);
      Named_object* no = this->package_->bindings()->add_package(alias, ret);
      if (!no->is_package())
        return NULL;
    }

  return ret;
}

// Register a package.  This package may or may not be imported.  This
// returns the Package structure for the package, creating if it
// necessary.  LOCATION is the location of the import statement that
// led us to see this package.  PKGPATH_SYMBOL is the symbol to use
// for names in the package; it may be the empty string, in which case
// we either get it later or make a guess when we need it.

Package*
Gogo::register_package(const std::string& pkgpath,
                       const std::string& pkgpath_symbol, Location location)
{
  Package* package = NULL;
  std::pair<Packages::iterator, bool> ins =
    this->packages_.insert(std::make_pair(pkgpath, package));
  if (!ins.second)
    {
      // We have seen this package name before.
      package = ins.first->second;
      go_assert(package != NULL && package->pkgpath() == pkgpath);
      if (!pkgpath_symbol.empty())
        package->set_pkgpath_symbol(pkgpath_symbol);
      if (Linemap::is_unknown_location(package->location()))
        package->set_location(location);
    }
  else
    {
      // First time we have seen this package name.
      package = new Package(pkgpath, pkgpath_symbol, location);
      go_assert(ins.first->second == NULL);
      ins.first->second = package;
    }

  return package;
}

// Start compiling a function.

Named_object*
Gogo::start_function(const std::string& name, Function_type* type,
                     bool add_method_to_type, Location location)
{
  bool at_top_level = this->functions_.empty();

  Block* block = new Block(NULL, location);

  Named_object* enclosing = (at_top_level
                         ? NULL
                         : this->functions_.back().function);

  Function* function = new Function(type, enclosing, block, location);

  if (type->is_method())
    {
      const Typed_identifier* receiver = type->receiver();
      Variable* this_param = new Variable(receiver->type(), NULL, false,
                                          true, true, location);
      std::string rname = receiver->name();
      if (rname.empty() || Gogo::is_sink_name(rname))
        {
          // We need to give receivers a name since they wind up in
          // DECL_ARGUMENTS.  FIXME.
          static unsigned int count;
          char buf[50];
          snprintf(buf, sizeof buf, "r.%u", count);
          ++count;
          rname = buf;
        }
      block->bindings()->add_variable(rname, NULL, this_param);
    }

  const Typed_identifier_list* parameters = type->parameters();
  bool is_varargs = type->is_varargs();
  if (parameters != NULL)
    {
      for (Typed_identifier_list::const_iterator p = parameters->begin();
           p != parameters->end();
           ++p)
        {
          Variable* param = new Variable(p->type(), NULL, false, true, false,
                                         p->location());
          if (is_varargs && p + 1 == parameters->end())
            param->set_is_varargs_parameter();

          std::string pname = p->name();
          if (pname.empty() || Gogo::is_sink_name(pname))
            {
              // We need to give parameters a name since they wind up
              // in DECL_ARGUMENTS.  FIXME.
              static unsigned int count;
              char buf[50];
              snprintf(buf, sizeof buf, "p.%u", count);
              ++count;
              pname = buf;
            }
          block->bindings()->add_variable(pname, NULL, param);
        }
    }

  function->create_result_variables(this);

  const std::string* pname;
  std::string nested_name;
  bool is_init = false;
  if (Gogo::unpack_hidden_name(name) == "init" && !type->is_method())
    {
      if ((type->parameters() != NULL && !type->parameters()->empty())
          || (type->results() != NULL && !type->results()->empty()))
        error_at(location,
                 "func init must have no arguments and no return values");
      // There can be multiple "init" functions, so give them each a
      // different name.
      static int init_count;
      char buf[30];
      snprintf(buf, sizeof buf, ".$init%d", init_count);
      ++init_count;
      nested_name = buf;
      pname = &nested_name;
      is_init = true;
    }
  else if (!name.empty())
    pname = &name;
  else
    {
      // Invent a name for a nested function.
      static int nested_count;
      char buf[30];
      snprintf(buf, sizeof buf, ".$nested%d", nested_count);
      ++nested_count;
      nested_name = buf;
      pname = &nested_name;
    }

  Named_object* ret;
  if (Gogo::is_sink_name(*pname))
    {
      static int sink_count;
      char buf[30];
      snprintf(buf, sizeof buf, ".$sink%d", sink_count);
      ++sink_count;
      ret = this->package_->bindings()->add_function(buf, NULL, function);
      ret->func_value()->set_is_sink();
    }
  else if (!type->is_method())
    {
      ret = this->package_->bindings()->add_function(*pname, NULL, function);
      if (!ret->is_function() || ret->func_value() != function)
        {
          // Redefinition error.  Invent a name to avoid knockon
          // errors.
          static int redefinition_count;
          char buf[30];
          snprintf(buf, sizeof buf, ".$redefined%d", redefinition_count);
          ++redefinition_count;
          ret = this->package_->bindings()->add_function(buf, NULL, function);
        }
    }
  else
    {
      if (!add_method_to_type)
        ret = Named_object::make_function(name, NULL, function);
      else
        {
          go_assert(at_top_level);
          Type* rtype = type->receiver()->type();

          // We want to look through the pointer created by the
          // parser, without getting an error if the type is not yet
          // defined.
          if (rtype->classification() == Type::TYPE_POINTER)
            rtype = rtype->points_to();

          if (rtype->is_error_type())
            ret = Named_object::make_function(name, NULL, function);
          else if (rtype->named_type() != NULL)
            {
              ret = rtype->named_type()->add_method(name, function);
              if (!ret->is_function())
                {
                  // Redefinition error.
                  ret = Named_object::make_function(name, NULL, function);
                }
            }
          else if (rtype->forward_declaration_type() != NULL)
            {
              Named_object* type_no =
                rtype->forward_declaration_type()->named_object();
              if (type_no->is_unknown())
                {
                  // If we are seeing methods it really must be a
                  // type.  Declare it as such.  An alternative would
                  // be to support lists of methods for unknown
                  // expressions.  Either way the error messages if
                  // this is not a type are going to get confusing.
                  Named_object* declared =
                    this->declare_package_type(type_no->name(),
                                               type_no->location());
                  go_assert(declared
                             == type_no->unknown_value()->real_named_object());
                }
              ret = rtype->forward_declaration_type()->add_method(name,
                                                                  function);
            }
          else
            {
              error_at(type->receiver()->location(),
                       "invalid receiver type (receiver must be a named type)");
              ret = Named_object::make_function(name, NULL, function);
            }
        }
      this->package_->bindings()->add_method(ret);
    }

  this->functions_.resize(this->functions_.size() + 1);
  Open_function& of(this->functions_.back());
  of.function = ret;
  of.blocks.push_back(block);

  if (is_init)
    {
      this->init_functions_.push_back(ret);
      this->need_init_fn_ = true;
    }

  return ret;
}

// Finish compiling a function.

void
Gogo::finish_function(Location location)
{
  this->finish_block(location);
  go_assert(this->functions_.back().blocks.empty());
  this->functions_.pop_back();
}

// Return the current function.

Named_object*
Gogo::current_function() const
{
  go_assert(!this->functions_.empty());
  return this->functions_.back().function;
}

// Start a new block.

void
Gogo::start_block(Location location)
{
  go_assert(!this->functions_.empty());
  Block* block = new Block(this->current_block(), location);
  this->functions_.back().blocks.push_back(block);
}

// Finish a block.

Block*
Gogo::finish_block(Location location)
{
  go_assert(!this->functions_.empty());
  go_assert(!this->functions_.back().blocks.empty());
  Block* block = this->functions_.back().blocks.back();
  this->functions_.back().blocks.pop_back();
  block->set_end_location(location);
  return block;
}

// Add an erroneous name.

Named_object*
Gogo::add_erroneous_name(const std::string& name)
{
  return this->package_->bindings()->add_erroneous_name(name);
}

// Add an unknown name.

Named_object*
Gogo::add_unknown_name(const std::string& name, Location location)
{
  return this->package_->bindings()->add_unknown_name(name, location);
}

// Declare a function.

Named_object*
Gogo::declare_function(const std::string& name, Function_type* type,
                       Location location)
{
  if (!type->is_method())
    return this->current_bindings()->add_function_declaration(name, NULL, type,
                                                              location);
  else
    {
      // We don't bother to add this to the list of global
      // declarations.
      Type* rtype = type->receiver()->type();

      // We want to look through the pointer created by the
      // parser, without getting an error if the type is not yet
      // defined.
      if (rtype->classification() == Type::TYPE_POINTER)
        rtype = rtype->points_to();

      if (rtype->is_error_type())
        return NULL;
      else if (rtype->named_type() != NULL)
        return rtype->named_type()->add_method_declaration(name, NULL, type,
                                                           location);
      else if (rtype->forward_declaration_type() != NULL)
        {
          Forward_declaration_type* ftype = rtype->forward_declaration_type();
          return ftype->add_method_declaration(name, NULL, type, location);
        }
      else
        {
          error_at(type->receiver()->location(),
                   "invalid receiver type (receiver must be a named type)");
          return Named_object::make_erroneous_name(name);
        }
    }
}

// Add a label definition.

Label*
Gogo::add_label_definition(const std::string& label_name,
                           Location location)
{
  go_assert(!this->functions_.empty());
  Function* func = this->functions_.back().function->func_value();
  Label* label = func->add_label_definition(this, label_name, location);
  this->add_statement(Statement::make_label_statement(label, location));
  return label;
}

// Add a label reference.

Label*
Gogo::add_label_reference(const std::string& label_name,
                          Location location, bool issue_goto_errors)
{
  go_assert(!this->functions_.empty());
  Function* func = this->functions_.back().function->func_value();
  return func->add_label_reference(this, label_name, location,
                                   issue_goto_errors);
}

// Return the current binding state.

Bindings_snapshot*
Gogo::bindings_snapshot(Location location)
{
  return new Bindings_snapshot(this->current_block(), location);
}

// Add a statement.

void
Gogo::add_statement(Statement* statement)
{
  go_assert(!this->functions_.empty()
             && !this->functions_.back().blocks.empty());
  this->functions_.back().blocks.back()->add_statement(statement);
}

// Add a block.

void
Gogo::add_block(Block* block, Location location)
{
  go_assert(!this->functions_.empty()
             && !this->functions_.back().blocks.empty());
  Statement* statement = Statement::make_block_statement(block, location);
  this->functions_.back().blocks.back()->add_statement(statement);
}

// Add a constant.

Named_object*
Gogo::add_constant(const Typed_identifier& tid, Expression* expr,
                   int iota_value)
{
  return this->current_bindings()->add_constant(tid, NULL, expr, iota_value);
}

// Add a type.

void
Gogo::add_type(const std::string& name, Type* type, Location location)
{
  Named_object* no = this->current_bindings()->add_type(name, NULL, type,
                                                        location);
  if (!this->in_global_scope() && no->is_type())
    {
      Named_object* f = this->functions_.back().function;
      unsigned int index;
      if (f->is_function())
        index = f->func_value()->new_local_type_index();
      else
        index = 0;
      no->type_value()->set_in_function(f, index);
    }
}

// Add a named type.

void
Gogo::add_named_type(Named_type* type)
{
  go_assert(this->in_global_scope());
  this->current_bindings()->add_named_type(type);
}

// Declare a type.

Named_object*
Gogo::declare_type(const std::string& name, Location location)
{
  Bindings* bindings = this->current_bindings();
  Named_object* no = bindings->add_type_declaration(name, NULL, location);
  if (!this->in_global_scope() && no->is_type_declaration())
    {
      Named_object* f = this->functions_.back().function;
      unsigned int index;
      if (f->is_function())
        index = f->func_value()->new_local_type_index();
      else
        index = 0;
      no->type_declaration_value()->set_in_function(f, index);
    }
  return no;
}

// Declare a type at the package level.

Named_object*
Gogo::declare_package_type(const std::string& name, Location location)
{
  return this->package_->bindings()->add_type_declaration(name, NULL, location);
}

// Declare a function at the package level.

Named_object*
Gogo::declare_package_function(const std::string& name, Function_type* type,
                               Location location)
{
  return this->package_->bindings()->add_function_declaration(name, NULL, type,
                                                              location);
}

// Define a type which was already declared.

void
Gogo::define_type(Named_object* no, Named_type* type)
{
  this->current_bindings()->define_type(no, type);
}

// Add a variable.

Named_object*
Gogo::add_variable(const std::string& name, Variable* variable)
{
  Named_object* no = this->current_bindings()->add_variable(name, NULL,
                                                            variable);

  // In a function the middle-end wants to see a DECL_EXPR node.
  if (no != NULL
      && no->is_variable()
      && !no->var_value()->is_parameter()
      && !this->functions_.empty())
    this->add_statement(Statement::make_variable_declaration(no));

  return no;
}

// Add a sink--a reference to the blank identifier _.

Named_object*
Gogo::add_sink()
{
  return Named_object::make_sink();
}

// Add a named object for a dot import.

void
Gogo::add_dot_import_object(Named_object* no)
{
  // If the name already exists, then it was defined in some file seen
  // earlier.  If the earlier name is just a declaration, don't add
  // this name, because that will cause the previous declaration to
  // merge to this imported name, which should not happen.  Just add
  // this name to the list of file block names to get appropriate
  // errors if we see a later definition.
  Named_object* e = this->package_->bindings()->lookup(no->name());
  if (e != NULL && e->package() == NULL)
    {
      if (e->is_unknown())
        e = e->resolve();
      if (e->package() == NULL
          && (e->is_type_declaration()
              || e->is_function_declaration()
              || e->is_unknown()))
        {
          this->add_file_block_name(no->name(), no->location());
          return;
        }
    }

  this->current_bindings()->add_named_object(no);
}

// Add a linkname.  This implements the go:linkname compiler directive.
// We only support this for functions and function declarations.

void
Gogo::add_linkname(const std::string& go_name, bool is_exported,
                   const std::string& ext_name, Location loc)
{
  Named_object* no =
    this->package_->bindings()->lookup(this->pack_hidden_name(go_name,
                                                              is_exported));
  if (no == NULL)
    error_at(loc, "%s is not defined", go_name.c_str());
  else if (no->is_function())
    no->func_value()->set_asm_name(ext_name);
  else if (no->is_function_declaration())
    no->func_declaration_value()->set_asm_name(ext_name);
  else
    error_at(loc,
             ("%s is not a function; "
              "//go:linkname is only supported for functions"),
             go_name.c_str());
}

// Mark all local variables used.  This is used when some types of
// parse error occur.

void
Gogo::mark_locals_used()
{
  for (Open_functions::iterator pf = this->functions_.begin();
       pf != this->functions_.end();
       ++pf)
    {
      for (std::vector<Block*>::iterator pb = pf->blocks.begin();
           pb != pf->blocks.end();
           ++pb)
        (*pb)->bindings()->mark_locals_used();
    }
}

// Record that we've seen an interface type.

void
Gogo::record_interface_type(Interface_type* itype)
{
  this->interface_types_.push_back(itype);
}

// Return an erroneous name that indicates that an error has already
// been reported.

std::string
Gogo::erroneous_name()
{
  static int erroneous_count;
  char name[50];
  snprintf(name, sizeof name, "$erroneous%d", erroneous_count);
  ++erroneous_count;
  return name;
}

// Return whether a name is an erroneous name.

bool
Gogo::is_erroneous_name(const std::string& name)
{
  return name.compare(0, 10, "$erroneous") == 0;
}

// Return a name for a thunk object.

std::string
Gogo::thunk_name()
{
  static int thunk_count;
  char thunk_name[50];
  snprintf(thunk_name, sizeof thunk_name, "$thunk%d", thunk_count);
  ++thunk_count;
  return thunk_name;
}

// Return whether a function is a thunk.

bool
Gogo::is_thunk(const Named_object* no)
{
  return no->name().compare(0, 6, "$thunk") == 0;
}

// Define the global names.  We do this only after parsing all the
// input files, because the program might define the global names
// itself.

void
Gogo::define_global_names()
{
  for (Bindings::const_declarations_iterator p =
         this->globals_->begin_declarations();
       p != this->globals_->end_declarations();
       ++p)
    {
      Named_object* global_no = p->second;
      std::string name(Gogo::pack_hidden_name(global_no->name(), false));
      Named_object* no = this->package_->bindings()->lookup(name);
      if (no == NULL)
        continue;
      no = no->resolve();
      if (no->is_type_declaration())
        {
          if (global_no->is_type())
            {
              if (no->type_declaration_value()->has_methods())
                error_at(no->location(),
                         "may not define methods for global type");
              no->set_type_value(global_no->type_value());
            }
          else
            {
              error_at(no->location(), "expected type");
              Type* errtype = Type::make_error_type();
              Named_object* err =
                Named_object::make_type("erroneous_type", NULL, errtype,
                                        Linemap::predeclared_location());
              no->set_type_value(err->type_value());
            }
        }
      else if (no->is_unknown())
        no->unknown_value()->set_real_named_object(global_no);
    }

  // Give an error if any name is defined in both the package block
  // and the file block.  For example, this can happen if one file
  // imports "fmt" and another file defines a global variable fmt.
  for (Bindings::const_declarations_iterator p =
         this->package_->bindings()->begin_declarations();
       p != this->package_->bindings()->end_declarations();
       ++p)
    {
      if (p->second->is_unknown()
          && p->second->unknown_value()->real_named_object() == NULL)
        {
          // No point in warning about an undefined name, as we will
          // get other errors later anyhow.
          continue;
        }
      File_block_names::const_iterator pf =
        this->file_block_names_.find(p->second->name());
      if (pf != this->file_block_names_.end())
        {
          std::string n = p->second->message_name();
          error_at(p->second->location(),
                   "%qs defined as both imported name and global name",
                   n.c_str());
          inform(pf->second, "%qs imported here", n.c_str());
        }

      // No package scope identifier may be named "init".
      if (!p->second->is_function()
          && Gogo::unpack_hidden_name(p->second->name()) == "init")
        {
          error_at(p->second->location(),
                   "cannot declare init - must be func");
        }
    }
}

// Clear out names in file scope.

void
Gogo::clear_file_scope()
{
  this->package_->bindings()->clear_file_scope(this);

  // Warn about packages which were imported but not used.
  bool quiet = saw_errors();
  for (Packages::iterator p = this->packages_.begin();
       p != this->packages_.end();
       ++p)
    {
      Package* package = p->second;
      if (package != this->package_ && !quiet)
        {
          for (Package::Aliases::const_iterator p1 = package->aliases().begin();
               p1 != package->aliases().end();
               ++p1)
            {
              if (!p1->second->used())
                {
                  // Give a more refined error message if the alias name is known.
                  std::string pkg_name = package->package_name();
                  if (p1->first != pkg_name && p1->first[0] != '.')
                    {
                      error_at(p1->second->location(),
                               "imported and not used: %s as %s",
                               Gogo::message_name(pkg_name).c_str(),
                               Gogo::message_name(p1->first).c_str());
                    }
                  else
                    error_at(p1->second->location(),
                             "imported and not used: %s",
                             Gogo::message_name(pkg_name).c_str());
                }
            }
        }
      package->clear_used();
    }

  this->current_file_imported_unsafe_ = false;
}

// Queue up a type specific function for later writing.  These are
// written out in write_specific_type_functions, called after the
// parse tree is lowered.

void
Gogo::queue_specific_type_function(Type* type, Named_type* name,
                                   const std::string& hash_name,
                                   Function_type* hash_fntype,
                                   const std::string& equal_name,
                                   Function_type* equal_fntype)
{
  go_assert(!this->specific_type_functions_are_written_);
  go_assert(!this->in_global_scope());
  Specific_type_function* tsf = new Specific_type_function(type, name,
                                                           hash_name,
                                                           hash_fntype,
                                                           equal_name,
                                                           equal_fntype);
  this->specific_type_functions_.push_back(tsf);
}

// Look for types which need specific hash or equality functions.

class Specific_type_functions : public Traverse
{
 public:
  Specific_type_functions(Gogo* gogo)
    : Traverse(traverse_types),
      gogo_(gogo)
  { }

  int
  type(Type*);

 private:
  Gogo* gogo_;
};

int
Specific_type_functions::type(Type* t)
{
  Named_object* hash_fn;
  Named_object* equal_fn;
  switch (t->classification())
    {
    case Type::TYPE_NAMED:
      {
        Named_type* nt = t->named_type();
        if (!t->compare_is_identity(this->gogo_) && t->is_comparable())
          t->type_functions(this->gogo_, nt, NULL, NULL, &hash_fn, &equal_fn);

        // If this is a struct type, we don't want to make functions
        // for the unnamed struct.
        Type* rt = nt->real_type();
        if (rt->struct_type() == NULL)
          {
            if (Type::traverse(rt, this) == TRAVERSE_EXIT)
              return TRAVERSE_EXIT;
          }
        else
          {
            // If this type is defined in another package, then we don't
            // need to worry about the unexported fields.
            bool is_defined_elsewhere = nt->named_object()->package() != NULL;
            const Struct_field_list* fields = rt->struct_type()->fields();
            for (Struct_field_list::const_iterator p = fields->begin();
                 p != fields->end();
                 ++p)
              {
                if (is_defined_elsewhere
                    && Gogo::is_hidden_name(p->field_name()))
                  continue;
                if (Type::traverse(p->type(), this) == TRAVERSE_EXIT)
                  return TRAVERSE_EXIT;
              }
          }

        return TRAVERSE_SKIP_COMPONENTS;
      }

    case Type::TYPE_STRUCT:
    case Type::TYPE_ARRAY:
      if (!t->compare_is_identity(this->gogo_) && t->is_comparable())
        t->type_functions(this->gogo_, NULL, NULL, NULL, &hash_fn, &equal_fn);
      break;

    default:
      break;
    }

  return TRAVERSE_CONTINUE;
}

// Write out type specific functions.

void
Gogo::write_specific_type_functions()
{
  Specific_type_functions stf(this);
  this->traverse(&stf);

  while (!this->specific_type_functions_.empty())
    {
      Specific_type_function* tsf = this->specific_type_functions_.back();
      this->specific_type_functions_.pop_back();
      tsf->type->write_specific_type_functions(this, tsf->name,
                                               tsf->hash_name,
                                               tsf->hash_fntype,
                                               tsf->equal_name,
                                               tsf->equal_fntype);
      delete tsf;
    }
  this->specific_type_functions_are_written_ = true;
}

// Traverse the tree.

void
Gogo::traverse(Traverse* traverse)
{
  // Traverse the current package first for consistency.  The other
  // packages will only contain imported types, constants, and
  // declarations.
  if (this->package_->bindings()->traverse(traverse, true) == TRAVERSE_EXIT)
    return;
  for (Packages::const_iterator p = this->packages_.begin();
       p != this->packages_.end();
       ++p)
    {
      if (p->second != this->package_)
        {
          if (p->second->bindings()->traverse(traverse, true) == TRAVERSE_EXIT)
            break;
        }
    }
}

// Add a type to verify.  This is used for types of sink variables, in
// order to give appropriate error messages.

void
Gogo::add_type_to_verify(Type* type)
{
  this->verify_types_.push_back(type);
}

// Traversal class used to verify types.

class Verify_types : public Traverse
{
 public:
  Verify_types()
    : Traverse(traverse_types)
  { }

  int
  type(Type*);
};

// Verify that a type is correct.

int
Verify_types::type(Type* t)
{
  if (!t->verify())
    return TRAVERSE_SKIP_COMPONENTS;
  return TRAVERSE_CONTINUE;
}

// Verify that all types are correct.

void
Gogo::verify_types()
{
  Verify_types traverse;
  this->traverse(&traverse);

  for (std::vector<Type*>::iterator p = this->verify_types_.begin();
       p != this->verify_types_.end();
       ++p)
    (*p)->verify();
  this->verify_types_.clear();
}

// Traversal class used to lower parse tree.

class Lower_parse_tree : public Traverse
{
 public:
  Lower_parse_tree(Gogo* gogo, Named_object* function)
    : Traverse(traverse_variables
               | traverse_constants
               | traverse_functions
               | traverse_statements
               | traverse_expressions),
      gogo_(gogo), function_(function), iota_value_(-1), inserter_()
  { }

  void
  set_inserter(const Statement_inserter* inserter)
  { this->inserter_ = *inserter; }

  int
  variable(Named_object*);

  int
  constant(Named_object*, bool);

  int
  function(Named_object*);

  int
  statement(Block*, size_t* pindex, Statement*);

  int
  expression(Expression**);

 private:
  // General IR.
  Gogo* gogo_;
  // The function we are traversing.
  Named_object* function_;
  // Value to use for the predeclared constant iota.
  int iota_value_;
  // Current statement inserter for use by expressions.
  Statement_inserter inserter_;
};

// Lower variables.

int
Lower_parse_tree::variable(Named_object* no)
{
  if (!no->is_variable())
    return TRAVERSE_CONTINUE;

  if (no->is_variable() && no->var_value()->is_global())
    {
      // Global variables can have loops in their initialization
      // expressions.  This is handled in lower_init_expression.
      no->var_value()->lower_init_expression(this->gogo_, this->function_,
                                             &this->inserter_);
      return TRAVERSE_CONTINUE;
    }

  // This is a local variable.  We are going to return
  // TRAVERSE_SKIP_COMPONENTS here because we want to traverse the
  // initialization expression when we reach the variable declaration
  // statement.  However, that means that we need to traverse the type
  // ourselves.
  if (no->var_value()->has_type())
    {
      Type* type = no->var_value()->type();
      if (type != NULL)
        {
          if (Type::traverse(type, this) == TRAVERSE_EXIT)
            return TRAVERSE_EXIT;
        }
    }
  go_assert(!no->var_value()->has_pre_init());

  return TRAVERSE_SKIP_COMPONENTS;
}

// Lower constants.  We handle constants specially so that we can set
// the right value for the predeclared constant iota.  This works in
// conjunction with the way we lower Const_expression objects.

int
Lower_parse_tree::constant(Named_object* no, bool)
{
  Named_constant* nc = no->const_value();

  // Don't get into trouble if the constant's initializer expression
  // refers to the constant itself.
  if (nc->lowering())
    return TRAVERSE_CONTINUE;
  nc->set_lowering();

  go_assert(this->iota_value_ == -1);
  this->iota_value_ = nc->iota_value();
  nc->traverse_expression(this);
  this->iota_value_ = -1;

  nc->clear_lowering();

  // We will traverse the expression a second time, but that will be
  // fast.

  return TRAVERSE_CONTINUE;
}

// Lower the body of a function, and set the closure type.  Record the
// function while lowering it, so that we can pass it down when
// lowering an expression.

int
Lower_parse_tree::function(Named_object* no)
{
  no->func_value()->set_closure_type();

  go_assert(this->function_ == NULL);
  this->function_ = no;
  int t = no->func_value()->traverse(this);
  this->function_ = NULL;

  if (t == TRAVERSE_EXIT)
    return t;
  return TRAVERSE_SKIP_COMPONENTS;
}

// Lower statement parse trees.

int
Lower_parse_tree::statement(Block* block, size_t* pindex, Statement* sorig)
{
  // Because we explicitly traverse the statement's contents
  // ourselves, we want to skip block statements here.  There is
  // nothing to lower in a block statement.
  if (sorig->is_block_statement())
    return TRAVERSE_CONTINUE;

  Statement_inserter hold_inserter(this->inserter_);
  this->inserter_ = Statement_inserter(block, pindex);

  // Lower the expressions first.
  int t = sorig->traverse_contents(this);
  if (t == TRAVERSE_EXIT)
    {
      this->inserter_ = hold_inserter;
      return t;
    }

  // Keep lowering until nothing changes.
  Statement* s = sorig;
  while (true)
    {
      Statement* snew = s->lower(this->gogo_, this->function_, block,
                                 &this->inserter_);
      if (snew == s)
        break;
      s = snew;
      t = s->traverse_contents(this);
      if (t == TRAVERSE_EXIT)
        {
          this->inserter_ = hold_inserter;
          return t;
        }
    }

  if (s != sorig)
    block->replace_statement(*pindex, s);

  this->inserter_ = hold_inserter;
  return TRAVERSE_SKIP_COMPONENTS;
}

// Lower expression parse trees.

int
Lower_parse_tree::expression(Expression** pexpr)
{
  // We have to lower all subexpressions first, so that we can get
  // their type if necessary.  This is awkward, because we don't have
  // a postorder traversal pass.
  if ((*pexpr)->traverse_subexpressions(this) == TRAVERSE_EXIT)
    return TRAVERSE_EXIT;
  // Keep lowering until nothing changes.
  while (true)
    {
      Expression* e = *pexpr;
      Expression* enew = e->lower(this->gogo_, this->function_,
                                  &this->inserter_, this->iota_value_);
      if (enew == e)
        break;
      if (enew->traverse_subexpressions(this) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
      *pexpr = enew;
    }
  return TRAVERSE_SKIP_COMPONENTS;
}

// Lower the parse tree.  This is called after the parse is complete,
// when all names should be resolved.

void
Gogo::lower_parse_tree()
{
  Lower_parse_tree lower_parse_tree(this, NULL);
  this->traverse(&lower_parse_tree);

  // There might be type definitions that involve expressions such as the
  // array length.  Make sure to lower these expressions as well.  Otherwise,
  // errors hidden within a type can introduce unexpected errors into later
  // passes.
  for (std::vector<Type*>::iterator p = this->verify_types_.begin();
       p != this->verify_types_.end();
       ++p)
    Type::traverse(*p, &lower_parse_tree);
}

// Lower a block.

void
Gogo::lower_block(Named_object* function, Block* block)
{
  Lower_parse_tree lower_parse_tree(this, function);
  block->traverse(&lower_parse_tree);
}

// Lower an expression.  INSERTER may be NULL, in which case the
// expression had better not need to create any temporaries.

void
Gogo::lower_expression(Named_object* function, Statement_inserter* inserter,
                       Expression** pexpr)
{
  Lower_parse_tree lower_parse_tree(this, function);
  if (inserter != NULL)
    lower_parse_tree.set_inserter(inserter);
  lower_parse_tree.expression(pexpr);
}

// Lower a constant.  This is called when lowering a reference to a
// constant.  We have to make sure that the constant has already been
// lowered.

void
Gogo::lower_constant(Named_object* no)
{
  go_assert(no->is_const());
  Lower_parse_tree lower(this, NULL);
  lower.constant(no, false);
}

// Traverse the tree to create function descriptors as needed.

class Create_function_descriptors : public Traverse
{
 public:
  Create_function_descriptors(Gogo* gogo)
    : Traverse(traverse_functions | traverse_expressions),
      gogo_(gogo)
  { }

  int
  function(Named_object*);

  int
  expression(Expression**);

 private:
  Gogo* gogo_;
};

// Create a descriptor for every top-level exported function.

int
Create_function_descriptors::function(Named_object* no)
{
  if (no->is_function()
      && no->func_value()->enclosing() == NULL
      && !no->func_value()->is_method()
      && !Gogo::is_hidden_name(no->name())
      && !Gogo::is_thunk(no))
    no->func_value()->descriptor(this->gogo_, no);

  return TRAVERSE_CONTINUE;
}

// If we see a function referenced in any way other than calling it,
// create a descriptor for it.

int
Create_function_descriptors::expression(Expression** pexpr)
{
  Expression* expr = *pexpr;

  Func_expression* fe = expr->func_expression();
  if (fe != NULL)
    {
      // We would not get here for a call to this function, so this is
      // a reference to a function other than calling it.  We need a
      // descriptor.
      if (fe->closure() != NULL)
        return TRAVERSE_CONTINUE;
      Named_object* no = fe->named_object();
      if (no->is_function() && !no->func_value()->is_method())
        no->func_value()->descriptor(this->gogo_, no);
      else if (no->is_function_declaration()
               && !no->func_declaration_value()->type()->is_method()
               && !Linemap::is_predeclared_location(no->location()))
        no->func_declaration_value()->descriptor(this->gogo_, no);
      return TRAVERSE_CONTINUE;
    }

  Bound_method_expression* bme = expr->bound_method_expression();
  if (bme != NULL)
    {
      // We would not get here for a call to this method, so this is a
      // method value.  We need to create a thunk.
      Bound_method_expression::create_thunk(this->gogo_, bme->method(),
                                            bme->function());
      return TRAVERSE_CONTINUE;
    }

  Interface_field_reference_expression* ifre =
    expr->interface_field_reference_expression();
  if (ifre != NULL)
    {
      // We would not get here for a call to this interface method, so
      // this is a method value.  We need to create a thunk.
      Interface_type* type = ifre->expr()->type()->interface_type();
      if (type != NULL)
        Interface_field_reference_expression::create_thunk(this->gogo_, type,
                                                           ifre->name());
      return TRAVERSE_CONTINUE;
    }

  Call_expression* ce = expr->call_expression();
  if (ce != NULL)
    {
      Expression* fn = ce->fn();
      if (fn->func_expression() != NULL
          || fn->bound_method_expression() != NULL
          || fn->interface_field_reference_expression() != NULL)
        {
          // Traverse the arguments but not the function.
          Expression_list* args = ce->args();
          if (args != NULL)
            {
              if (args->traverse(this) == TRAVERSE_EXIT)
                return TRAVERSE_EXIT;
            }
          return TRAVERSE_SKIP_COMPONENTS;
        }
    }

  return TRAVERSE_CONTINUE;
}

// Create function descriptors as needed.  We need a function
// descriptor for all exported functions and for all functions that
// are referenced without being called.

void
Gogo::create_function_descriptors()
{
  // Create a function descriptor for any exported function that is
  // declared in this package.  This is so that we have a descriptor
  // for functions written in assembly.  Gather the descriptors first
  // so that we don't add declarations while looping over them.
  std::vector<Named_object*> fndecls;
  Bindings* b = this->package_->bindings();
  for (Bindings::const_declarations_iterator p = b->begin_declarations();
       p != b->end_declarations();
       ++p)
    {
      Named_object* no = p->second;
      if (no->is_function_declaration()
          && !no->func_declaration_value()->type()->is_method()
          && !Linemap::is_predeclared_location(no->location())
          && !Gogo::is_hidden_name(no->name()))
        fndecls.push_back(no);
    }
  for (std::vector<Named_object*>::const_iterator p = fndecls.begin();
       p != fndecls.end();
       ++p)
    (*p)->func_declaration_value()->descriptor(this, *p);
  fndecls.clear();

  Create_function_descriptors cfd(this);
  this->traverse(&cfd);
}

// Look for interface types to finalize methods of inherited
// interfaces.

class Finalize_methods : public Traverse
{
 public:
  Finalize_methods(Gogo* gogo)
    : Traverse(traverse_types),
      gogo_(gogo)
  { }

  int
  type(Type*);

 private:
  Gogo* gogo_;
};

// Finalize the methods of an interface type.

int
Finalize_methods::type(Type* t)
{
  // Check the classification so that we don't finalize the methods
  // twice for a named interface type.
  switch (t->classification())
    {
    case Type::TYPE_INTERFACE:
      t->interface_type()->finalize_methods();
      break;

    case Type::TYPE_NAMED:
      {
        // We have to finalize the methods of the real type first.
        // But if the real type is a struct type, then we only want to
        // finalize the methods of the field types, not of the struct
        // type itself.  We don't want to add methods to the struct,
        // since it has a name.
        Named_type* nt = t->named_type();
        Type* rt = nt->real_type();
        if (rt->classification() != Type::TYPE_STRUCT)
          {
            if (Type::traverse(rt, this) == TRAVERSE_EXIT)
              return TRAVERSE_EXIT;
          }
        else
          {
            if (rt->struct_type()->traverse_field_types(this) == TRAVERSE_EXIT)
              return TRAVERSE_EXIT;
          }

        nt->finalize_methods(this->gogo_);

        // If this type is defined in a different package, then finalize the
        // types of all the methods, since we won't see them otherwise.
        if (nt->named_object()->package() != NULL && nt->has_any_methods())
          {
            const Methods* methods = nt->methods();
            for (Methods::const_iterator p = methods->begin();
                 p != methods->end();
                 ++p)
              {
                if (Type::traverse(p->second->type(), this) == TRAVERSE_EXIT)
                  return TRAVERSE_EXIT;
              }
          }

        // Finalize the types of all methods that are declared but not
        // defined, since we won't see the declarations otherwise.
        if (nt->named_object()->package() == NULL
            && nt->local_methods() != NULL)
          {
            const Bindings* methods = nt->local_methods();
            for (Bindings::const_declarations_iterator p =
                   methods->begin_declarations();
                 p != methods->end_declarations();
                 p++)
              {
                if (p->second->is_function_declaration())
                  {
                    Type* mt = p->second->func_declaration_value()->type();
                    if (Type::traverse(mt, this) == TRAVERSE_EXIT)
                      return TRAVERSE_EXIT;
                  }
              }
          }

        return TRAVERSE_SKIP_COMPONENTS;
      }

    case Type::TYPE_STRUCT:
      // Traverse the field types first in case there is an embedded
      // field with methods that the struct should inherit.
      if (t->struct_type()->traverse_field_types(this) == TRAVERSE_EXIT)
          return TRAVERSE_EXIT;
      t->struct_type()->finalize_methods(this->gogo_);
      return TRAVERSE_SKIP_COMPONENTS;

    default:
      break;
    }

  return TRAVERSE_CONTINUE;
}

// Finalize method lists and build stub methods for types.

void
Gogo::finalize_methods()
{
  Finalize_methods finalize(this);
  this->traverse(&finalize);
}

// Set types for unspecified variables and constants.

void
Gogo::determine_types()
{
  Bindings* bindings = this->current_bindings();
  for (Bindings::const_definitions_iterator p = bindings->begin_definitions();
       p != bindings->end_definitions();
       ++p)
    {
      if ((*p)->is_function())
        (*p)->func_value()->determine_types();
      else if ((*p)->is_variable())
        (*p)->var_value()->determine_type();
      else if ((*p)->is_const())
        (*p)->const_value()->determine_type();

      // See if a variable requires us to build an initialization
      // function.  We know that we will see all global variables
      // here.
      if (!this->need_init_fn_ && (*p)->is_variable())
        {
          Variable* variable = (*p)->var_value();

          // If this is a global variable which requires runtime
          // initialization, we need an initialization function.
          if (!variable->is_global())
            ;
          else if (variable->init() == NULL)
            ;
          else if (variable->type()->interface_type() != NULL)
            this->need_init_fn_ = true;
          else if (variable->init()->is_constant())
            ;
          else if (!variable->init()->is_composite_literal())
            this->need_init_fn_ = true;
          else if (variable->init()->is_nonconstant_composite_literal())
            this->need_init_fn_ = true;

          // If this is a global variable which holds a pointer value,
          // then we need an initialization function to register it as a
          // GC root.
          if (variable->is_global() && variable->type()->has_pointer())
            this->need_init_fn_ = true;
        }
    }

  // Determine the types of constants in packages.
  for (Packages::const_iterator p = this->packages_.begin();
       p != this->packages_.end();
       ++p)
    p->second->determine_types();
}

// Traversal class used for type checking.

class Check_types_traverse : public Traverse
{
 public:
  Check_types_traverse(Gogo* gogo)
    : Traverse(traverse_variables
               | traverse_constants
               | traverse_functions
               | traverse_statements
               | traverse_expressions),
      gogo_(gogo)
  { }

  int
  variable(Named_object*);

  int
  constant(Named_object*, bool);

  int
  function(Named_object*);

  int
  statement(Block*, size_t* pindex, Statement*);

  int
  expression(Expression**);

 private:
  // General IR.
  Gogo* gogo_;
};

// Check that a variable initializer has the right type.

int
Check_types_traverse::variable(Named_object* named_object)
{
  if (named_object->is_variable())
    {
      Variable* var = named_object->var_value();

      // Give error if variable type is not defined.
      var->type()->base();

      Expression* init = var->init();
      std::string reason;
      if (init != NULL
          && !Type::are_assignable(var->type(), init->type(), &reason))
        {
          if (reason.empty())
            error_at(var->location(), "incompatible type in initialization");
          else
            error_at(var->location(),
                     "incompatible type in initialization (%s)",
                     reason.c_str());
          init = Expression::make_error(named_object->location());
          var->clear_init();
        }
      else if (init != NULL
               && init->func_expression() != NULL)
        {
          Named_object* no = init->func_expression()->named_object();
          Function_type* fntype;
          if (no->is_function())
            fntype = no->func_value()->type();
          else if (no->is_function_declaration())
            fntype = no->func_declaration_value()->type();
          else
            go_unreachable();

          // Builtin functions cannot be used as function values for variable
          // initialization.
          if (fntype->is_builtin())
            {
              error_at(init->location(),
                       "invalid use of special builtin function %qs; "
                       "must be called",
                       no->message_name().c_str());
            }
        }
      if (!var->is_used()
          && !var->is_global()
          && !var->is_parameter()
          && !var->is_receiver()
          && !var->type()->is_error()
          && (init == NULL || !init->is_error_expression())
          && !Lex::is_invalid_identifier(named_object->name()))
        error_at(var->location(), "%qs declared and not used",
                 named_object->message_name().c_str());
    }
  return TRAVERSE_CONTINUE;
}

// Check that a constant initializer has the right type.

int
Check_types_traverse::constant(Named_object* named_object, bool)
{
  Named_constant* constant = named_object->const_value();
  Type* ctype = constant->type();
  if (ctype->integer_type() == NULL
      && ctype->float_type() == NULL
      && ctype->complex_type() == NULL
      && !ctype->is_boolean_type()
      && !ctype->is_string_type())
    {
      if (ctype->is_nil_type())
        error_at(constant->location(), "const initializer cannot be nil");
      else if (!ctype->is_error())
        error_at(constant->location(), "invalid constant type");
      constant->set_error();
    }
  else if (!constant->expr()->is_constant())
    {
      error_at(constant->expr()->location(), "expression is not constant");
      constant->set_error();
    }
  else if (!Type::are_assignable(constant->type(), constant->expr()->type(),
                                 NULL))
    {
      error_at(constant->location(),
               "initialization expression has wrong type");
      constant->set_error();
    }
  return TRAVERSE_CONTINUE;
}

// There are no types to check in a function, but this is where we
// issue warnings about labels which are defined but not referenced.

int
Check_types_traverse::function(Named_object* no)
{
  no->func_value()->check_labels();
  return TRAVERSE_CONTINUE;
}

// Check that types are valid in a statement.

int
Check_types_traverse::statement(Block*, size_t*, Statement* s)
{
  s->check_types(this->gogo_);
  return TRAVERSE_CONTINUE;
}

// Check that types are valid in an expression.

int
Check_types_traverse::expression(Expression** expr)
{
  (*expr)->check_types(this->gogo_);
  return TRAVERSE_CONTINUE;
}

// Check that types are valid.

void
Gogo::check_types()
{
  Check_types_traverse traverse(this);
  this->traverse(&traverse);

  Bindings* bindings = this->current_bindings();
  for (Bindings::const_declarations_iterator p = bindings->begin_declarations();
       p != bindings->end_declarations();
       ++p)
    {
      // Also check the types in a function declaration's signature.
      Named_object* no = p->second;
      if (no->is_function_declaration())
        no->func_declaration_value()->check_types();
    }
}

// Check the types in a single block.

void
Gogo::check_types_in_block(Block* block)
{
  Check_types_traverse traverse(this);
  block->traverse(&traverse);
}

// A traversal class used to find a single shortcut operator within an
// expression.

class Find_shortcut : public Traverse
{
 public:
  Find_shortcut()
    : Traverse(traverse_blocks
               | traverse_statements
               | traverse_expressions),
      found_(NULL)
  { }

  // A pointer to the expression which was found, or NULL if none was
  // found.
  Expression**
  found() const
  { return this->found_; }

 protected:
  int
  block(Block*)
  { return TRAVERSE_SKIP_COMPONENTS; }

  int
  statement(Block*, size_t*, Statement*)
  { return TRAVERSE_SKIP_COMPONENTS; }

  int
  expression(Expression**);

 private:
  Expression** found_;
};

// Find a shortcut expression.

int
Find_shortcut::expression(Expression** pexpr)
{
  Expression* expr = *pexpr;
  Binary_expression* be = expr->binary_expression();
  if (be == NULL)
    return TRAVERSE_CONTINUE;
  Operator op = be->op();
  if (op != OPERATOR_OROR && op != OPERATOR_ANDAND)
    return TRAVERSE_CONTINUE;
  go_assert(this->found_ == NULL);
  this->found_ = pexpr;
  return TRAVERSE_EXIT;
}

// A traversal class used to turn shortcut operators into explicit if
// statements.

class Shortcuts : public Traverse
{
 public:
  Shortcuts(Gogo* gogo)
    : Traverse(traverse_variables
               | traverse_statements),
      gogo_(gogo)
  { }

 protected:
  int
  variable(Named_object*);

  int
  statement(Block*, size_t*, Statement*);

 private:
  // Convert a shortcut operator.
  Statement*
  convert_shortcut(Block* enclosing, Expression** pshortcut);

  // The IR.
  Gogo* gogo_;
};

// Remove shortcut operators in a single statement.

int
Shortcuts::statement(Block* block, size_t* pindex, Statement* s)
{
  // FIXME: This approach doesn't work for switch statements, because
  // we add the new statements before the whole switch when we need to
  // instead add them just before the switch expression.  The right
  // fix is probably to lower switch statements with nonconstant cases
  // to a series of conditionals.
  if (s->switch_statement() != NULL)
    return TRAVERSE_CONTINUE;

  while (true)
    {
      Find_shortcut find_shortcut;

      // If S is a variable declaration, then ordinary traversal won't
      // do anything.  We want to explicitly traverse the
      // initialization expression if there is one.
      Variable_declaration_statement* vds = s->variable_declaration_statement();
      Expression* init = NULL;
      if (vds == NULL)
        s->traverse_contents(&find_shortcut);
      else
        {
          init = vds->var()->var_value()->init();
          if (init == NULL)
            return TRAVERSE_CONTINUE;
          init->traverse(&init, &find_shortcut);
        }
      Expression** pshortcut = find_shortcut.found();
      if (pshortcut == NULL)
        return TRAVERSE_CONTINUE;

      Statement* snew = this->convert_shortcut(block, pshortcut);
      block->insert_statement_before(*pindex, snew);
      ++*pindex;

      if (pshortcut == &init)
        vds->var()->var_value()->set_init(init);
    }
}

// Remove shortcut operators in the initializer of a global variable.

int
Shortcuts::variable(Named_object* no)
{
  if (no->is_result_variable())
    return TRAVERSE_CONTINUE;
  Variable* var = no->var_value();
  Expression* init = var->init();
  if (!var->is_global() || init == NULL)
    return TRAVERSE_CONTINUE;

  while (true)
    {
      Find_shortcut find_shortcut;
      init->traverse(&init, &find_shortcut);
      Expression** pshortcut = find_shortcut.found();
      if (pshortcut == NULL)
        return TRAVERSE_CONTINUE;

      Statement* snew = this->convert_shortcut(NULL, pshortcut);
      var->add_preinit_statement(this->gogo_, snew);
      if (pshortcut == &init)
        var->set_init(init);
    }
}

// Given an expression which uses a shortcut operator, return a
// statement which implements it, and update *PSHORTCUT accordingly.

Statement*
Shortcuts::convert_shortcut(Block* enclosing, Expression** pshortcut)
{
  Binary_expression* shortcut = (*pshortcut)->binary_expression();
  Expression* left = shortcut->left();
  Expression* right = shortcut->right();
  Location loc = shortcut->location();

  Block* retblock = new Block(enclosing, loc);
  retblock->set_end_location(loc);

  Temporary_statement* ts = Statement::make_temporary(shortcut->type(),
                                                      left, loc);
  retblock->add_statement(ts);

  Block* block = new Block(retblock, loc);
  block->set_end_location(loc);
  Expression* tmpref = Expression::make_temporary_reference(ts, loc);
  Statement* assign = Statement::make_assignment(tmpref, right, loc);
  block->add_statement(assign);

  Expression* cond = Expression::make_temporary_reference(ts, loc);
  if (shortcut->binary_expression()->op() == OPERATOR_OROR)
    cond = Expression::make_unary(OPERATOR_NOT, cond, loc);

  Statement* if_statement = Statement::make_if_statement(cond, block, NULL,
                                                         loc);
  retblock->add_statement(if_statement);

  *pshortcut = Expression::make_temporary_reference(ts, loc);

  delete shortcut;

  // Now convert any shortcut operators in LEFT and RIGHT.
  Shortcuts shortcuts(this->gogo_);
  retblock->traverse(&shortcuts);

  return Statement::make_block_statement(retblock, loc);
}

// Turn shortcut operators into explicit if statements.  Doing this
// considerably simplifies the order of evaluation rules.

void
Gogo::remove_shortcuts()
{
  Shortcuts shortcuts(this);
  this->traverse(&shortcuts);
}

// A traversal class which finds all the expressions which must be
// evaluated in order within a statement or larger expression.  This
// is used to implement the rules about order of evaluation.

class Find_eval_ordering : public Traverse
{
 private:
  typedef std::vector<Expression**> Expression_pointers;

 public:
  Find_eval_ordering()
    : Traverse(traverse_blocks
               | traverse_statements
               | traverse_expressions),
      exprs_()
  { }

  size_t
  size() const
  { return this->exprs_.size(); }

  typedef Expression_pointers::const_iterator const_iterator;

  const_iterator
  begin() const
  { return this->exprs_.begin(); }

  const_iterator
  end() const
  { return this->exprs_.end(); }

 protected:
  int
  block(Block*)
  { return TRAVERSE_SKIP_COMPONENTS; }

  int
  statement(Block*, size_t*, Statement*)
  { return TRAVERSE_SKIP_COMPONENTS; }

  int
  expression(Expression**);

 private:
  // A list of pointers to expressions with side-effects.
  Expression_pointers exprs_;
};

// If an expression must be evaluated in order, put it on the list.

int
Find_eval_ordering::expression(Expression** expression_pointer)
{
  // We have to look at subexpressions before this one.
  if ((*expression_pointer)->traverse_subexpressions(this) == TRAVERSE_EXIT)
    return TRAVERSE_EXIT;
  if ((*expression_pointer)->must_eval_in_order())
    this->exprs_.push_back(expression_pointer);
  return TRAVERSE_SKIP_COMPONENTS;
}

// A traversal class for ordering evaluations.

class Order_eval : public Traverse
{
 public:
  Order_eval(Gogo* gogo)
    : Traverse(traverse_variables
               | traverse_statements),
      gogo_(gogo)
  { }

  int
  variable(Named_object*);

  int
  statement(Block*, size_t*, Statement*);

 private:
  // The IR.
  Gogo* gogo_;
};

// Implement the order of evaluation rules for a statement.

int
Order_eval::statement(Block* block, size_t* pindex, Statement* s)
{
  // FIXME: This approach doesn't work for switch statements, because
  // we add the new statements before the whole switch when we need to
  // instead add them just before the switch expression.  The right
  // fix is probably to lower switch statements with nonconstant cases
  // to a series of conditionals.
  if (s->switch_statement() != NULL)
    return TRAVERSE_CONTINUE;

  Find_eval_ordering find_eval_ordering;

  // If S is a variable declaration, then ordinary traversal won't do
  // anything.  We want to explicitly traverse the initialization
  // expression if there is one.
  Variable_declaration_statement* vds = s->variable_declaration_statement();
  Expression* init = NULL;
  Expression* orig_init = NULL;
  if (vds == NULL)
    s->traverse_contents(&find_eval_ordering);
  else
    {
      init = vds->var()->var_value()->init();
      if (init == NULL)
        return TRAVERSE_CONTINUE;
      orig_init = init;

      // It might seem that this could be
      // init->traverse_subexpressions.  Unfortunately that can fail
      // in a case like
      //   var err os.Error
      //   newvar, err := call(arg())
      // Here newvar will have an init of call result 0 of
      // call(arg()).  If we only traverse subexpressions, we will
      // only find arg(), and we won't bother to move anything out.
      // Then we get to the assignment to err, we will traverse the
      // whole statement, and this time we will find both call() and
      // arg(), and so we will move them out.  This will cause them to
      // be put into temporary variables before the assignment to err
      // but after the declaration of newvar.  To avoid that problem,
      // we traverse the entire expression here.
      Expression::traverse(&init, &find_eval_ordering);
    }

  size_t c = find_eval_ordering.size();
  if (c == 0)
    return TRAVERSE_CONTINUE;

  // If there is only one expression with a side-effect, we can
  // usually leave it in place.
  if (c == 1)
    {
      switch (s->classification())
        {
        case Statement::STATEMENT_ASSIGNMENT:
          // For an assignment statement, we need to evaluate an
          // expression on the right hand side before we evaluate any
          // index expression on the left hand side, so for that case
          // we always move the expression.  Otherwise we mishandle
          // m[0] = len(m) where m is a map.
          break;

        case Statement::STATEMENT_EXPRESSION:
          {
            // If this is a call statement that doesn't return any
            // values, it will not have been counted as a value to
            // move.  We need to move any subexpressions in case they
            // are themselves call statements that require passing a
            // closure.
            Expression* expr = s->expression_statement()->expr();
            if (expr->call_expression() != NULL
                && expr->call_expression()->result_count() == 0)
              break;
            return TRAVERSE_CONTINUE;
          }

        default:
          // We can leave the expression in place.
          return TRAVERSE_CONTINUE;
        }
    }

  bool is_thunk = s->thunk_statement() != NULL;
  for (Find_eval_ordering::const_iterator p = find_eval_ordering.begin();
       p != find_eval_ordering.end();
       ++p)
    {
      Expression** pexpr = *p;

      // The last expression in a thunk will be the call passed to go
      // or defer, which we must not evaluate early.
      if (is_thunk && p + 1 == find_eval_ordering.end())
        break;

      Location loc = (*pexpr)->location();
      Statement* s;
      if ((*pexpr)->call_expression() == NULL
          || (*pexpr)->call_expression()->result_count() < 2)
        {
          Temporary_statement* ts = Statement::make_temporary(NULL, *pexpr,
                                                              loc);
          s = ts;
          *pexpr = Expression::make_temporary_reference(ts, loc);
        }
      else
        {
          // A call expression which returns multiple results needs to
          // be handled specially.  We can't create a temporary
          // because there is no type to give it.  Any actual uses of
          // the values will be done via Call_result_expressions.
          s = Statement::make_statement(*pexpr, true);
        }

      block->insert_statement_before(*pindex, s);
      ++*pindex;
    }

  if (init != orig_init)
    vds->var()->var_value()->set_init(init);

  return TRAVERSE_CONTINUE;
}

// Implement the order of evaluation rules for the initializer of a
// global variable.

int
Order_eval::variable(Named_object* no)
{
  if (no->is_result_variable())
    return TRAVERSE_CONTINUE;
  Variable* var = no->var_value();
  Expression* init = var->init();
  if (!var->is_global() || init == NULL)
    return TRAVERSE_CONTINUE;

  Find_eval_ordering find_eval_ordering;
  Expression::traverse(&init, &find_eval_ordering);

  if (find_eval_ordering.size() <= 1)
    {
      // If there is only one expression with a side-effect, we can
      // leave it in place.
      return TRAVERSE_SKIP_COMPONENTS;
    }

  Expression* orig_init = init;

  for (Find_eval_ordering::const_iterator p = find_eval_ordering.begin();
       p != find_eval_ordering.end();
       ++p)
    {
      Expression** pexpr = *p;
      Location loc = (*pexpr)->location();
      Statement* s;
      if ((*pexpr)->call_expression() == NULL
          || (*pexpr)->call_expression()->result_count() < 2)
        {
          Temporary_statement* ts = Statement::make_temporary(NULL, *pexpr,
                                                              loc);
          s = ts;
          *pexpr = Expression::make_temporary_reference(ts, loc);
        }
      else
        {
          // A call expression which returns multiple results needs to
          // be handled specially.
          s = Statement::make_statement(*pexpr, true);
        }
      var->add_preinit_statement(this->gogo_, s);
    }

  if (init != orig_init)
    var->set_init(init);

  return TRAVERSE_SKIP_COMPONENTS;
}

// Use temporary variables to implement the order of evaluation rules.

void
Gogo::order_evaluations()
{
  Order_eval order_eval(this);
  this->traverse(&order_eval);
}

// Traversal to flatten parse tree after order of evaluation rules are applied.

class Flatten : public Traverse
{
 public:
  Flatten(Gogo* gogo, Named_object* function)
    : Traverse(traverse_variables
               | traverse_functions
               | traverse_statements
               | traverse_expressions),
      gogo_(gogo), function_(function), inserter_()
  { }

  void
  set_inserter(const Statement_inserter* inserter)
  { this->inserter_ = *inserter; }

  int
  variable(Named_object*);

  int
  function(Named_object*);

  int
  statement(Block*, size_t* pindex, Statement*);

  int
  expression(Expression**);

 private:
  // General IR.
  Gogo* gogo_;
  // The function we are traversing.
  Named_object* function_;
  // Current statement inserter for use by expressions.
  Statement_inserter inserter_;
};

// Flatten variables.

int
Flatten::variable(Named_object* no)
{
  if (!no->is_variable())
    return TRAVERSE_CONTINUE;

  if (no->is_variable() && no->var_value()->is_global())
    {
      // Global variables can have loops in their initialization
      // expressions.  This is handled in flatten_init_expression.
      no->var_value()->flatten_init_expression(this->gogo_, this->function_,
                                               &this->inserter_);
      return TRAVERSE_CONTINUE;
    }

  go_assert(!no->var_value()->has_pre_init());

  return TRAVERSE_SKIP_COMPONENTS;
}

// Flatten the body of a function.  Record the function while flattening it,
// so that we can pass it down when flattening an expression.

int
Flatten::function(Named_object* no)
{
  go_assert(this->function_ == NULL);
  this->function_ = no;
  int t = no->func_value()->traverse(this);
  this->function_ = NULL;

  if (t == TRAVERSE_EXIT)
    return t;
  return TRAVERSE_SKIP_COMPONENTS;
}

// Flatten statement parse trees.

int
Flatten::statement(Block* block, size_t* pindex, Statement* sorig)
{
  // Because we explicitly traverse the statement's contents
  // ourselves, we want to skip block statements here.  There is
  // nothing to flatten in a block statement.
  if (sorig->is_block_statement())
    return TRAVERSE_CONTINUE;

  Statement_inserter hold_inserter(this->inserter_);
  this->inserter_ = Statement_inserter(block, pindex);

  // Flatten the expressions first.
  int t = sorig->traverse_contents(this);
  if (t == TRAVERSE_EXIT)
    {
      this->inserter_ = hold_inserter;
      return t;
    }

  // Keep flattening until nothing changes.
  Statement* s = sorig;
  while (true)
    {
      Statement* snew = s->flatten(this->gogo_, this->function_, block,
                                   &this->inserter_);
      if (snew == s)
        break;
      s = snew;
      t = s->traverse_contents(this);
      if (t == TRAVERSE_EXIT)
        {
          this->inserter_ = hold_inserter;
          return t;
        }
    }

  if (s != sorig)
    block->replace_statement(*pindex, s);

  this->inserter_ = hold_inserter;
  return TRAVERSE_SKIP_COMPONENTS;
}

// Flatten expression parse trees.

int
Flatten::expression(Expression** pexpr)
{
  // Keep flattening until nothing changes.
  while (true)
    {
      Expression* e = *pexpr;
      if (e->traverse_subexpressions(this) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;

      Expression* enew = e->flatten(this->gogo_, this->function_,
                                    &this->inserter_);
      if (enew == e)
        break;
      *pexpr = enew;
    }
  return TRAVERSE_SKIP_COMPONENTS;
}

// Flatten a block.

void
Gogo::flatten_block(Named_object* function, Block* block)
{
  Flatten flatten(this, function);
  block->traverse(&flatten);
}

// Flatten an expression.  INSERTER may be NULL, in which case the
// expression had better not need to create any temporaries.

void
Gogo::flatten_expression(Named_object* function, Statement_inserter* inserter,
                         Expression** pexpr)
{
  Flatten flatten(this, function);
  if (inserter != NULL)
    flatten.set_inserter(inserter);
  flatten.expression(pexpr);
}

void
Gogo::flatten()
{
  Flatten flatten(this, NULL);
  this->traverse(&flatten);
}

// Traversal to convert calls to the predeclared recover function to
// pass in an argument indicating whether it can recover from a panic
// or not.

class Convert_recover : public Traverse
{
 public:
  Convert_recover(Named_object* arg)
    : Traverse(traverse_expressions),
      arg_(arg)
  { }

 protected:
  int
  expression(Expression**);

 private:
  // The argument to pass to the function.
  Named_object* arg_;
};

// Convert calls to recover.

int
Convert_recover::expression(Expression** pp)
{
  Call_expression* ce = (*pp)->call_expression();
  if (ce != NULL && ce->is_recover_call())
    ce->set_recover_arg(Expression::make_var_reference(this->arg_,
                                                       ce->location()));
  return TRAVERSE_CONTINUE;
}

// Traversal for build_recover_thunks.

class Build_recover_thunks : public Traverse
{
 public:
  Build_recover_thunks(Gogo* gogo)
    : Traverse(traverse_functions),
      gogo_(gogo)
  { }

  int
  function(Named_object*);

 private:
  Expression*
  can_recover_arg(Location);

  // General IR.
  Gogo* gogo_;
};

// If this function calls recover, turn it into a thunk.

int
Build_recover_thunks::function(Named_object* orig_no)
{
  Function* orig_func = orig_no->func_value();
  if (!orig_func->calls_recover()
      || orig_func->is_recover_thunk()
      || orig_func->has_recover_thunk())
    return TRAVERSE_CONTINUE;

  Gogo* gogo = this->gogo_;
  Location location = orig_func->location();

  static int count;
  char buf[50];

  Function_type* orig_fntype = orig_func->type();
  Typed_identifier_list* new_params = new Typed_identifier_list();
  std::string receiver_name;
  if (orig_fntype->is_method())
    {
      const Typed_identifier* receiver = orig_fntype->receiver();
      snprintf(buf, sizeof buf, "rt.%u", count);
      ++count;
      receiver_name = buf;
      new_params->push_back(Typed_identifier(receiver_name, receiver->type(),
                                             receiver->location()));
    }
  const Typed_identifier_list* orig_params = orig_fntype->parameters();
  if (orig_params != NULL && !orig_params->empty())
    {
      for (Typed_identifier_list::const_iterator p = orig_params->begin();
           p != orig_params->end();
           ++p)
        {
          snprintf(buf, sizeof buf, "pt.%u", count);
          ++count;
          new_params->push_back(Typed_identifier(buf, p->type(),
                                                 p->location()));
        }
    }
  snprintf(buf, sizeof buf, "pr.%u", count);
  ++count;
  std::string can_recover_name = buf;
  new_params->push_back(Typed_identifier(can_recover_name,
                                         Type::lookup_bool_type(),
                                         orig_fntype->location()));

  const Typed_identifier_list* orig_results = orig_fntype->results();
  Typed_identifier_list* new_results;
  if (orig_results == NULL || orig_results->empty())
    new_results = NULL;
  else
    {
      new_results = new Typed_identifier_list();
      for (Typed_identifier_list::const_iterator p = orig_results->begin();
           p != orig_results->end();
           ++p)
        new_results->push_back(Typed_identifier("", p->type(), p->location()));
    }

  Function_type *new_fntype = Type::make_function_type(NULL, new_params,
                                                       new_results,
                                                       orig_fntype->location());
  if (orig_fntype->is_varargs())
    new_fntype->set_is_varargs();

  std::string name = orig_no->name();
  if (orig_fntype->is_method())
    name += "$" + orig_fntype->receiver()->type()->mangled_name(gogo);
  name += "$recover";
  Named_object *new_no = gogo->start_function(name, new_fntype, false,
                                              location);
  Function *new_func = new_no->func_value();
  if (orig_func->enclosing() != NULL)
    new_func->set_enclosing(orig_func->enclosing());

  // We build the code for the original function attached to the new
  // function, and then swap the original and new function bodies.
  // This means that existing references to the original function will
  // then refer to the new function.  That makes this code a little
  // confusing, in that the reference to NEW_NO really refers to the
  // other function, not the one we are building.

  Expression* closure = NULL;
  if (orig_func->needs_closure())
    {
      // For the new function we are creating, declare a new parameter
      // variable NEW_CLOSURE_NO and set it to be the closure variable
      // of the function.  This will be set to the closure value
      // passed in by the caller.  Then pass a reference to this
      // variable as the closure value when calling the original
      // function.  In other words, simply pass the closure value
      // through the thunk we are creating.
      Named_object* orig_closure_no = orig_func->closure_var();
      Variable* orig_closure_var = orig_closure_no->var_value();
      Variable* new_var = new Variable(orig_closure_var->type(), NULL, false,
                                       false, false, location);
      new_var->set_is_closure();
      snprintf(buf, sizeof buf, "closure.%u", count);
      ++count;
      Named_object* new_closure_no = Named_object::make_variable(buf, NULL,
                                                                 new_var);
      new_func->set_closure_var(new_closure_no);
      closure = Expression::make_var_reference(new_closure_no, location);
    }

  Expression* fn = Expression::make_func_reference(new_no, closure, location);

  Expression_list* args = new Expression_list();
  if (new_params != NULL)
    {
      // Note that we skip the last parameter, which is the boolean
      // indicating whether recover can succed.
      for (Typed_identifier_list::const_iterator p = new_params->begin();
           p + 1 != new_params->end();
           ++p)
        {
          Named_object* p_no = gogo->lookup(p->name(), NULL);
          go_assert(p_no != NULL
                     && p_no->is_variable()
                     && p_no->var_value()->is_parameter());
          args->push_back(Expression::make_var_reference(p_no, location));
        }
    }
  args->push_back(this->can_recover_arg(location));

  gogo->start_block(location);

  Call_expression* call = Expression::make_call(fn, args, false, location);

  // Any varargs call has already been lowered.
  call->set_varargs_are_lowered();

  Statement* s = Statement::make_return_from_call(call, location);
  s->determine_types();
  gogo->add_statement(s);

  Block* b = gogo->finish_block(location);

  gogo->add_block(b, location);

  // Lower the call in case it returns multiple results.
  gogo->lower_block(new_no, b);

  gogo->finish_function(location);

  // Swap the function bodies and types.
  new_func->swap_for_recover(orig_func);
  orig_func->set_is_recover_thunk();
  new_func->set_calls_recover();
  new_func->set_has_recover_thunk();

  Bindings* orig_bindings = orig_func->block()->bindings();
  Bindings* new_bindings = new_func->block()->bindings();
  if (orig_fntype->is_method())
    {
      // We changed the receiver to be a regular parameter.  We have
      // to update the binding accordingly in both functions.
      Named_object* orig_rec_no = orig_bindings->lookup_local(receiver_name);
      go_assert(orig_rec_no != NULL
                 && orig_rec_no->is_variable()
                 && !orig_rec_no->var_value()->is_receiver());
      orig_rec_no->var_value()->set_is_receiver();

      std::string new_receiver_name(orig_fntype->receiver()->name());
      if (new_receiver_name.empty())
        {
          // Find the receiver.  It was named "r.NNN" in
          // Gogo::start_function.
          for (Bindings::const_definitions_iterator p =
                 new_bindings->begin_definitions();
               p != new_bindings->end_definitions();
               ++p)
            {
              const std::string& pname((*p)->name());
              if (pname[0] == 'r' && pname[1] == '.')
                {
                  new_receiver_name = pname;
                  break;
                }
            }
          go_assert(!new_receiver_name.empty());
        }
      Named_object* new_rec_no = new_bindings->lookup_local(new_receiver_name);
      if (new_rec_no == NULL)
        go_assert(saw_errors());
      else
        {
          go_assert(new_rec_no->is_variable()
                     && new_rec_no->var_value()->is_receiver());
          new_rec_no->var_value()->set_is_not_receiver();
        }
    }

  // Because we flipped blocks but not types, the can_recover
  // parameter appears in the (now) old bindings as a parameter.
  // Change it to a local variable, whereupon it will be discarded.
  Named_object* can_recover_no = orig_bindings->lookup_local(can_recover_name);
  go_assert(can_recover_no != NULL
             && can_recover_no->is_variable()
             && can_recover_no->var_value()->is_parameter());
  orig_bindings->remove_binding(can_recover_no);

  // Add the can_recover argument to the (now) new bindings, and
  // attach it to any recover statements.
  Variable* can_recover_var = new Variable(Type::lookup_bool_type(), NULL,
                                           false, true, false, location);
  can_recover_no = new_bindings->add_variable(can_recover_name, NULL,
                                              can_recover_var);
  Convert_recover convert_recover(can_recover_no);
  new_func->traverse(&convert_recover);

  // Update the function pointers in any named results.
  new_func->update_result_variables();
  orig_func->update_result_variables();

  return TRAVERSE_CONTINUE;
}

// Return the expression to pass for the .can_recover parameter to the
// new function.  This indicates whether a call to recover may return
// non-nil.  The expression is
// __go_can_recover(__builtin_return_address()).

Expression*
Build_recover_thunks::can_recover_arg(Location location)
{
  static Named_object* builtin_return_address;
  if (builtin_return_address == NULL)
    {
      const Location bloc = Linemap::predeclared_location();

      Typed_identifier_list* param_types = new Typed_identifier_list();
      Type* uint_type = Type::lookup_integer_type("uint");
      param_types->push_back(Typed_identifier("l", uint_type, bloc));

      Typed_identifier_list* return_types = new Typed_identifier_list();
      Type* voidptr_type = Type::make_pointer_type(Type::make_void_type());
      return_types->push_back(Typed_identifier("", voidptr_type, bloc));

      Function_type* fntype = Type::make_function_type(NULL, param_types,
                                                       return_types, bloc);
      builtin_return_address =
        Named_object::make_function_declaration("__builtin_return_address",
                                                NULL, fntype, bloc);
      const char* n = "__builtin_return_address";
      builtin_return_address->func_declaration_value()->set_asm_name(n);
    }

  static Named_object* can_recover;
  if (can_recover == NULL)
    {
      const Location bloc = Linemap::predeclared_location();
      Typed_identifier_list* param_types = new Typed_identifier_list();
      Type* voidptr_type = Type::make_pointer_type(Type::make_void_type());
      param_types->push_back(Typed_identifier("a", voidptr_type, bloc));
      Type* boolean_type = Type::lookup_bool_type();
      Typed_identifier_list* results = new Typed_identifier_list();
      results->push_back(Typed_identifier("", boolean_type, bloc));
      Function_type* fntype = Type::make_function_type(NULL, param_types,
                                                       results, bloc);
      can_recover = Named_object::make_function_declaration("__go_can_recover",
                                                            NULL, fntype,
                                                            bloc);
      can_recover->func_declaration_value()->set_asm_name("__go_can_recover");
    }

  Expression* fn = Expression::make_func_reference(builtin_return_address,
                                                   NULL, location);

  Expression* zexpr = Expression::make_integer_ul(0, NULL, location);
  Expression_list *args = new Expression_list();
  args->push_back(zexpr);

  Expression* call = Expression::make_call(fn, args, false, location);

  args = new Expression_list();
  args->push_back(call);

  fn = Expression::make_func_reference(can_recover, NULL, location);
  return Expression::make_call(fn, args, false, location);
}

// Build thunks for functions which call recover.  We build a new
// function with an extra parameter, which is whether a call to
// recover can succeed.  We then move the body of this function to
// that one.  We then turn this function into a thunk which calls the
// new one, passing the value of
// __go_can_recover(__builtin_return_address()).  The function will be
// marked as not splitting the stack.  This will cooperate with the
// implementation of defer to make recover do the right thing.

void
Gogo::build_recover_thunks()
{
  Build_recover_thunks build_recover_thunks(this);
  this->traverse(&build_recover_thunks);
}

// Build a call to the runtime error function.

Expression*
Gogo::runtime_error(int code, Location location)
{
  Type* int32_type = Type::lookup_integer_type("int32");
  Expression* code_expr = Expression::make_integer_ul(code, int32_type,
                                                      location);
  return Runtime::make_call(Runtime::RUNTIME_ERROR, location, 1, code_expr);
}

// Look for named types to see whether we need to create an interface
// method table.

class Build_method_tables : public Traverse
{
 public:
  Build_method_tables(Gogo* gogo,
                      const std::vector<Interface_type*>& interfaces)
    : Traverse(traverse_types),
      gogo_(gogo), interfaces_(interfaces)
  { }

  int
  type(Type*);

 private:
  // The IR.
  Gogo* gogo_;
  // A list of locally defined interfaces which have hidden methods.
  const std::vector<Interface_type*>& interfaces_;
};

// Build all required interface method tables for types.  We need to
// ensure that we have an interface method table for every interface
// which has a hidden method, for every named type which implements
// that interface.  Normally we can just build interface method tables
// as we need them.  However, in some cases we can require an
// interface method table for an interface defined in a different
// package for a type defined in that package.  If that interface and
// type both use a hidden method, that is OK.  However, we will not be
// able to build that interface method table when we need it, because
// the type's hidden method will be static.  So we have to build it
// here, and just refer it from other packages as needed.

void
Gogo::build_interface_method_tables()
{
  if (saw_errors())
    return;

  std::vector<Interface_type*> hidden_interfaces;
  hidden_interfaces.reserve(this->interface_types_.size());
  for (std::vector<Interface_type*>::const_iterator pi =
         this->interface_types_.begin();
       pi != this->interface_types_.end();
       ++pi)
    {
      const Typed_identifier_list* methods = (*pi)->methods();
      if (methods == NULL)
        continue;
      for (Typed_identifier_list::const_iterator pm = methods->begin();
           pm != methods->end();
           ++pm)
        {
          if (Gogo::is_hidden_name(pm->name()))
            {
              hidden_interfaces.push_back(*pi);
              break;
            }
        }
    }

  if (!hidden_interfaces.empty())
    {
      // Now traverse the tree looking for all named types.
      Build_method_tables bmt(this, hidden_interfaces);
      this->traverse(&bmt);
    }

  // We no longer need the list of interfaces.

  this->interface_types_.clear();
}

// This is called for each type.  For a named type, for each of the
// interfaces with hidden methods that it implements, create the
// method table.

int
Build_method_tables::type(Type* type)
{
  Named_type* nt = type->named_type();
  Struct_type* st = type->struct_type();
  if (nt != NULL || st != NULL)
    {
      Translate_context context(this->gogo_, NULL, NULL, NULL);
      for (std::vector<Interface_type*>::const_iterator p =
             this->interfaces_.begin();
           p != this->interfaces_.end();
           ++p)
        {
          // We ask whether a pointer to the named type implements the
          // interface, because a pointer can implement more methods
          // than a value.
          if (nt != NULL)
            {
              if ((*p)->implements_interface(Type::make_pointer_type(nt),
                                             NULL))
                {
                  nt->interface_method_table(*p, false)->get_backend(&context);
                  nt->interface_method_table(*p, true)->get_backend(&context);
                }
            }
          else
            {
              if ((*p)->implements_interface(Type::make_pointer_type(st),
                                             NULL))
                {
                  st->interface_method_table(*p, false)->get_backend(&context);
                  st->interface_method_table(*p, true)->get_backend(&context);
                }
            }
        }
    }
  return TRAVERSE_CONTINUE;
}

// Return an expression which allocates memory to hold values of type TYPE.

Expression*
Gogo::allocate_memory(Type* type, Location location)
{
  Expression* td = Expression::make_type_descriptor(type, location);
  Expression* size =
    Expression::make_type_info(type, Expression::TYPE_INFO_SIZE);
  return Runtime::make_call(Runtime::NEW, location, 2, td, size);
}

// Traversal class used to check for return statements.

class Check_return_statements_traverse : public Traverse
{
 public:
  Check_return_statements_traverse()
    : Traverse(traverse_functions)
  { }

  int
  function(Named_object*);
};

// Check that a function has a return statement if it needs one.

int
Check_return_statements_traverse::function(Named_object* no)
{
  Function* func = no->func_value();
  const Function_type* fntype = func->type();
  const Typed_identifier_list* results = fntype->results();

  // We only need a return statement if there is a return value.
  if (results == NULL || results->empty())
    return TRAVERSE_CONTINUE;

  if (func->block()->may_fall_through())
    error_at(func->block()->end_location(),
             "missing return at end of function");

  return TRAVERSE_CONTINUE;
}

// Check return statements.

void
Gogo::check_return_statements()
{
  Check_return_statements_traverse traverse;
  this->traverse(&traverse);
}

// Export identifiers as requested.

void
Gogo::do_exports()
{
  // For now we always stream to a section.  Later we may want to
  // support streaming to a separate file.
  Stream_to_section stream;

  // Write out either the prefix or pkgpath depending on how we were
  // invoked.
  std::string prefix;
  std::string pkgpath;
  if (this->pkgpath_from_option_)
    pkgpath = this->pkgpath_;
  else if (this->prefix_from_option_)
    prefix = this->prefix_;
  else if (this->is_main_package())
    pkgpath = "main";
  else
    prefix = "go";

  Export exp(&stream);
  exp.register_builtin_types(this);
  exp.export_globals(this->package_name(),
                     prefix,
                     pkgpath,
                     this->packages_,
                     this->imports_,
                     (this->need_init_fn_ && !this->is_main_package()
                      ? this->get_init_fn_name()
                      : ""),
                     this->imported_init_fns_,
                     this->package_->bindings());

  if (!this->c_header_.empty() && !saw_errors())
    this->write_c_header();
}

// Write the top level named struct types in C format to a C header
// file.  This is used when building the runtime package, to share
// struct definitions between C and Go.

void
Gogo::write_c_header()
{
  std::ofstream out;
  out.open(this->c_header_.c_str());
  if (out.fail())
    {
      error("cannot open %s: %m", this->c_header_.c_str());
      return;
    }

  std::list<Named_object*> types;
  Bindings* top = this->package_->bindings();
  for (Bindings::const_definitions_iterator p = top->begin_definitions();
       p != top->end_definitions();
       ++p)
    {
      Named_object* no = *p;
      if (no->is_type() && no->type_value()->struct_type() != NULL)
        types.push_back(no);
      if (no->is_const() && no->const_value()->type()->integer_type() != NULL)
        {
          Numeric_constant nc;
          unsigned long val;
          if (no->const_value()->expr()->numeric_constant_value(&nc)
              && nc.to_unsigned_long(&val) == Numeric_constant::NC_UL_VALID)
            {
              out << "#define " << no->message_name() << ' ' << val
                  << std::endl;
            }
        }
    }

  std::vector<const Named_object*> written;
  int loop = 0;
  while (!types.empty())
    {
      Named_object* no = types.front();
      types.pop_front();

      std::vector<const Named_object*> requires;
      std::vector<const Named_object*> declare;
      if (!no->type_value()->struct_type()->can_write_to_c_header(&requires,
                                                                  &declare))
        continue;

      bool ok = true;
      for (std::vector<const Named_object*>::const_iterator pr
             = requires.begin();
           pr != requires.end() && ok;
           ++pr)
        {
          for (std::list<Named_object*>::const_iterator pt = types.begin();
               pt != types.end() && ok;
               ++pt)
            if (*pr == *pt)
              ok = false;
        }
      if (!ok)
        {
          ++loop;
          if (loop > 10000)
            {
              // This should be impossible since the code parsed and
              // type checked.
              go_unreachable();
            }

          types.push_back(no);
          continue;
        }

      for (std::vector<const Named_object*>::const_iterator pd
             = declare.begin();
           pd != declare.end();
           ++pd)
        {
          if (*pd == no)
            continue;

          std::vector<const Named_object*> drequires;
          std::vector<const Named_object*> ddeclare;
          if (!(*pd)->type_value()->struct_type()->
              can_write_to_c_header(&drequires, &ddeclare))
            continue;

          bool done = false;
          for (std::vector<const Named_object*>::const_iterator pw
                 = written.begin();
               pw != written.end();
               ++pw)
            {
              if (*pw == *pd)
                {
                  done = true;
                  break;
                }
            }
          if (!done)
            {
              out << std::endl;
              out << "struct " << (*pd)->message_name() << ";" << std::endl;
              written.push_back(*pd);
            }
        }

      out << std::endl;
      out << "struct " << no->message_name() << " {" << std::endl;
      no->type_value()->struct_type()->write_to_c_header(out);
      out << "};" << std::endl;
      written.push_back(no);
    }

  out.close();
  if (out.fail())
    error("error writing to %s: %m", this->c_header_.c_str());
}

// Find the blocks in order to convert named types defined in blocks.

class Convert_named_types : public Traverse
{
 public:
  Convert_named_types(Gogo* gogo)
    : Traverse(traverse_blocks),
      gogo_(gogo)
  { }

 protected:
  int
  block(Block* block);

 private:
  Gogo* gogo_;
};

int
Convert_named_types::block(Block* block)
{
  this->gogo_->convert_named_types_in_bindings(block->bindings());
  return TRAVERSE_CONTINUE;
}

// Convert all named types to the backend representation.  Since named
// types can refer to other types, this needs to be done in the right
// sequence, which is handled by Named_type::convert.  Here we arrange
// to call that for each named type.

void
Gogo::convert_named_types()
{
  this->convert_named_types_in_bindings(this->globals_);
  for (Packages::iterator p = this->packages_.begin();
       p != this->packages_.end();
       ++p)
    {
      Package* package = p->second;
      this->convert_named_types_in_bindings(package->bindings());
    }

  Convert_named_types cnt(this);
  this->traverse(&cnt);

  // Make all the builtin named types used for type descriptors, and
  // then convert them.  They will only be written out if they are
  // needed.
  Type::make_type_descriptor_type();
  Type::make_type_descriptor_ptr_type();
  Function_type::make_function_type_descriptor_type();
  Pointer_type::make_pointer_type_descriptor_type();
  Struct_type::make_struct_type_descriptor_type();
  Array_type::make_array_type_descriptor_type();
  Array_type::make_slice_type_descriptor_type();
  Map_type::make_map_type_descriptor_type();
  Channel_type::make_chan_type_descriptor_type();
  Interface_type::make_interface_type_descriptor_type();
  Expression::make_func_descriptor_type();
  Type::convert_builtin_named_types(this);

  Runtime::convert_types(this);

  this->named_types_are_converted_ = true;
}

// Convert all names types in a set of bindings.

void
Gogo::convert_named_types_in_bindings(Bindings* bindings)
{
  for (Bindings::const_definitions_iterator p = bindings->begin_definitions();
       p != bindings->end_definitions();
       ++p)
    {
      if ((*p)->is_type())
        (*p)->type_value()->convert(this);
    }
}

// Class Function.

Function::Function(Function_type* type, Named_object* enclosing, Block* block,
                   Location location)
  : type_(type), enclosing_(enclosing), results_(NULL),
    closure_var_(NULL), block_(block), location_(location), labels_(),
    local_type_count_(0), descriptor_(NULL), fndecl_(NULL), defer_stack_(NULL),
    pragmas_(0), is_sink_(false), results_are_named_(false),
    is_unnamed_type_stub_method_(false), calls_recover_(false),
    is_recover_thunk_(false), has_recover_thunk_(false),
    calls_defer_retaddr_(false), is_type_specific_function_(false),
    in_unique_section_(false)
{
}

// Create the named result variables.

void
Function::create_result_variables(Gogo* gogo)
{
  const Typed_identifier_list* results = this->type_->results();
  if (results == NULL || results->empty())
    return;

  if (!results->front().name().empty())
    this->results_are_named_ = true;

  this->results_ = new Results();
  this->results_->reserve(results->size());

  Block* block = this->block_;
  int index = 0;
  for (Typed_identifier_list::const_iterator p = results->begin();
       p != results->end();
       ++p, ++index)
    {
      std::string name = p->name();
      if (name.empty() || Gogo::is_sink_name(name))
        {
          static int result_counter;
          char buf[100];
          snprintf(buf, sizeof buf, "$ret%d", result_counter);
          ++result_counter;
          name = gogo->pack_hidden_name(buf, false);
        }
      Result_variable* result = new Result_variable(p->type(), this, index,
                                                    p->location());
      Named_object* no = block->bindings()->add_result_variable(name, result);
      if (no->is_result_variable())
        this->results_->push_back(no);
      else
        {
          static int dummy_result_count;
          char buf[100];
          snprintf(buf, sizeof buf, "$dret%d", dummy_result_count);
          ++dummy_result_count;
          name = gogo->pack_hidden_name(buf, false);
          no = block->bindings()->add_result_variable(name, result);
          go_assert(no->is_result_variable());
          this->results_->push_back(no);
        }
    }
}

// Update the named result variables when cloning a function which
// calls recover.

void
Function::update_result_variables()
{
  if (this->results_ == NULL)
    return;

  for (Results::iterator p = this->results_->begin();
       p != this->results_->end();
       ++p)
    (*p)->result_var_value()->set_function(this);
}

// Whether this method should not be included in the type descriptor.

bool
Function::nointerface() const
{
  go_assert(this->is_method());
  return (this->pragmas_ & GOPRAGMA_NOINTERFACE) != 0;
}

// Record that this method should not be included in the type
// descriptor.

void
Function::set_nointerface()
{
  this->pragmas_ |= GOPRAGMA_NOINTERFACE;
}

// Return the closure variable, creating it if necessary.

Named_object*
Function::closure_var()
{
  if (this->closure_var_ == NULL)
    {
      go_assert(this->descriptor_ == NULL);
      // We don't know the type of the variable yet.  We add fields as
      // we find them.
      Location loc = this->type_->location();
      Struct_field_list* sfl = new Struct_field_list;
      Type* struct_type = Type::make_struct_type(sfl, loc);
      Variable* var = new Variable(Type::make_pointer_type(struct_type),
                                   NULL, false, false, false, loc);
      var->set_is_used();
      var->set_is_closure();
      this->closure_var_ = Named_object::make_variable("$closure", NULL, var);
      // Note that the new variable is not in any binding contour.
    }
  return this->closure_var_;
}

// Set the type of the closure variable.

void
Function::set_closure_type()
{
  if (this->closure_var_ == NULL)
    return;
  Named_object* closure = this->closure_var_;
  Struct_type* st = closure->var_value()->type()->deref()->struct_type();

  // The first field of a closure is always a pointer to the function
  // code.
  Type* voidptr_type = Type::make_pointer_type(Type::make_void_type());
  st->push_field(Struct_field(Typed_identifier(".$f", voidptr_type,
                                               this->location_)));

  unsigned int index = 1;
  for (Closure_fields::const_iterator p = this->closure_fields_.begin();
       p != this->closure_fields_.end();
       ++p, ++index)
    {
      Named_object* no = p->first;
      char buf[20];
      snprintf(buf, sizeof buf, "%u", index);
      std::string n = no->name() + buf;
      Type* var_type;
      if (no->is_variable())
        var_type = no->var_value()->type();
      else
        var_type = no->result_var_value()->type();
      Type* field_type = Type::make_pointer_type(var_type);
      st->push_field(Struct_field(Typed_identifier(n, field_type, p->second)));
    }
}

// Return whether this function is a method.

bool
Function::is_method() const
{
  return this->type_->is_method();
}

// Add a label definition.

Label*
Function::add_label_definition(Gogo* gogo, const std::string& label_name,
                               Location location)
{
  Label* lnull = NULL;
  std::pair<Labels::iterator, bool> ins =
    this->labels_.insert(std::make_pair(label_name, lnull));
  Label* label;
  if (label_name == "_")
    {
      label = Label::create_dummy_label();
      if (ins.second)
        ins.first->second = label;
    }
  else if (ins.second)
    {
      // This is a new label.
      label = new Label(label_name);
      ins.first->second = label;
    }
  else
    {
      // The label was already in the hash table.
      label = ins.first->second;
      if (label->is_defined())
        {
          error_at(location, "label %qs already defined",
                   Gogo::message_name(label_name).c_str());
          inform(label->location(), "previous definition of %qs was here",
                 Gogo::message_name(label_name).c_str());
          return new Label(label_name);
        }
    }

  label->define(location, gogo->bindings_snapshot(location));

  // Issue any errors appropriate for any previous goto's to this
  // label.
  const std::vector<Bindings_snapshot*>& refs(label->refs());
  for (std::vector<Bindings_snapshot*>::const_iterator p = refs.begin();
       p != refs.end();
       ++p)
    (*p)->check_goto_to(gogo->current_block());
  label->clear_refs();

  return label;
}

// Add a reference to a label.

Label*
Function::add_label_reference(Gogo* gogo, const std::string& label_name,
                              Location location, bool issue_goto_errors)
{
  Label* lnull = NULL;
  std::pair<Labels::iterator, bool> ins =
    this->labels_.insert(std::make_pair(label_name, lnull));
  Label* label;
  if (!ins.second)
    {
      // The label was already in the hash table.
      label = ins.first->second;
    }
  else
    {
      go_assert(ins.first->second == NULL);
      label = new Label(label_name);
      ins.first->second = label;
    }

  label->set_is_used();

  if (issue_goto_errors)
    {
      Bindings_snapshot* snapshot = label->snapshot();
      if (snapshot != NULL)
        snapshot->check_goto_from(gogo->current_block(), location);
      else
        label->add_snapshot_ref(gogo->bindings_snapshot(location));
    }

  return label;
}

// Warn about labels that are defined but not used.

void
Function::check_labels() const
{
  for (Labels::const_iterator p = this->labels_.begin();
       p != this->labels_.end();
       p++)
    {
      Label* label = p->second;
      if (!label->is_used())
        error_at(label->location(), "label %qs defined and not used",
                 Gogo::message_name(label->name()).c_str());
    }
}

// Swap one function with another.  This is used when building the
// thunk we use to call a function which calls recover.  It may not
// work for any other case.

void
Function::swap_for_recover(Function *x)
{
  go_assert(this->enclosing_ == x->enclosing_);
  std::swap(this->results_, x->results_);
  std::swap(this->closure_var_, x->closure_var_);
  std::swap(this->block_, x->block_);
  go_assert(this->location_ == x->location_);
  go_assert(this->fndecl_ == NULL && x->fndecl_ == NULL);
  go_assert(this->defer_stack_ == NULL && x->defer_stack_ == NULL);
}

// Traverse the tree.

int
Function::traverse(Traverse* traverse)
{
  unsigned int traverse_mask = traverse->traverse_mask();

  if ((traverse_mask
       & (Traverse::traverse_types | Traverse::traverse_expressions))
      != 0)
    {
      if (Type::traverse(this->type_, traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }

  // FIXME: We should check traverse_functions here if nested
  // functions are stored in block bindings.
  if (this->block_ != NULL
      && (traverse_mask
          & (Traverse::traverse_variables
             | Traverse::traverse_constants
             | Traverse::traverse_blocks
             | Traverse::traverse_statements
             | Traverse::traverse_expressions
             | Traverse::traverse_types)) != 0)
    {
      if (this->block_->traverse(traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }

  return TRAVERSE_CONTINUE;
}

// Work out types for unspecified variables and constants.

void
Function::determine_types()
{
  if (this->block_ != NULL)
    this->block_->determine_types();
}

// Return the function descriptor, the value you get when you refer to
// the function in Go code without calling it.

Expression*
Function::descriptor(Gogo*, Named_object* no)
{
  go_assert(!this->is_method());
  go_assert(this->closure_var_ == NULL);
  if (this->descriptor_ == NULL)
    this->descriptor_ = Expression::make_func_descriptor(no);
  return this->descriptor_;
}

// Get a pointer to the variable representing the defer stack for this
// function, making it if necessary.  The value of the variable is set
// by the runtime routines to true if the function is returning,
// rather than panicing through.  A pointer to this variable is used
// as a marker for the functions on the defer stack associated with
// this function.  A function-specific variable permits inlining a
// function which uses defer.

Expression*
Function::defer_stack(Location location)
{
  if (this->defer_stack_ == NULL)
    {
      Type* t = Type::lookup_bool_type();
      Expression* n = Expression::make_boolean(false, location);
      this->defer_stack_ = Statement::make_temporary(t, n, location);
      this->defer_stack_->set_is_address_taken();
    }
  Expression* ref = Expression::make_temporary_reference(this->defer_stack_,
                                                         location);
  return Expression::make_unary(OPERATOR_AND, ref, location);
}

// Export the function.

void
Function::export_func(Export* exp, const std::string& name) const
{
  Function::export_func_with_type(exp, name, this->type_);
}

// Export a function with a type.

void
Function::export_func_with_type(Export* exp, const std::string& name,
                                const Function_type* fntype)
{
  exp->write_c_string("func ");

  if (fntype->is_method())
    {
      exp->write_c_string("(");
      const Typed_identifier* receiver = fntype->receiver();
      exp->write_name(receiver->name());
      exp->write_escape(receiver->note());
      exp->write_c_string(" ");
      exp->write_type(receiver->type());
      exp->write_c_string(") ");
    }

  exp->write_string(name);

  exp->write_c_string(" (");
  const Typed_identifier_list* parameters = fntype->parameters();
  if (parameters != NULL)
    {
      size_t i = 0;
      bool is_varargs = fntype->is_varargs();
      bool first = true;
      for (Typed_identifier_list::const_iterator p = parameters->begin();
           p != parameters->end();
           ++p, ++i)
        {
          if (first)
            first = false;
          else
            exp->write_c_string(", ");
          exp->write_name(p->name());
          exp->write_escape(p->note());
          exp->write_c_string(" ");
          if (!is_varargs || p + 1 != parameters->end())
            exp->write_type(p->type());
          else
            {
              exp->write_c_string("...");
              exp->write_type(p->type()->array_type()->element_type());
            }
        }
    }
  exp->write_c_string(")");

  const Typed_identifier_list* results = fntype->results();
  if (results != NULL)
    {
      if (results->size() == 1 && results->begin()->name().empty())
        {
          exp->write_c_string(" ");
          exp->write_type(results->begin()->type());
        }
      else
        {
          exp->write_c_string(" (");
          bool first = true;
          for (Typed_identifier_list::const_iterator p = results->begin();
               p != results->end();
               ++p)
            {
              if (first)
                first = false;
              else
                exp->write_c_string(", ");
              exp->write_name(p->name());
              exp->write_escape(p->note());
              exp->write_c_string(" ");
              exp->write_type(p->type());
            }
          exp->write_c_string(")");
        }
    }
  exp->write_c_string(";\n");
}

// Import a function.

void
Function::import_func(Import* imp, std::string* pname,
                      Typed_identifier** preceiver,
                      Typed_identifier_list** pparameters,
                      Typed_identifier_list** presults,
                      bool* is_varargs)
{
  imp->require_c_string("func ");

  *preceiver = NULL;
  if (imp->peek_char() == '(')
    {
      imp->require_c_string("(");
      std::string name = imp->read_name();
      std::string escape_note = imp->read_escape();
      imp->require_c_string(" ");
      Type* rtype = imp->read_type();
      *preceiver = new Typed_identifier(name, rtype, imp->location());
      (*preceiver)->set_note(escape_note);
      imp->require_c_string(") ");
    }

  *pname = imp->read_identifier();

  Typed_identifier_list* parameters;
  *is_varargs = false;
  imp->require_c_string(" (");
  if (imp->peek_char() == ')')
    parameters = NULL;
  else
    {
      parameters = new Typed_identifier_list();
      while (true)
        {
          std::string name = imp->read_name();
          std::string escape_note = imp->read_escape();
          imp->require_c_string(" ");

          if (imp->match_c_string("..."))
            {
              imp->advance(3);
              *is_varargs = true;
            }

          Type* ptype = imp->read_type();
          if (*is_varargs)
            ptype = Type::make_array_type(ptype, NULL);
          Typed_identifier t = Typed_identifier(name, ptype, imp->location());
          t.set_note(escape_note);
          parameters->push_back(t);
          if (imp->peek_char() != ',')
            break;
          go_assert(!*is_varargs);
          imp->require_c_string(", ");
        }
    }
  imp->require_c_string(")");
  *pparameters = parameters;

  Typed_identifier_list* results;
  if (imp->peek_char() != ' ')
    results = NULL;
  else
    {
      results = new Typed_identifier_list();
      imp->require_c_string(" ");
      if (imp->peek_char() != '(')
        {
          Type* rtype = imp->read_type();
          results->push_back(Typed_identifier("", rtype, imp->location()));
        }
      else
        {
          imp->require_c_string("(");
          while (true)
            {
              std::string name = imp->read_name();
              std::string note = imp->read_escape();
              imp->require_c_string(" ");
              Type* rtype = imp->read_type();
              Typed_identifier t = Typed_identifier(name, rtype,
                                                    imp->location());
              t.set_note(note);
              results->push_back(t);
              if (imp->peek_char() != ',')
                break;
              imp->require_c_string(", ");
            }
          imp->require_c_string(")");
        }
    }
  imp->require_c_string(";\n");
  *presults = results;
}

// Get the backend representation.

Bfunction*
Function::get_or_make_decl(Gogo* gogo, Named_object* no)
{
  if (this->fndecl_ == NULL)
    {
      std::string asm_name;
      bool is_visible = false;
      if (no->package() != NULL)
        ;
      else if (this->enclosing_ != NULL || Gogo::is_thunk(no))
        ;
      else if (Gogo::unpack_hidden_name(no->name()) == "init"
               && !this->type_->is_method())
        ;
      else if (no->name() == gogo->get_init_fn_name())
        {
          is_visible = true;
          asm_name = no->name();
        }
      else if (Gogo::unpack_hidden_name(no->name()) == "main"
               && gogo->is_main_package())
        is_visible = true;
      // Methods have to be public even if they are hidden because
      // they can be pulled into type descriptors when using
      // anonymous fields.
      else if (!Gogo::is_hidden_name(no->name())
               || this->type_->is_method())
        {
          if (!this->is_unnamed_type_stub_method_)
            is_visible = true;
          std::string pkgpath = gogo->pkgpath_symbol();
          if (this->type_->is_method()
              && Gogo::is_hidden_name(no->name())
              && Gogo::hidden_name_pkgpath(no->name()) != gogo->pkgpath())
            {
              // This is a method we created for an unexported
              // method of an imported embedded type.  We need to
              // use the pkgpath of the imported package to avoid
              // a possible name collision.  See bug478 for a test
              // case.
              pkgpath = Gogo::hidden_name_pkgpath(no->name());
              pkgpath = Gogo::pkgpath_for_symbol(pkgpath);
            }

          asm_name = pkgpath;
          asm_name.append(1, '.');
          asm_name.append(Gogo::unpack_hidden_name(no->name()));
          if (this->type_->is_method())
            {
              asm_name.append(1, '.');
              Type* rtype = this->type_->receiver()->type();
              asm_name.append(rtype->mangled_name(gogo));
            }
        }

      if (!this->asm_name_.empty())
        {
          asm_name = this->asm_name_;
          is_visible = true;
        }

      // If a function calls the predeclared recover function, we
      // can't inline it, because recover behaves differently in a
      // function passed directly to defer.  If this is a recover
      // thunk that we built to test whether a function can be
      // recovered, we can't inline it, because that will mess up
      // our return address comparison.
      bool is_inlinable = !(this->calls_recover_ || this->is_recover_thunk_);

      // If a function calls __go_set_defer_retaddr, then mark it as
      // uninlinable.  This prevents the GCC backend from splitting
      // the function; splitting the function is a bad idea because we
      // want the return address label to be in the same function as
      // the call.
      if (this->calls_defer_retaddr_)
        is_inlinable = false;

      // Check the //go:noinline compiler directive.
      if ((this->pragmas_ & GOPRAGMA_NOINLINE) != 0)
        is_inlinable = false;

      // If this is a thunk created to call a function which calls
      // the predeclared recover function, we need to disable
      // stack splitting for the thunk.
      bool disable_split_stack = this->is_recover_thunk_;

      // Check the //go:nosplit compiler directive.
      if ((this->pragmas_ & GOPRAGMA_NOSPLIT) != 0)
        disable_split_stack = true;

      // This should go into a unique section if that has been
      // requested elsewhere, or if this is a nointerface function.
      // We want to put a nointerface function into a unique section
      // because there is a good chance that the linker garbage
      // collection can discard it.
      bool in_unique_section = (this->in_unique_section_
                                || (this->is_method() && this->nointerface()));

      Btype* functype = this->type_->get_backend_fntype(gogo);
      this->fndecl_ =
          gogo->backend()->function(functype, no->get_id(gogo), asm_name,
                                    is_visible, false, is_inlinable,
                                    disable_split_stack, in_unique_section,
                                    this->location());
    }
  return this->fndecl_;
}

// Get the backend representation.

Bfunction*
Function_declaration::get_or_make_decl(Gogo* gogo, Named_object* no)
{
  if (this->fndecl_ == NULL)
    {
      // Let Go code use an asm declaration to pick up a builtin
      // function.
      if (!this->asm_name_.empty())
        {
          Bfunction* builtin_decl =
            gogo->backend()->lookup_builtin(this->asm_name_);
          if (builtin_decl != NULL)
            {
              this->fndecl_ = builtin_decl;
              return this->fndecl_;
            }
        }

      std::string asm_name;
      if (this->asm_name_.empty())
        {
          asm_name = (no->package() == NULL
                                  ? gogo->pkgpath_symbol()
                                  : no->package()->pkgpath_symbol());
          asm_name.append(1, '.');
          asm_name.append(Gogo::unpack_hidden_name(no->name()));
          if (this->fntype_->is_method())
            {
              asm_name.append(1, '.');
              Type* rtype = this->fntype_->receiver()->type();
              asm_name.append(rtype->mangled_name(gogo));
            }
        }

      Btype* functype = this->fntype_->get_backend_fntype(gogo);
      this->fndecl_ =
          gogo->backend()->function(functype, no->get_id(gogo), asm_name,
                                    true, true, true, false, false,
                                    this->location());
    }

  return this->fndecl_;
}

// Build the descriptor for a function declaration.  This won't
// necessarily happen if the package has just a declaration for the
// function and no other reference to it, but we may still need the
// descriptor for references from other packages.
void
Function_declaration::build_backend_descriptor(Gogo* gogo)
{
  if (this->descriptor_ != NULL)
    {
      Translate_context context(gogo, NULL, NULL, NULL);
      this->descriptor_->get_backend(&context);
    }
}

// Check that the types used in this declaration's signature are defined.
// Reports errors for any undefined type.

void
Function_declaration::check_types() const
{
  // Calling Type::base will give errors for any undefined types.
  Function_type* fntype = this->type();
  if (fntype->receiver() != NULL)
    fntype->receiver()->type()->base();
  if (fntype->parameters() != NULL)
    {
      const Typed_identifier_list* params = fntype->parameters();
      for (Typed_identifier_list::const_iterator p = params->begin();
           p != params->end();
           ++p)
        p->type()->base();
    }
}

// Return the function's decl after it has been built.

Bfunction*
Function::get_decl() const
{
  go_assert(this->fndecl_ != NULL);
  return this->fndecl_;
}

// Build the backend representation for the function code.

void
Function::build(Gogo* gogo, Named_object* named_function)
{
  Translate_context context(gogo, named_function, NULL, NULL);

  // A list of parameter variables for this function.
  std::vector<Bvariable*> param_vars;

  // Variables that need to be declared for this function and their
  // initial values.
  std::vector<Bvariable*> vars;
  std::vector<Bexpression*> var_inits;
  for (Bindings::const_definitions_iterator p =
         this->block_->bindings()->begin_definitions();
       p != this->block_->bindings()->end_definitions();
       ++p)
    {
      Location loc = (*p)->location();
      if ((*p)->is_variable() && (*p)->var_value()->is_parameter())
        {
          Bvariable* bvar = (*p)->get_backend_variable(gogo, named_function);
          Bvariable* parm_bvar = bvar;

          // We always pass the receiver to a method as a pointer.  If
          // the receiver is declared as a non-pointer type, then we
          // copy the value into a local variable.
          if ((*p)->var_value()->is_receiver()
              && (*p)->var_value()->type()->points_to() == NULL)
            {
              std::string name = (*p)->name() + ".pointer";
              Type* var_type = (*p)->var_value()->type();
              Variable* parm_var =
                  new Variable(Type::make_pointer_type(var_type), NULL, false,
                               true, false, loc);
              Named_object* parm_no =
                  Named_object::make_variable(name, NULL, parm_var);
              parm_bvar = parm_no->get_backend_variable(gogo, named_function);

              vars.push_back(bvar);
              Expression* parm_ref =
                  Expression::make_var_reference(parm_no, loc);
              parm_ref = Expression::make_unary(OPERATOR_MULT, parm_ref, loc);
              if ((*p)->var_value()->is_in_heap())
                parm_ref = Expression::make_heap_expression(parm_ref, loc);
              var_inits.push_back(parm_ref->get_backend(&context));
            }
          else if ((*p)->var_value()->is_in_heap())
            {
              // If we take the address of a parameter, then we need
              // to copy it into the heap.
              std::string parm_name = (*p)->name() + ".param";
              Variable* parm_var = new Variable((*p)->var_value()->type(), NULL,
                                                false, true, false, loc);
              Named_object* parm_no =
                  Named_object::make_variable(parm_name, NULL, parm_var);
              parm_bvar = parm_no->get_backend_variable(gogo, named_function);

              vars.push_back(bvar);
              Expression* var_ref =
                  Expression::make_var_reference(parm_no, loc);
              var_ref = Expression::make_heap_expression(var_ref, loc);
              var_inits.push_back(var_ref->get_backend(&context));
            }
          param_vars.push_back(parm_bvar);
        }
      else if ((*p)->is_result_variable())
        {
          Bvariable* bvar = (*p)->get_backend_variable(gogo, named_function);

          Type* type = (*p)->result_var_value()->type();
          Bexpression* init;
          if (!(*p)->result_var_value()->is_in_heap())
            {
              Btype* btype = type->get_backend(gogo);
              init = gogo->backend()->zero_expression(btype);
            }
          else
            init = Expression::make_allocation(type,
                                               loc)->get_backend(&context);

          vars.push_back(bvar);
          var_inits.push_back(init);
        }
    }
  if (!gogo->backend()->function_set_parameters(this->fndecl_, param_vars))
    {
      go_assert(saw_errors());
      return;
    }

  // If we need a closure variable, make sure to create it.
  // It gets installed in the function as a side effect of creation.
  if (this->closure_var_ != NULL)
    {
      go_assert(this->closure_var_->var_value()->is_closure());
      this->closure_var_->get_backend_variable(gogo, named_function);
    }

  if (this->block_ != NULL)
    {
      // Declare variables if necessary.
      Bblock* var_decls = NULL;

      Bstatement* defer_init = NULL;
      if (!vars.empty() || this->defer_stack_ != NULL)
        {
          var_decls =
              gogo->backend()->block(this->fndecl_, NULL, vars,
                                     this->block_->start_location(),
                                     this->block_->end_location());

          if (this->defer_stack_ != NULL)
            {
              Translate_context dcontext(gogo, named_function, this->block_,
                                         var_decls);
              defer_init = this->defer_stack_->get_backend(&dcontext);
            }
        }

      // Build the backend representation for all the statements in the
      // function.
      Translate_context context(gogo, named_function, NULL, NULL);
      Bblock* code_block = this->block_->get_backend(&context);

      // Initialize variables if necessary.
      std::vector<Bstatement*> init;
      go_assert(vars.size() == var_inits.size());
      for (size_t i = 0; i < vars.size(); ++i)
        {
          Bstatement* init_stmt =
              gogo->backend()->init_statement(vars[i], var_inits[i]);
          init.push_back(init_stmt);
        }
      if (defer_init != NULL)
        init.push_back(defer_init);
      Bstatement* var_init = gogo->backend()->statement_list(init);

      // Initialize all variables before executing this code block.
      Bstatement* code_stmt = gogo->backend()->block_statement(code_block);
      code_stmt = gogo->backend()->compound_statement(var_init, code_stmt);

      // If we have a defer stack, initialize it at the start of a
      // function.
      Bstatement* except = NULL;
      Bstatement* fini = NULL;
      if (defer_init != NULL)
        {
          // Clean up the defer stack when we leave the function.
          this->build_defer_wrapper(gogo, named_function, &except, &fini);

          // Wrap the code for this function in an exception handler to handle
          // defer calls.
          code_stmt =
              gogo->backend()->exception_handler_statement(code_stmt,
                                                           except, fini,
                                                           this->location_);
        }

      // Stick the code into the block we built for the receiver, if
      // we built one.
      if (var_decls != NULL)
        {
          std::vector<Bstatement*> code_stmt_list(1, code_stmt);
          gogo->backend()->block_add_statements(var_decls, code_stmt_list);
          code_stmt = gogo->backend()->block_statement(var_decls);
        }

      if (!gogo->backend()->function_set_body(this->fndecl_, code_stmt))
        {
          go_assert(saw_errors());
          return;
        }
    }

  // If we created a descriptor for the function, make sure we emit it.
  if (this->descriptor_ != NULL)
    {
      Translate_context context(gogo, NULL, NULL, NULL);
      this->descriptor_->get_backend(&context);
    }
}

// Build the wrappers around function code needed if the function has
// any defer statements.  This sets *EXCEPT to an exception handler
// and *FINI to a finally handler.

void
Function::build_defer_wrapper(Gogo* gogo, Named_object* named_function,
                              Bstatement** except, Bstatement** fini)
{
  Location end_loc = this->block_->end_location();

  // Add an exception handler.  This is used if a panic occurs.  Its
  // purpose is to stop the stack unwinding if a deferred function
  // calls recover.  There are more details in
  // libgo/runtime/go-unwind.c.

  std::vector<Bstatement*> stmts;
  Expression* call = Runtime::make_call(Runtime::CHECK_DEFER, end_loc, 1,
                                        this->defer_stack(end_loc));
  Translate_context context(gogo, named_function, NULL, NULL);
  Bexpression* defer = call->get_backend(&context);
  stmts.push_back(gogo->backend()->expression_statement(defer));

  Bstatement* ret_bstmt = this->return_value(gogo, named_function, end_loc);
  if (ret_bstmt != NULL)
    stmts.push_back(ret_bstmt);

  go_assert(*except == NULL);
  *except = gogo->backend()->statement_list(stmts);

  call = Runtime::make_call(Runtime::CHECK_DEFER, end_loc, 1,
                            this->defer_stack(end_loc));
  defer = call->get_backend(&context);

  call = Runtime::make_call(Runtime::UNDEFER, end_loc, 1,
                            this->defer_stack(end_loc));
  Bexpression* undefer = call->get_backend(&context);
  Bstatement* function_defer =
      gogo->backend()->function_defer_statement(this->fndecl_, undefer, defer,
                                                end_loc);
  stmts = std::vector<Bstatement*>(1, function_defer);
  if (this->type_->results() != NULL
      && !this->type_->results()->empty()
      && !this->type_->results()->front().name().empty())
    {
      // If the result variables are named, and we are returning from
      // this function rather than panicing through it, we need to
      // return them again, because they might have been changed by a
      // defer function.  The runtime routines set the defer_stack
      // variable to true if we are returning from this function.

      ret_bstmt = this->return_value(gogo, named_function, end_loc);
      Bexpression* nil = Expression::make_nil(end_loc)->get_backend(&context);
      Bexpression* ret =
          gogo->backend()->compound_expression(ret_bstmt, nil, end_loc);
      Expression* ref =
        Expression::make_temporary_reference(this->defer_stack_, end_loc);
      Bexpression* bref = ref->get_backend(&context);
      ret = gogo->backend()->conditional_expression(NULL, bref, ret, NULL,
                                                    end_loc);
      stmts.push_back(gogo->backend()->expression_statement(ret));
    }

  go_assert(*fini == NULL);
  *fini = gogo->backend()->statement_list(stmts);
}

// Return the statement that assigns values to this function's result struct.

Bstatement*
Function::return_value(Gogo* gogo, Named_object* named_function,
                       Location location) const
{
  const Typed_identifier_list* results = this->type_->results();
  if (results == NULL || results->empty())
    return NULL;

  go_assert(this->results_ != NULL);
  if (this->results_->size() != results->size())
    {
      go_assert(saw_errors());
      return gogo->backend()->error_statement();
    }

  std::vector<Bexpression*> vals(results->size());
  for (size_t i = 0; i < vals.size(); ++i)
    {
      Named_object* no = (*this->results_)[i];
      Bvariable* bvar = no->get_backend_variable(gogo, named_function);
      Bexpression* val = gogo->backend()->var_expression(bvar, location);
      if (no->result_var_value()->is_in_heap())
        {
          Btype* bt = no->result_var_value()->type()->get_backend(gogo);
          val = gogo->backend()->indirect_expression(bt, val, true, location);
        }
      vals[i] = val;
    }
  return gogo->backend()->return_statement(this->fndecl_, vals, location);
}

// Class Block.

Block::Block(Block* enclosing, Location location)
  : enclosing_(enclosing), statements_(),
    bindings_(new Bindings(enclosing == NULL
                           ? NULL
                           : enclosing->bindings())),
    start_location_(location),
    end_location_(UNKNOWN_LOCATION)
{
}

// Add a statement to a block.

void
Block::add_statement(Statement* statement)
{
  this->statements_.push_back(statement);
}

// Add a statement to the front of a block.  This is slow but is only
// used for reference counts of parameters.

void
Block::add_statement_at_front(Statement* statement)
{
  this->statements_.insert(this->statements_.begin(), statement);
}

// Replace a statement in a block.

void
Block::replace_statement(size_t index, Statement* s)
{
  go_assert(index < this->statements_.size());
  this->statements_[index] = s;
}

// Add a statement before another statement.

void
Block::insert_statement_before(size_t index, Statement* s)
{
  go_assert(index < this->statements_.size());
  this->statements_.insert(this->statements_.begin() + index, s);
}

// Add a statement after another statement.

void
Block::insert_statement_after(size_t index, Statement* s)
{
  go_assert(index < this->statements_.size());
  this->statements_.insert(this->statements_.begin() + index + 1, s);
}

// Traverse the tree.

int
Block::traverse(Traverse* traverse)
{
  unsigned int traverse_mask = traverse->traverse_mask();

  if ((traverse_mask & Traverse::traverse_blocks) != 0)
    {
      int t = traverse->block(this);
      if (t == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
      else if (t == TRAVERSE_SKIP_COMPONENTS)
        return TRAVERSE_CONTINUE;
    }

  if ((traverse_mask
       & (Traverse::traverse_variables
          | Traverse::traverse_constants
          | Traverse::traverse_expressions
          | Traverse::traverse_types)) != 0)
    {
      const unsigned int e_or_t = (Traverse::traverse_expressions
                                   | Traverse::traverse_types);
      const unsigned int e_or_t_or_s = (e_or_t
                                        | Traverse::traverse_statements);
      for (Bindings::const_definitions_iterator pb =
             this->bindings_->begin_definitions();
           pb != this->bindings_->end_definitions();
           ++pb)
        {
          int t = TRAVERSE_CONTINUE;
          switch ((*pb)->classification())
            {
            case Named_object::NAMED_OBJECT_CONST:
              if ((traverse_mask & Traverse::traverse_constants) != 0)
                t = traverse->constant(*pb, false);
              if (t == TRAVERSE_CONTINUE
                  && (traverse_mask & e_or_t) != 0)
                {
                  Type* tc = (*pb)->const_value()->type();
                  if (tc != NULL
                      && Type::traverse(tc, traverse) == TRAVERSE_EXIT)
                    return TRAVERSE_EXIT;
                  t = (*pb)->const_value()->traverse_expression(traverse);
                }
              break;

            case Named_object::NAMED_OBJECT_VAR:
            case Named_object::NAMED_OBJECT_RESULT_VAR:
              if ((traverse_mask & Traverse::traverse_variables) != 0)
                t = traverse->variable(*pb);
              if (t == TRAVERSE_CONTINUE
                  && (traverse_mask & e_or_t) != 0)
                {
                  if ((*pb)->is_result_variable()
                      || (*pb)->var_value()->has_type())
                    {
                      Type* tv = ((*pb)->is_variable()
                                  ? (*pb)->var_value()->type()
                                  : (*pb)->result_var_value()->type());
                      if (tv != NULL
                          && Type::traverse(tv, traverse) == TRAVERSE_EXIT)
                        return TRAVERSE_EXIT;
                    }
                }
              if (t == TRAVERSE_CONTINUE
                  && (traverse_mask & e_or_t_or_s) != 0
                  && (*pb)->is_variable())
                t = (*pb)->var_value()->traverse_expression(traverse,
                                                            traverse_mask);
              break;

            case Named_object::NAMED_OBJECT_FUNC:
            case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
              go_unreachable();

            case Named_object::NAMED_OBJECT_TYPE:
              if ((traverse_mask & e_or_t) != 0)
                t = Type::traverse((*pb)->type_value(), traverse);
              break;

            case Named_object::NAMED_OBJECT_TYPE_DECLARATION:
            case Named_object::NAMED_OBJECT_UNKNOWN:
            case Named_object::NAMED_OBJECT_ERRONEOUS:
              break;

            case Named_object::NAMED_OBJECT_PACKAGE:
            case Named_object::NAMED_OBJECT_SINK:
              go_unreachable();

            default:
              go_unreachable();
            }

          if (t == TRAVERSE_EXIT)
            return TRAVERSE_EXIT;
        }
    }

  // No point in checking traverse_mask here--if we got here we always
  // want to walk the statements.  The traversal can insert new
  // statements before or after the current statement.  Inserting
  // statements before the current statement requires updating I via
  // the pointer; those statements will not be traversed.  Any new
  // statements inserted after the current statement will be traversed
  // in their turn.
  for (size_t i = 0; i < this->statements_.size(); ++i)
    {
      if (this->statements_[i]->traverse(this, &i, traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }

  return TRAVERSE_CONTINUE;
}

// Work out types for unspecified variables and constants.

void
Block::determine_types()
{
  for (Bindings::const_definitions_iterator pb =
         this->bindings_->begin_definitions();
       pb != this->bindings_->end_definitions();
       ++pb)
    {
      if ((*pb)->is_variable())
        (*pb)->var_value()->determine_type();
      else if ((*pb)->is_const())
        (*pb)->const_value()->determine_type();
    }

  for (std::vector<Statement*>::const_iterator ps = this->statements_.begin();
       ps != this->statements_.end();
       ++ps)
    (*ps)->determine_types();
}

// Return true if the statements in this block may fall through.

bool
Block::may_fall_through() const
{
  if (this->statements_.empty())
    return true;
  return this->statements_.back()->may_fall_through();
}

// Convert a block to the backend representation.

Bblock*
Block::get_backend(Translate_context* context)
{
  Gogo* gogo = context->gogo();
  Named_object* function = context->function();
  std::vector<Bvariable*> vars;
  vars.reserve(this->bindings_->size_definitions());
  for (Bindings::const_definitions_iterator pv =
         this->bindings_->begin_definitions();
       pv != this->bindings_->end_definitions();
       ++pv)
    {
      if ((*pv)->is_variable() && !(*pv)->var_value()->is_parameter())
        vars.push_back((*pv)->get_backend_variable(gogo, function));
    }

  go_assert(function != NULL);
  Bfunction* bfunction =
    function->func_value()->get_or_make_decl(gogo, function);
  Bblock* ret = context->backend()->block(bfunction, context->bblock(),
                                          vars, this->start_location_,
                                          this->end_location_);

  Translate_context subcontext(gogo, function, this, ret);
  std::vector<Bstatement*> bstatements;
  bstatements.reserve(this->statements_.size());
  for (std::vector<Statement*>::const_iterator p = this->statements_.begin();
       p != this->statements_.end();
       ++p)
    bstatements.push_back((*p)->get_backend(&subcontext));

  context->backend()->block_add_statements(ret, bstatements);

  return ret;
}

// Class Bindings_snapshot.

Bindings_snapshot::Bindings_snapshot(const Block* b, Location location)
  : block_(b), counts_(), location_(location)
{
  while (b != NULL)
    {
      this->counts_.push_back(b->bindings()->size_definitions());
      b = b->enclosing();
    }
}

// Report errors appropriate for a goto from B to this.

void
Bindings_snapshot::check_goto_from(const Block* b, Location loc)
{
  size_t dummy;
  if (!this->check_goto_block(loc, b, this->block_, &dummy))
    return;
  this->check_goto_defs(loc, this->block_,
                        this->block_->bindings()->size_definitions(),
                        this->counts_[0]);
}

// Report errors appropriate for a goto from this to B.

void
Bindings_snapshot::check_goto_to(const Block* b)
{
  size_t index;
  if (!this->check_goto_block(this->location_, this->block_, b, &index))
    return;
  this->check_goto_defs(this->location_, b, this->counts_[index],
                        b->bindings()->size_definitions());
}

// Report errors appropriate for a goto at LOC from BFROM to BTO.
// Return true if all is well, false if we reported an error.  If this
// returns true, it sets *PINDEX to the number of blocks BTO is above
// BFROM.

bool
Bindings_snapshot::check_goto_block(Location loc, const Block* bfrom,
                                    const Block* bto, size_t* pindex)
{
  // It is an error if BTO is not either BFROM or above BFROM.
  size_t index = 0;
  for (const Block* pb = bfrom; pb != bto; pb = pb->enclosing(), ++index)
    {
      if (pb == NULL)
        {
          error_at(loc, "goto jumps into block");
          inform(bto->start_location(), "goto target block starts here");
          return false;
        }
    }
  *pindex = index;
  return true;
}

// Report errors appropriate for a goto at LOC ending at BLOCK, where
// CFROM is the number of names defined at the point of the goto and
// CTO is the number of names defined at the point of the label.

void
Bindings_snapshot::check_goto_defs(Location loc, const Block* block,
                                   size_t cfrom, size_t cto)
{
  if (cfrom < cto)
    {
      Bindings::const_definitions_iterator p =
        block->bindings()->begin_definitions();
      for (size_t i = 0; i < cfrom; ++i)
        {
          go_assert(p != block->bindings()->end_definitions());
          ++p;
        }
      go_assert(p != block->bindings()->end_definitions());

      std::string n = (*p)->message_name();
      error_at(loc, "goto jumps over declaration of %qs", n.c_str());
      inform((*p)->location(), "%qs defined here", n.c_str());
    }
}

// Class Function_declaration.

// Return the function descriptor.

Expression*
Function_declaration::descriptor(Gogo*, Named_object* no)
{
  go_assert(!this->fntype_->is_method());
  if (this->descriptor_ == NULL)
    this->descriptor_ = Expression::make_func_descriptor(no);
  return this->descriptor_;
}

// Class Variable.

Variable::Variable(Type* type, Expression* init, bool is_global,
                   bool is_parameter, bool is_receiver,
                   Location location)
  : type_(type), init_(init), preinit_(NULL), location_(location),
    backend_(NULL), is_global_(is_global), is_parameter_(is_parameter),
    is_closure_(false), is_receiver_(is_receiver),
    is_varargs_parameter_(false), is_used_(false),
    is_address_taken_(false), is_non_escaping_address_taken_(false),
    seen_(false), init_is_lowered_(false), init_is_flattened_(false),
    type_from_init_tuple_(false), type_from_range_index_(false),
    type_from_range_value_(false), type_from_chan_element_(false),
    is_type_switch_var_(false), determined_type_(false),
    in_unique_section_(false), escapes_(true)
{
  go_assert(type != NULL || init != NULL);
  go_assert(!is_parameter || init == NULL);
}

// Traverse the initializer expression.

int
Variable::traverse_expression(Traverse* traverse, unsigned int traverse_mask)
{
  if (this->preinit_ != NULL)
    {
      if (this->preinit_->traverse(traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }
  if (this->init_ != NULL
      && ((traverse_mask
           & (Traverse::traverse_expressions | Traverse::traverse_types))
          != 0))
    {
      if (Expression::traverse(&this->init_, traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }
  return TRAVERSE_CONTINUE;
}

// Lower the initialization expression after parsing is complete.

void
Variable::lower_init_expression(Gogo* gogo, Named_object* function,
                                Statement_inserter* inserter)
{
  Named_object* dep = gogo->var_depends_on(this);
  if (dep != NULL && dep->is_variable())
    dep->var_value()->lower_init_expression(gogo, function, inserter);

  if (this->init_ != NULL && !this->init_is_lowered_)
    {
      if (this->seen_)
        {
          // We will give an error elsewhere, this is just to prevent
          // an infinite loop.
          return;
        }
      this->seen_ = true;

      Statement_inserter global_inserter;
      if (this->is_global_)
        {
          global_inserter = Statement_inserter(gogo, this);
          inserter = &global_inserter;
        }

      gogo->lower_expression(function, inserter, &this->init_);

      this->seen_ = false;

      this->init_is_lowered_ = true;
    }
}

// Flatten the initialization expression after ordering evaluations.

void
Variable::flatten_init_expression(Gogo* gogo, Named_object* function,
                                  Statement_inserter* inserter)
{
  Named_object* dep = gogo->var_depends_on(this);
  if (dep != NULL && dep->is_variable())
    dep->var_value()->flatten_init_expression(gogo, function, inserter);

  if (this->init_ != NULL && !this->init_is_flattened_)
    {
      if (this->seen_)
        {
          // We will give an error elsewhere, this is just to prevent
          // an infinite loop.
          return;
        }
      this->seen_ = true;

      Statement_inserter global_inserter;
      if (this->is_global_)
        {
          global_inserter = Statement_inserter(gogo, this);
          inserter = &global_inserter;
        }

      gogo->flatten_expression(function, inserter, &this->init_);

      // If an interface conversion is needed, we need a temporary
      // variable.
      if (this->type_ != NULL
          && !Type::are_identical(this->type_, this->init_->type(), false,
                                  NULL)
          && this->init_->type()->interface_type() != NULL
          && !this->init_->is_variable())
        {
          Temporary_statement* temp =
            Statement::make_temporary(NULL, this->init_, this->location_);
          inserter->insert(temp);
          this->init_ = Expression::make_temporary_reference(temp,
                                                             this->location_);
        }

      this->seen_ = false;
      this->init_is_flattened_ = true;
    }
}

// Get the preinit block.

Block*
Variable::preinit_block(Gogo* gogo)
{
  go_assert(this->is_global_);
  if (this->preinit_ == NULL)
    this->preinit_ = new Block(NULL, this->location());

  // If a global variable has a preinitialization statement, then we
  // need to have an initialization function.
  gogo->set_need_init_fn();

  return this->preinit_;
}

// Add a statement to be run before the initialization expression.

void
Variable::add_preinit_statement(Gogo* gogo, Statement* s)
{
  Block* b = this->preinit_block(gogo);
  b->add_statement(s);
  b->set_end_location(s->location());
}

// Whether this variable has a type.

bool
Variable::has_type() const
{
  if (this->type_ == NULL)
    return false;

  // A variable created in a type switch case nil does not actually
  // have a type yet.  It will be changed to use the initializer's
  // type in determine_type.
  if (this->is_type_switch_var_
      && this->type_->is_nil_constant_as_type())
    return false;

  return true;
}

// In an assignment which sets a variable to a tuple of EXPR, return
// the type of the first element of the tuple.

Type*
Variable::type_from_tuple(Expression* expr, bool report_error) const
{
  if (expr->map_index_expression() != NULL)
    {
      Map_type* mt = expr->map_index_expression()->get_map_type();
      if (mt == NULL)
        return Type::make_error_type();
      return mt->val_type();
    }
  else if (expr->receive_expression() != NULL)
    {
      Expression* channel = expr->receive_expression()->channel();
      Type* channel_type = channel->type();
      if (channel_type->channel_type() == NULL)
        return Type::make_error_type();
      return channel_type->channel_type()->element_type();
    }
  else
    {
      if (report_error)
        error_at(this->location(), "invalid tuple definition");
      return Type::make_error_type();
    }
}

// Given EXPR used in a range clause, return either the index type or
// the value type of the range, depending upon GET_INDEX_TYPE.

Type*
Variable::type_from_range(Expression* expr, bool get_index_type,
                          bool report_error) const
{
  Type* t = expr->type();
  if (t->array_type() != NULL
      || (t->points_to() != NULL
          && t->points_to()->array_type() != NULL
          && !t->points_to()->is_slice_type()))
    {
      if (get_index_type)
        return Type::lookup_integer_type("int");
      else
        return t->deref()->array_type()->element_type();
    }
  else if (t->is_string_type())
    {
      if (get_index_type)
        return Type::lookup_integer_type("int");
      else
        return Type::lookup_integer_type("int32");
    }
  else if (t->map_type() != NULL)
    {
      if (get_index_type)
        return t->map_type()->key_type();
      else
        return t->map_type()->val_type();
    }
  else if (t->channel_type() != NULL)
    {
      if (get_index_type)
        return t->channel_type()->element_type();
      else
        {
          if (report_error)
            error_at(this->location(),
                     "invalid definition of value variable for channel range");
          return Type::make_error_type();
        }
    }
  else
    {
      if (report_error)
        error_at(this->location(), "invalid type for range clause");
      return Type::make_error_type();
    }
}

// EXPR should be a channel.  Return the channel's element type.

Type*
Variable::type_from_chan_element(Expression* expr, bool report_error) const
{
  Type* t = expr->type();
  if (t->channel_type() != NULL)
    return t->channel_type()->element_type();
  else
    {
      if (report_error)
        error_at(this->location(), "expected channel");
      return Type::make_error_type();
    }
}

// Return the type of the Variable.  This may be called before
// Variable::determine_type is called, which means that we may need to
// get the type from the initializer.  FIXME: If we combine lowering
// with type determination, then this should be unnecessary.

Type*
Variable::type()
{
  // A variable in a type switch with a nil case will have the wrong
  // type here.  This gets fixed up in determine_type, below.
  Type* type = this->type_;
  Expression* init = this->init_;
  if (this->is_type_switch_var_
      && type != NULL
      && this->type_->is_nil_constant_as_type())
    {
      Type_guard_expression* tge = this->init_->type_guard_expression();
      go_assert(tge != NULL);
      init = tge->expr();
      type = NULL;
    }

  if (this->seen_)
    {
      if (this->type_ == NULL || !this->type_->is_error_type())
        {
          error_at(this->location_, "variable initializer refers to itself");
          this->type_ = Type::make_error_type();
        }
      return this->type_;
    }

  this->seen_ = true;

  if (type != NULL)
    ;
  else if (this->type_from_init_tuple_)
    type = this->type_from_tuple(init, false);
  else if (this->type_from_range_index_ || this->type_from_range_value_)
    type = this->type_from_range(init, this->type_from_range_index_, false);
  else if (this->type_from_chan_element_)
    type = this->type_from_chan_element(init, false);
  else
    {
      go_assert(init != NULL);
      type = init->type();
      go_assert(type != NULL);

      // Variables should not have abstract types.
      if (type->is_abstract())
        type = type->make_non_abstract_type();

      if (type->is_void_type())
        type = Type::make_error_type();
    }

  this->seen_ = false;

  return type;
}

// Fetch the type from a const pointer, in which case it should have
// been set already.

Type*
Variable::type() const
{
  go_assert(this->type_ != NULL);
  return this->type_;
}

// Set the type if necessary.

void
Variable::determine_type()
{
  if (this->determined_type_)
    return;
  this->determined_type_ = true;

  if (this->preinit_ != NULL)
    this->preinit_->determine_types();

  // A variable in a type switch with a nil case will have the wrong
  // type here.  It will have an initializer which is a type guard.
  // We want to initialize it to the value without the type guard, and
  // use the type of that value as well.
  if (this->is_type_switch_var_
      && this->type_ != NULL
      && this->type_->is_nil_constant_as_type())
    {
      Type_guard_expression* tge = this->init_->type_guard_expression();
      go_assert(tge != NULL);
      this->type_ = NULL;
      this->init_ = tge->expr();
    }

  if (this->init_ == NULL)
    go_assert(this->type_ != NULL && !this->type_->is_abstract());
  else if (this->type_from_init_tuple_)
    {
      Expression *init = this->init_;
      init->determine_type_no_context();
      this->type_ = this->type_from_tuple(init, true);
      this->init_ = NULL;
    }
  else if (this->type_from_range_index_ || this->type_from_range_value_)
    {
      Expression* init = this->init_;
      init->determine_type_no_context();
      this->type_ = this->type_from_range(init, this->type_from_range_index_,
                                          true);
      this->init_ = NULL;
    }
  else if (this->type_from_chan_element_)
    {
      Expression* init = this->init_;
      init->determine_type_no_context();
      this->type_ = this->type_from_chan_element(init, true);
      this->init_ = NULL;
    }
  else
    {
      Type_context context(this->type_, false);
      this->init_->determine_type(&context);
      if (this->type_ == NULL)
        {
          Type* type = this->init_->type();
          go_assert(type != NULL);
          if (type->is_abstract())
            type = type->make_non_abstract_type();

          if (type->is_void_type())
            {
              error_at(this->location_, "variable has no type");
              type = Type::make_error_type();
            }
          else if (type->is_nil_type())
            {
              error_at(this->location_, "variable defined to nil type");
              type = Type::make_error_type();
            }
          else if (type->is_call_multiple_result_type())
            {
              error_at(this->location_,
                       "single variable set to multiple-value function call");
              type = Type::make_error_type();
            }

          this->type_ = type;
        }
    }
}

// Get the initial value of a variable.  This does not
// consider whether the variable is in the heap--it returns the
// initial value as though it were always stored in the stack.

Bexpression*
Variable::get_init(Gogo* gogo, Named_object* function)
{
  go_assert(this->preinit_ == NULL);
  Location loc = this->location();
  if (this->init_ == NULL)
    {
      go_assert(!this->is_parameter_);
      if (this->is_global_ || this->is_in_heap())
        return NULL;
      Btype* btype = this->type()->get_backend(gogo);
      return gogo->backend()->zero_expression(btype);
    }
  else
    {
      Translate_context context(gogo, function, NULL, NULL);
      Expression* init = Expression::make_cast(this->type(), this->init_, loc);
      return init->get_backend(&context);
    }
}

// Get the initial value of a variable when a block is required.
// VAR_DECL is the decl to set; it may be NULL for a sink variable.

Bstatement*
Variable::get_init_block(Gogo* gogo, Named_object* function,
                         Bvariable* var_decl)
{
  go_assert(this->preinit_ != NULL);

  // We want to add the variable assignment to the end of the preinit
  // block.

  Translate_context context(gogo, function, NULL, NULL);
  Bblock* bblock = this->preinit_->get_backend(&context);

  // It's possible to have pre-init statements without an initializer
  // if the pre-init statements set the variable.
  Bstatement* decl_init = NULL;
  if (this->init_ != NULL)
    {
      if (var_decl == NULL)
        {
          Bexpression* init_bexpr = this->init_->get_backend(&context);
          decl_init = gogo->backend()->expression_statement(init_bexpr);
        }
      else
        {
          Location loc = this->location();
          Expression* val_expr =
              Expression::make_cast(this->type(), this->init_, loc);
          Bexpression* val = val_expr->get_backend(&context);
          Bexpression* var_ref = gogo->backend()->var_expression(var_decl, loc);
          decl_init = gogo->backend()->assignment_statement(var_ref, val, loc);
        }
    }
  Bstatement* block_stmt = gogo->backend()->block_statement(bblock);
  if (decl_init != NULL)
    block_stmt = gogo->backend()->compound_statement(block_stmt, decl_init);
  return block_stmt;
}

// Export the variable

void
Variable::export_var(Export* exp, const std::string& name) const
{
  go_assert(this->is_global_);
  exp->write_c_string("var ");
  exp->write_string(name);
  exp->write_c_string(" ");
  exp->write_type(this->type());
  exp->write_c_string(";\n");
}

// Import a variable.

void
Variable::import_var(Import* imp, std::string* pname, Type** ptype)
{
  imp->require_c_string("var ");
  *pname = imp->read_identifier();
  imp->require_c_string(" ");
  *ptype = imp->read_type();
  imp->require_c_string(";\n");
}

// Convert a variable to the backend representation.

Bvariable*
Variable::get_backend_variable(Gogo* gogo, Named_object* function,
                               const Package* package, const std::string& name)
{
  if (this->backend_ == NULL)
    {
      Backend* backend = gogo->backend();
      Type* type = this->type_;
      if (type->is_error_type()
          || (type->is_undefined()
              && (!this->is_global_ || package == NULL)))
        this->backend_ = backend->error_variable();
      else
        {
          bool is_parameter = this->is_parameter_;
          if (this->is_receiver_ && type->points_to() == NULL)
            is_parameter = false;
          if (this->is_in_heap())
            {
              is_parameter = false;
              type = Type::make_pointer_type(type);
            }

          std::string n = Gogo::unpack_hidden_name(name);
          Btype* btype = type->get_backend(gogo);

          Bvariable* bvar;
          if (Map_type::is_zero_value(this))
            bvar = Map_type::backend_zero_value(gogo);
          else if (this->is_global_)
            bvar = backend->global_variable((package == NULL
                                             ? gogo->package_name()
                                             : package->package_name()),
                                            (package == NULL
                                             ? gogo->pkgpath_symbol()
                                             : package->pkgpath_symbol()),
                                            n,
                                            btype,
                                            package != NULL,
                                            Gogo::is_hidden_name(name),
                                            this->in_unique_section_,
                                            this->location_);
          else if (function == NULL)
            {
              go_assert(saw_errors());
              bvar = backend->error_variable();
            }
          else
            {
              Bfunction* bfunction = function->func_value()->get_decl();
              bool is_address_taken = (this->is_non_escaping_address_taken_
                                       && !this->is_in_heap());
              if (this->is_closure())
                bvar = backend->static_chain_variable(bfunction, n, btype,
                                                      this->location_);
              else if (is_parameter)
                bvar = backend->parameter_variable(bfunction, n, btype,
                                                   is_address_taken,
                                                   this->location_);
              else
                bvar = backend->local_variable(bfunction, n, btype,
                                               is_address_taken,
                                               this->location_);
            }
          this->backend_ = bvar;
        }
    }
  return this->backend_;
}

// Class Result_variable.

// Convert a result variable to the backend representation.

Bvariable*
Result_variable::get_backend_variable(Gogo* gogo, Named_object* function,
                                      const std::string& name)
{
  if (this->backend_ == NULL)
    {
      Backend* backend = gogo->backend();
      Type* type = this->type_;
      if (type->is_error())
        this->backend_ = backend->error_variable();
      else
        {
          if (this->is_in_heap())
            type = Type::make_pointer_type(type);
          Btype* btype = type->get_backend(gogo);
          Bfunction* bfunction = function->func_value()->get_decl();
          std::string n = Gogo::unpack_hidden_name(name);
          bool is_address_taken = (this->is_non_escaping_address_taken_
                                   && !this->is_in_heap());
          this->backend_ = backend->local_variable(bfunction, n, btype,
                                                   is_address_taken,
                                                   this->location_);
        }
    }
  return this->backend_;
}

// Class Named_constant.

// Traverse the initializer expression.

int
Named_constant::traverse_expression(Traverse* traverse)
{
  return Expression::traverse(&this->expr_, traverse);
}

// Determine the type of the constant.

void
Named_constant::determine_type()
{
  if (this->type_ != NULL)
    {
      Type_context context(this->type_, false);
      this->expr_->determine_type(&context);
    }
  else
    {
      // A constant may have an abstract type.
      Type_context context(NULL, true);
      this->expr_->determine_type(&context);
      this->type_ = this->expr_->type();
      go_assert(this->type_ != NULL);
    }
}

// Indicate that we found and reported an error for this constant.

void
Named_constant::set_error()
{
  this->type_ = Type::make_error_type();
  this->expr_ = Expression::make_error(this->location_);
}

// Export a constant.

void
Named_constant::export_const(Export* exp, const std::string& name) const
{
  exp->write_c_string("const ");
  exp->write_string(name);
  exp->write_c_string(" ");
  if (!this->type_->is_abstract())
    {
      exp->write_type(this->type_);
      exp->write_c_string(" ");
    }
  exp->write_c_string("= ");
  this->expr()->export_expression(exp);
  exp->write_c_string(";\n");
}

// Import a constant.

void
Named_constant::import_const(Import* imp, std::string* pname, Type** ptype,
                             Expression** pexpr)
{
  imp->require_c_string("const ");
  *pname = imp->read_identifier();
  imp->require_c_string(" ");
  if (imp->peek_char() == '=')
    *ptype = NULL;
  else
    {
      *ptype = imp->read_type();
      imp->require_c_string(" ");
    }
  imp->require_c_string("= ");
  *pexpr = Expression::import_expression(imp);
  imp->require_c_string(";\n");
}

// Get the backend representation.

Bexpression*
Named_constant::get_backend(Gogo* gogo, Named_object* const_no)
{
  if (this->bconst_ == NULL)
    {
      Translate_context subcontext(gogo, NULL, NULL, NULL);
      Type* type = this->type();
      Location loc = this->location();

      Expression* const_ref = Expression::make_const_reference(const_no, loc);
      Bexpression* const_decl = const_ref->get_backend(&subcontext);
      if (type != NULL && type->is_numeric_type())
        {
          Btype* btype = type->get_backend(gogo);
          std::string name = const_no->get_id(gogo);
          const_decl =
            gogo->backend()->named_constant_expression(btype, name,
                                                       const_decl, loc);
        }
      this->bconst_ = const_decl;
    }
  return this->bconst_;
}

// Add a method.

Named_object*
Type_declaration::add_method(const std::string& name, Function* function)
{
  Named_object* ret = Named_object::make_function(name, NULL, function);
  this->methods_.push_back(ret);
  return ret;
}

// Add a method declaration.

Named_object*
Type_declaration::add_method_declaration(const std::string&  name,
                                         Package* package,
                                         Function_type* type,
                                         Location location)
{
  Named_object* ret = Named_object::make_function_declaration(name, package,
                                                              type, location);
  this->methods_.push_back(ret);
  return ret;
}

// Return whether any methods ere defined.

bool
Type_declaration::has_methods() const
{
  return !this->methods_.empty();
}

// Define methods for the real type.

void
Type_declaration::define_methods(Named_type* nt)
{
  for (std::vector<Named_object*>::const_iterator p = this->methods_.begin();
       p != this->methods_.end();
       ++p)
    nt->add_existing_method(*p);
}

// We are using the type.  Return true if we should issue a warning.

bool
Type_declaration::using_type()
{
  bool ret = !this->issued_warning_;
  this->issued_warning_ = true;
  return ret;
}

// Class Unknown_name.

// Set the real named object.

void
Unknown_name::set_real_named_object(Named_object* no)
{
  go_assert(this->real_named_object_ == NULL);
  go_assert(!no->is_unknown());
  this->real_named_object_ = no;
}

// Class Named_object.

Named_object::Named_object(const std::string& name,
                           const Package* package,
                           Classification classification)
  : name_(name), package_(package), classification_(classification),
    is_redefinition_(false)
{
  if (Gogo::is_sink_name(name))
    go_assert(classification == NAMED_OBJECT_SINK);
}

// Make an unknown name.  This is used by the parser.  The name must
// be resolved later.  Unknown names are only added in the current
// package.

Named_object*
Named_object::make_unknown_name(const std::string& name,
                                Location location)
{
  Named_object* named_object = new Named_object(name, NULL,
                                                NAMED_OBJECT_UNKNOWN);
  Unknown_name* value = new Unknown_name(location);
  named_object->u_.unknown_value = value;
  return named_object;
}

// Make a constant.

Named_object*
Named_object::make_constant(const Typed_identifier& tid,
                            const Package* package, Expression* expr,
                            int iota_value)
{
  Named_object* named_object = new Named_object(tid.name(), package,
                                                NAMED_OBJECT_CONST);
  Named_constant* named_constant = new Named_constant(tid.type(), expr,
                                                      iota_value,
                                                      tid.location());
  named_object->u_.const_value = named_constant;
  return named_object;
}

// Make a named type.

Named_object*
Named_object::make_type(const std::string& name, const Package* package,
                        Type* type, Location location)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_TYPE);
  Named_type* named_type = Type::make_named_type(named_object, type, location);
  named_object->u_.type_value = named_type;
  return named_object;
}

// Make a type declaration.

Named_object*
Named_object::make_type_declaration(const std::string& name,
                                    const Package* package,
                                    Location location)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_TYPE_DECLARATION);
  Type_declaration* type_declaration = new Type_declaration(location);
  named_object->u_.type_declaration = type_declaration;
  return named_object;
}

// Make a variable.

Named_object*
Named_object::make_variable(const std::string& name, const Package* package,
                            Variable* variable)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_VAR);
  named_object->u_.var_value = variable;
  return named_object;
}

// Make a result variable.

Named_object*
Named_object::make_result_variable(const std::string& name,
                                   Result_variable* result)
{
  Named_object* named_object = new Named_object(name, NULL,
                                                NAMED_OBJECT_RESULT_VAR);
  named_object->u_.result_var_value = result;
  return named_object;
}

// Make a sink.  This is used for the special blank identifier _.

Named_object*
Named_object::make_sink()
{
  return new Named_object("_", NULL, NAMED_OBJECT_SINK);
}

// Make a named function.

Named_object*
Named_object::make_function(const std::string& name, const Package* package,
                            Function* function)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_FUNC);
  named_object->u_.func_value = function;
  return named_object;
}

// Make a function declaration.

Named_object*
Named_object::make_function_declaration(const std::string& name,
                                        const Package* package,
                                        Function_type* fntype,
                                        Location location)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_FUNC_DECLARATION);
  Function_declaration *func_decl = new Function_declaration(fntype, location);
  named_object->u_.func_declaration_value = func_decl;
  return named_object;
}

// Make a package.

Named_object*
Named_object::make_package(const std::string& alias, Package* package)
{
  Named_object* named_object = new Named_object(alias, NULL,
                                                NAMED_OBJECT_PACKAGE);
  named_object->u_.package_value = package;
  return named_object;
}

// Return the name to use in an error message.

std::string
Named_object::message_name() const
{
  if (this->package_ == NULL)
    return Gogo::message_name(this->name_);
  std::string ret;
  if (this->package_->has_package_name())
    ret = this->package_->package_name();
  else
    ret = this->package_->pkgpath();
  ret = Gogo::message_name(ret);
  ret += '.';
  ret += Gogo::message_name(this->name_);
  return ret;
}

// Set the type when a declaration is defined.

void
Named_object::set_type_value(Named_type* named_type)
{
  go_assert(this->classification_ == NAMED_OBJECT_TYPE_DECLARATION);
  Type_declaration* td = this->u_.type_declaration;
  td->define_methods(named_type);
  unsigned int index;
  Named_object* in_function = td->in_function(&index);
  if (in_function != NULL)
    named_type->set_in_function(in_function, index);
  delete td;
  this->classification_ = NAMED_OBJECT_TYPE;
  this->u_.type_value = named_type;
}

// Define a function which was previously declared.

void
Named_object::set_function_value(Function* function)
{
  go_assert(this->classification_ == NAMED_OBJECT_FUNC_DECLARATION);
  if (this->func_declaration_value()->has_descriptor())
    {
      Expression* descriptor =
        this->func_declaration_value()->descriptor(NULL, NULL);
      function->set_descriptor(descriptor);
    }
  this->classification_ = NAMED_OBJECT_FUNC;
  // FIXME: We should free the old value.
  this->u_.func_value = function;
}

// Declare an unknown object as a type declaration.

void
Named_object::declare_as_type()
{
  go_assert(this->classification_ == NAMED_OBJECT_UNKNOWN);
  Unknown_name* unk = this->u_.unknown_value;
  this->classification_ = NAMED_OBJECT_TYPE_DECLARATION;
  this->u_.type_declaration = new Type_declaration(unk->location());
  delete unk;
}

// Return the location of a named object.

Location
Named_object::location() const
{
  switch (this->classification_)
    {
    default:
    case NAMED_OBJECT_UNINITIALIZED:
      go_unreachable();

    case NAMED_OBJECT_ERRONEOUS:
      return Linemap::unknown_location();

    case NAMED_OBJECT_UNKNOWN:
      return this->unknown_value()->location();

    case NAMED_OBJECT_CONST:
      return this->const_value()->location();

    case NAMED_OBJECT_TYPE:
      return this->type_value()->location();

    case NAMED_OBJECT_TYPE_DECLARATION:
      return this->type_declaration_value()->location();

    case NAMED_OBJECT_VAR:
      return this->var_value()->location();

    case NAMED_OBJECT_RESULT_VAR:
      return this->result_var_value()->location();

    case NAMED_OBJECT_SINK:
      go_unreachable();

    case NAMED_OBJECT_FUNC:
      return this->func_value()->location();

    case NAMED_OBJECT_FUNC_DECLARATION:
      return this->func_declaration_value()->location();

    case NAMED_OBJECT_PACKAGE:
      return this->package_value()->location();
    }
}

// Export a named object.

void
Named_object::export_named_object(Export* exp) const
{
  switch (this->classification_)
    {
    default:
    case NAMED_OBJECT_UNINITIALIZED:
    case NAMED_OBJECT_UNKNOWN:
      go_unreachable();

    case NAMED_OBJECT_ERRONEOUS:
      break;

    case NAMED_OBJECT_CONST:
      this->const_value()->export_const(exp, this->name_);
      break;

    case NAMED_OBJECT_TYPE:
      this->type_value()->export_named_type(exp, this->name_);
      break;

    case NAMED_OBJECT_TYPE_DECLARATION:
      error_at(this->type_declaration_value()->location(),
               "attempt to export %<%s%> which was declared but not defined",
               this->message_name().c_str());
      break;

    case NAMED_OBJECT_FUNC_DECLARATION:
      this->func_declaration_value()->export_func(exp, this->name_);
      break;

    case NAMED_OBJECT_VAR:
      this->var_value()->export_var(exp, this->name_);
      break;

    case NAMED_OBJECT_RESULT_VAR:
    case NAMED_OBJECT_SINK:
      go_unreachable();

    case NAMED_OBJECT_FUNC:
      this->func_value()->export_func(exp, this->name_);
      break;
    }
}

// Convert a variable to the backend representation.

Bvariable*
Named_object::get_backend_variable(Gogo* gogo, Named_object* function)
{
  if (this->classification_ == NAMED_OBJECT_VAR)
    return this->var_value()->get_backend_variable(gogo, function,
                                                   this->package_, this->name_);
  else if (this->classification_ == NAMED_OBJECT_RESULT_VAR)
    return this->result_var_value()->get_backend_variable(gogo, function,
                                                          this->name_);
  else
    go_unreachable();
}


// Return the external identifier for this object.

std::string
Named_object::get_id(Gogo* gogo)
{
  go_assert(!this->is_variable() && !this->is_result_variable());
  std::string decl_name;
  if (this->is_function_declaration()
      && !this->func_declaration_value()->asm_name().empty())
    decl_name = this->func_declaration_value()->asm_name();
  else if (this->is_type()
           && Linemap::is_predeclared_location(this->type_value()->location()))
    {
      // We don't need the package name for builtin types.
      decl_name = Gogo::unpack_hidden_name(this->name_);
    }
  else
    {
      std::string package_name;
      if (this->package_ == NULL)
        package_name = gogo->package_name();
      else
        package_name = this->package_->package_name();

      // Note that this will be misleading if this is an unexported
      // method generated for an embedded imported type.  In that case
      // the unexported method should have the package name of the
      // package from which it is imported, but we are going to give
      // it our package name.  Fixing this would require knowing the
      // package name, but we only know the package path.  It might be
      // better to use package paths here anyhow.  This doesn't affect
      // the assembler code, because we always set that name in
      // Function::get_or_make_decl anyhow.  FIXME.

      decl_name = package_name + '.' + Gogo::unpack_hidden_name(this->name_);

      Function_type* fntype;
      if (this->is_function())
        fntype = this->func_value()->type();
      else if (this->is_function_declaration())
        fntype = this->func_declaration_value()->type();
      else
        fntype = NULL;
      if (fntype != NULL && fntype->is_method())
        {
          decl_name.push_back('.');
          decl_name.append(fntype->receiver()->type()->mangled_name(gogo));
        }
    }
  if (this->is_type())
    {
      unsigned int index;
      const Named_object* in_function = this->type_value()->in_function(&index);
      if (in_function != NULL)
        {
          decl_name += '$' + Gogo::unpack_hidden_name(in_function->name());
          if (index > 0)
            {
              char buf[30];
              snprintf(buf, sizeof buf, "%u", index);
              decl_name += '$';
              decl_name += buf;
            }
        }
    }
  return decl_name;
}

// Get the backend representation for this named object.

void
Named_object::get_backend(Gogo* gogo, std::vector<Bexpression*>& const_decls,
                          std::vector<Btype*>& type_decls,
                          std::vector<Bfunction*>& func_decls)
{
  switch (this->classification_)
    {
    case NAMED_OBJECT_CONST:
      if (!Gogo::is_erroneous_name(this->name_))
        const_decls.push_back(this->u_.const_value->get_backend(gogo, this));
      break;

    case NAMED_OBJECT_TYPE:
      {
        Named_type* named_type = this->u_.type_value;
        if (!Gogo::is_erroneous_name(this->name_))
          type_decls.push_back(named_type->get_backend(gogo));

        // We need to produce a type descriptor for every named
        // type, and for a pointer to every named type, since
        // other files or packages might refer to them.  We need
        // to do this even for hidden types, because they might
        // still be returned by some function.  Simply calling the
        // type_descriptor method is enough to create the type
        // descriptor, even though we don't do anything with it.
        if (this->package_ == NULL && !saw_errors())
          {
            named_type->
                type_descriptor_pointer(gogo, Linemap::predeclared_location());
            named_type->gc_symbol_pointer(gogo);
            Type* pn = Type::make_pointer_type(named_type);
            pn->type_descriptor_pointer(gogo, Linemap::predeclared_location());
            pn->gc_symbol_pointer(gogo);
          }
      }
      break;

    case NAMED_OBJECT_TYPE_DECLARATION:
      error("reference to undefined type %qs",
            this->message_name().c_str());
      return;

    case NAMED_OBJECT_VAR:
    case NAMED_OBJECT_RESULT_VAR:
    case NAMED_OBJECT_SINK:
      go_unreachable();

    case NAMED_OBJECT_FUNC:
      {
        Function* func = this->u_.func_value;
        if (!Gogo::is_erroneous_name(this->name_))
          func_decls.push_back(func->get_or_make_decl(gogo, this));

        if (func->block() != NULL)
          func->build(gogo, this);
      }
      break;

    case NAMED_OBJECT_ERRONEOUS:
      break;

    default:
      go_unreachable();
    }
}

// Class Bindings.

Bindings::Bindings(Bindings* enclosing)
  : enclosing_(enclosing), named_objects_(), bindings_()
{
}

// Clear imports.

void
Bindings::clear_file_scope(Gogo* gogo)
{
  Contour::iterator p = this->bindings_.begin();
  while (p != this->bindings_.end())
    {
      bool keep;
      if (p->second->package() != NULL)
        keep = false;
      else if (p->second->is_package())
        keep = false;
      else if (p->second->is_function()
               && !p->second->func_value()->type()->is_method()
               && Gogo::unpack_hidden_name(p->second->name()) == "init")
        keep = false;
      else
        keep = true;

      if (keep)
        ++p;
      else
        {
          gogo->add_file_block_name(p->second->name(), p->second->location());
          p = this->bindings_.erase(p);
        }
    }
}

// Look up a symbol.

Named_object*
Bindings::lookup(const std::string& name) const
{
  Contour::const_iterator p = this->bindings_.find(name);
  if (p != this->bindings_.end())
    return p->second->resolve();
  else if (this->enclosing_ != NULL)
    return this->enclosing_->lookup(name);
  else
    return NULL;
}

// Look up a symbol locally.

Named_object*
Bindings::lookup_local(const std::string& name) const
{
  Contour::const_iterator p = this->bindings_.find(name);
  if (p == this->bindings_.end())
    return NULL;
  return p->second;
}

// Remove an object from a set of bindings.  This is used for a
// special case in thunks for functions which call recover.

void
Bindings::remove_binding(Named_object* no)
{
  Contour::iterator pb = this->bindings_.find(no->name());
  go_assert(pb != this->bindings_.end());
  this->bindings_.erase(pb);
  for (std::vector<Named_object*>::iterator pn = this->named_objects_.begin();
       pn != this->named_objects_.end();
       ++pn)
    {
      if (*pn == no)
        {
          this->named_objects_.erase(pn);
          return;
        }
    }
  go_unreachable();
}

// Add a method to the list of objects.  This is not added to the
// lookup table.  This is so that we have a single list of objects
// declared at the top level, which we walk through when it's time to
// convert to trees.

void
Bindings::add_method(Named_object* method)
{
  this->named_objects_.push_back(method);
}

// Add a generic Named_object to a Contour.

Named_object*
Bindings::add_named_object_to_contour(Contour* contour,
                                      Named_object* named_object)
{
  go_assert(named_object == named_object->resolve());
  const std::string& name(named_object->name());
  go_assert(!Gogo::is_sink_name(name));

  std::pair<Contour::iterator, bool> ins =
    contour->insert(std::make_pair(name, named_object));
  if (!ins.second)
    {
      // The name was already there.
      if (named_object->package() != NULL
          && ins.first->second->package() == named_object->package()
          && (ins.first->second->classification()
              == named_object->classification()))
        {
          // This is a second import of the same object.
          return ins.first->second;
        }
      ins.first->second = this->new_definition(ins.first->second,
                                               named_object);
      return ins.first->second;
    }
  else
    {
      // Don't push declarations on the list.  We push them on when
      // and if we find the definitions.  That way we genericize the
      // functions in order.
      if (!named_object->is_type_declaration()
          && !named_object->is_function_declaration()
          && !named_object->is_unknown())
        this->named_objects_.push_back(named_object);
      return named_object;
    }
}

// We had an existing named object OLD_OBJECT, and we've seen a new
// one NEW_OBJECT with the same name.  FIXME: This does not free the
// new object when we don't need it.

Named_object*
Bindings::new_definition(Named_object* old_object, Named_object* new_object)
{
  if (new_object->is_erroneous() && !old_object->is_erroneous())
    return new_object;

  std::string reason;
  switch (old_object->classification())
    {
    default:
    case Named_object::NAMED_OBJECT_UNINITIALIZED:
      go_unreachable();

    case Named_object::NAMED_OBJECT_ERRONEOUS:
      return old_object;

    case Named_object::NAMED_OBJECT_UNKNOWN:
      {
        Named_object* real = old_object->unknown_value()->real_named_object();
        if (real != NULL)
          return this->new_definition(real, new_object);
        go_assert(!new_object->is_unknown());
        old_object->unknown_value()->set_real_named_object(new_object);
        if (!new_object->is_type_declaration()
            && !new_object->is_function_declaration())
          this->named_objects_.push_back(new_object);
        return new_object;
      }

    case Named_object::NAMED_OBJECT_CONST:
      break;

    case Named_object::NAMED_OBJECT_TYPE:
      if (new_object->is_type_declaration())
        return old_object;
      break;

    case Named_object::NAMED_OBJECT_TYPE_DECLARATION:
      if (new_object->is_type_declaration())
        return old_object;
      if (new_object->is_type())
        {
          old_object->set_type_value(new_object->type_value());
          new_object->type_value()->set_named_object(old_object);
          this->named_objects_.push_back(old_object);
          return old_object;
        }
      break;

    case Named_object::NAMED_OBJECT_VAR:
    case Named_object::NAMED_OBJECT_RESULT_VAR:
      // We have already given an error in the parser for cases where
      // one parameter or result variable redeclares another one.
      if ((new_object->is_variable()
           && new_object->var_value()->is_parameter())
          || new_object->is_result_variable())
        return old_object;
      break;

    case Named_object::NAMED_OBJECT_SINK:
      go_unreachable();

    case Named_object::NAMED_OBJECT_FUNC:
      if (new_object->is_function_declaration())
        {
          if (!new_object->func_declaration_value()->asm_name().empty())
            sorry("__asm__ for function definitions");
          Function_type* old_type = old_object->func_value()->type();
          Function_type* new_type =
            new_object->func_declaration_value()->type();
          if (old_type->is_valid_redeclaration(new_type, &reason))
            return old_object;
        }
      break;

    case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
      {
        if (new_object->is_function())
          {
            Function_type* old_type =
                old_object->func_declaration_value()->type();
            Function_type* new_type = new_object->func_value()->type();
            if (old_type->is_valid_redeclaration(new_type, &reason))
              {
                if (!old_object->func_declaration_value()->asm_name().empty())
                  sorry("__asm__ for function definitions");
                old_object->set_function_value(new_object->func_value());
                this->named_objects_.push_back(old_object);
                return old_object;
              }
          }
      }
      break;

    case Named_object::NAMED_OBJECT_PACKAGE:
      break;
    }

  std::string n = old_object->message_name();
  if (reason.empty())
    error_at(new_object->location(), "redefinition of %qs", n.c_str());
  else
    error_at(new_object->location(), "redefinition of %qs: %s", n.c_str(),
             reason.c_str());
  old_object->set_is_redefinition();
  new_object->set_is_redefinition();

  inform(old_object->location(), "previous definition of %qs was here",
         n.c_str());

  return old_object;
}

// Add a named type.

Named_object*
Bindings::add_named_type(Named_type* named_type)
{
  return this->add_named_object(named_type->named_object());
}

// Add a function.

Named_object*
Bindings::add_function(const std::string& name, const Package* package,
                       Function* function)
{
  return this->add_named_object(Named_object::make_function(name, package,
                                                            function));
}

// Add a function declaration.

Named_object*
Bindings::add_function_declaration(const std::string& name,
                                   const Package* package,
                                   Function_type* type,
                                   Location location)
{
  Named_object* no = Named_object::make_function_declaration(name, package,
                                                             type, location);
  return this->add_named_object(no);
}

// Define a type which was previously declared.

void
Bindings::define_type(Named_object* no, Named_type* type)
{
  no->set_type_value(type);
  this->named_objects_.push_back(no);
}

// Mark all local variables as used.  This is used for some types of
// parse error.

void
Bindings::mark_locals_used()
{
  for (std::vector<Named_object*>::iterator p = this->named_objects_.begin();
       p != this->named_objects_.end();
       ++p)
    if ((*p)->is_variable())
      (*p)->var_value()->set_is_used();
}

// Traverse bindings.

int
Bindings::traverse(Traverse* traverse, bool is_global)
{
  unsigned int traverse_mask = traverse->traverse_mask();

  // We don't use an iterator because we permit the traversal to add
  // new global objects.
  const unsigned int e_or_t = (Traverse::traverse_expressions
                               | Traverse::traverse_types);
  const unsigned int e_or_t_or_s = (e_or_t
                                    | Traverse::traverse_statements);
  for (size_t i = 0; i < this->named_objects_.size(); ++i)
    {
      Named_object* p = this->named_objects_[i];
      int t = TRAVERSE_CONTINUE;
      switch (p->classification())
        {
        case Named_object::NAMED_OBJECT_CONST:
          if ((traverse_mask & Traverse::traverse_constants) != 0)
            t = traverse->constant(p, is_global);
          if (t == TRAVERSE_CONTINUE
              && (traverse_mask & e_or_t) != 0)
            {
              Type* tc = p->const_value()->type();
              if (tc != NULL
                  && Type::traverse(tc, traverse) == TRAVERSE_EXIT)
                return TRAVERSE_EXIT;
              t = p->const_value()->traverse_expression(traverse);
            }
          break;

        case Named_object::NAMED_OBJECT_VAR:
        case Named_object::NAMED_OBJECT_RESULT_VAR:
          if ((traverse_mask & Traverse::traverse_variables) != 0)
            t = traverse->variable(p);
          if (t == TRAVERSE_CONTINUE
              && (traverse_mask & e_or_t) != 0)
            {
              if (p->is_result_variable()
                  || p->var_value()->has_type())
                {
                  Type* tv = (p->is_variable()
                              ? p->var_value()->type()
                              : p->result_var_value()->type());
                  if (tv != NULL
                      && Type::traverse(tv, traverse) == TRAVERSE_EXIT)
                    return TRAVERSE_EXIT;
                }
            }
          if (t == TRAVERSE_CONTINUE
              && (traverse_mask & e_or_t_or_s) != 0
              && p->is_variable())
            t = p->var_value()->traverse_expression(traverse, traverse_mask);
          break;

        case Named_object::NAMED_OBJECT_FUNC:
          if ((traverse_mask & Traverse::traverse_functions) != 0)
            t = traverse->function(p);

          if (t == TRAVERSE_CONTINUE
              && (traverse_mask
                  & (Traverse::traverse_variables
                     | Traverse::traverse_constants
                     | Traverse::traverse_functions
                     | Traverse::traverse_blocks
                     | Traverse::traverse_statements
                     | Traverse::traverse_expressions
                     | Traverse::traverse_types)) != 0)
            t = p->func_value()->traverse(traverse);
          break;

        case Named_object::NAMED_OBJECT_PACKAGE:
          // These are traversed in Gogo::traverse.
          go_assert(is_global);
          break;

        case Named_object::NAMED_OBJECT_TYPE:
          if ((traverse_mask & e_or_t) != 0)
            t = Type::traverse(p->type_value(), traverse);
          break;

        case Named_object::NAMED_OBJECT_TYPE_DECLARATION:
        case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
        case Named_object::NAMED_OBJECT_UNKNOWN:
        case Named_object::NAMED_OBJECT_ERRONEOUS:
          break;

        case Named_object::NAMED_OBJECT_SINK:
        default:
          go_unreachable();
        }

      if (t == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }

  // If we need to traverse types, check the function declarations,
  // which have types.  Also check any methods of a type declaration.
  if ((traverse_mask & e_or_t) != 0)
    {
      for (Bindings::const_declarations_iterator p =
             this->begin_declarations();
           p != this->end_declarations();
           ++p)
        {
          if (p->second->is_function_declaration())
            {
              if (Type::traverse(p->second->func_declaration_value()->type(),
                                 traverse)
                  == TRAVERSE_EXIT)
                return TRAVERSE_EXIT;
            }
          else if (p->second->is_type_declaration())
            {
              const std::vector<Named_object*>* methods =
                p->second->type_declaration_value()->methods();
              for (std::vector<Named_object*>::const_iterator pm =
                     methods->begin();
                   pm != methods->end();
                   pm++)
                {
                  Named_object* no = *pm;
                  Type *t;
                  if (no->is_function())
                    t = no->func_value()->type();
                  else if (no->is_function_declaration())
                    t = no->func_declaration_value()->type();
                  else
                    continue;
                  if (Type::traverse(t, traverse) == TRAVERSE_EXIT)
                    return TRAVERSE_EXIT;
                }
            }
        }
    }

  return TRAVERSE_CONTINUE;
}

// Class Label.

// Clear any references to this label.

void
Label::clear_refs()
{
  for (std::vector<Bindings_snapshot*>::iterator p = this->refs_.begin();
       p != this->refs_.end();
       ++p)
    delete *p;
  this->refs_.clear();
}

// Get the backend representation for a label.

Blabel*
Label::get_backend_label(Translate_context* context)
{
  if (this->blabel_ == NULL)
    {
      Function* function = context->function()->func_value();
      Bfunction* bfunction = function->get_decl();
      this->blabel_ = context->backend()->label(bfunction, this->name_,
                                                this->location_);
    }
  return this->blabel_;
}

// Return an expression for the address of this label.

Bexpression*
Label::get_addr(Translate_context* context, Location location)
{
  Blabel* label = this->get_backend_label(context);
  return context->backend()->label_address(label, location);
}

// Return the dummy label that represents any instance of the blank label.

Label*
Label::create_dummy_label()
{
  static Label* dummy_label;
  if (dummy_label == NULL)
    {
      dummy_label = new Label("_");
      dummy_label->set_is_used();
    }
  return dummy_label;
}

// Class Unnamed_label.

// Get the backend representation for an unnamed label.

Blabel*
Unnamed_label::get_blabel(Translate_context* context)
{
  if (this->blabel_ == NULL)
    {
      Function* function = context->function()->func_value();
      Bfunction* bfunction = function->get_decl();
      this->blabel_ = context->backend()->label(bfunction, "",
                                                this->location_);
    }
  return this->blabel_;
}

// Return a statement which defines this unnamed label.

Bstatement*
Unnamed_label::get_definition(Translate_context* context)
{
  Blabel* blabel = this->get_blabel(context);
  return context->backend()->label_definition_statement(blabel);
}

// Return a goto statement to this unnamed label.

Bstatement*
Unnamed_label::get_goto(Translate_context* context, Location location)
{
  Blabel* blabel = this->get_blabel(context);
  return context->backend()->goto_statement(blabel, location);
}

// Class Package.

Package::Package(const std::string& pkgpath,
                 const std::string& pkgpath_symbol, Location location)
  : pkgpath_(pkgpath), pkgpath_symbol_(pkgpath_symbol),
    package_name_(), bindings_(new Bindings(NULL)),
    location_(location)
{
  go_assert(!pkgpath.empty());
}

// Set the package name.

void
Package::set_package_name(const std::string& package_name, Location location)
{
  go_assert(!package_name.empty());
  if (this->package_name_.empty())
    this->package_name_ = package_name;
  else if (this->package_name_ != package_name)
    error_at(location,
             "saw two different packages with the same package path %s: %s, %s",
             this->pkgpath_.c_str(), this->package_name_.c_str(),
             package_name.c_str());
}

// Return the pkgpath symbol, which is a prefix for symbols defined in
// this package.

std::string
Package::pkgpath_symbol() const
{
  if (this->pkgpath_symbol_.empty())
    return Gogo::pkgpath_for_symbol(this->pkgpath_);
  return this->pkgpath_symbol_;
}

// Set the package path symbol.

void
Package::set_pkgpath_symbol(const std::string& pkgpath_symbol)
{
  go_assert(!pkgpath_symbol.empty());
  if (this->pkgpath_symbol_.empty())
    this->pkgpath_symbol_ = pkgpath_symbol;
  else
    go_assert(this->pkgpath_symbol_ == pkgpath_symbol);
}

// Note that symbol from this package was and qualified by ALIAS.

void
Package::note_usage(const std::string& alias) const
{
  Aliases::const_iterator p = this->aliases_.find(alias);
  go_assert(p != this->aliases_.end());
  p->second->note_usage();
}

// Forget a given usage.  If forgetting this usage means this package becomes
// unused, report that error.

void
Package::forget_usage(Expression* usage) const
{
  if (this->fake_uses_.empty())
    return;

  std::set<Expression*>::iterator p = this->fake_uses_.find(usage);
  go_assert(p != this->fake_uses_.end());
  this->fake_uses_.erase(p);

  if (this->fake_uses_.empty())
    error_at(this->location(), "imported and not used: %s",
             Gogo::message_name(this->package_name()).c_str());
}

// Clear the used field for the next file.  If the only usages of this package
// are possibly fake, keep the fake usages for lowering.

void
Package::clear_used()
{
  std::string dot_alias = "." + this->package_name();
  Aliases::const_iterator p = this->aliases_.find(dot_alias);
  if (p != this->aliases_.end() && p->second->used() > this->fake_uses_.size())
    this->fake_uses_.clear();

  this->aliases_.clear();
}

Package_alias*
Package::add_alias(const std::string& alias, Location location)
{
  Aliases::const_iterator p = this->aliases_.find(alias);
  if (p == this->aliases_.end())
    {
      std::pair<Aliases::iterator, bool> ret;
      ret = this->aliases_.insert(std::make_pair(alias,
                                                 new Package_alias(location)));
      p = ret.first;
    }
  return p->second;
}

// Determine types of constants.  Everything else in a package
// (variables, function declarations) should already have a fixed
// type.  Constants may have abstract types.

void
Package::determine_types()
{
  Bindings* bindings = this->bindings_;
  for (Bindings::const_definitions_iterator p = bindings->begin_definitions();
       p != bindings->end_definitions();
       ++p)
    {
      if ((*p)->is_const())
        (*p)->const_value()->determine_type();
    }
}

// Class Traverse.

// Destructor.

Traverse::~Traverse()
{
  if (this->types_seen_ != NULL)
    delete this->types_seen_;
  if (this->expressions_seen_ != NULL)
    delete this->expressions_seen_;
}

// Record that we are looking at a type, and return true if we have
// already seen it.

bool
Traverse::remember_type(const Type* type)
{
  if (type->is_error_type())
    return true;
  go_assert((this->traverse_mask() & traverse_types) != 0
             || (this->traverse_mask() & traverse_expressions) != 0);
  // We mostly only have to remember named types.  But it turns out
  // that an interface type can refer to itself without using a name
  // by relying on interface inheritance, as in
  // type I interface { F() interface{I} }
  if (type->classification() != Type::TYPE_NAMED
      && type->classification() != Type::TYPE_INTERFACE)
    return false;
  if (this->types_seen_ == NULL)
    this->types_seen_ = new Types_seen();
  std::pair<Types_seen::iterator, bool> ins = this->types_seen_->insert(type);
  return !ins.second;
}

// Record that we are looking at an expression, and return true if we
// have already seen it.

bool
Traverse::remember_expression(const Expression* expression)
{
  go_assert((this->traverse_mask() & traverse_types) != 0
             || (this->traverse_mask() & traverse_expressions) != 0);
  if (this->expressions_seen_ == NULL)
    this->expressions_seen_ = new Expressions_seen();
  std::pair<Expressions_seen::iterator, bool> ins =
    this->expressions_seen_->insert(expression);
  return !ins.second;
}

// The default versions of these functions should never be called: the
// traversal mask indicates which functions may be called.

int
Traverse::variable(Named_object*)
{
  go_unreachable();
}

int
Traverse::constant(Named_object*, bool)
{
  go_unreachable();
}

int
Traverse::function(Named_object*)
{
  go_unreachable();
}

int
Traverse::block(Block*)
{
  go_unreachable();
}

int
Traverse::statement(Block*, size_t*, Statement*)
{
  go_unreachable();
}

int
Traverse::expression(Expression**)
{
  go_unreachable();
}

int
Traverse::type(Type*)
{
  go_unreachable();
}

// Class Statement_inserter.

void
Statement_inserter::insert(Statement* s)
{
  if (this->block_ != NULL)
    {
      go_assert(this->pindex_ != NULL);
      this->block_->insert_statement_before(*this->pindex_, s);
      ++*this->pindex_;
    }
  else if (this->var_ != NULL)
    this->var_->add_preinit_statement(this->gogo_, s);
  else
    go_assert(saw_errors());
}