1999-10-04 Mark Mitchell <mark@codesourcery.com>

[official-gcc.git] / gcc / cp / except.c

/* Handle exceptional things in C++.
   Copyright (C) 1989, 92-97, 1998, 1999 Free Software Foundation, Inc.
   Contributed by Michael Tiemann <tiemann@cygnus.com>
   Rewritten by Mike Stump <mrs@cygnus.com>, based upon an
   initial re-implementation courtesy Tad Hunt.

This file is part of GNU CC.

GNU CC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU CC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */


#include "config.h"
#include "system.h"
#include "tree.h"
#include "rtl.h"
#include "cp-tree.h"
#include "flags.h"
#include "obstack.h"
#include "expr.h"
#include "output.h"
#include "except.h"
#include "defaults.h"
#include "toplev.h"
#include "eh-common.h"

static void push_eh_cleanup PROTO((void));
static tree build_eh_type_type PROTO((tree));
static tree call_eh_info PROTO((void));
static void push_eh_info PROTO((void));
static tree get_eh_info PROTO((void));
static tree get_eh_value PROTO((void));
#if 0
static tree get_eh_type PROTO((void));
static tree get_eh_caught PROTO((void));
static tree get_eh_handlers PROTO((void));
#endif
static tree do_pop_exception PROTO((void));
static tree build_eh_type_type_ref PROTO((tree));
static tree build_terminate_handler PROTO((void));
static tree alloc_eh_object PROTO((tree));
static int complete_ptr_ref_or_void_ptr_p PROTO((tree, tree));
static void initialize_handler_parm PROTO((tree));
static tree expand_throw PROTO((tree));

#if 0
/* This is the startup, and finish stuff per exception table.  */

/* XXX - Tad: exception handling section */
#ifndef EXCEPT_SECTION_ASM_OP
#define EXCEPT_SECTION_ASM_OP   "section\t.gcc_except_table,\"a\",@progbits"
#endif

#ifdef EXCEPT_SECTION_ASM_OP

 /* on machines which support it, the exception table lives in another section,
        but it needs a label so we can reference it...  This sets up that
    label! */
asm (EXCEPT_SECTION_ASM_OP);
exception_table __EXCEPTION_TABLE__[1] = { (void*)0, (void*)0, (void*)0 };
asm (TEXT_SECTION_ASM_OP);

#endif /* EXCEPT_SECTION_ASM_OP */

#ifdef EXCEPT_SECTION_ASM_OP

 /* we need to know where the end of the exception table is... so this
    is how we do it! */

asm (EXCEPT_SECTION_ASM_OP);
exception_table __EXCEPTION_END__[1] = { (void*)-1, (void*)-1, (void*)-1 };
asm (TEXT_SECTION_ASM_OP);

#endif /* EXCEPT_SECTION_ASM_OP */

#endif

#include "decl.h"
#include "insn-flags.h"
#include "obstack.h"

/* ======================================================================
   Briefly the algorithm works like this:

     When a constructor or start of a try block is encountered,
     push_eh_entry (&eh_stack) is called.  Push_eh_entry () creates a
     new entry in the unwind protection stack and returns a label to
     output to start the protection for that block.

     When a destructor or end try block is encountered, pop_eh_entry
     (&eh_stack) is called.  Pop_eh_entry () returns the eh_entry it
     created when push_eh_entry () was called.  The eh_entry structure
     contains three things at this point.  The start protect label,
     the end protect label, and the exception handler label.  The end
     protect label should be output before the call to the destructor
     (if any). If it was a destructor, then its parse tree is stored
     in the finalization variable in the eh_entry structure.  Otherwise
     the finalization variable is set to NULL to reflect the fact that
     it is the end of a try block.  Next, this modified eh_entry node
     is enqueued in the finalizations queue by calling
     enqueue_eh_entry (&queue,entry).

        +---------------------------------------------------------------+
        |XXX: Will need modification to deal with partially             |
        |                       constructed arrays of objects           |
        |                                                               |
        |       Basically, this consists of keeping track of how many   |
        |       of the objects have been constructed already (this      |
        |       should be in a register though, so that shouldn't be a  |
        |       problem.                                                |
        +---------------------------------------------------------------+

     When a catch block is encountered, there is a lot of work to be
     done.

     Since we don't want to generate the catch block inline with the
     regular flow of the function, we need to have some way of doing
     so.  Luckily, we can use sequences to defer the catch sections.
     When the start of a catch block is encountered, we start the
     sequence.  After the catch block is generated, we end the
     sequence.

     Next we must insure that when the catch block is executed, all
     finalizations for the matching try block have been completed.  If
     any of those finalizations throw an exception, we must call
     terminate according to the ARM (section r.15.6.1).  What this
     means is that we need to dequeue and emit finalizations for each
     entry in the eh_queue until we get to an entry with a NULL
     finalization field.  For any of the finalization entries, if it
     is not a call to terminate (), we must protect it by giving it
     another start label, end label, and exception handler label,
     setting its finalization tree to be a call to terminate (), and
     enqueue'ing this new eh_entry to be output at an outer level.
     Finally, after all that is done, we can get around to outputting
     the catch block which basically wraps all the "catch (...) {...}"
     statements in a big if/then/else construct that matches the
     correct block to call.
     
     ===================================================================== */

/* ====================================================================== */

/* sets up all the global eh stuff that needs to be initialized at the
   start of compilation.  */

void
init_exception_processing ()
{
  /* void vtype () */
  tree vtype = build_function_type (void_type_node, void_list_node);
  
  if (flag_honor_std)
    push_namespace (get_identifier ("std"));
  terminate_node = auto_function (get_identifier ("terminate"), vtype);
  TREE_THIS_VOLATILE (terminate_node) = 1;
  if (flag_honor_std)
    pop_namespace ();

  set_exception_lang_code (EH_LANG_C_plus_plus);
  set_exception_version_code (1);

  /* If we use setjmp/longjmp EH, arrange for all cleanup actions to
     be protected with __terminate.  */
  protect_cleanup_actions_with_terminate = 1;
}

/* Retrieve a pointer to the cp_eh_info node for the current exception.  */

static tree
call_eh_info ()
{
  tree fn;

  fn = get_identifier ("__start_cp_handler");
  if (IDENTIFIER_GLOBAL_VALUE (fn))
    fn = IDENTIFIER_GLOBAL_VALUE (fn);
  else
    {
      tree t1, t, fields[7];

      /* Declare cp_eh_info * __start_cp_handler (void),
         as defined in exception.cc. */
      push_permanent_obstack ();

      /* struct cp_eh_info.  This must match exception.cc.  Note that this
         type is not pushed anywhere.  */
      t1= make_lang_type (RECORD_TYPE);
      fields[0] = build_lang_decl (FIELD_DECL, 
                    get_identifier ("handler_label"), ptr_type_node);
      fields[1] = build_lang_decl (FIELD_DECL, 
                    get_identifier ("dynamic_handler_chain"), ptr_type_node);
      fields[2] = build_lang_decl (FIELD_DECL, 
                    get_identifier ("info"), ptr_type_node);
      fields[3] = build_lang_decl (FIELD_DECL, 
                    get_identifier ("table_index"), ptr_type_node);
      /* N.B.: The fourth field LEN is expected to be
         the number of fields - 1, not the total number of fields.  */
      finish_builtin_type (t1, "eh_context", fields, 3, ptr_type_node);
      t1 = build_pointer_type (t1);

      t1= make_lang_type (RECORD_TYPE);
      fields[0] = build_lang_decl (FIELD_DECL, 
                    get_identifier ("match_function"), ptr_type_node);
      fields[1] = build_lang_decl (FIELD_DECL, 
                    get_identifier ("language"), short_integer_type_node);
      fields[2] = build_lang_decl (FIELD_DECL, 
                    get_identifier ("version"), short_integer_type_node);
      /* N.B.: The fourth field LEN is expected to be
         the number of fields - 1, not the total number of fields.  */
      finish_builtin_type (t1, "__eh_info", fields, 2, ptr_type_node);
      t = make_lang_type (RECORD_TYPE);
      fields[0] = build_lang_decl (FIELD_DECL, 
                                   get_identifier ("eh_info"), t1);
      fields[1] = build_lang_decl (FIELD_DECL, get_identifier ("value"),
                                   ptr_type_node);
      fields[2] = build_lang_decl (FIELD_DECL, get_identifier ("type"),
                                   ptr_type_node);
      fields[3] = build_lang_decl
        (FIELD_DECL, get_identifier ("cleanup"),
         build_pointer_type (build_function_type
                             (ptr_type_node, tree_cons
                              (NULL_TREE, ptr_type_node, void_list_node))));
      fields[4] = build_lang_decl (FIELD_DECL, get_identifier ("caught"),
                                   boolean_type_node);
      fields[5] = build_lang_decl (FIELD_DECL, get_identifier ("next"),
                                   build_pointer_type (t));
      fields[6] = build_lang_decl
        (FIELD_DECL, get_identifier ("handlers"), long_integer_type_node);
      /* N.B.: The fourth field LEN is expected to be
         the number of fields - 1, not the total number of fields.  */
      finish_builtin_type (t, "cp_eh_info", fields, 6, ptr_type_node);
      t = build_pointer_type (t);

      /* And now the function.  */
      fn = build_lang_decl (FUNCTION_DECL, fn,
                            build_function_type (t, void_list_node));
      DECL_EXTERNAL (fn) = 1;
      TREE_PUBLIC (fn) = 1;
      DECL_ARTIFICIAL (fn) = 1;
      pushdecl_top_level (fn);
      make_function_rtl (fn);
      pop_obstacks ();
    }
  mark_used (fn);
  return build_function_call (fn, NULL_TREE);
}

/* Retrieve a pointer to the cp_eh_info node for the current exception
   and save it in the current binding level.  */

static void
push_eh_info ()
{
  tree decl, fn = call_eh_info ();

  /* Remember the pointer to the current exception info; it won't change
     during this catch block.  */
  decl = build_decl (VAR_DECL, get_identifier ("__exception_info"),
                     TREE_TYPE (fn));
  DECL_ARTIFICIAL (decl) = 1;
  DECL_INITIAL (decl) = fn;
  decl = pushdecl (decl);
  cp_finish_decl (decl, fn, NULL_TREE, 0, 0);
}

/* Returns a reference to the cp_eh_info node for the current exception.  */

static tree
get_eh_info ()
{
  /* Look for the pointer pushed in push_eh_info.  */
  tree t = lookup_name (get_identifier ("__exception_info"), 0);
  return build_indirect_ref (t, NULL_PTR);
}

/* Returns a reference to the current exception object.  */

static tree
get_eh_value ()
{
  return build_component_ref (get_eh_info (), get_identifier ("value"),
                              NULL_TREE, 0);
}

/* Returns a reference to the current exception type.  */

#if 0
static tree
get_eh_type ()
{
  return build_component_ref (get_eh_info (), get_identifier ("type"),
                              NULL_TREE, 0);
}

/* Returns a reference to whether or not the current exception
   has been caught.  */

static tree
get_eh_caught ()
{
  return build_component_ref (get_eh_info (), get_identifier ("caught"),
                              NULL_TREE, 0);
}

/* Returns a reference to whether or not the current exception
   has been caught.  */

static tree
get_eh_handlers ()
{
  return build_component_ref (get_eh_info (), get_identifier ("handlers"),
                              NULL_TREE, 0);
}
#endif

/* Build a type value for use at runtime for a type that is matched
   against by the exception handling system.  */

static tree
build_eh_type_type (type)
     tree type;
{
  if (type == error_mark_node)
    return error_mark_node;

  /* peel back references, so they match.  */
  if (TREE_CODE (type) == REFERENCE_TYPE)
    type = TREE_TYPE (type);

  /* Peel off cv qualifiers.  */
  type = TYPE_MAIN_VARIANT (type);

  return build1 (ADDR_EXPR, ptr_type_node, get_typeid_1 (type));
}

/* Build the address of a typeinfo function for use in the runtime
   matching field of the new exception model */

static tree
build_eh_type_type_ref (type)
     tree type;
{
  tree exp;

  if (type == error_mark_node)
    return error_mark_node;

  /* peel back references, so they match.  */
  if (TREE_CODE (type) == REFERENCE_TYPE)
    type = TREE_TYPE (type);

  /* Peel off cv qualifiers.  */
  type = TYPE_MAIN_VARIANT (type);

  exp = get_tinfo_fn (type);
  exp = build1 (ADDR_EXPR, ptr_type_node, exp);

  return (exp);
}

/* This routine is called to mark all the symbols representing runtime
   type functions in the exception table as haveing been referenced.
   This will make sure code is emitted for them. Called from finish_file. */
void 
mark_all_runtime_matches () 
{
  int x,num;
  void **ptr;
  tree exp;
  
  num = find_all_handler_type_matches (&ptr);
  if (num == 0 || ptr == NULL)
    return;
  
  for (x=0; x <num; x++)
    {
      exp = (tree) ptr[x];
      if (TREE_CODE (exp) == ADDR_EXPR)
        {
          exp = TREE_OPERAND (exp, 0);
          if (TREE_CODE (exp) == FUNCTION_DECL)
            TREE_SYMBOL_REFERENCED (DECL_ASSEMBLER_NAME (exp)) = 1;
        }
    }
  
  free (ptr);
}

/* Build up a call to __cp_pop_exception, to destroy the exception object
   for the current catch block.  HANDLER is either true or false, telling
   the library whether or not it is being called from an exception handler;
   if it is, it avoids destroying the object on rethrow.  */

static tree
do_pop_exception ()
{
  tree fn, cleanup;
  fn = get_identifier ("__cp_pop_exception");
  if (IDENTIFIER_GLOBAL_VALUE (fn))
    fn = IDENTIFIER_GLOBAL_VALUE (fn);
  else
    {
      /* Declare void __cp_pop_exception (void *),
         as defined in exception.cc. */
      push_permanent_obstack ();
      fn = build_lang_decl
        (FUNCTION_DECL, fn,
         build_function_type (void_type_node, tree_cons
                              (NULL_TREE, ptr_type_node, void_list_node)));
      DECL_EXTERNAL (fn) = 1;
      TREE_PUBLIC (fn) = 1;
      DECL_ARTIFICIAL (fn) = 1;
      pushdecl_top_level (fn);
      make_function_rtl (fn);
      pop_obstacks ();
    }

  mark_used (fn);
  /* Arrange to do a dynamically scoped cleanup upon exit from this region.  */
  cleanup = lookup_name (get_identifier ("__exception_info"), 0);
  cleanup = build_function_call (fn, tree_cons
                                 (NULL_TREE, cleanup, NULL_TREE));
  return cleanup;
}

/* This routine creates the cleanup for the current exception.  */

static void
push_eh_cleanup ()
{
  int yes;

  yes = suspend_momentary ();
  /* All cleanups must last longer than normal.  */
  finish_decl_cleanup (NULL_TREE, do_pop_exception ());
  resume_momentary (yes);
}

/* Build up a call to terminate on the function obstack, for use as an
   exception handler.  */

static tree
build_terminate_handler ()
{
  int yes = suspend_momentary ();
  tree term = build_function_call (terminate_node, NULL_TREE);
  resume_momentary (yes);
  return term;
}

/* Initialize the catch parameter DECL.  */

static void 
initialize_handler_parm (decl)
     tree decl;
{
  tree exp;
  tree init;
  tree init_type;

  /* Make sure we mark the catch param as used, otherwise we'll get a
     warning about an unused ((anonymous)).  */
  TREE_USED (decl) = 1;

  /* Figure out the type that the initializer is.  */
  init_type = TREE_TYPE (decl);
  if (TREE_CODE (init_type) != REFERENCE_TYPE
      && TREE_CODE (init_type) != POINTER_TYPE)
    init_type = build_reference_type (init_type);

  exp = get_eh_value ();

  /* Since pointers are passed by value, initialize a reference to
     pointer catch parm with the address of the value slot.  */ 
  if (TREE_CODE (init_type) == REFERENCE_TYPE 
      && TREE_CODE (TREE_TYPE (init_type)) == POINTER_TYPE)
    exp = build_unary_op (ADDR_EXPR, exp, 1);

  exp = ocp_convert (init_type , exp, CONV_IMPLICIT|CONV_FORCE_TEMP, 0);

  init = convert_from_reference (exp);

  /* If the constructor for the catch parm exits via an exception, we
     must call terminate.  See eh23.C.  */
  if (TYPE_NEEDS_CONSTRUCTING (TREE_TYPE (decl)))
    {
      /* Generate the copy constructor call directly so we can wrap it.
         See also expand_default_init.  */
      init = ocp_convert (TREE_TYPE (decl), init,
                          CONV_IMPLICIT|CONV_FORCE_TEMP, 0);
      init = build (TRY_CATCH_EXPR, TREE_TYPE (init), init,
                    build_terminate_handler ());
    }

  /* Let `cp_finish_decl' know that this initializer is ok.  */
  DECL_INITIAL (decl) = error_mark_node;
  decl = pushdecl (decl);

  start_decl_1 (decl);
  cp_finish_decl (decl, init, NULL_TREE, 0,
                  LOOKUP_ONLYCONVERTING|DIRECT_BIND);
}

/* Call this to start a catch block.  DECL is the catch parameter.  */

tree
expand_start_catch_block (decl)
     tree decl;
{
  tree compound_stmt_1;
  tree compound_stmt_2;
  tree type;

  if (! doing_eh (1))
    return NULL_TREE;

  /* Make sure this declaration is reasonable.  */
  if (decl && !complete_ptr_ref_or_void_ptr_p (TREE_TYPE (decl), NULL_TREE))
    decl = NULL_TREE;

  /* Create a binding level for the eh_info and the exception object
     cleanup.  */
  compound_stmt_1 = begin_compound_stmt (/*has_no_scope=*/0);

  if (decl)
    type = build_eh_type_type_ref (TREE_TYPE (decl));
  else
    type = NULL_TREE;
  begin_catch_block (type);

  push_eh_info ();
  push_eh_cleanup ();

  /* Create a binding level for the parm.  */
  compound_stmt_2 = begin_compound_stmt (/*has_no_scope=*/0);

  if (decl)
    initialize_handler_parm (decl);

  return build_tree_list (compound_stmt_1, compound_stmt_2);
}


/* Call this to end a catch block.  Its responsible for emitting the
   code to handle jumping back to the correct place, and for emitting
   the label to jump to if this catch block didn't match.  */

void
expand_end_catch_block (blocks)
     tree blocks;
{
  tree compound_stmt_1 = blocks ? TREE_PURPOSE (blocks): NULL_TREE;
  tree compound_stmt_2 = blocks ? TREE_VALUE (blocks): NULL_TREE;

  if (! doing_eh (1))
    return;

  /* The exception being handled is rethrown if control reaches the end of
     a handler of the function-try-block of a constructor or destructor.  */
  if (in_function_try_handler
      && (DECL_CONSTRUCTOR_P (current_function_decl)
          || DECL_DESTRUCTOR_P (current_function_decl)))
    finish_expr_stmt (build_throw (NULL_TREE));

  /* Cleanup the EH parameter.  */
  finish_compound_stmt (/*has_no_scope=*/0, compound_stmt_1);
    /* Cleanup the EH object.  */
  finish_compound_stmt (/*has_no_scope=*/0, compound_stmt_2);
}

/* An exception spec is implemented more or less like:

   try {
     function body;
   } catch (...) {
     void *p[] = { typeid(raises) };
     __check_eh_spec (p, count);
   }

   __check_eh_spec in exception.cc handles all the details.  */

tree
expand_start_eh_spec ()
{
  return begin_try_block ();
}

void
expand_end_eh_spec (raises, try_block)
     tree raises;
     tree try_block;
{
  tree tmp, fn, decl, types = NULL_TREE;
  tree blocks;
  tree handler;
  int count = 0;

  finish_try_block (try_block);
  handler = begin_handler ();
  blocks = finish_handler_parms (NULL_TREE, handler);

  /* Build up an array of type_infos.  */
  for (; raises && TREE_VALUE (raises); raises = TREE_CHAIN (raises))
    {
      types = tree_cons
        (NULL_TREE, build_eh_type_type (TREE_VALUE (raises)), types);
      ++count;
    }

  types = build_nt (CONSTRUCTOR, NULL_TREE, types);
  TREE_HAS_CONSTRUCTOR (types) = 1;

  /* We can't pass the CONSTRUCTOR directly, so stick it in a variable.  */
  tmp = build_cplus_array_type (const_ptr_type_node, NULL_TREE);
  decl = build_decl (VAR_DECL, NULL_TREE, tmp);
  DECL_ARTIFICIAL (decl) = 1;
  DECL_INITIAL (decl) = types;
  cp_finish_decl (decl, types, NULL_TREE, 0, 0);

  decl = decay_conversion (decl);

  fn = get_identifier ("__check_eh_spec");
  if (IDENTIFIER_GLOBAL_VALUE (fn))
    fn = IDENTIFIER_GLOBAL_VALUE (fn);
  else
    {
      push_permanent_obstack ();

      tmp = tree_cons
        (NULL_TREE, integer_type_node, tree_cons
         (NULL_TREE, TREE_TYPE (decl), void_list_node));
      tmp = build_function_type (void_type_node, tmp);
  
      fn = build_lang_decl (FUNCTION_DECL, fn, tmp);
      DECL_EXTERNAL (fn) = 1;
      TREE_PUBLIC (fn) = 1;
      DECL_ARTIFICIAL (fn) = 1;
      TREE_THIS_VOLATILE (fn) = 1;
      pushdecl_top_level (fn);
      make_function_rtl (fn);
      pop_obstacks ();
    }

  mark_used (fn);
  tmp = tree_cons (NULL_TREE, build_int_2 (count, 0), 
                   tree_cons (NULL_TREE, decl, NULL_TREE));
  tmp = build_call (fn, TREE_TYPE (TREE_TYPE (fn)), tmp);
  finish_expr_stmt (tmp);

  finish_handler (blocks, handler);
  finish_handler_sequence (try_block);
}

/* This is called to expand all the toplevel exception handling
   finalization for a function.  It should only be called once per
   function.  */

void
expand_exception_blocks ()
{
  do_pending_stack_adjust ();
  push_to_sequence (catch_clauses);
  expand_leftover_cleanups ();
  do_pending_stack_adjust ();
  catch_clauses = get_insns ();
  end_sequence ();

  if (catch_clauses)
    {
      rtx funcend = gen_label_rtx ();
      emit_jump (funcend);

      /* We cannot protect n regions this way if we must flow into the
         EH region through the top of the region, as we have to with
         the setjmp/longjmp approach.  */
      if (exceptions_via_longjmp == 0)
        expand_eh_region_start ();

      emit_insns (catch_clauses);
      catch_clauses = NULL_RTX;

      if (exceptions_via_longjmp == 0)
        expand_eh_region_end (build_terminate_handler ());

      expand_leftover_cleanups ();

      emit_label (funcend);
    }
}

tree
start_anon_func ()
{
  static int counter = 0;
  int old_interface_unknown = interface_unknown;
  char name[32];
  tree params;
  tree t;

  push_to_top_level ();

  /* No need to mangle this.  */
  push_lang_context (lang_name_c);

  interface_unknown = 1;

  params = void_list_node;
  /* tcf stands for throw clean function.  */
  sprintf (name, "__tcf_%d", counter++);
  t = make_call_declarator (get_identifier (name), params, NULL_TREE,
                            NULL_TREE);
  start_function (decl_tree_cons (NULL_TREE, get_identifier ("static"),
                                  void_list_node),
                  t, NULL_TREE, SF_DEFAULT);
  do_pushlevel ();

  interface_unknown = old_interface_unknown;

  pop_lang_context ();

  return current_function_decl;
}

void
end_anon_func ()
{
  do_poplevel ();

  expand_body (finish_function (lineno, 0));

  pop_from_top_level ();
}

/* Return a pointer to a buffer for an exception object of type TYPE.  */

static tree
alloc_eh_object (type)
     tree type;
{
  tree fn, exp;

  fn = get_identifier ("__eh_alloc");
  if (IDENTIFIER_GLOBAL_VALUE (fn))
    fn = IDENTIFIER_GLOBAL_VALUE (fn);
  else
    {
      /* Declare __eh_alloc (size_t), as defined in exception.cc.  */
      tree tmp;
      push_permanent_obstack ();
      tmp = tree_cons (NULL_TREE, sizetype, void_list_node);
      fn = build_lang_decl (FUNCTION_DECL, fn,
                            build_function_type (ptr_type_node, tmp));
      DECL_EXTERNAL (fn) = 1;
      TREE_PUBLIC (fn) = 1;
      DECL_ARTIFICIAL (fn) = 1;
      pushdecl_top_level (fn);
      make_function_rtl (fn);
      pop_obstacks ();
    }

  mark_used (fn);
  exp = build_function_call (fn, tree_cons
                             (NULL_TREE, size_in_bytes (type), NULL_TREE));
  exp = build1 (NOP_EXPR, build_pointer_type (type), exp);
  return exp;
}

/* Expand a throw statement.  This follows the following
   algorithm:

        1. Allocate space to save the current PC onto the stack.
        2. Generate and emit a label and save its address into the
                newly allocated stack space since we can't save the pc directly.
        3. If this is the first call to throw in this function:
                generate a label for the throw block
        4. jump to the throw block label.  */

tree
expand_throw (exp)
     tree exp;
{
  tree fn;

  if (! doing_eh (1))
    return error_mark_node;

  if (exp)
    {
      tree throw_type;
      tree cleanup = NULL_TREE, e;
      tree stmt_expr;
      tree compound_stmt;
      tree try_block;

      begin_init_stmts (&stmt_expr, &compound_stmt);

      /* throw expression */
      /* First, decay it.  */
      exp = decay_conversion (exp);

      /* cleanup_type is void (*)(void *, int),
         the internal type of a destructor. */
      if (cleanup_type == NULL_TREE)
        cleanup_type = build_pointer_type
          (build_function_type
           (void_type_node, tree_cons
            (NULL_TREE, ptr_type_node, tree_cons
             (NULL_TREE, integer_type_node, void_list_node))));

      if (TYPE_PTR_P (TREE_TYPE (exp)))
        throw_type = build_eh_type_type (TREE_TYPE (exp));
      else
        {
          tree object, ptr;

          /* OK, this is kind of wacky.  The WP says that we call
             terminate

             when the exception handling mechanism, after completing
             evaluation of the expression to be thrown but before the
             exception is caught (_except.throw_), calls a user function
             that exits via an uncaught exception.

             So we have to protect the actual initialization of the
             exception object with terminate(), but evaluate the expression
             first.  We also expand the call to __eh_alloc
             first.  Since there could be temps in the expression, we need
             to handle that, too.  */

          my_friendly_assert (stmts_are_full_exprs_p == 1, 19990926);

          /* Store the throw expression into a temp.  This can be less
             efficient than storing it into the allocated space directly, but
             oh well.  To do this efficiently we would need to insinuate
             ourselves into expand_call.  */
          if (TREE_SIDE_EFFECTS (exp))
            {
              tree temp = create_temporary_var (TREE_TYPE (exp));
              DECL_INITIAL (temp) = exp;
              cp_finish_decl (temp, exp, NULL_TREE, 0, LOOKUP_ONLYCONVERTING);
              exp = temp;
            }

          /* Allocate the space for the exception.  */
          ptr = save_expr (alloc_eh_object (TREE_TYPE (exp)));
          finish_expr_stmt (ptr);

          try_block = begin_try_block ();
          object = build_indirect_ref (ptr, NULL_PTR);
          exp = build_modify_expr (object, INIT_EXPR, exp);

          if (exp == error_mark_node)
            error ("  in thrown expression");

          finish_expr_stmt (exp);
          finish_cleanup_try_block (try_block);
          finish_cleanup (build_terminate_handler (), try_block);

          throw_type = build_eh_type_type (TREE_TYPE (object));

          if (TYPE_HAS_DESTRUCTOR (TREE_TYPE (object)))
            {
              cleanup = lookup_fnfields (TYPE_BINFO (TREE_TYPE (object)),
                                         dtor_identifier, 0);
              cleanup = TREE_VALUE (cleanup);
              mark_used (cleanup);
              mark_addressable (cleanup);
              /* Pretend it's a normal function.  */
              cleanup = build1 (ADDR_EXPR, cleanup_type, cleanup);
            }

          exp = ptr;
        }

      /* Cast EXP to `void *' so that it will match the prototype for
         __cp_push_exception.  */
      exp = convert (ptr_type_node, exp);

      if (cleanup == NULL_TREE)
        {
          cleanup = build_int_2 (0, 0);
          TREE_TYPE (cleanup) = cleanup_type;
        }

      fn = get_identifier ("__cp_push_exception");
      if (IDENTIFIER_GLOBAL_VALUE (fn))
        fn = IDENTIFIER_GLOBAL_VALUE (fn);
      else
        {
          /* Declare __cp_push_exception (void*, void*, void (*)(void*, int)),
             as defined in exception.cc.  */
          tree tmp;
          push_permanent_obstack ();
          tmp = tree_cons
            (NULL_TREE, ptr_type_node, tree_cons
             (NULL_TREE, ptr_type_node, tree_cons
              (NULL_TREE, cleanup_type, void_list_node)));
          fn = build_lang_decl (FUNCTION_DECL, fn,
                                build_function_type (void_type_node, tmp));
          DECL_EXTERNAL (fn) = 1;
          TREE_PUBLIC (fn) = 1;
          DECL_ARTIFICIAL (fn) = 1;
          pushdecl_top_level (fn);
          make_function_rtl (fn);
          pop_obstacks ();
        }

      mark_used (fn);
      e = tree_cons (NULL_TREE, exp, tree_cons
                     (NULL_TREE, throw_type, tree_cons
                      (NULL_TREE, cleanup, NULL_TREE)));
      finish_expr_stmt (build_function_call (fn, e));

      exp = finish_init_stmts (stmt_expr, compound_stmt);
    }
  else
    {
      /* rethrow current exception; note that it's no longer caught.  */

      tree fn = get_identifier ("__uncatch_exception");
      if (IDENTIFIER_GLOBAL_VALUE (fn))
        fn = IDENTIFIER_GLOBAL_VALUE (fn);
      else
        {
          /* Declare void __uncatch_exception (void)
             as defined in exception.cc. */
          push_permanent_obstack ();
          fn = build_lang_decl (FUNCTION_DECL, fn,
                                build_function_type (void_type_node,
                                                     void_list_node));
          DECL_EXTERNAL (fn) = 1;
          TREE_PUBLIC (fn) = 1;
          DECL_ARTIFICIAL (fn) = 1;
          pushdecl_top_level (fn);
          make_function_rtl (fn);
          pop_obstacks ();
        }

      mark_used (fn);
      exp = build_function_call (fn, NULL_TREE);
    }

  return exp;
}

/* Build a throw expression.  */

tree
build_throw (e)
     tree e;
{
  if (e == error_mark_node)
    return e;

  if (processing_template_decl)
    return build_min (THROW_EXPR, void_type_node, e);

  if (e == null_node)
    cp_warning ("throwing NULL, which has integral, not pointer type");
  
  if (e != NULL_TREE)
    {
      if (!complete_ptr_ref_or_void_ptr_p (TREE_TYPE (e), e))
        return error_mark_node;
    }

  e = expand_throw (e);
  e = build1 (THROW_EXPR, void_type_node, e);
  TREE_SIDE_EFFECTS (e) = 1;
  TREE_USED (e) = 1;

  return e;
}

/* Make sure TYPE is complete, pointer to complete, reference to
   complete, or pointer to cv void. Issue diagnostic on failure.
   Return the zero on failure and non-zero on success. FROM can be
   the expr or decl from whence TYPE came, if available.  */

static int
complete_ptr_ref_or_void_ptr_p (type, from)
     tree type;
     tree from;
{
  int is_ptr;
  
  /* Check complete.  */
  type = complete_type_or_else (type, from);
  if (!type)
    return 0;
  
  /* Or a pointer or ref to one, or cv void *.  */
  is_ptr = TREE_CODE (type) == POINTER_TYPE;
  if (is_ptr || TREE_CODE (type) == REFERENCE_TYPE)
    {
      tree core = TREE_TYPE (type);
  
      if (is_ptr && same_type_p (TYPE_MAIN_VARIANT (core), void_type_node))
        /* OK */;
      else if (!complete_type_or_else (core, from))
        return 0;
    }
  return 1;
}