* builtin-types.def (BT_FN_VOID_PTR_VAR): New.

[official-gcc.git] / libjava / verify.cc

// defineclass.cc - defining a class from .class format.

/* Copyright (C) 2001  Free Software Foundation

   This file is part of libgcj.

This software is copyrighted work licensed under the terms of the
Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
details.  */

// Written by Tom Tromey <tromey@redhat.com>

// Define VERIFY_DEBUG to enable debugging output.

#include <config.h>

#include <jvm.h>
#include <gcj/cni.h>
#include <java-insns.h>
#include <java-interp.h>

#ifdef INTERPRETER

#include <java/lang/Class.h>
#include <java/lang/VerifyError.h>
#include <java/lang/Throwable.h>
#include <java/lang/reflect/Modifier.h>
#include <java/lang/StringBuffer.h>

#ifdef VERIFY_DEBUG
#include <stdio.h>
#endif /* VERIFY_DEBUG */

// TO DO
// * read more about when classes must be loaded
// * class loader madness
// * Lots and lots of debugging and testing
// * type representation is still ugly.  look for the big switches
// * at least one GC problem :-(


// This is global because __attribute__ doesn't seem to work on static
// methods.
static void verify_fail (char *msg, jint pc = -1)
  __attribute__ ((__noreturn__));

static void debug_print (const char *fmt, ...)
  __attribute__ ((format (printf, 1, 2)));

static inline void
debug_print (const char *fmt, ...)
{
#ifdef VERIFY_DEBUG
  va_list ap;
  va_start (ap, fmt);
  vfprintf (stderr, fmt, ap);
  va_end (ap);
#endif /* VERIFY_DEBUG */
}

class _Jv_BytecodeVerifier
{
private:

  static const int FLAG_INSN_START = 1;
  static const int FLAG_BRANCH_TARGET = 2;
  static const int FLAG_JSR_TARGET = 4;

  struct state;
  struct type;
  struct subr_info;
  struct linked_utf8;

  // The current PC.
  int PC;
  // The PC corresponding to the start of the current instruction.
  int start_PC;

  // The current state of the stack, locals, etc.
  state *current_state;

  // We store the state at branch targets, for merging.  This holds
  // such states.
  state **states;

  // We keep a linked list of all the PCs which we must reverify.
  // The link is done using the PC values.  This is the head of the
  // list.
  int next_verify_pc;

  // We keep some flags for each instruction.  The values are the
  // FLAG_* constants defined above.
  char *flags;

  // We need to keep track of which instructions can call a given
  // subroutine.  FIXME: this is inefficient.  We keep a linked list
  // of all calling `jsr's at at each jsr target.
  subr_info **jsr_ptrs;

  // The current top of the stack, in terms of slots.
  int stacktop;
  // The current depth of the stack.  This will be larger than
  // STACKTOP when wide types are on the stack.
  int stackdepth;

  // The bytecode itself.
  unsigned char *bytecode;
  // The exceptions.
  _Jv_InterpException *exception;

  // Defining class.
  jclass current_class;
  // This method.
  _Jv_InterpMethod *current_method;

  // A linked list of utf8 objects we allocate.  This is really ugly,
  // but without this our utf8 objects would be collected.
  linked_utf8 *utf8_list;

  struct linked_utf8
  {
    _Jv_Utf8Const *val;
    linked_utf8 *next;
  };

  _Jv_Utf8Const *make_utf8_const (char *s, int len)
  {
    _Jv_Utf8Const *val = _Jv_makeUtf8Const (s, len);
    _Jv_Utf8Const *r = (_Jv_Utf8Const *) _Jv_Malloc (sizeof (_Jv_Utf8Const)
                                                     + val->length
                                                     + 1);
    r->length = val->length;
    r->hash = val->hash;
    memcpy (r->data, val->data, val->length + 1);

    linked_utf8 *lu = (linked_utf8 *) _Jv_Malloc (sizeof (linked_utf8));
    lu->val = r;
    lu->next = utf8_list;
    utf8_list = lu;

    return r;
  }

  // This enum holds a list of tags for all the different types we
  // need to handle.  Reference types are treated specially by the
  // type class.
  enum type_val
  {
    void_type,

    // The values for primitive types are chosen to correspond to values
    // specified to newarray.
    boolean_type = 4,
    char_type = 5,
    float_type = 6,
    double_type = 7,
    byte_type = 8,
    short_type = 9,
    int_type = 10,
    long_type = 11,

    // Used when overwriting second word of a double or long in the
    // local variables.  Also used after merging local variable states
    // to indicate an unusable value.
    unsuitable_type,
    return_address_type,
    continuation_type,

    // There is an obscure special case which requires us to note when
    // a local variable has not been used by a subroutine.  See
    // push_jump_merge for more information.
    unused_by_subroutine_type,

    // Everything after `reference_type' must be a reference type.
    reference_type,
    null_type,
    unresolved_reference_type,
    uninitialized_reference_type,
    uninitialized_unresolved_reference_type
  };

  // Return the type_val corresponding to a primitive signature
  // character.  For instance `I' returns `int.class'.
  static type_val get_type_val_for_signature (jchar sig)
  {
    type_val rt;
    switch (sig)
      {
      case 'Z':
        rt = boolean_type;
        break;
      case 'B':
        rt = byte_type;
        break;
      case 'C':
        rt = char_type;
        break;
      case 'S':
        rt = short_type;
        break;
      case 'I':
        rt = int_type;
        break;
      case 'J':
        rt = long_type;
        break;
      case 'F':
        rt = float_type;
        break;
      case 'D':
        rt = double_type;
        break;
      case 'V':
        rt = void_type;
        break;
      default:
        verify_fail ("invalid signature");
      }
    return rt;
  }

  // Return the type_val corresponding to a primitive class.
  static type_val get_type_val_for_signature (jclass k)
  {
    return get_type_val_for_signature ((jchar) k->method_count);
  }

  // This is like _Jv_IsAssignableFrom, but it works even if SOURCE or
  // TARGET haven't been prepared.
  static bool is_assignable_from_slow (jclass target, jclass source)
  {
    // This will terminate when SOURCE==Object.
    while (true)
      {
        if (source == target)
          return true;

        if (target->isPrimitive () || source->isPrimitive ())
          return false;

        // _Jv_IsAssignableFrom can handle a target which is an
        // interface even if it hasn't been prepared.
        if ((target->state > JV_STATE_LINKED || target->isInterface ())
            && source->state > JV_STATE_LINKED)
          return _Jv_IsAssignableFrom (target, source);

        if (target->isArray ())
          {
            if (! source->isArray ())
              return false;
            target = target->getComponentType ();
            source = source->getComponentType ();
          }
        else if (target->isInterface ())
          {
            for (int i = 0; i < source->interface_count; ++i)
              {
                // We use a recursive call because we also need to
                // check superinterfaces.
                if (is_assignable_from_slow (target, source->interfaces[i]))
                    return true;
              }
            return false;
          }
        else if (target == &java::lang::Object::class$)
          return true;
        else if (source->isInterface ()
                 || source == &java::lang::Object::class$)
          return false;
        else
          source = source->getSuperclass ();
      }
  }

  // This is used to keep track of which `jsr's correspond to a given
  // jsr target.
  struct subr_info
  {
    // PC of the instruction just after the jsr.
    int pc;
    // Link.
    subr_info *next;
  };

  // The `type' class is used to represent a single type in the
  // verifier.
  struct type
  {
    // The type.
    type_val key;
    // Some associated data.
    union
    {
      // For a resolved reference type, this is a pointer to the class.
      jclass klass;
      // For other reference types, this it the name of the class.
      _Jv_Utf8Const *name;
    } data;
    // This is used when constructing a new object.  It is the PC of the
    // `new' instruction which created the object.  We use the special
    // value -2 to mean that this is uninitialized, and the special
    // value -1 for the case where the current method is itself the
    // <init> method.
    int pc;

    static const int UNINIT = -2;
    static const int SELF = -1;

    // Basic constructor.
    type ()
    {
      key = unsuitable_type;
      data.klass = NULL;
      pc = UNINIT;
    }

    // Make a new instance given the type tag.  We assume a generic
    // `reference_type' means Object.
    type (type_val k)
    {
      key = k;
      data.klass = NULL;
      if (key == reference_type)
        data.klass = &java::lang::Object::class$;
      pc = UNINIT;
    }

    // Make a new instance given a class.
    type (jclass klass)
    {
      key = reference_type;
      data.klass = klass;
      pc = UNINIT;
    }

    // Make a new instance given the name of a class.
    type (_Jv_Utf8Const *n)
    {
      key = unresolved_reference_type;
      data.name = n;
      pc = UNINIT;
    }

    // Copy constructor.
    type (const type &t)
    {
      key = t.key;
      data = t.data;
      pc = t.pc;
    }

    // These operators are required because libgcj can't link in
    // -lstdc++.
    void *operator new[] (size_t bytes)
    {
      return _Jv_Malloc (bytes);
    }

    void operator delete[] (void *mem)
    {
      _Jv_Free (mem);
    }

    type& operator= (type_val k)
    {
      key = k;
      data.klass = NULL;
      pc = UNINIT;
      return *this;
    }

    type& operator= (const type& t)
    {
      key = t.key;
      data = t.data;
      pc = t.pc;
      return *this;
    }

    // Promote a numeric type.
    type &promote ()
    {
      if (key == boolean_type || key == char_type
          || key == byte_type || key == short_type)
        key = int_type;
      return *this;
    }

    // If *THIS is an unresolved reference type, resolve it.
    void resolve ()
    {
      if (key != unresolved_reference_type
          && key != uninitialized_unresolved_reference_type)
        return;

      // FIXME: class loader
      using namespace java::lang;
      // We might see either kind of name.  Sigh.
      if (data.name->data[0] == 'L'
          && data.name->data[data.name->length - 1] == ';')
        data.klass = _Jv_FindClassFromSignature (data.name->data, NULL);
      else
        data.klass = Class::forName (_Jv_NewStringUtf8Const (data.name),
                                     false, NULL);
      key = (key == unresolved_reference_type
             ? reference_type
             : uninitialized_reference_type);
    }

    // Mark this type as the uninitialized result of `new'.
    void set_uninitialized (int npc)
    {
      if (key == reference_type)
        key = uninitialized_reference_type;
      else if (key == unresolved_reference_type)
        key = uninitialized_unresolved_reference_type;
      else
        verify_fail ("internal error in type::uninitialized");
      pc = npc;
    }

    // Mark this type as now initialized.
    void set_initialized (int npc)
    {
      if (npc != UNINIT && pc == npc
          && (key == uninitialized_reference_type
              || key == uninitialized_unresolved_reference_type))
        {
          key = (key == uninitialized_reference_type
                 ? reference_type
                 : unresolved_reference_type);
          pc = UNINIT;
        }
    }


    // Return true if an object of type K can be assigned to a variable
    // of type *THIS.  Handle various special cases too.  Might modify
    // *THIS or K.  Note however that this does not perform numeric
    // promotion.
    bool compatible (type &k)
    {
      // Any type is compatible with the unsuitable type.
      if (key == unsuitable_type)
        return true;

      if (key < reference_type || k.key < reference_type)
        return key == k.key;

      // The `null' type is convertible to any reference type.
      // FIXME: is this correct for THIS?
      if (key == null_type || k.key == null_type)
        return true;

      // Any reference type is convertible to Object.  This is a special
      // case so we don't need to unnecessarily resolve a class.
      if (key == reference_type
          && data.klass == &java::lang::Object::class$)
        return true;

      // An initialized type and an uninitialized type are not
      // compatible.
      if (isinitialized () != k.isinitialized ())
        return false;

      // Two uninitialized objects are compatible if either:
      // * The PCs are identical, or
      // * One PC is UNINIT.
      if (! isinitialized ())
        {
          if (pc != k.pc && pc != UNINIT && k.pc != UNINIT)
            return false;
        }

      // Two unresolved types are equal if their names are the same.
      if (! isresolved ()
          && ! k.isresolved ()
          && _Jv_equalUtf8Consts (data.name, k.data.name))
        return true;

      // We must resolve both types and check assignability.
      resolve ();
      k.resolve ();
      return is_assignable_from_slow (data.klass, k.data.klass);
    }

    bool isvoid () const
    {
      return key == void_type;
    }

    bool iswide () const
    {
      return key == long_type || key == double_type;
    }

    // Return number of stack or local variable slots taken by this
    // type.
    int depth () const
    {
      return iswide () ? 2 : 1;
    }

    bool isarray () const
    {
      // We treat null_type as not an array.  This is ok based on the
      // current uses of this method.
      if (key == reference_type)
        return data.klass->isArray ();
      else if (key == unresolved_reference_type)
        return data.name->data[0] == '[';
      return false;
    }

    bool isinterface ()
    {
      resolve ();
      if (key != reference_type)
        return false;
      return data.klass->isInterface ();
    }

    bool isabstract ()
    {
      resolve ();
      if (key != reference_type)
        return false;
      using namespace java::lang::reflect;
      return Modifier::isAbstract (data.klass->getModifiers ());
    }

    // Return the element type of an array.
    type element_type ()
    {
      // FIXME: maybe should do string manipulation here.
      resolve ();
      if (key != reference_type)
        verify_fail ("programmer error in type::element_type()");

      jclass k = data.klass->getComponentType ();
      if (k->isPrimitive ())
        return type (get_type_val_for_signature (k));
      return type (k);
    }

    // Return the array type corresponding to an initialized
    // reference.  We could expand this to work for other kinds of
    // types, but currently we don't need to.
    type to_array ()
    {
      // Resolving isn't ideal, because it might force us to load
      // another class, but it's easy.  FIXME?
      if (key == unresolved_reference_type)
        resolve ();

      if (key == reference_type)
        return type (_Jv_GetArrayClass (data.klass,
                                        data.klass->getClassLoader ()));
      else
        verify_fail ("internal error in type::to_array()");
    }

    bool isreference () const
    {
      return key >= reference_type;
    }

    int get_pc () const
    {
      return pc;
    }

    bool isinitialized () const
    {
      return (key == reference_type
              || key == null_type
              || key == unresolved_reference_type);
    }

    bool isresolved () const
    {
      return (key == reference_type
              || key == null_type
              || key == uninitialized_reference_type);
    }

    void verify_dimensions (int ndims)
    {
      // The way this is written, we don't need to check isarray().
      if (key == reference_type)
        {
          jclass k = data.klass;
          while (k->isArray () && ndims > 0)
            {
              k = k->getComponentType ();
              --ndims;
            }
        }
      else
        {
          // We know KEY == unresolved_reference_type.
          char *p = data.name->data;
          while (*p++ == '[' && ndims-- > 0)
            ;
        }

      if (ndims > 0)
        verify_fail ("array type has fewer dimensions than required");
    }

    // Merge OLD_TYPE into this.  On error throw exception.
    bool merge (type& old_type, bool local_semantics = false)
    {
      bool changed = false;
      bool refo = old_type.isreference ();
      bool refn = isreference ();
      if (refo && refn)
        {
          if (old_type.key == null_type)
            ;
          else if (key == null_type)
            {
              *this = old_type;
              changed = true;
            }
          else if (isinitialized () != old_type.isinitialized ())
            verify_fail ("merging initialized and uninitialized types");
          else
            {
              if (! isinitialized ())
                {
                  if (pc == UNINIT)
                    pc = old_type.pc;
                  else if (old_type.pc == UNINIT)
                    ;
                  else if (pc != old_type.pc)
                    verify_fail ("merging different uninitialized types");
                }

              if (! isresolved ()
                  && ! old_type.isresolved ()
                  && _Jv_equalUtf8Consts (data.name, old_type.data.name))
                {
                  // Types are identical.
                }
              else
                {
                  resolve ();
                  old_type.resolve ();

                  jclass k = data.klass;
                  jclass oldk = old_type.data.klass;

                  int arraycount = 0;
                  while (k->isArray () && oldk->isArray ())
                    {
                      ++arraycount;
                      k = k->getComponentType ();
                      oldk = oldk->getComponentType ();
                    }

                  // This loop will end when we hit Object.
                  while (true)
                    {
                      if (is_assignable_from_slow (k, oldk))
                        break;
                      k = k->getSuperclass ();
                      changed = true;
                    }

                  if (changed)
                    {
                      while (arraycount > 0)
                        {
                          // FIXME: Class loader.
                          k = _Jv_GetArrayClass (k, NULL);
                          --arraycount;
                        }
                      data.klass = k;
                    }
                }
            }
        }
      else if (refo || refn || key != old_type.key)
        {
          if (local_semantics)
            {
              // If we're merging into an "unused" slot, then we
              // simply accept whatever we're merging from.
              if (key == unused_by_subroutine_type)
                {
                  *this = old_type;
                  changed = true;
                }
              else if (old_type.key == unused_by_subroutine_type)
                {
                  // Do nothing.
                }
              // If we already have an `unsuitable' type, then we
              // don't need to change again.
              else if (key != unsuitable_type)
                {
                  key = unsuitable_type;
                  changed = true;
                }
            }
          else
            verify_fail ("unmergeable type");
        }
      return changed;
    }

#ifdef VERIFY_DEBUG
    void print (void) const
    {
      char c = '?';
      switch (key)
        {
        case boolean_type: c = 'Z'; break;
        case byte_type: c = 'B'; break;
        case char_type: c = 'C'; break;
        case short_type: c = 'S'; break;
        case int_type: c = 'I'; break;
        case long_type: c = 'J'; break;
        case float_type: c = 'F'; break;
        case double_type: c = 'D'; break;
        case void_type: c = 'V'; break;
        case unsuitable_type: c = '-'; break;
        case return_address_type: c = 'r'; break;
        case continuation_type: c = '+'; break;
        case unused_by_subroutine_type: c = '_'; break;
        case reference_type: c = 'L'; break;
        case null_type: c = '@'; break;
        case unresolved_reference_type: c = 'l'; break;
        case uninitialized_reference_type: c = 'U'; break;
        case uninitialized_unresolved_reference_type: c = 'u'; break;
        }
      debug_print ("%c", c);
    }
#endif /* VERIFY_DEBUG */
  };

  // This class holds all the state information we need for a given
  // location.
  struct state
  {
    // Current top of stack.
    int stacktop;
    // Current stack depth.  This is like the top of stack but it
    // includes wide variable information.
    int stackdepth;
    // The stack.
    type *stack;
    // The local variables.
    type *locals;
    // This is used in subroutines to keep track of which local
    // variables have been accessed.
    bool *local_changed;
    // If not 0, then we are in a subroutine.  The value is the PC of
    // the subroutine's entry point.  We can use 0 as an exceptional
    // value because PC=0 can never be a subroutine.
    int subroutine;
    // This is used to keep a linked list of all the states which
    // require re-verification.  We use the PC to keep track.
    int next;

    // INVALID marks a state which is not on the linked list of states
    // requiring reverification.
    static const int INVALID = -1;
    // NO_NEXT marks the state at the end of the reverification list.
    static const int NO_NEXT = -2;

    state ()
    {
      stack = NULL;
      locals = NULL;
      local_changed = NULL;
    }

    state (int max_stack, int max_locals)
    {
      stacktop = 0;
      stackdepth = 0;
      stack = new type[max_stack];
      for (int i = 0; i < max_stack; ++i)
        stack[i] = unsuitable_type;
      locals = new type[max_locals];
      local_changed = (bool *) _Jv_Malloc (sizeof (bool) * max_locals);
      for (int i = 0; i < max_locals; ++i)
        {
          locals[i] = unsuitable_type;
          local_changed[i] = false;
        }
      next = INVALID;
      subroutine = 0;
    }

    state (const state *orig, int max_stack, int max_locals,
           bool ret_semantics = false)
    {
      stack = new type[max_stack];
      locals = new type[max_locals];
      local_changed = (bool *) _Jv_Malloc (sizeof (bool) * max_locals);
      copy (orig, max_stack, max_locals, ret_semantics);
      next = INVALID;
    }

    ~state ()
    {
      if (stack)
        delete[] stack;
      if (locals)
        delete[] locals;
      if (local_changed)
        _Jv_Free (local_changed);
    }

    void *operator new[] (size_t bytes)
    {
      return _Jv_Malloc (bytes);
    }

    void operator delete[] (void *mem)
    {
      _Jv_Free (mem);
    }

    void *operator new (size_t bytes)
    {
      return _Jv_Malloc (bytes);
    }

    void operator delete (void *mem)
    {
      _Jv_Free (mem);
    }

    void copy (const state *copy, int max_stack, int max_locals,
               bool ret_semantics = false)
    {
      stacktop = copy->stacktop;
      stackdepth = copy->stackdepth;
      subroutine = copy->subroutine;
      for (int i = 0; i < max_stack; ++i)
        stack[i] = copy->stack[i];
      for (int i = 0; i < max_locals; ++i)
        {
          // See push_jump_merge to understand this case.
          if (ret_semantics)
            locals[i] = type (copy->local_changed[i]
                              ? unsuitable_type
                              : unused_by_subroutine_type);
          else
            locals[i] = copy->locals[i];
          local_changed[i] = copy->local_changed[i];
        }
      // Don't modify `next'.
    }

    // Modify this state to reflect entry to an exception handler.
    void set_exception (type t, int max_stack)
    {
      stackdepth = 1;
      stacktop = 1;
      stack[0] = t;
      for (int i = stacktop; i < max_stack; ++i)
        stack[i] = unsuitable_type;

      // FIXME: subroutine handling?
    }

    // Merge STATE into this state.  Destructively modifies this state.
    // Returns true if the new state was in fact changed.  Will throw an
    // exception if the states are not mergeable.
    bool merge (state *state_old, bool ret_semantics,
                int max_locals)
    {
      bool changed = false;

      // Merge subroutine states.  *THIS and *STATE_OLD must be in the
      // same subroutine.  Also, recursive subroutine calls must be
      // avoided.
      if (subroutine == state_old->subroutine)
        {
          // Nothing.
        }
      else if (subroutine == 0)
        {
          subroutine = state_old->subroutine;
          changed = true;
        }
      else
        verify_fail ("subroutines merged");

      // Merge stacks.
      if (state_old->stacktop != stacktop)
        verify_fail ("stack sizes differ");
      for (int i = 0; i < state_old->stacktop; ++i)
        {
          if (stack[i].merge (state_old->stack[i]))
            changed = true;
        }

      // Merge local variables.
      for (int i = 0; i < max_locals; ++i)
        {
          if (! ret_semantics || local_changed[i])
            {
              if (locals[i].merge (state_old->locals[i], true))
                {
                  changed = true;
                  note_variable (i);
                }
            }

          // If we're in a subroutine, we must compute the union of
          // all the changed local variables.
          if (state_old->local_changed[i])
            note_variable (i);
        }

      return changed;
    }

    // Throw an exception if there is an uninitialized object on the
    // stack or in a local variable.  EXCEPTION_SEMANTICS controls
    // whether we're using backwards-branch or exception-handing
    // semantics.
    void check_no_uninitialized_objects (int max_locals,
                                         bool exception_semantics = false)
    {
      if (! exception_semantics)
        {
          for (int i = 0; i < stacktop; ++i)
            if (stack[i].isreference () && ! stack[i].isinitialized ())
              verify_fail ("uninitialized object on stack");
        }

      for (int i = 0; i < max_locals; ++i)
        if (locals[i].isreference () && ! locals[i].isinitialized ())
          verify_fail ("uninitialized object in local variable");
    }

    // Note that a local variable was modified.
    void note_variable (int index)
    {
      if (subroutine > 0)
        local_changed[index] = true;
    }

    // Mark each `new'd object we know of that was allocated at PC as
    // initialized.
    void set_initialized (int pc, int max_locals)
    {
      for (int i = 0; i < stacktop; ++i)
        stack[i].set_initialized (pc);
      for (int i = 0; i < max_locals; ++i)
        locals[i].set_initialized (pc);
    }

    // Return true if this state is the unmerged result of a `ret'.
    bool is_unmerged_ret_state (int max_locals) const
    {
      for (int i = 0; i < max_locals; ++i)
        {
          if (locals[i].key == unused_by_subroutine_type)
            return true;
        }
      return false;
    }

#ifdef VERIFY_DEBUG
    void print (const char *leader, int pc,
                int max_stack, int max_locals) const
    {
      debug_print ("%s [%4d]:   [stack] ", leader, pc);
      int i;
      for (i = 0; i < stacktop; ++i)
        stack[i].print ();
      for (; i < max_stack; ++i)
        debug_print (".");
      debug_print ("    [local] ");
      for (i = 0; i < max_locals; ++i)
        locals[i].print ();
      debug_print ("   | %p\n", this);
    }
#else
    inline void print (const char *, int, int, int) const
    {
    }
#endif /* VERIFY_DEBUG */
  };

  type pop_raw ()
  {
    if (current_state->stacktop <= 0)
      verify_fail ("stack empty", start_PC);
    type r = current_state->stack[--current_state->stacktop];
    current_state->stackdepth -= r.depth ();
    if (current_state->stackdepth < 0)
      verify_fail ("stack empty", start_PC);
    return r;
  }

  type pop32 ()
  {
    type r = pop_raw ();
    if (r.iswide ())
      verify_fail ("narrow pop of wide type", start_PC);
    return r;
  }

  type pop64 ()
  {
    type r = pop_raw ();
    if (! r.iswide ())
      verify_fail ("wide pop of narrow type", start_PC);
    return r;
  }

  type pop_type (type match)
  {
    match.promote ();
    type t = pop_raw ();
    if (! match.compatible (t))
      verify_fail ("incompatible type on stack", start_PC);
    return t;
  }

  // Pop a reference type or a return address.
  type pop_ref_or_return ()
  {
    type t = pop_raw ();
    if (! t.isreference () && t.key != return_address_type)
      verify_fail ("expected reference or return address on stack", start_PC);
    return t;
  }

  void push_type (type t)
  {
    // If T is a numeric type like short, promote it to int.
    t.promote ();

    int depth = t.depth ();
    if (current_state->stackdepth + depth > current_method->max_stack)
      verify_fail ("stack overflow");
    current_state->stack[current_state->stacktop++] = t;
    current_state->stackdepth += depth;
  }

  void set_variable (int index, type t)
  {
    // If T is a numeric type like short, promote it to int.
    t.promote ();

    int depth = t.depth ();
    if (index > current_method->max_locals - depth)
      verify_fail ("invalid local variable");
    current_state->locals[index] = t;
    current_state->note_variable (index);

    if (depth == 2)
      {
        current_state->locals[index + 1] = continuation_type;
        current_state->note_variable (index + 1);
      }
    if (index > 0 && current_state->locals[index - 1].iswide ())
      {
        current_state->locals[index - 1] = unsuitable_type;
        // There's no need to call note_variable here.
      }
  }

  type get_variable (int index, type t)
  {
    int depth = t.depth ();
    if (index > current_method->max_locals - depth)
      verify_fail ("invalid local variable", start_PC);
    if (! t.compatible (current_state->locals[index]))
      verify_fail ("incompatible type in local variable", start_PC);
    if (depth == 2)
      {
        type t (continuation_type);
        if (! current_state->locals[index + 1].compatible (t))
          verify_fail ("invalid local variable", start_PC);
      }
    return current_state->locals[index];
  }

  // Make sure ARRAY is an array type and that its elements are
  // compatible with type ELEMENT.  Returns the actual element type.
  type require_array_type (type array, type element)
  {
    if (! array.isarray ())
      verify_fail ("array required");

    type t = array.element_type ();
    if (! element.compatible (t))
      {
        // Special case for byte arrays, which must also be boolean
        // arrays.
        bool ok = true;
        if (element.key == byte_type)
          {
            type e2 (boolean_type);
            ok = e2.compatible (t);
          }
        if (! ok)
          verify_fail ("incompatible array element type");
      }

    // Return T and not ELEMENT, because T might be specialized.
    return t;
  }

  jint get_byte ()
  {
    if (PC >= current_method->code_length)
      verify_fail ("premature end of bytecode");
    return (jint) bytecode[PC++] & 0xff;
  }

  jint get_ushort ()
  {
    jint b1 = get_byte ();
    jint b2 = get_byte ();
    return (jint) ((b1 << 8) | b2) & 0xffff;
  }

  jint get_short ()
  {
    jint b1 = get_byte ();
    jint b2 = get_byte ();
    jshort s = (b1 << 8) | b2;
    return (jint) s;
  }

  jint get_int ()
  {
    jint b1 = get_byte ();
    jint b2 = get_byte ();
    jint b3 = get_byte ();
    jint b4 = get_byte ();
    return (b1 << 24) | (b2 << 16) | (b3 << 8) | b4;
  }

  int compute_jump (int offset)
  {
    int npc = start_PC + offset;
    if (npc < 0 || npc >= current_method->code_length)
      verify_fail ("branch out of range", start_PC);
    return npc;
  }

  // Merge the indicated state into the state at the branch target and
  // schedule a new PC if there is a change.  If RET_SEMANTICS is
  // true, then we are merging from a `ret' instruction into the
  // instruction after a `jsr'.  This is a special case with its own
  // modified semantics.
  void push_jump_merge (int npc, state *nstate, bool ret_semantics = false)
  {
    bool changed = true;
    if (states[npc] == NULL)
      {
        // There's a weird situation here.  If are examining the
        // branch that results from a `ret', and there is not yet a
        // state available at the branch target (the instruction just
        // after the `jsr'), then we have to construct a special kind
        // of state at that point for future merging.  This special
        // state has the type `unused_by_subroutine_type' in each slot
        // which was not modified by the subroutine.
        states[npc] = new state (nstate, current_method->max_stack,
                                 current_method->max_locals, ret_semantics);
        debug_print ("== New state in push_jump_merge\n");
        states[npc]->print ("New", npc, current_method->max_stack,
                            current_method->max_locals);
      }
    else
      {
        debug_print ("== Merge states in push_jump_merge\n");
        nstate->print ("Frm", start_PC, current_method->max_stack,
                       current_method->max_locals);
        states[npc]->print (" To", npc, current_method->max_stack,
                            current_method->max_locals);
        changed = states[npc]->merge (nstate, ret_semantics,
                                      current_method->max_locals);
        states[npc]->print ("New", npc, current_method->max_stack,
                            current_method->max_locals);
      }

    if (changed && states[npc]->next == state::INVALID)
      {
        // The merge changed the state, and the new PC isn't yet on our
        // list of PCs to re-verify.
        states[npc]->next = next_verify_pc;
        next_verify_pc = npc;
      }
  }

  void push_jump (int offset)
  {
    int npc = compute_jump (offset);
    if (npc < PC)
      current_state->check_no_uninitialized_objects (current_method->max_locals);
    push_jump_merge (npc, current_state);
  }

  void push_exception_jump (type t, int pc)
  {
    current_state->check_no_uninitialized_objects (current_method->max_locals,
                                                  true);
    state s (current_state, current_method->max_stack,
             current_method->max_locals);
    s.set_exception (t, current_method->max_stack);
    push_jump_merge (pc, &s);
  }

  int pop_jump ()
  {
    int *prev_loc = &next_verify_pc;
    int npc = next_verify_pc;
    bool skipped = false;

    while (npc != state::NO_NEXT)
      {
        // If the next available PC is an unmerged `ret' state, then
        // we aren't yet ready to handle it.  That's because we would
        // need all kind of special cases to do so.  So instead we
        // defer this jump until after we've processed it via a
        // fall-through.  This has to happen because the instruction
        // before this one must be a `jsr'.
        if (! states[npc]->is_unmerged_ret_state (current_method->max_locals))
          {
            *prev_loc = states[npc]->next;
            states[npc]->next = state::INVALID;
            return npc;
          }

        skipped = true;
        prev_loc = &states[npc]->next;
        npc = states[npc]->next;
      }

    // If we've skipped states and there is nothing else, that's a
    // bug.
    if (skipped)
      verify_fail ("pop_jump: can't happen");
    return state::NO_NEXT;
  }

  void invalidate_pc ()
  {
    PC = state::NO_NEXT;
  }

  void note_branch_target (int pc, bool is_jsr_target = false)
  {
    if (pc <= PC && ! (flags[pc] & FLAG_INSN_START))
      verify_fail ("branch not to instruction start");
    flags[pc] |= FLAG_BRANCH_TARGET;
    if (is_jsr_target)
      {
        // Record the jsr which called this instruction.
        subr_info *info = (subr_info *) _Jv_Malloc (sizeof (subr_info));
        info->pc = PC;
        info->next = jsr_ptrs[pc];
        jsr_ptrs[pc] = info;
        flags[pc] |= FLAG_JSR_TARGET;
      }
  }

  void skip_padding ()
  {
    while ((PC % 4) > 0)
      if (get_byte () != 0)
        verify_fail ("found nonzero padding byte");
  }

  // Return the subroutine to which the instruction at PC belongs.
  int get_subroutine (int pc)
  {
    if (states[pc] == NULL)
      return 0;
    return states[pc]->subroutine;
  }

  // Do the work for a `ret' instruction.  INDEX is the index into the
  // local variables.
  void handle_ret_insn (int index)
  {
    get_variable (index, return_address_type);

    int csub = current_state->subroutine;
    if (csub == 0)
      verify_fail ("no subroutine");

    for (subr_info *subr = jsr_ptrs[csub]; subr != NULL; subr = subr->next)
      {
        // Temporarily modify the current state so it looks like we're
        // in the enclosing context.
        current_state->subroutine = get_subroutine (subr->pc);
        if (subr->pc < PC)
          current_state->check_no_uninitialized_objects (current_method->max_locals);
        push_jump_merge (subr->pc, current_state, true);
      }

    current_state->subroutine = csub;
    invalidate_pc ();
  }

  // We're in the subroutine SUB, calling a subroutine at DEST.  Make
  // sure this subroutine isn't already on the stack.
  void check_nonrecursive_call (int sub, int dest)
  {
    if (sub == 0)
      return;
    if (sub == dest)
      verify_fail ("recursive subroutine call");
    for (subr_info *info = jsr_ptrs[sub]; info != NULL; info = info->next)
      check_nonrecursive_call (get_subroutine (info->pc), dest);
  }

  void handle_jsr_insn (int offset)
  {
    int npc = compute_jump (offset);

    if (npc < PC)
      current_state->check_no_uninitialized_objects (current_method->max_locals);
    check_nonrecursive_call (current_state->subroutine, npc);

    // Temporarily modify the current state so that it looks like we are
    // in the subroutine.
    push_type (return_address_type);
    int save = current_state->subroutine;
    current_state->subroutine = npc;

    // Merge into the subroutine.
    push_jump_merge (npc, current_state);

    // Undo our modifications.
    current_state->subroutine = save;
    pop_type (return_address_type);
  }

  jclass construct_primitive_array_type (type_val prim)
  {
    jclass k = NULL;
    switch (prim)
      {
      case boolean_type:
        k = JvPrimClass (boolean);
        break;
      case char_type:
        k = JvPrimClass (char);
        break;
      case float_type:
        k = JvPrimClass (float);
        break;
      case double_type:
        k = JvPrimClass (double);
        break;
      case byte_type:
        k = JvPrimClass (byte);
        break;
      case short_type:
        k = JvPrimClass (short);
        break;
      case int_type:
        k = JvPrimClass (int);
        break;
      case long_type:
        k = JvPrimClass (long);
        break;
      default:
        verify_fail ("unknown type in construct_primitive_array_type");
      }
    k = _Jv_GetArrayClass (k, NULL);
    return k;
  }

  // This pass computes the location of branch targets and also
  // instruction starts.
  void branch_prepass ()
  {
    flags = (char *) _Jv_Malloc (current_method->code_length);
    jsr_ptrs = (subr_info **) _Jv_Malloc (sizeof (subr_info *)
                                          * current_method->code_length);

    for (int i = 0; i < current_method->code_length; ++i)
      {
        flags[i] = 0;
        jsr_ptrs[i] = NULL;
      }

    bool last_was_jsr = false;

    PC = 0;
    while (PC < current_method->code_length)
      {
        flags[PC] |= FLAG_INSN_START;

        // If the previous instruction was a jsr, then the next
        // instruction is a branch target -- the branch being the
        // corresponding `ret'.
        if (last_was_jsr)
          note_branch_target (PC);
        last_was_jsr = false;

        start_PC = PC;
        java_opcode opcode = (java_opcode) bytecode[PC++];
        switch (opcode)
          {
          case op_nop:
          case op_aconst_null:
          case op_iconst_m1:
          case op_iconst_0:
          case op_iconst_1:
          case op_iconst_2:
          case op_iconst_3:
          case op_iconst_4:
          case op_iconst_5:
          case op_lconst_0:
          case op_lconst_1:
          case op_fconst_0:
          case op_fconst_1:
          case op_fconst_2:
          case op_dconst_0:
          case op_dconst_1:
          case op_iload_0:
          case op_iload_1:
          case op_iload_2:
          case op_iload_3:
          case op_lload_0:
          case op_lload_1:
          case op_lload_2:
          case op_lload_3:
          case op_fload_0:
          case op_fload_1:
          case op_fload_2:
          case op_fload_3:
          case op_dload_0:
          case op_dload_1:
          case op_dload_2:
          case op_dload_3:
          case op_aload_0:
          case op_aload_1:
          case op_aload_2:
          case op_aload_3:
          case op_iaload:
          case op_laload:
          case op_faload:
          case op_daload:
          case op_aaload:
          case op_baload:
          case op_caload:
          case op_saload:
          case op_istore_0:
          case op_istore_1:
          case op_istore_2:
          case op_istore_3:
          case op_lstore_0:
          case op_lstore_1:
          case op_lstore_2:
          case op_lstore_3:
          case op_fstore_0:
          case op_fstore_1:
          case op_fstore_2:
          case op_fstore_3:
          case op_dstore_0:
          case op_dstore_1:
          case op_dstore_2:
          case op_dstore_3:
          case op_astore_0:
          case op_astore_1:
          case op_astore_2:
          case op_astore_3:
          case op_iastore:
          case op_lastore:
          case op_fastore:
          case op_dastore:
          case op_aastore:
          case op_bastore:
          case op_castore:
          case op_sastore:
          case op_pop:
          case op_pop2:
          case op_dup:
          case op_dup_x1:
          case op_dup_x2:
          case op_dup2:
          case op_dup2_x1:
          case op_dup2_x2:
          case op_swap:
          case op_iadd:
          case op_isub:
          case op_imul:
          case op_idiv:
          case op_irem:
          case op_ishl:
          case op_ishr:
          case op_iushr:
          case op_iand:
          case op_ior:
          case op_ixor:
          case op_ladd:
          case op_lsub:
          case op_lmul:
          case op_ldiv:
          case op_lrem:
          case op_lshl:
          case op_lshr:
          case op_lushr:
          case op_land:
          case op_lor:
          case op_lxor:
          case op_fadd:
          case op_fsub:
          case op_fmul:
          case op_fdiv:
          case op_frem:
          case op_dadd:
          case op_dsub:
          case op_dmul:
          case op_ddiv:
          case op_drem:
          case op_ineg:
          case op_i2b:
          case op_i2c:
          case op_i2s:
          case op_lneg:
          case op_fneg:
          case op_dneg:
          case op_i2l:
          case op_i2f:
          case op_i2d:
          case op_l2i:
          case op_l2f:
          case op_l2d:
          case op_f2i:
          case op_f2l:
          case op_f2d:
          case op_d2i:
          case op_d2l:
          case op_d2f:
          case op_lcmp:
          case op_fcmpl:
          case op_fcmpg:
          case op_dcmpl:
          case op_dcmpg:
          case op_monitorenter:
          case op_monitorexit:
          case op_ireturn:
          case op_lreturn:
          case op_freturn:
          case op_dreturn:
          case op_areturn:
          case op_return:
          case op_athrow:
          case op_arraylength:
            break;

          case op_bipush:
          case op_ldc:
          case op_iload:
          case op_lload:
          case op_fload:
          case op_dload:
          case op_aload:
          case op_istore:
          case op_lstore:
          case op_fstore:
          case op_dstore:
          case op_astore:
          case op_ret:
          case op_newarray:
            get_byte ();
            break;

          case op_iinc:
          case op_sipush:
          case op_ldc_w:
          case op_ldc2_w:
          case op_getstatic:
          case op_getfield:
          case op_putfield:
          case op_putstatic:
          case op_new:
          case op_anewarray:
          case op_instanceof:
          case op_checkcast:
          case op_invokespecial:
          case op_invokestatic:
          case op_invokevirtual:
            get_short ();
            break;

          case op_multianewarray:
            get_short ();
            get_byte ();
            break;

          case op_jsr:
            last_was_jsr = true;
            // Fall through.
          case op_ifeq:
          case op_ifne:
          case op_iflt:
          case op_ifge:
          case op_ifgt:
          case op_ifle:
          case op_if_icmpeq:
          case op_if_icmpne:
          case op_if_icmplt:
          case op_if_icmpge:
          case op_if_icmpgt:
          case op_if_icmple:
          case op_if_acmpeq:
          case op_if_acmpne:
          case op_ifnull:
          case op_ifnonnull:
          case op_goto:
            note_branch_target (compute_jump (get_short ()), last_was_jsr);
            break;

          case op_tableswitch:
            {
              skip_padding ();
              note_branch_target (compute_jump (get_int ()));
              jint low = get_int ();
              jint hi = get_int ();
              if (low > hi)
                verify_fail ("invalid tableswitch", start_PC);
              for (int i = low; i <= hi; ++i)
                note_branch_target (compute_jump (get_int ()));
            }
            break;

          case op_lookupswitch:
            {
              skip_padding ();
              note_branch_target (compute_jump (get_int ()));
              int npairs = get_int ();
              if (npairs < 0)
                verify_fail ("too few pairs in lookupswitch", start_PC);
              while (npairs-- > 0)
                {
                  get_int ();
                  note_branch_target (compute_jump (get_int ()));
                }
            }
            break;

          case op_invokeinterface:
            get_short ();
            get_byte ();
            get_byte ();
            break;

          case op_wide:
            {
              opcode = (java_opcode) get_byte ();
              get_short ();
              if (opcode == op_iinc)
                get_short ();
            }
            break;

          case op_jsr_w:
            last_was_jsr = true;
            // Fall through.
          case op_goto_w:
            note_branch_target (compute_jump (get_int ()), last_was_jsr);
            break;

          default:
            verify_fail ("unrecognized instruction in branch_prepass",
                         start_PC);
          }

        // See if any previous branch tried to branch to the middle of
        // this instruction.
        for (int pc = start_PC + 1; pc < PC; ++pc)
          {
            if ((flags[pc] & FLAG_BRANCH_TARGET))
              verify_fail ("branch to middle of instruction", pc);
          }
      }

    // Verify exception handlers.
    for (int i = 0; i < current_method->exc_count; ++i)
      {
        if (! (flags[exception[i].handler_pc] & FLAG_INSN_START))
          verify_fail ("exception handler not at instruction start",
                       exception[i].handler_pc);
        if (! (flags[exception[i].start_pc] & FLAG_INSN_START))
          verify_fail ("exception start not at instruction start",
                       exception[i].start_pc);
        if (exception[i].end_pc != current_method->code_length
            && ! (flags[exception[i].end_pc] & FLAG_INSN_START))
          verify_fail ("exception end not at instruction start",
                       exception[i].end_pc);

        flags[exception[i].handler_pc] |= FLAG_BRANCH_TARGET;
      }
  }

  void check_pool_index (int index)
  {
    if (index < 0 || index >= current_class->constants.size)
      verify_fail ("constant pool index out of range", start_PC);
  }

  type check_class_constant (int index)
  {
    check_pool_index (index);
    _Jv_Constants *pool = &current_class->constants;
    if (pool->tags[index] == JV_CONSTANT_ResolvedClass)
      return type (pool->data[index].clazz);
    else if (pool->tags[index] == JV_CONSTANT_Class)
      return type (pool->data[index].utf8);
    verify_fail ("expected class constant", start_PC);
  }

  type check_constant (int index)
  {
    check_pool_index (index);
    _Jv_Constants *pool = &current_class->constants;
    if (pool->tags[index] == JV_CONSTANT_ResolvedString
        || pool->tags[index] == JV_CONSTANT_String)
      return type (&java::lang::String::class$);
    else if (pool->tags[index] == JV_CONSTANT_Integer)
      return type (int_type);
    else if (pool->tags[index] == JV_CONSTANT_Float)
      return type (float_type);
    verify_fail ("String, int, or float constant expected", start_PC);
  }

  type check_wide_constant (int index)
  {
    check_pool_index (index);
    _Jv_Constants *pool = &current_class->constants;
    if (pool->tags[index] == JV_CONSTANT_Long)
      return type (long_type);
    else if (pool->tags[index] == JV_CONSTANT_Double)
      return type (double_type);
    verify_fail ("long or double constant expected", start_PC);
  }

  // Helper for both field and method.  These are laid out the same in
  // the constant pool.
  type handle_field_or_method (int index, int expected,
                               _Jv_Utf8Const **name,
                               _Jv_Utf8Const **fmtype)
  {
    check_pool_index (index);
    _Jv_Constants *pool = &current_class->constants;
    if (pool->tags[index] != expected)
      verify_fail ("didn't see expected constant", start_PC);
    // Once we know we have a Fieldref or Methodref we assume that it
    // is correctly laid out in the constant pool.  I think the code
    // in defineclass.cc guarantees this.
    _Jv_ushort class_index, name_and_type_index;
    _Jv_loadIndexes (&pool->data[index],
                     class_index,
                     name_and_type_index);
    _Jv_ushort name_index, desc_index;
    _Jv_loadIndexes (&pool->data[name_and_type_index],
                     name_index, desc_index);

    *name = pool->data[name_index].utf8;
    *fmtype = pool->data[desc_index].utf8;

    return check_class_constant (class_index);
  }

  // Return field's type, compute class' type if requested.
  type check_field_constant (int index, type *class_type = NULL)
  {
    _Jv_Utf8Const *name, *field_type;
    type ct = handle_field_or_method (index,
                                      JV_CONSTANT_Fieldref,
                                      &name, &field_type);
    if (class_type)
      *class_type = ct;
    if (field_type->data[0] == '[' || field_type->data[0] == 'L')
      return type (field_type);
    return get_type_val_for_signature (field_type->data[0]);
  }

  type check_method_constant (int index, bool is_interface,
                              _Jv_Utf8Const **method_name,
                              _Jv_Utf8Const **method_signature)
  {
    return handle_field_or_method (index,
                                   (is_interface
                                    ? JV_CONSTANT_InterfaceMethodref
                                    : JV_CONSTANT_Methodref),
                                   method_name, method_signature);
  }

  type get_one_type (char *&p)
  {
    char *start = p;

    int arraycount = 0;
    while (*p == '[')
      {
        ++arraycount;
        ++p;
      }

    char v = *p++;

    if (v == 'L')
      {
        while (*p != ';')
          ++p;
        ++p;
        _Jv_Utf8Const *name = make_utf8_const (start, p - start);
        return type (name);
      }

    // Casting to jchar here is ok since we are looking at an ASCII
    // character.
    type_val rt = get_type_val_for_signature (jchar (v));

    if (arraycount == 0)
      {
        // Callers of this function eventually push their arguments on
        // the stack.  So, promote them here.
        return type (rt).promote ();
      }

    jclass k = construct_primitive_array_type (rt);
    while (--arraycount > 0)
      k = _Jv_GetArrayClass (k, NULL);
    return type (k);
  }

  void compute_argument_types (_Jv_Utf8Const *signature,
                               type *types)
  {
    char *p = signature->data;
    // Skip `('.
    ++p;

    int i = 0;
    while (*p != ')')
      types[i++] = get_one_type (p);
  }

  type compute_return_type (_Jv_Utf8Const *signature)
  {
    char *p = signature->data;
    while (*p != ')')
      ++p;
    ++p;
    return get_one_type (p);
  }

  void check_return_type (type onstack)
  {
    type rt = compute_return_type (current_method->self->signature);
    if (! rt.compatible (onstack))
      verify_fail ("incompatible return type", start_PC);
  }

  void verify_instructions_0 ()
  {
    current_state = new state (current_method->max_stack,
                               current_method->max_locals);

    PC = 0;
    start_PC = 0;

    {
      int var = 0;

      using namespace java::lang::reflect;
      if (! Modifier::isStatic (current_method->self->accflags))
        {
          type kurr (current_class);
          if (_Jv_equalUtf8Consts (current_method->self->name, gcj::init_name))
            kurr.set_uninitialized (type::SELF);
          set_variable (0, kurr);
          ++var;
        }

      // We have to handle wide arguments specially here.
      int arg_count = _Jv_count_arguments (current_method->self->signature);
      type arg_types[arg_count];
      compute_argument_types (current_method->self->signature, arg_types);
      for (int i = 0; i < arg_count; ++i)
        {
          set_variable (var, arg_types[i]);
          ++var;
          if (arg_types[i].iswide ())
            ++var;
        }
    }

    states = (state **) _Jv_Malloc (sizeof (state *)
                                    * current_method->code_length);
    for (int i = 0; i < current_method->code_length; ++i)
      states[i] = NULL;

    next_verify_pc = state::NO_NEXT;

    while (true)
      {
        // If the PC was invalidated, get a new one from the work list.
        if (PC == state::NO_NEXT)
          {
            PC = pop_jump ();
            if (PC == state::INVALID)
              verify_fail ("can't happen: saw state::INVALID");
            if (PC == state::NO_NEXT)
              break;
            // Set up the current state.
            current_state->copy (states[PC], current_method->max_stack,
                                 current_method->max_locals);
          }
        else
          {
            // Control can't fall off the end of the bytecode.  We
            // only need to check this in the fall-through case,
            // because branch bounds are checked when they are
            // pushed.
            if (PC >= current_method->code_length)
              verify_fail ("fell off end");

            // We only have to do this checking in the situation where
            // control flow falls through from the previous
            // instruction.  Otherwise merging is done at the time we
            // push the branch.
            if (states[PC] != NULL)
              {
                // We've already visited this instruction.  So merge
                // the states together.  If this yields no change then
                // we don't have to re-verify.  However, if the new
                // state is an the result of an unmerged `ret', we
                // must continue through it.
                debug_print ("== Fall through merge\n");
                states[PC]->print ("Old", PC, current_method->max_stack,
                                   current_method->max_locals);
                current_state->print ("Cur", PC, current_method->max_stack,
                                      current_method->max_locals);
                if (! current_state->merge (states[PC], false,
                                            current_method->max_locals)
                    && ! states[PC]->is_unmerged_ret_state (current_method->max_locals))
                  {
                    debug_print ("== Fall through optimization\n");
                    invalidate_pc ();
                    continue;
                  }
                // Save a copy of it for later.
                states[PC]->copy (current_state, current_method->max_stack,
                                  current_method->max_locals);
                current_state->print ("New", PC, current_method->max_stack,
                                      current_method->max_locals);
              }
          }

        // We only have to keep saved state at branch targets.  If
        // we're at a branch target and the state here hasn't been set
        // yet, we set it now.
        if (states[PC] == NULL && (flags[PC] & FLAG_BRANCH_TARGET))
          {
            states[PC] = new state (current_state, current_method->max_stack,
                                    current_method->max_locals);
          }

        // Set this before handling exceptions so that debug output is
        // sane.
        start_PC = PC;

        // Update states for all active exception handlers.  Ordinarily
        // there are not many exception handlers.  So we simply run
        // through them all.
        for (int i = 0; i < current_method->exc_count; ++i)
          {
            if (PC >= exception[i].start_pc && PC < exception[i].end_pc)
              {
                type handler (&java::lang::Throwable::class$);
                if (exception[i].handler_type != 0)
                  handler = check_class_constant (exception[i].handler_type);
                push_exception_jump (handler, exception[i].handler_pc);
              }
          }

        current_state->print ("   ", PC, current_method->max_stack,
                              current_method->max_locals);
        java_opcode opcode = (java_opcode) bytecode[PC++];
        switch (opcode)
          {
          case op_nop:
            break;

          case op_aconst_null:
            push_type (null_type);
            break;

          case op_iconst_m1:
          case op_iconst_0:
          case op_iconst_1:
          case op_iconst_2:
          case op_iconst_3:
          case op_iconst_4:
          case op_iconst_5:
            push_type (int_type);
            break;

          case op_lconst_0:
          case op_lconst_1:
            push_type (long_type);
            break;

          case op_fconst_0:
          case op_fconst_1:
          case op_fconst_2:
            push_type (float_type);
            break;

          case op_dconst_0:
          case op_dconst_1:
            push_type (double_type);
            break;

          case op_bipush:
            get_byte ();
            push_type (int_type);
            break;

          case op_sipush:
            get_short ();
            push_type (int_type);
            break;

          case op_ldc:
            push_type (check_constant (get_byte ()));
            break;
          case op_ldc_w:
            push_type (check_constant (get_ushort ()));
            break;
          case op_ldc2_w:
            push_type (check_wide_constant (get_ushort ()));
            break;

          case op_iload:
            push_type (get_variable (get_byte (), int_type));
            break;
          case op_lload:
            push_type (get_variable (get_byte (), long_type));
            break;
          case op_fload:
            push_type (get_variable (get_byte (), float_type));
            break;
          case op_dload:
            push_type (get_variable (get_byte (), double_type));
            break;
          case op_aload:
            push_type (get_variable (get_byte (), reference_type));
            break;

          case op_iload_0:
          case op_iload_1:
          case op_iload_2:
          case op_iload_3:
            push_type (get_variable (opcode - op_iload_0, int_type));
            break;
          case op_lload_0:
          case op_lload_1:
          case op_lload_2:
          case op_lload_3:
            push_type (get_variable (opcode - op_lload_0, long_type));
            break;
          case op_fload_0:
          case op_fload_1:
          case op_fload_2:
          case op_fload_3:
            push_type (get_variable (opcode - op_fload_0, float_type));
            break;
          case op_dload_0:
          case op_dload_1:
          case op_dload_2:
          case op_dload_3:
            push_type (get_variable (opcode - op_dload_0, double_type));
            break;
          case op_aload_0:
          case op_aload_1:
          case op_aload_2:
          case op_aload_3:
            push_type (get_variable (opcode - op_aload_0, reference_type));
            break;
          case op_iaload:
            pop_type (int_type);
            push_type (require_array_type (pop_type (reference_type),
                                           int_type));
            break;
          case op_laload:
            pop_type (int_type);
            push_type (require_array_type (pop_type (reference_type),
                                           long_type));
            break;
          case op_faload:
            pop_type (int_type);
            push_type (require_array_type (pop_type (reference_type),
                                           float_type));
            break;
          case op_daload:
            pop_type (int_type);
            push_type (require_array_type (pop_type (reference_type),
                                           double_type));
            break;
          case op_aaload:
            pop_type (int_type);
            push_type (require_array_type (pop_type (reference_type),
                                           reference_type));
            break;
          case op_baload:
            pop_type (int_type);
            require_array_type (pop_type (reference_type), byte_type);
            push_type (int_type);
            break;
          case op_caload:
            pop_type (int_type);
            require_array_type (pop_type (reference_type), char_type);
            push_type (int_type);
            break;
          case op_saload:
            pop_type (int_type);
            require_array_type (pop_type (reference_type), short_type);
            push_type (int_type);
            break;
          case op_istore:
            set_variable (get_byte (), pop_type (int_type));
            break;
          case op_lstore:
            set_variable (get_byte (), pop_type (long_type));
            break;
          case op_fstore:
            set_variable (get_byte (), pop_type (float_type));
            break;
          case op_dstore:
            set_variable (get_byte (), pop_type (double_type));
            break;
          case op_astore:
            set_variable (get_byte (), pop_ref_or_return ());
            break;
          case op_istore_0:
          case op_istore_1:
          case op_istore_2:
          case op_istore_3:
            set_variable (opcode - op_istore_0, pop_type (int_type));
            break;
          case op_lstore_0:
          case op_lstore_1:
          case op_lstore_2:
          case op_lstore_3:
            set_variable (opcode - op_lstore_0, pop_type (long_type));
            break;
          case op_fstore_0:
          case op_fstore_1:
          case op_fstore_2:
          case op_fstore_3:
            set_variable (opcode - op_fstore_0, pop_type (float_type));
            break;
          case op_dstore_0:
          case op_dstore_1:
          case op_dstore_2:
          case op_dstore_3:
            set_variable (opcode - op_dstore_0, pop_type (double_type));
            break;
          case op_astore_0:
          case op_astore_1:
          case op_astore_2:
          case op_astore_3:
            set_variable (opcode - op_astore_0, pop_ref_or_return ());
            break;
          case op_iastore:
            pop_type (int_type);
            pop_type (int_type);
            require_array_type (pop_type (reference_type), int_type);
            break;
          case op_lastore:
            pop_type (long_type);
            pop_type (int_type);
            require_array_type (pop_type (reference_type), long_type);
            break;
          case op_fastore:
            pop_type (float_type);
            pop_type (int_type);
            require_array_type (pop_type (reference_type), float_type);
            break;
          case op_dastore:
            pop_type (double_type);
            pop_type (int_type);
            require_array_type (pop_type (reference_type), double_type);
            break;
          case op_aastore:
            pop_type (reference_type);
            pop_type (int_type);
            require_array_type (pop_type (reference_type), reference_type);
            break;
          case op_bastore:
            pop_type (int_type);
            pop_type (int_type);
            require_array_type (pop_type (reference_type), byte_type);
            break;
          case op_castore:
            pop_type (int_type);
            pop_type (int_type);
            require_array_type (pop_type (reference_type), char_type);
            break;
          case op_sastore:
            pop_type (int_type);
            pop_type (int_type);
            require_array_type (pop_type (reference_type), short_type);
            break;
          case op_pop:
            pop32 ();
            break;
          case op_pop2:
            pop64 ();
            break;
          case op_dup:
            {
              type t = pop32 ();
              push_type (t);
              push_type (t);
            }
            break;
          case op_dup_x1:
            {
              type t1 = pop32 ();
              type t2 = pop32 ();
              push_type (t1);
              push_type (t2);
              push_type (t1);
            }
            break;
          case op_dup_x2:
            {
              type t1 = pop32 ();
              type t2 = pop_raw ();
              if (! t2.iswide ())
                {
                  type t3 = pop32 ();
                  push_type (t1);
                  push_type (t3);
                }
              else
                push_type (t1);
              push_type (t2);
              push_type (t1);
            }
            break;
          case op_dup2:
            {
              type t = pop_raw ();
              if (! t.iswide ())
                {
                  type t2 = pop32 ();
                  push_type (t2);
                  push_type (t);
                  push_type (t2);
                }
              push_type (t);
            }
            break;
          case op_dup2_x1:
            {
              type t1 = pop_raw ();
              type t2 = pop32 ();
              if (! t1.iswide ())
                {
                  type t3 = pop32 ();
                  push_type (t2);
                  push_type (t1);
                  push_type (t3);
                }
              else
                push_type (t1);
              push_type (t2);
              push_type (t1);
            }
            break;
          case op_dup2_x2:
            {
              // FIXME
              type t1 = pop_raw ();
              if (t1.iswide ())
                {
                  type t2 = pop_raw ();
                  if (t2.iswide ())
                    {
                      push_type (t1);
                      push_type (t2);
                    }
                  else
                    {
                      type t3 = pop32 ();
                      push_type (t1);
                      push_type (t3);
                      push_type (t2);
                    }
                  push_type (t1);
                }
              else
                {
                  type t2 = pop32 ();
                  type t3 = pop_raw ();
                  if (t3.iswide ())
                    {
                      push_type (t2);
                      push_type (t1);
                    }
                  else
                    {
                      type t4 = pop32 ();
                      push_type (t2);
                      push_type (t1);
                      push_type (t4);
                    }
                  push_type (t3);
                  push_type (t2);
                  push_type (t1);
                }
            }
            break;
          case op_swap:
            {
              type t1 = pop32 ();
              type t2 = pop32 ();
              push_type (t1);
              push_type (t2);
            }
            break;
          case op_iadd:
          case op_isub:
          case op_imul:
          case op_idiv:
          case op_irem:
          case op_ishl:
          case op_ishr:
          case op_iushr:
          case op_iand:
          case op_ior:
          case op_ixor:
            pop_type (int_type);
            push_type (pop_type (int_type));
            break;
          case op_ladd:
          case op_lsub:
          case op_lmul:
          case op_ldiv:
          case op_lrem:
          case op_land:
          case op_lor:
          case op_lxor:
            pop_type (long_type);
            push_type (pop_type (long_type));
            break;
          case op_lshl:
          case op_lshr:
          case op_lushr:
            pop_type (int_type);
            push_type (pop_type (long_type));
            break;
          case op_fadd:
          case op_fsub:
          case op_fmul:
          case op_fdiv:
          case op_frem:
            pop_type (float_type);
            push_type (pop_type (float_type));
            break;
          case op_dadd:
          case op_dsub:
          case op_dmul:
          case op_ddiv:
          case op_drem:
            pop_type (double_type);
            push_type (pop_type (double_type));
            break;
          case op_ineg:
          case op_i2b:
          case op_i2c:
          case op_i2s:
            push_type (pop_type (int_type));
            break;
          case op_lneg:
            push_type (pop_type (long_type));
            break;
          case op_fneg:
            push_type (pop_type (float_type));
            break;
          case op_dneg:
            push_type (pop_type (double_type));
            break;
          case op_iinc:
            get_variable (get_byte (), int_type);
            get_byte ();
            break;
          case op_i2l:
            pop_type (int_type);
            push_type (long_type);
            break;
          case op_i2f:
            pop_type (int_type);
            push_type (float_type);
            break;
          case op_i2d:
            pop_type (int_type);
            push_type (double_type);
            break;
          case op_l2i:
            pop_type (long_type);
            push_type (int_type);
            break;
          case op_l2f:
            pop_type (long_type);
            push_type (float_type);
            break;
          case op_l2d:
            pop_type (long_type);
            push_type (double_type);
            break;
          case op_f2i:
            pop_type (float_type);
            push_type (int_type);
            break;
          case op_f2l:
            pop_type (float_type);
            push_type (long_type);
            break;
          case op_f2d:
            pop_type (float_type);
            push_type (double_type);
            break;
          case op_d2i:
            pop_type (double_type);
            push_type (int_type);
            break;
          case op_d2l:
            pop_type (double_type);
            push_type (long_type);
            break;
          case op_d2f:
            pop_type (double_type);
            push_type (float_type);
            break;
          case op_lcmp:
            pop_type (long_type);
            pop_type (long_type);
            push_type (int_type);
            break;
          case op_fcmpl:
          case op_fcmpg:
            pop_type (float_type);
            pop_type (float_type);
            push_type (int_type);
            break;
          case op_dcmpl:
          case op_dcmpg:
            pop_type (double_type);
            pop_type (double_type);
            push_type (int_type);
            break;
          case op_ifeq:
          case op_ifne:
          case op_iflt:
          case op_ifge:
          case op_ifgt:
          case op_ifle:
            pop_type (int_type);
            push_jump (get_short ());
            break;
          case op_if_icmpeq:
          case op_if_icmpne:
          case op_if_icmplt:
          case op_if_icmpge:
          case op_if_icmpgt:
          case op_if_icmple:
            pop_type (int_type);
            pop_type (int_type);
            push_jump (get_short ());
            break;
          case op_if_acmpeq:
          case op_if_acmpne:
            pop_type (reference_type);
            pop_type (reference_type);
            push_jump (get_short ());
            break;
          case op_goto:
            push_jump (get_short ());
            invalidate_pc ();
            break;
          case op_jsr:
            handle_jsr_insn (get_short ());
            break;
          case op_ret:
            handle_ret_insn (get_byte ());
            break;
          case op_tableswitch:
            {
              pop_type (int_type);
              skip_padding ();
              push_jump (get_int ());
              jint low = get_int ();
              jint high = get_int ();
              // Already checked LOW -vs- HIGH.
              for (int i = low; i <= high; ++i)
                push_jump (get_int ());
              invalidate_pc ();
            }
            break;

          case op_lookupswitch:
            {
              pop_type (int_type);
              skip_padding ();
              push_jump (get_int ());
              jint npairs = get_int ();
              // Already checked NPAIRS >= 0.
              jint lastkey = 0;
              for (int i = 0; i < npairs; ++i)
                {
                  jint key = get_int ();
                  if (i > 0 && key <= lastkey)
                    verify_fail ("lookupswitch pairs unsorted", start_PC);
                  lastkey = key;
                  push_jump (get_int ());
                }
              invalidate_pc ();
            }
            break;
          case op_ireturn:
            check_return_type (pop_type (int_type));
            invalidate_pc ();
            break;
          case op_lreturn:
            check_return_type (pop_type (long_type));
            invalidate_pc ();
            break;
          case op_freturn:
            check_return_type (pop_type (float_type));
            invalidate_pc ();
            break;
          case op_dreturn:
            check_return_type (pop_type (double_type));
            invalidate_pc ();
            break;
          case op_areturn:
            check_return_type (pop_type (reference_type));
            invalidate_pc ();
            break;
          case op_return:
            check_return_type (void_type);
            invalidate_pc ();
            break;
          case op_getstatic:
            push_type (check_field_constant (get_ushort ()));
            break;
          case op_putstatic:
            pop_type (check_field_constant (get_ushort ()));
            break;
          case op_getfield:
            {
              type klass;
              type field = check_field_constant (get_ushort (), &klass);
              pop_type (klass);
              push_type (field);
            }
            break;
          case op_putfield:
            {
              type klass;
              type field = check_field_constant (get_ushort (), &klass);
              pop_type (field);
              pop_type (klass);
            }
            break;

          case op_invokevirtual:
          case op_invokespecial:
          case op_invokestatic:
          case op_invokeinterface:
            {
              _Jv_Utf8Const *method_name, *method_signature;
              type class_type
                = check_method_constant (get_ushort (),
                                         opcode == op_invokeinterface,
                                         &method_name,
                                         &method_signature);
              int arg_count = _Jv_count_arguments (method_signature);
              if (opcode == op_invokeinterface)
                {
                  int nargs = get_byte ();
                  if (nargs == 0)
                    verify_fail ("too few arguments to invokeinterface",
                                 start_PC);
                  if (get_byte () != 0)
                    verify_fail ("invokeinterface dummy byte is wrong",
                                 start_PC);
                  if (nargs - 1 != arg_count)
                    verify_fail ("wrong argument count for invokeinterface",
                                 start_PC);
                }

              bool is_init = false;
              if (_Jv_equalUtf8Consts (method_name, gcj::init_name))
                {
                  is_init = true;
                  if (opcode != op_invokespecial)
                    verify_fail ("can't invoke <init>", start_PC);
                }
              else if (method_name->data[0] == '<')
                verify_fail ("can't invoke method starting with `<'",
                             start_PC);

              // Pop arguments and check types.
              type arg_types[arg_count];
              compute_argument_types (method_signature, arg_types);
              for (int i = arg_count - 1; i >= 0; --i)
                pop_type (arg_types[i]);

              if (opcode != op_invokestatic)
                {
                  type t = class_type;
                  if (is_init)
                    {
                      // In this case the PC doesn't matter.
                      t.set_uninitialized (type::UNINIT);
                    }
                  t = pop_type (t);
                  if (is_init)
                    current_state->set_initialized (t.get_pc (),
                                                    current_method->max_locals);
                }

              type rt = compute_return_type (method_signature);
              if (! rt.isvoid ())
                push_type (rt);
            }
            break;

          case op_new:
            {
              type t = check_class_constant (get_ushort ());
              if (t.isarray () || t.isinterface () || t.isabstract ())
                verify_fail ("type is array, interface, or abstract",
                             start_PC);
              t.set_uninitialized (start_PC);
              push_type (t);
            }
            break;

          case op_newarray:
            {
              int atype = get_byte ();
              // We intentionally have chosen constants to make this
              // valid.
              if (atype < boolean_type || atype > long_type)
                verify_fail ("type not primitive", start_PC);
              pop_type (int_type);
              push_type (construct_primitive_array_type (type_val (atype)));
            }
            break;
          case op_anewarray:
            pop_type (int_type);
            push_type (check_class_constant (get_ushort ()).to_array ());
            break;
          case op_arraylength:
            {
              type t = pop_type (reference_type);
              if (! t.isarray ())
                verify_fail ("array type expected", start_PC);
              push_type (int_type);
            }
            break;
          case op_athrow:
            pop_type (type (&java::lang::Throwable::class$));
            invalidate_pc ();
            break;
          case op_checkcast:
            pop_type (reference_type);
            push_type (check_class_constant (get_ushort ()));
            break;
          case op_instanceof:
            pop_type (reference_type);
            check_class_constant (get_ushort ());
            push_type (int_type);
            break;
          case op_monitorenter:
            pop_type (reference_type);
            break;
          case op_monitorexit:
            pop_type (reference_type);
            break;
          case op_wide:
            {
              switch (get_byte ())
                {
                case op_iload:
                  push_type (get_variable (get_ushort (), int_type));
                  break;
                case op_lload:
                  push_type (get_variable (get_ushort (), long_type));
                  break;
                case op_fload:
                  push_type (get_variable (get_ushort (), float_type));
                  break;
                case op_dload:
                  push_type (get_variable (get_ushort (), double_type));
                  break;
                case op_aload:
                  push_type (get_variable (get_ushort (), reference_type));
                  break;
                case op_istore:
                  set_variable (get_ushort (), pop_type (int_type));
                  break;
                case op_lstore:
                  set_variable (get_ushort (), pop_type (long_type));
                  break;
                case op_fstore:
                  set_variable (get_ushort (), pop_type (float_type));
                  break;
                case op_dstore:
                  set_variable (get_ushort (), pop_type (double_type));
                  break;
                case op_astore:
                  set_variable (get_ushort (), pop_type (reference_type));
                  break;
                case op_ret:
                  handle_ret_insn (get_short ());
                  break;
                case op_iinc:
                  get_variable (get_ushort (), int_type);
                  get_short ();
                  break;
                default:
                  verify_fail ("unrecognized wide instruction", start_PC);
                }
            }
            break;
          case op_multianewarray:
            {
              type atype = check_class_constant (get_ushort ());
              int dim = get_byte ();
              if (dim < 1)
                verify_fail ("too few dimensions to multianewarray", start_PC);
              atype.verify_dimensions (dim);
              for (int i = 0; i < dim; ++i)
                pop_type (int_type);
              push_type (atype);
            }
            break;
          case op_ifnull:
          case op_ifnonnull:
            pop_type (reference_type);
            push_jump (get_short ());
            break;
          case op_goto_w:
            push_jump (get_int ());
            invalidate_pc ();
            break;
          case op_jsr_w:
            handle_jsr_insn (get_int ());
            break;

          default:
            // Unrecognized opcode.
            verify_fail ("unrecognized instruction in verify_instructions_0",
                         start_PC);
          }
      }
  }

public:

  void verify_instructions ()
  {
    branch_prepass ();
    verify_instructions_0 ();
  }

  _Jv_BytecodeVerifier (_Jv_InterpMethod *m)
  {
    // We just print the text as utf-8.  This is just for debugging
    // anyway.
    debug_print ("--------------------------------\n");
    debug_print ("-- Verifying method `%s'\n", m->self->name->data);

    current_method = m;
    bytecode = m->bytecode ();
    exception = m->exceptions ();
    current_class = m->defining_class;

    states = NULL;
    flags = NULL;
    jsr_ptrs = NULL;
    utf8_list = NULL;
  }

  ~_Jv_BytecodeVerifier ()
  {
    if (states)
      _Jv_Free (states);
    if (flags)
      _Jv_Free (flags);
    if (jsr_ptrs)
      _Jv_Free (jsr_ptrs);
    while (utf8_list != NULL)
      {
        linked_utf8 *n = utf8_list->next;
        _Jv_Free (utf8_list->val);
        _Jv_Free (utf8_list);
        utf8_list = n;
      }
  }
};

void
_Jv_VerifyMethod (_Jv_InterpMethod *meth)
{
  _Jv_BytecodeVerifier v (meth);
  v.verify_instructions ();
}

// FIXME: add more info, like PC, when required.
static void
verify_fail (char *s, jint pc)
{
  using namespace java::lang;
  StringBuffer *buf = new StringBuffer ();

  buf->append (JvNewStringLatin1 ("verification failed"));
  if (pc != -1)
    {
      buf->append (JvNewStringLatin1 (" at PC "));
      buf->append (pc);
    }
  buf->append (JvNewStringLatin1 (": "));
  buf->append (JvNewStringLatin1 (s));
  throw new java::lang::VerifyError (buf->toString ());
}

#endif  /* INTERPRETER */