gimplify.c

/* Tree lowering pass.  This pass converts the GENERIC functions-as-trees
   tree representation into the GIMPLE form.
   Copyright (C) 2002, 2003, 2004 Free Software Foundation, Inc.
   Major work done by Sebastian Pop <s.pop@laposte.net>,
   Diego Novillo <dnovillo@redhat.com> and Jason Merrill <jason@redhat.com>.

This file is part of GCC.

GCC 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.

GCC 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 GCC; 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 "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "rtl.h"
#include "errors.h"
#include "varray.h"
#include "tree-gimple.h"
#include "tree-inline.h"
#include "diagnostic.h"
#include "langhooks.h"
#include "langhooks-def.h"
#include "tree-flow.h"
#include "cgraph.h"
#include "timevar.h"
#include "except.h"
#include "hashtab.h"
#include "flags.h"
#include "real.h"
#include "function.h"
#include "output.h"
#include "expr.h"
#include "ggc.h"
#include "target.h"

static struct gimplify_ctx
{
  tree current_bind_expr;
  tree temps;
  tree conditional_cleanups;
  tree exit_label;
  tree return_temp;
  varray_type case_labels;
  /* The formal temporary table.  Should this be persistent?  */
  htab_t temp_htab;
  int conditions;
  bool save_stack;
  bool into_ssa;
} *gimplify_ctxp;


/* Formal (expression) temporary table handling: Multiple occurrences of
   the same scalar expression are evaluated into the same temporary.  */

typedef struct gimple_temp_hash_elt
{
  tree val;   /* Key */
  tree temp;  /* Value */
} elt_t;

/* Forward declarations.  */
static enum gimplify_status gimplify_compound_expr (tree *, tree *, bool);
#ifdef ENABLE_CHECKING
static bool cpt_same_type (tree a, tree b);
#endif


/* Return a hash value for a formal temporary table entry.  */

static hashval_t
gimple_tree_hash (const void *p)
{
  tree t = ((const elt_t *) p)->val;
  return iterative_hash_expr (t, 0);
}

/* Compare two formal temporary table entries.  */

static int
gimple_tree_eq (const void *p1, const void *p2)
{
  tree t1 = ((const elt_t *) p1)->val;
  tree t2 = ((const elt_t *) p2)->val;
  enum tree_code code = TREE_CODE (t1);

  if (TREE_CODE (t2) != code
      || TREE_TYPE (t1) != TREE_TYPE (t2))
    return 0;

  if (!operand_equal_p (t1, t2, 0))
    return 0;

  /* Only allow them to compare equal if they also hash equal; otherwise
     results are nondeterminate, and we fail bootstrap comparison.  */
  gcc_assert (gimple_tree_hash (p1) == gimple_tree_hash (p2));

  return 1;
}

/* Set up a context for the gimplifier.  */

void
push_gimplify_context (void)
{
  gcc_assert (!gimplify_ctxp);
  gimplify_ctxp
    = (struct gimplify_ctx *) xcalloc (1, sizeof (struct gimplify_ctx));
  if (optimize)
    gimplify_ctxp->temp_htab
      = htab_create (1000, gimple_tree_hash, gimple_tree_eq, free);
  else
    gimplify_ctxp->temp_htab = NULL;
}

/* Tear down a context for the gimplifier.  If BODY is non-null, then
   put the temporaries into the outer BIND_EXPR.  Otherwise, put them
   in the unexpanded_var_list.  */

void
pop_gimplify_context (tree body)
{
  tree t;

  gcc_assert (gimplify_ctxp && !gimplify_ctxp->current_bind_expr);

  for (t = gimplify_ctxp->temps; t ; t = TREE_CHAIN (t))
    DECL_GIMPLE_FORMAL_TEMP_P (t) = 0;

  if (body)
    declare_tmp_vars (gimplify_ctxp->temps, body);
  else
    record_vars (gimplify_ctxp->temps);

#if 0
  if (!quiet_flag && optimize)
    fprintf (stderr, " collisions: %f ",
	     htab_collisions (gimplify_ctxp->temp_htab));
#endif

  if (optimize)
    htab_delete (gimplify_ctxp->temp_htab);
  free (gimplify_ctxp);
  gimplify_ctxp = NULL;
}

void
gimple_push_bind_expr (tree bind)
{
  TREE_CHAIN (bind) = gimplify_ctxp->current_bind_expr;
  gimplify_ctxp->current_bind_expr = bind;
}

void
gimple_pop_bind_expr (void)
{
  gimplify_ctxp->current_bind_expr
    = TREE_CHAIN (gimplify_ctxp->current_bind_expr);
}

tree
gimple_current_bind_expr (void)
{
  return gimplify_ctxp->current_bind_expr;
}

/* Returns true iff there is a COND_EXPR between us and the innermost
   CLEANUP_POINT_EXPR.  This info is used by gimple_push_cleanup.  */

static bool
gimple_conditional_context (void)
{
  return gimplify_ctxp->conditions > 0;
}

/* Note that we've entered a COND_EXPR.  */

static void
gimple_push_condition (void)
{
  ++(gimplify_ctxp->conditions);
}

/* Note that we've left a COND_EXPR.  If we're back at unconditional scope
   now, add any conditional cleanups we've seen to the prequeue.  */

static void
gimple_pop_condition (tree *pre_p)
{
  int conds = --(gimplify_ctxp->conditions);

  gcc_assert (conds >= 0);
  if (conds == 0)
    {
      append_to_statement_list (gimplify_ctxp->conditional_cleanups, pre_p);
      gimplify_ctxp->conditional_cleanups = NULL_TREE;
    }
}

/* A subroutine of append_to_statement_list{,_force}.  */

static void
append_to_statement_list_1 (tree t, tree *list_p, bool side_effects)
{
  tree list = *list_p;
  tree_stmt_iterator i;

  if (!side_effects)
    return;

  if (!list)
    {
      if (t && TREE_CODE (t) == STATEMENT_LIST)
	{
	  *list_p = t;
	  return;
	}
      *list_p = list = alloc_stmt_list ();
    }

  i = tsi_last (list);
  tsi_link_after (&i, t, TSI_CONTINUE_LINKING);
}

/* Add T to the end of the list container pointed by LIST_P.
   If T is an expression with no effects, it is ignored.  */

void
append_to_statement_list (tree t, tree *list_p)
{
  append_to_statement_list_1 (t, list_p, t ? TREE_SIDE_EFFECTS (t) : false);
}

/* Similar, but the statement is always added, regardless of side effects.  */

void
append_to_statement_list_force (tree t, tree *list_p)
{
  append_to_statement_list_1 (t, list_p, t != NULL);
}

/* Both gimplify the statement T and append it to LIST_P.  */

void
gimplify_and_add (tree t, tree *list_p)
{
  gimplify_stmt (&t);
  append_to_statement_list (t, list_p);
}

/* Strip off a legitimate source ending from the input string NAME of
   length LEN.  Rather than having to know the names used by all of
   our front ends, we strip off an ending of a period followed by
   up to five characters.  (Java uses ".class".)  */

static inline void
remove_suffix (char *name, int len)
{
  int i;

  for (i = 2;  i < 8 && len > i;  i++)
    {
      if (name[len - i] == '.')
	{
	  name[len - i] = '\0';
	  break;
	}
    }
}

/* Create a nameless artificial label and put it in the current function
   context.  Returns the newly created label.  */

tree
create_artificial_label (void)
{
  tree lab = build_decl (LABEL_DECL, NULL_TREE, void_type_node);

  DECL_ARTIFICIAL (lab) = 1;
  DECL_CONTEXT (lab) = current_function_decl;
  return lab;
}

/* Create a new temporary name with PREFIX.  Returns an identifier.  */

static GTY(()) unsigned int tmp_var_id_num;

tree
create_tmp_var_name (const char *prefix)
{
  char *tmp_name;

  if (prefix)
    {
      char *preftmp = ASTRDUP (prefix);

      remove_suffix (preftmp, strlen (preftmp));
      prefix = preftmp;
    }

  ASM_FORMAT_PRIVATE_NAME (tmp_name, prefix ? prefix : "T", tmp_var_id_num++);
  return get_identifier (tmp_name);
}


/* Create a new temporary variable declaration of type TYPE.
   Does NOT push it into the current binding.  */

tree
create_tmp_var_raw (tree type, const char *prefix)
{
  tree tmp_var;
  tree new_type;

  /* Make the type of the variable writable.  */
  new_type = build_type_variant (type, 0, 0);
  TYPE_ATTRIBUTES (new_type) = TYPE_ATTRIBUTES (type);

  tmp_var = build_decl (VAR_DECL, prefix ? create_tmp_var_name (prefix) : NULL,
			type);

  /* The variable was declared by the compiler.  */
  DECL_ARTIFICIAL (tmp_var) = 1;
  /* And we don't want debug info for it.  */
  DECL_IGNORED_P (tmp_var) = 1;

  /* Make the variable writable.  */
  TREE_READONLY (tmp_var) = 0;

  DECL_EXTERNAL (tmp_var) = 0;
  TREE_STATIC (tmp_var) = 0;
  TREE_USED (tmp_var) = 1;

  return tmp_var;
}

/* Create a new temporary variable declaration of type TYPE.  DOES push the
   variable into the current binding.  Further, assume that this is called
   only from gimplification or optimization, at which point the creation of
   certain types are bugs.  */

tree
create_tmp_var (tree type, const char *prefix)
{
  tree tmp_var;

  /* We don't allow types that are addressable (meaning we can't make copies),
     incomplete, or of variable size.  */
  gcc_assert (!TREE_ADDRESSABLE (type)
	      && COMPLETE_TYPE_P (type)
	      && TREE_CODE (TYPE_SIZE_UNIT (type)) == INTEGER_CST);

  tmp_var = create_tmp_var_raw (type, prefix);
  gimple_add_tmp_var (tmp_var);
  return tmp_var;
}

/*  Given a tree, try to return a useful variable name that we can use
    to prefix a temporary that is being assigned the value of the tree.
    I.E. given  <temp> = &A, return A.  */

const char *
get_name (tree t)
{
  tree stripped_decl;

  stripped_decl = t;
  STRIP_NOPS (stripped_decl);
  if (DECL_P (stripped_decl) && DECL_NAME (stripped_decl))
    return IDENTIFIER_POINTER (DECL_NAME (stripped_decl));
  else
    {
      switch (TREE_CODE (stripped_decl))
	{
	case ADDR_EXPR:
	  return get_name (TREE_OPERAND (stripped_decl, 0));
	  break;
	default:
	  return NULL;
	}
    }
}

/* Create a temporary with a name derived from VAL.  Subroutine of
   lookup_tmp_var; nobody else should call this function.  */

static inline tree
create_tmp_from_val (tree val)
{
  return create_tmp_var (TREE_TYPE (val), get_name (val));
}

/* Create a temporary to hold the value of VAL.  If IS_FORMAL, try to reuse
   an existing expression temporary.  */

static tree
lookup_tmp_var (tree val, bool is_formal)
{
  tree ret;

  /* If not optimizing, never really reuse a temporary.  local-alloc
     won't allocate any variable that is used in more than one basic
     block, which means it will go into memory, causing much extra
     work in reload and final and poorer code generation, outweighing
     the extra memory allocation here.  */
  if (!optimize || !is_formal || TREE_SIDE_EFFECTS (val))
    ret = create_tmp_from_val (val);
  else
    {
      elt_t elt, *elt_p;
      void **slot;

      elt.val = val;
      slot = htab_find_slot (gimplify_ctxp->temp_htab, (void *)&elt, INSERT);
      if (*slot == NULL)
	{
	  elt_p = xmalloc (sizeof (*elt_p));
	  elt_p->val = val;
	  elt_p->temp = ret = create_tmp_from_val (val);
	  *slot = (void *) elt_p;
	}
      else
	{
	  elt_p = (elt_t *) *slot;
          ret = elt_p->temp;
	}
    }

  if (is_formal)
    DECL_GIMPLE_FORMAL_TEMP_P (ret) = 1;

  return ret;
}

/* Returns a formal temporary variable initialized with VAL.  PRE_P is as
   in gimplify_expr.  Only use this function if:

   1) The value of the unfactored expression represented by VAL will not
      change between the initialization and use of the temporary, and
   2) The temporary will not be otherwise modified.

   For instance, #1 means that this is inappropriate for SAVE_EXPR temps,
   and #2 means it is inappropriate for && temps.

   For other cases, use get_initialized_tmp_var instead.  */

static tree
internal_get_tmp_var (tree val, tree *pre_p, tree *post_p, bool is_formal)
{
  tree t, mod;

  gimplify_expr (&val, pre_p, post_p, is_gimple_formal_tmp_rhs, fb_rvalue);

  t = lookup_tmp_var (val, is_formal);

  mod = build (MODIFY_EXPR, TREE_TYPE (t), t, val);

  if (EXPR_HAS_LOCATION (val))
    SET_EXPR_LOCUS (mod, EXPR_LOCUS (val));
  else
    SET_EXPR_LOCATION (mod, input_location);

  /* gimplify_modify_expr might want to reduce this further.  */
  gimplify_and_add (mod, pre_p);

  /* If we're gimplifying into ssa, gimplify_modify_expr will have
     given our temporary an ssa name.  Find and return it.  */
  if (gimplify_ctxp->into_ssa)
    t = TREE_OPERAND (mod, 0);

  return t;
}

tree
get_formal_tmp_var (tree val, tree *pre_p)
{
  return internal_get_tmp_var (val, pre_p, NULL, true);
}

/* Returns a temporary variable initialized with VAL.  PRE_P and POST_P
   are as in gimplify_expr.  */

tree
get_initialized_tmp_var (tree val, tree *pre_p, tree *post_p)
{
  return internal_get_tmp_var (val, pre_p, post_p, false);
}

/* Declares all the variables in VARS in SCOPE.  */

void
declare_tmp_vars (tree vars, tree scope)
{
  tree last = vars;
  if (last)
    {
      tree temps;

      /* C99 mode puts the default 'return 0;' for main outside the outer
	 braces.  So drill down until we find an actual scope.  */
      while (TREE_CODE (scope) == COMPOUND_EXPR)
	scope = TREE_OPERAND (scope, 0);

      gcc_assert (TREE_CODE (scope) == BIND_EXPR);

      temps = nreverse (last);
      TREE_CHAIN (last) = BIND_EXPR_VARS (scope);
      BIND_EXPR_VARS (scope) = temps;
    }
}

void
gimple_add_tmp_var (tree tmp)
{
  gcc_assert (!TREE_CHAIN (tmp) && !DECL_SEEN_IN_BIND_EXPR_P (tmp));

  DECL_CONTEXT (tmp) = current_function_decl;
  DECL_SEEN_IN_BIND_EXPR_P (tmp) = 1;

  if (gimplify_ctxp)
    {
      TREE_CHAIN (tmp) = gimplify_ctxp->temps;
      gimplify_ctxp->temps = tmp;
    }
  else if (cfun)
    record_vars (tmp);
  else
    declare_tmp_vars (tmp, DECL_SAVED_TREE (current_function_decl));
}

/* Determines whether to assign a locus to the statement STMT.  */

static bool
should_carry_locus_p (tree stmt)
{
  /* Don't emit a line note for a label.  We particularly don't want to
     emit one for the break label, since it doesn't actually correspond
     to the beginning of the loop/switch.  */
  if (TREE_CODE (stmt) == LABEL_EXPR)
    return false;

  /* Do not annotate empty statements, since it confuses gcov.  */
  if (!TREE_SIDE_EFFECTS (stmt))
    return false;

  return true;
}

static void
annotate_one_with_locus (tree t, location_t locus)
{
  if (EXPR_P (t) && ! EXPR_HAS_LOCATION (t) && should_carry_locus_p (t))
    SET_EXPR_LOCATION (t, locus);
}

void
annotate_all_with_locus (tree *stmt_p, location_t locus)
{
  tree_stmt_iterator i;

  if (!*stmt_p)
    return;

  for (i = tsi_start (*stmt_p); !tsi_end_p (i); tsi_next (&i))
    {
      tree t = tsi_stmt (i);

      /* Assuming we've already been gimplified, we shouldn't
	  see nested chaining constructs anymore.  */
      gcc_assert (TREE_CODE (t) != STATEMENT_LIST
		  && TREE_CODE (t) != COMPOUND_EXPR);

      annotate_one_with_locus (t, locus);
    }
}

/* Similar to copy_tree_r() but do not copy SAVE_EXPR or TARGET_EXPR nodes.
   These nodes model computations that should only be done once.  If we
   were to unshare something like SAVE_EXPR(i++), the gimplification
   process would create wrong code.  */

static tree
mostly_copy_tree_r (tree *tp, int *walk_subtrees, void *data)
{
  enum tree_code code = TREE_CODE (*tp);
  /* Don't unshare types, decls, constants and SAVE_EXPR nodes.  */
  if (TREE_CODE_CLASS (code) == tcc_type
      || TREE_CODE_CLASS (code) == tcc_declaration
      || TREE_CODE_CLASS (code) == tcc_constant
      || code == SAVE_EXPR || code == TARGET_EXPR
      /* We can't do anything sensible with a BLOCK used as an expression,
	 but we also can't abort when we see it because of non-expression
	 uses.  So just avert our eyes and cross our fingers.  Silly Java.  */
      || code == BLOCK)
    *walk_subtrees = 0;
  else
    {
      gcc_assert (code != BIND_EXPR);
      copy_tree_r (tp, walk_subtrees, data);
    }

  return NULL_TREE;
}

/* Callback for walk_tree to unshare most of the shared trees rooted at
   *TP.  If *TP has been visited already (i.e., TREE_VISITED (*TP) == 1),
   then *TP is deep copied by calling copy_tree_r.

   This unshares the same trees as copy_tree_r with the exception of
   SAVE_EXPR nodes.  These nodes model computations that should only be
   done once.  If we were to unshare something like SAVE_EXPR(i++), the
   gimplification process would create wrong code.  */

static tree
copy_if_shared_r (tree *tp, int *walk_subtrees ATTRIBUTE_UNUSED,
		  void *data ATTRIBUTE_UNUSED)
{
  tree t = *tp;
  enum tree_code code = TREE_CODE (t);

  /* Skip types, decls, and constants.  But we do want to look at their
     types and the bounds of types.  Mark them as visited so we properly
     unmark their subtrees on the unmark pass.  If we've already seen them,
     don't look down further.  */
  if (TREE_CODE_CLASS (code) == tcc_type
      || TREE_CODE_CLASS (code) == tcc_declaration
      || TREE_CODE_CLASS (code) == tcc_constant)
    {
      if (TREE_VISITED (t))
	*walk_subtrees = 0;
      else
	TREE_VISITED (t) = 1;
    }

  /* If this node has been visited already, unshare it and don't look
     any deeper.  */
  else if (TREE_VISITED (t))
    {
      walk_tree (tp, mostly_copy_tree_r, NULL, NULL);
      *walk_subtrees = 0;
    }

  /* Otherwise, mark the tree as visited and keep looking.  */
  else
    TREE_VISITED (t) = 1;

  return NULL_TREE;
}

static tree
unmark_visited_r (tree *tp, int *walk_subtrees ATTRIBUTE_UNUSED,
		  void *data ATTRIBUTE_UNUSED)
{
  if (TREE_VISITED (*tp))
    TREE_VISITED (*tp) = 0;
  else
    *walk_subtrees = 0;

  return NULL_TREE;
}

/* Unshare all the trees in BODY_P, a pointer into the body of FNDECL, and the
   bodies of any nested functions if we are unsharing the entire body of
   FNDECL.  */

static void
unshare_body (tree *body_p, tree fndecl)
{
  struct cgraph_node *cgn = cgraph_node (fndecl);

  walk_tree (body_p, copy_if_shared_r, NULL, NULL);
  if (body_p == &DECL_SAVED_TREE (fndecl))
    for (cgn = cgn->nested; cgn; cgn = cgn->next_nested)
      unshare_body (&DECL_SAVED_TREE (cgn->decl), cgn->decl);
}

/* Likewise, but mark all trees as not visited.  */

static void
unvisit_body (tree *body_p, tree fndecl)
{
  struct cgraph_node *cgn = cgraph_node (fndecl);

  walk_tree (body_p, unmark_visited_r, NULL, NULL);
  if (body_p == &DECL_SAVED_TREE (fndecl))
    for (cgn = cgn->nested; cgn; cgn = cgn->next_nested)
      unvisit_body (&DECL_SAVED_TREE (cgn->decl), cgn->decl);
}

/* Unshare T and all the trees reached from T via TREE_CHAIN.  */

void
unshare_all_trees (tree t)
{
  walk_tree (&t, copy_if_shared_r, NULL, NULL);
  walk_tree (&t, unmark_visited_r, NULL, NULL);
}

/* Unconditionally make an unshared copy of EXPR.  This is used when using
   stored expressions which span multiple functions, such as BINFO_VTABLE,
   as the normal unsharing process can't tell that they're shared.  */

tree
unshare_expr (tree expr)
{
  walk_tree (&expr, mostly_copy_tree_r, NULL, NULL);
  return expr;
}

/* A terser interface for building a representation of a exception
   specification.  */

tree
gimple_build_eh_filter (tree body, tree allowed, tree failure)
{
  tree t;

  /* FIXME should the allowed types go in TREE_TYPE?  */
  t = build (EH_FILTER_EXPR, void_type_node, allowed, NULL_TREE);
  append_to_statement_list (failure, &EH_FILTER_FAILURE (t));

  t = build (TRY_CATCH_EXPR, void_type_node, NULL_TREE, t);
  append_to_statement_list (body, &TREE_OPERAND (t, 0));

  return t;
}


/* WRAPPER is a code such as BIND_EXPR or CLEANUP_POINT_EXPR which can both
   contain statements and have a value.  Assign its value to a temporary
   and give it void_type_node.  Returns the temporary, or NULL_TREE if
   WRAPPER was already void.  */

tree
voidify_wrapper_expr (tree wrapper, tree temp)
{
  if (!VOID_TYPE_P (TREE_TYPE (wrapper)))
    {
      tree *p, sub = wrapper;

    restart:
      /* Set p to point to the body of the wrapper.  */
      switch (TREE_CODE (sub))
	{
	case BIND_EXPR:
	  /* For a BIND_EXPR, the body is operand 1.  */
	  p = &BIND_EXPR_BODY (sub);
	  break;

	default:
	  p = &TREE_OPERAND (sub, 0);
	  break;
	}

      /* Advance to the last statement.  Set all container types to void.  */
      if (TREE_CODE (*p) == STATEMENT_LIST)
	{
	  tree_stmt_iterator i = tsi_last (*p);
	  p = tsi_end_p (i) ? NULL : tsi_stmt_ptr (i);
	}
      else
	{
	  for (; TREE_CODE (*p) == COMPOUND_EXPR; p = &TREE_OPERAND (*p, 1))
	    {
	      TREE_SIDE_EFFECTS (*p) = 1;
	      TREE_TYPE (*p) = void_type_node;
	    }
	}

      if (p == NULL || IS_EMPTY_STMT (*p))
	;
      /* Look through exception handling.  */
      else if (TREE_CODE (*p) == TRY_FINALLY_EXPR
	       || TREE_CODE (*p) == TRY_CATCH_EXPR)
	{
	  sub = *p;
	  goto restart;
	}
      /* The C++ frontend already did this for us.  */
      else if (TREE_CODE (*p) == INIT_EXPR
	       || TREE_CODE (*p) == TARGET_EXPR)
	temp = TREE_OPERAND (*p, 0);
      /* If we're returning a dereference, move the dereference
	 outside the wrapper.  */
      else if (TREE_CODE (*p) == INDIRECT_REF)
	{
	  tree ptr = TREE_OPERAND (*p, 0);
	  temp = create_tmp_var (TREE_TYPE (ptr), "retval");
	  *p = build (MODIFY_EXPR, TREE_TYPE (ptr), temp, ptr);
	  temp = build1 (INDIRECT_REF, TREE_TYPE (TREE_TYPE (temp)), temp);
	  /* If this is a BIND_EXPR for a const inline function, it might not
	     have TREE_SIDE_EFFECTS set.  That is no longer accurate.  */
	  TREE_SIDE_EFFECTS (wrapper) = 1;
	}
      else
	{
	  if (!temp)
	    temp = create_tmp_var (TREE_TYPE (wrapper), "retval");
	  *p = build (MODIFY_EXPR, TREE_TYPE (temp), temp, *p);
	  TREE_SIDE_EFFECTS (wrapper) = 1;
	}

      TREE_TYPE (wrapper) = void_type_node;
      return temp;
    }

  return NULL_TREE;
}

/* Prepare calls to builtins to SAVE and RESTORE the stack as well as
   a temporary through which they communicate.  */

static void
build_stack_save_restore (tree *save, tree *restore)
{
  tree save_call, tmp_var;

  save_call =
      build_function_call_expr (implicit_built_in_decls[BUILT_IN_STACK_SAVE],
				NULL_TREE);
  tmp_var = create_tmp_var (ptr_type_node, "saved_stack");

  *save = build (MODIFY_EXPR, ptr_type_node, tmp_var, save_call);
  *restore =
    build_function_call_expr (implicit_built_in_decls[BUILT_IN_STACK_RESTORE],
			      tree_cons (NULL_TREE, tmp_var, NULL_TREE));
}

/* Gimplify a BIND_EXPR.  Just voidify and recurse.  */

static enum gimplify_status
gimplify_bind_expr (tree *expr_p, tree temp, tree *pre_p)
{
  tree bind_expr = *expr_p;
  bool old_save_stack = gimplify_ctxp->save_stack;
  tree t;

  temp = voidify_wrapper_expr (bind_expr, temp);

  /* Mark variables seen in this bind expr.  */
  for (t = BIND_EXPR_VARS (bind_expr); t ; t = TREE_CHAIN (t))
    DECL_SEEN_IN_BIND_EXPR_P (t) = 1;

  gimple_push_bind_expr (bind_expr);
  gimplify_ctxp->save_stack = false;

  gimplify_to_stmt_list (&BIND_EXPR_BODY (bind_expr));

  if (gimplify_ctxp->save_stack)
    {
      tree stack_save, stack_restore;

      /* Save stack on entry and restore it on exit.  Add a try_finally
	 block to achieve this.  Note that mudflap depends on the
	 format of the emitted code: see mx_register_decls().  */
      build_stack_save_restore (&stack_save, &stack_restore);

      t = build (TRY_FINALLY_EXPR, void_type_node,
		 BIND_EXPR_BODY (bind_expr), NULL_TREE);
      append_to_statement_list (stack_restore, &TREE_OPERAND (t, 1));

      BIND_EXPR_BODY (bind_expr) = NULL_TREE;
      append_to_statement_list (stack_save, &BIND_EXPR_BODY (bind_expr));
      append_to_statement_list (t, &BIND_EXPR_BODY (bind_expr));
    }

  gimplify_ctxp->save_stack = old_save_stack;
  gimple_pop_bind_expr ();

  if (temp)
    {
      *expr_p = temp;
      append_to_statement_list (bind_expr, pre_p);
      return GS_OK;
    }
  else
    return GS_ALL_DONE;
}

/* Gimplify a RETURN_EXPR.  If the expression to be returned is not a
   GIMPLE value, it is assigned to a new temporary and the statement is
   re-written to return the temporary.

   PRE_P points to the list where side effects that must happen before
   STMT should be stored.  */

static enum gimplify_status
gimplify_return_expr (tree stmt, tree *pre_p)
{
  tree ret_expr = TREE_OPERAND (stmt, 0);
  tree result_decl, result;

  if (!ret_expr || TREE_CODE (ret_expr) == RESULT_DECL
      || ret_expr == error_mark_node)
    return GS_ALL_DONE;

  if (VOID_TYPE_P (TREE_TYPE (TREE_TYPE (current_function_decl))))
    result_decl = NULL_TREE;
  else
    {
      result_decl = TREE_OPERAND (ret_expr, 0);
      if (TREE_CODE (result_decl) == INDIRECT_REF)
	/* See through a return by reference.  */
	result_decl = TREE_OPERAND (result_decl, 0);

      gcc_assert ((TREE_CODE (ret_expr) == MODIFY_EXPR
		   || TREE_CODE (ret_expr) == INIT_EXPR)
		  && TREE_CODE (result_decl) == RESULT_DECL);
    }

  /* If aggregate_value_p is true, then we can return the bare RESULT_DECL.
     Recall that aggregate_value_p is FALSE for any aggregate type that is
     returned in registers.  If we're returning values in registers, then
     we don't want to extend the lifetime of the RESULT_DECL, particularly
     across another call.  In addition, for those aggregates for which
     hard_function_value generates a PARALLEL, we'll abort during normal
     expansion of structure assignments; there's special code in expand_return
     to handle this case that does not exist in expand_expr.  */
  if (!result_decl
      || aggregate_value_p (result_decl, TREE_TYPE (current_function_decl)))
    result = result_decl;
  else if (gimplify_ctxp->return_temp)
    result = gimplify_ctxp->return_temp;
  else
    {
      result = create_tmp_var (TREE_TYPE (result_decl), NULL);

      /* ??? With complex control flow (usually involving abnormal edges),
	 we can wind up warning about an uninitialized value for this.  Due
	 to how this variable is constructed and initialized, this is never
	 true.  Give up and never warn.  */
      TREE_NO_WARNING (result) = 1;

      gimplify_ctxp->return_temp = result;
    }

  /* Smash the lhs of the MODIFY_EXPR to the temporary we plan to use.
     Then gimplify the whole thing.  */
  if (result != result_decl)
    TREE_OPERAND (ret_expr, 0) = result;

  gimplify_and_add (TREE_OPERAND (stmt, 0), pre_p);

  /* If we didn't use a temporary, then the result is just the result_decl.
     Otherwise we need a simple copy.  This should already be gimple.  */
  if (result == result_decl)
    ret_expr = result;
  else
    ret_expr = build (MODIFY_EXPR, TREE_TYPE (result), result_decl, result);
  TREE_OPERAND (stmt, 0) = ret_expr;

  return GS_ALL_DONE;
}

/* Gimplifies a DECL_EXPR node *STMT_P by making any necessary allocation
   and initialization explicit.  */

static enum gimplify_status
gimplify_decl_expr (tree *stmt_p)
{
  tree stmt = *stmt_p;
  tree decl = DECL_EXPR_DECL (stmt);

  *stmt_p = NULL_TREE;

  if (TREE_TYPE (decl) == error_mark_node)
    return GS_ERROR;

  else if (TREE_CODE (decl) == TYPE_DECL)
    gimplify_type_sizes (TREE_TYPE (decl), stmt_p);

  else if (TREE_CODE (decl) == VAR_DECL && !DECL_EXTERNAL (decl))
    {
      tree init = DECL_INITIAL (decl);

      if (!TREE_CONSTANT (DECL_SIZE (decl)))
	{
	  /* This is a variable-sized decl.  Simplify its size and mark it
	     for deferred expansion.  Note that mudflap depends on the format
	     of the emitted code: see mx_register_decls().  */
	  tree t, args, addr, ptr_type;

	  gimplify_type_sizes (TREE_TYPE (decl), stmt_p);
	  gimplify_one_sizepos (&DECL_SIZE (decl), stmt_p);
	  gimplify_one_sizepos (&DECL_SIZE_UNIT (decl), stmt_p);

	  /* All occurrences of this decl in final gimplified code will be