--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/tree-ssa-dse.c	Fri Jul 17 14:47:48 2009 +0900
@@ -0,0 +1,782 @@
+/* Dead store elimination
+   Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009
+   Free Software Foundation, Inc.
+
+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 3, 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 COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "ggc.h"
+#include "tree.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "basic-block.h"
+#include "timevar.h"
+#include "diagnostic.h"
+#include "tree-flow.h"
+#include "tree-pass.h"
+#include "tree-dump.h"
+#include "domwalk.h"
+#include "flags.h"
+#include "langhooks.h"
+
+/* This file implements dead store elimination.
+
+   A dead store is a store into a memory location which will later be
+   overwritten by another store without any intervening loads.  In this
+   case the earlier store can be deleted.
+
+   In our SSA + virtual operand world we use immediate uses of virtual
+   operands to detect dead stores.  If a store's virtual definition
+   is used precisely once by a later store to the same location which
+   post dominates the first store, then the first store is dead. 
+
+   The single use of the store's virtual definition ensures that
+   there are no intervening aliased loads and the requirement that
+   the second load post dominate the first ensures that if the earlier
+   store executes, then the later stores will execute before the function
+   exits.
+
+   It may help to think of this as first moving the earlier store to
+   the point immediately before the later store.  Again, the single
+   use of the virtual definition and the post-dominance relationship
+   ensure that such movement would be safe.  Clearly if there are 
+   back to back stores, then the second is redundant.
+
+   Reviewing section 10.7.2 in Morgan's "Building an Optimizing Compiler"
+   may also help in understanding this code since it discusses the
+   relationship between dead store and redundant load elimination.  In
+   fact, they are the same transformation applied to different views of
+   the CFG.  */
+
+
+struct dse_global_data
+{
+  /* This is the global bitmap for store statements.
+
+     Each statement has a unique ID.  When we encounter a store statement
+     that we want to record, set the bit corresponding to the statement's
+     unique ID in this bitmap.  */
+  bitmap stores;
+};
+
+/* We allocate a bitmap-per-block for stores which are encountered
+   during the scan of that block.  This allows us to restore the 
+   global bitmap of stores when we finish processing a block.  */
+struct dse_block_local_data
+{
+  bitmap stores;
+};
+
+/* Basic blocks of the potentially dead store and the following
+   store, for memory_address_same.  */
+struct address_walk_data
+{
+  basic_block store1_bb, store2_bb;
+};
+
+static bool gate_dse (void);
+static unsigned int tree_ssa_dse (void);
+static void dse_initialize_block_local_data (struct dom_walk_data *,
+					     basic_block,
+					     bool);
+static void dse_optimize_stmt (struct dom_walk_data *,
+			       basic_block,
+			       gimple_stmt_iterator);
+static void dse_record_phis (struct dom_walk_data *, basic_block);
+static void dse_finalize_block (struct dom_walk_data *, basic_block);
+static void record_voperand_set (bitmap, bitmap *, unsigned int);
+
+/* Returns uid of statement STMT.  */
+
+static unsigned
+get_stmt_uid (gimple stmt)
+{
+  if (gimple_code (stmt) == GIMPLE_PHI)
+    return SSA_NAME_VERSION (gimple_phi_result (stmt))
+           + gimple_stmt_max_uid (cfun);
+
+  return gimple_uid (stmt);
+}
+
+/* Set bit UID in bitmaps GLOBAL and *LOCAL, creating *LOCAL as needed.  */
+
+static void
+record_voperand_set (bitmap global, bitmap *local, unsigned int uid)
+{
+  /* Lazily allocate the bitmap.  Note that we do not get a notification
+     when the block local data structures die, so we allocate the local
+     bitmap backed by the GC system.  */
+  if (*local == NULL)
+    *local = BITMAP_GGC_ALLOC ();
+
+  /* Set the bit in the local and global bitmaps.  */
+  bitmap_set_bit (*local, uid);
+  bitmap_set_bit (global, uid);
+}
+
+/* Initialize block local data structures.  */
+
+static void
+dse_initialize_block_local_data (struct dom_walk_data *walk_data,
+				 basic_block bb ATTRIBUTE_UNUSED,
+				 bool recycled)
+{
+  struct dse_block_local_data *bd
+    = (struct dse_block_local_data *)
+	VEC_last (void_p, walk_data->block_data_stack);
+
+  /* If we are given a recycled block local data structure, ensure any
+     bitmap associated with the block is cleared.  */
+  if (recycled)
+    {
+      if (bd->stores)
+	bitmap_clear (bd->stores);
+    }
+}
+
+/* Helper function for memory_address_same via walk_tree.  Returns
+   non-NULL if it finds an SSA_NAME which is part of the address,
+   such that the definition of the SSA_NAME post-dominates the store
+   we want to delete but not the store that we believe makes it
+   redundant.  This indicates that the address may change between
+   the two stores.  */
+
+static tree
+memory_ssa_name_same (tree *expr_p, int *walk_subtrees ATTRIBUTE_UNUSED,
+		      void *data)
+{
+  struct address_walk_data *walk_data = (struct address_walk_data *) data;
+  tree expr = *expr_p;
+  gimple def_stmt;
+  basic_block def_bb;
+
+  if (TREE_CODE (expr) != SSA_NAME)
+    return NULL_TREE;
+
+  /* If we've found a default definition, then there's no problem.  Both
+     stores will post-dominate it.  And def_bb will be NULL.  */
+  if (SSA_NAME_IS_DEFAULT_DEF (expr))
+    return NULL_TREE;
+
+  def_stmt = SSA_NAME_DEF_STMT (expr);
+  def_bb = gimple_bb (def_stmt);
+
+  /* DEF_STMT must dominate both stores.  So if it is in the same
+     basic block as one, it does not post-dominate that store.  */
+  if (walk_data->store1_bb != def_bb
+      && dominated_by_p (CDI_POST_DOMINATORS, walk_data->store1_bb, def_bb))
+    {
+      if (walk_data->store2_bb == def_bb
+	  || !dominated_by_p (CDI_POST_DOMINATORS, walk_data->store2_bb,
+			      def_bb))
+	/* Return non-NULL to stop the walk.  */
+	return *expr_p;
+    }
+
+  return NULL_TREE;
+}
+
+/* Return TRUE if the destination memory address in STORE1 and STORE2
+   might be modified after STORE1, before control reaches STORE2.  */
+
+static bool
+memory_address_same (gimple store1, gimple store2)
+{
+  struct address_walk_data walk_data;
+
+  walk_data.store1_bb = gimple_bb (store1);
+  walk_data.store2_bb = gimple_bb (store2);
+
+  return (walk_tree (gimple_assign_lhs_ptr (store1), memory_ssa_name_same,
+		     &walk_data, NULL)
+	  == NULL);
+}
+
+/* Return true if there is a stmt that kills the lhs of STMT and is in the
+   virtual def-use chain of STMT without a use in between the kill and STMT.
+   Returns false if no such stmt is found.
+   *FIRST_USE_P is set to the first use of the single virtual def of
+   STMT.  *USE_P is set to the vop killed by *USE_STMT.  */
+
+static bool
+get_kill_of_stmt_lhs (gimple stmt,
+		      use_operand_p * first_use_p,
+ 		      use_operand_p * use_p, gimple * use_stmt)
+{
+  tree lhs;
+
+  gcc_assert (is_gimple_assign (stmt));
+
+  lhs = gimple_assign_lhs (stmt);
+
+  /* We now walk the chain of single uses of the single VDEFs.
+     We succeeded finding a kill if the lhs of the use stmt is
+     equal to the original lhs.  We can keep walking to the next
+     use if there are no possible uses of the original lhs in
+     the stmt.  */
+  do
+    {
+      tree use_lhs;
+      def_operand_p def_p;
+
+      /* The stmt must have a single VDEF.  */
+      def_p = SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_VDEF);
+      if (def_p == NULL_DEF_OPERAND_P)
+	return false;
+
+      /* Get the single immediate use of the def.  */
+      if (!single_imm_use (DEF_FROM_PTR (def_p), first_use_p, &stmt))
+	return false;
+      first_use_p = use_p;
+
+      /* If there are possible hidden uses, give up.  */
+      if (!gimple_assign_single_p (stmt)
+	  || (TREE_CODE (gimple_assign_rhs1 (stmt)) != SSA_NAME
+	      && !is_gimple_min_invariant (gimple_assign_rhs1 (stmt))))
+	return false;
+
+      /* If the use stmts lhs matches the original lhs we have
+	 found the kill, otherwise continue walking.  */
+      use_lhs = gimple_assign_lhs (stmt);
+      if (operand_equal_p (use_lhs, lhs, 0))
+	{
+	  *use_stmt = stmt;
+	  return true;
+	}
+    }
+  while (1);
+}
+
+/* A helper of dse_optimize_stmt.
+   Given a GIMPLE_ASSIGN in STMT, check that each VDEF has one
+   use, and that one use is another VDEF clobbering the first one.
+
+   Return TRUE if the above conditions are met, otherwise FALSE.  */
+
+static bool
+dse_possible_dead_store_p (gimple stmt,
+			   use_operand_p *first_use_p,
+			   use_operand_p *use_p,
+			   gimple *use_stmt,
+			   struct dse_global_data *dse_gd,
+			   struct dse_block_local_data *bd)
+{
+  ssa_op_iter op_iter;
+  bool fail = false;
+  def_operand_p var1;
+  vuse_vec_p vv;
+  tree defvar = NULL_TREE;
+  tree prev_defvar = NULL_TREE;
+  gimple temp;
+
+  /* We want to verify that each virtual definition in STMT has
+     precisely one use and that all the virtual definitions are
+     used by the same single statement.  When complete, we
+     want USE_STMT to refer to the one statement which uses
+     all of the virtual definitions from STMT.  */
+  *use_stmt = NULL;
+  FOR_EACH_SSA_VDEF_OPERAND (var1, vv, stmt, op_iter)
+    {
+      defvar = DEF_FROM_PTR (var1);
+
+      /* If this virtual def does not have precisely one use, then
+	 we will not be able to eliminate STMT.  */
+      if (!has_single_use (defvar))
+	{
+	  fail = true;
+	  break;
+	}
+
+      /* Get the one and only immediate use of DEFVAR.  */
+      single_imm_use (defvar, use_p, &temp);
+      gcc_assert (*use_p != NULL_USE_OPERAND_P);
+      *first_use_p = *use_p;
+
+      /* ???  If we hit a GIMPLE_PHI we could skip to the PHI_RESULT uses.
+	 Don't bother to do that for now.  */
+      if (gimple_code (temp) == GIMPLE_PHI)
+	{
+	  fail = true;
+	  break;
+	}
+
+      /* In the case of memory partitions, we may get:
+
+	   # MPT.764_162 = VDEF <MPT.764_161(D)>
+	   x = {};
+	   # MPT.764_167 = VDEF <MPT.764_162>
+	   y = {};
+
+	   So we must make sure we're talking about the same LHS.
+      */
+      if (is_gimple_assign (temp))
+	{
+	  tree base1 = get_base_address (gimple_assign_lhs (stmt));
+	  tree base2 = get_base_address (gimple_assign_lhs (temp));
+
+	  while (base1 && INDIRECT_REF_P (base1))
+	    base1 = TREE_OPERAND (base1, 0);
+	  while (base2 && INDIRECT_REF_P (base2))
+	    base2 = TREE_OPERAND (base2, 0);
+
+	  if (base1 != base2)
+	    {
+	      fail = true;
+	      break;
+	    }
+	}
+
+      /* If the immediate use of DEF_VAR is not the same as the
+	 previously find immediate uses, then we will not be able
+	 to eliminate STMT.  */
+      if (*use_stmt == NULL)
+	{
+	  *use_stmt = temp;
+	  prev_defvar = defvar;
+	}
+      else if (temp != *use_stmt)
+	{
+	  fail = true;
+	  break;
+	}
+    }
+
+  if (fail)
+    {
+      record_voperand_set (dse_gd->stores, &bd->stores, gimple_uid (stmt));
+      return false;
+    }
+
+  return true;
+}
+
+
+/* Attempt to eliminate dead stores in the statement referenced by BSI.
+
+   A dead store is a store into a memory location which will later be
+   overwritten by another store without any intervening loads.  In this
+   case the earlier store can be deleted.
+
+   In our SSA + virtual operand world we use immediate uses of virtual
+   operands to detect dead stores.  If a store's virtual definition
+   is used precisely once by a later store to the same location which
+   post dominates the first store, then the first store is dead.  */
+
+static void
+dse_optimize_stmt (struct dom_walk_data *walk_data,
+		   basic_block bb ATTRIBUTE_UNUSED,
+		   gimple_stmt_iterator gsi)
+{
+  struct dse_block_local_data *bd
+    = (struct dse_block_local_data *)
+	VEC_last (void_p, walk_data->block_data_stack);
+  struct dse_global_data *dse_gd
+    = (struct dse_global_data *) walk_data->global_data;
+  gimple stmt = gsi_stmt (gsi);
+
+  /* If this statement has no virtual defs, then there is nothing
+     to do.  */
+  if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VDEF))
+    return;
+
+  /* We know we have virtual definitions.  If this is a GIMPLE_ASSIGN
+     that's not also a function call, then record it into our table.  */
+  if (is_gimple_call (stmt) && gimple_call_fndecl (stmt))
+    return;
+
+  if (gimple_has_volatile_ops (stmt))
+    return;
+
+  if (is_gimple_assign (stmt))
+    {
+      use_operand_p first_use_p = NULL_USE_OPERAND_P;
+      use_operand_p use_p = NULL;
+      gimple use_stmt;
+
+      if (!dse_possible_dead_store_p (stmt, &first_use_p, &use_p, &use_stmt, 
+				      dse_gd, bd))
+	return;
+
+      /* If we have precisely one immediate use at this point, then we may
+	 have found redundant store.  Make sure that the stores are to
+	 the same memory location.  This includes checking that any
+	 SSA-form variables in the address will have the same values.  */
+      if (use_p != NULL_USE_OPERAND_P
+          && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
+          && !operand_equal_p (gimple_assign_lhs (stmt),
+                               gimple_assign_lhs (use_stmt), 0)
+          && memory_address_same (stmt, use_stmt))
+        {
+          /* If we have precisely one immediate use at this point, but
+             the stores are not to the same memory location then walk the
+             virtual def-use chain to get the stmt which stores to that same
+             memory location.  */
+          if (!get_kill_of_stmt_lhs (stmt, &first_use_p, &use_p, &use_stmt))
+            {
+              record_voperand_set (dse_gd->stores, &bd->stores, 
+				   gimple_uid (stmt));
+              return;
+            }
+        }
+
+      /* If we have precisely one immediate use at this point and the
+	 stores are to the same memory location or there is a chain of
+	 virtual uses from stmt and the stmt which stores to that same
+	 memory location, then we may have found redundant store.  */
+      if (use_p != NULL_USE_OPERAND_P
+	  && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
+	  && operand_equal_p (gimple_assign_lhs (stmt),
+			      gimple_assign_lhs (use_stmt), 0)
+	  && memory_address_same (stmt, use_stmt))
+	{
+	  ssa_op_iter op_iter;
+	  def_operand_p var1;
+	  vuse_vec_p vv;
+	  tree stmt_lhs;
+
+	  /* If use_stmt is or might be a nop assignment, e.g. for
+	     struct { ... } S a, b, *p; ...
+	     b = a; b = b;
+	     or
+	     b = a; b = *p; where p might be &b,
+	     or
+	     *p = a; *p = b; where p might be &b,
+	     or
+	     *p = *u; *p = *v; where p might be v, then USE_STMT
+	     acts as a use as well as definition, so store in STMT
+	     is not dead.  */
+	  if (gimple_loaded_syms (use_stmt)
+	      && bitmap_intersect_p (gimple_loaded_syms (use_stmt),
+				     gimple_stored_syms (use_stmt)))
+	    {
+              record_voperand_set (dse_gd->stores, &bd->stores, 
+				   gimple_uid (stmt));
+	      return;
+	    }
+
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+            {
+              fprintf (dump_file, "  Deleted dead store '");
+              print_gimple_stmt (dump_file, gsi_stmt (gsi), dump_flags, 0);
+              fprintf (dump_file, "'\n");
+            }
+
+	  /* Then we need to fix the operand of the consuming stmt.  */
+	  stmt_lhs = USE_FROM_PTR (first_use_p);
+	  FOR_EACH_SSA_VDEF_OPERAND (var1, vv, stmt, op_iter)
+	    {
+	      tree usevar;
+	      gimple temp;
+
+	      single_imm_use (DEF_FROM_PTR (var1), &use_p, &temp);
+	      gcc_assert (VUSE_VECT_NUM_ELEM (*vv) == 1);
+	      usevar = VUSE_ELEMENT_VAR (*vv, 0);
+	      SET_USE (use_p, usevar);
+
+	      /* Make sure we propagate the ABNORMAL bit setting.  */
+	      if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (stmt_lhs))
+		SSA_NAME_OCCURS_IN_ABNORMAL_PHI (usevar) = 1;
+	    }
+
+	  /* Remove the dead store.  */
+	  gsi_remove (&gsi, true);
+
+	  /* And release any SSA_NAMEs set in this statement back to the
+	     SSA_NAME manager.  */
+	  release_defs (stmt);
+	}
+
+      record_voperand_set (dse_gd->stores, &bd->stores, gimple_uid (stmt));
+    }
+}
+
+/* Record that we have seen the PHIs at the start of BB which correspond
+   to virtual operands.  */
+static void
+dse_record_phis (struct dom_walk_data *walk_data, basic_block bb)
+{
+  struct dse_block_local_data *bd
+    = (struct dse_block_local_data *)
+	VEC_last (void_p, walk_data->block_data_stack);
+  struct dse_global_data *dse_gd
+    = (struct dse_global_data *) walk_data->global_data;
+  gimple phi;
+  gimple_stmt_iterator gsi;
+
+  for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+    {
+      phi = gsi_stmt (gsi);
+      if (!is_gimple_reg (gimple_phi_result (phi)))
+	record_voperand_set (dse_gd->stores, &bd->stores, get_stmt_uid (phi));
+    }
+}
+
+static void
+dse_finalize_block (struct dom_walk_data *walk_data,
+		    basic_block bb ATTRIBUTE_UNUSED)
+{
+  struct dse_block_local_data *bd
+    = (struct dse_block_local_data *)
+	VEC_last (void_p, walk_data->block_data_stack);
+  struct dse_global_data *dse_gd
+    = (struct dse_global_data *) walk_data->global_data;
+  bitmap stores = dse_gd->stores;
+  unsigned int i;
+  bitmap_iterator bi;
+
+  /* Unwind the stores noted in this basic block.  */
+  if (bd->stores)
+    EXECUTE_IF_SET_IN_BITMAP (bd->stores, 0, i, bi)
+      {
+	bitmap_clear_bit (stores, i);
+      }
+}
+
+/* Main entry point.  */
+
+static unsigned int
+tree_ssa_dse (void)
+{
+  struct dom_walk_data walk_data;
+  struct dse_global_data dse_gd;
+
+  renumber_gimple_stmt_uids ();
+
+  /* We might consider making this a property of each pass so that it
+     can be [re]computed on an as-needed basis.  Particularly since
+     this pass could be seen as an extension of DCE which needs post
+     dominators.  */
+  calculate_dominance_info (CDI_POST_DOMINATORS);
+
+  /* Dead store elimination is fundamentally a walk of the post-dominator
+     tree and a backwards walk of statements within each block.  */
+  walk_data.walk_stmts_backward = true;
+  walk_data.dom_direction = CDI_POST_DOMINATORS;
+  walk_data.initialize_block_local_data = dse_initialize_block_local_data;
+  walk_data.before_dom_children_before_stmts = NULL;
+  walk_data.before_dom_children_walk_stmts = dse_optimize_stmt;
+  walk_data.before_dom_children_after_stmts = dse_record_phis;
+  walk_data.after_dom_children_before_stmts = NULL;
+  walk_data.after_dom_children_walk_stmts = NULL;
+  walk_data.after_dom_children_after_stmts = dse_finalize_block;
+  walk_data.interesting_blocks = NULL;
+
+  walk_data.block_local_data_size = sizeof (struct dse_block_local_data);
+
+  /* This is the main hash table for the dead store elimination pass.  */
+  dse_gd.stores = BITMAP_ALLOC (NULL);
+  walk_data.global_data = &dse_gd;
+
+  /* Initialize the dominator walker.  */
+  init_walk_dominator_tree (&walk_data);
+
+  /* Recursively walk the dominator tree.  */
+  walk_dominator_tree (&walk_data, EXIT_BLOCK_PTR);
+
+  /* Finalize the dominator walker.  */
+  fini_walk_dominator_tree (&walk_data);
+
+  /* Release the main bitmap.  */
+  BITMAP_FREE (dse_gd.stores);
+
+  /* For now, just wipe the post-dominator information.  */
+  free_dominance_info (CDI_POST_DOMINATORS);
+  return 0;
+}
+
+static bool
+gate_dse (void)
+{
+  return flag_tree_dse != 0;
+}
+
+struct gimple_opt_pass pass_dse = 
+{
+ {
+  GIMPLE_PASS,
+  "dse",			/* name */
+  gate_dse,			/* gate */
+  tree_ssa_dse,			/* execute */
+  NULL,				/* sub */
+  NULL,				/* next */
+  0,				/* static_pass_number */
+  TV_TREE_DSE,			/* tv_id */
+  PROP_cfg
+    | PROP_ssa
+    | PROP_alias,		/* properties_required */
+  0,				/* properties_provided */
+  0,				/* properties_destroyed */
+  0,				/* todo_flags_start */
+  TODO_dump_func
+    | TODO_ggc_collect
+    | TODO_verify_ssa		/* todo_flags_finish */
+ }
+};
+
+/* A very simple dead store pass eliminating write only local variables.
+   The pass does not require alias information and thus can be run before
+   inlining to quickly eliminate artifacts of some common C++ constructs.  */
+
+static unsigned int
+execute_simple_dse (void)
+{
+  gimple_stmt_iterator gsi;
+  basic_block bb;
+  bitmap variables_loaded = BITMAP_ALLOC (NULL);
+  unsigned int todo = 0;
+
+  /* Collect into VARIABLES LOADED all variables that are read in function
+     body.  */
+  FOR_EACH_BB (bb)
+    for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+
+      if (gimple_loaded_syms (gsi_stmt (gsi)))
+	bitmap_ior_into (variables_loaded,
+			 gimple_loaded_syms (gsi_stmt (gsi)));
+
+  /* Look for statements writing into the write only variables.
+     And try to remove them.  */
+
+  FOR_EACH_BB (bb)
+    for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi);)
+      {
+	gimple stmt = gsi_stmt (gsi);
+        tree op;
+	bool removed = false;
+        ssa_op_iter iter;
+	tree size;
+
+	if (is_gimple_assign (stmt)
+	    && AGGREGATE_TYPE_P (TREE_TYPE (gimple_assign_lhs (stmt)))
+	    && (size = lang_hooks.expr_size (gimple_assign_lhs (stmt)))
+	    && integer_zerop (size))
+	  {
+	    if (dump_file && (dump_flags & TDF_DETAILS))
+	      {
+		fprintf (dump_file, "  Deleted zero-sized store '");
+		print_gimple_stmt (dump_file, stmt, 0, dump_flags);
+		fprintf (dump_file, "'\n");
+	      }
+	    removed = true;
+	    gsi_remove (&gsi, true);
+	    todo |= TODO_cleanup_cfg;
+	  }
+	else if (gimple_stored_syms (stmt)
+		 && !bitmap_empty_p (gimple_stored_syms (stmt))
+		 && (is_gimple_assign (stmt)
+		     || (is_gimple_call (stmt)
+			 && gimple_call_lhs (stmt)))
+		 && !bitmap_intersect_p (gimple_stored_syms (stmt),
+					 variables_loaded))
+	  {
+	    unsigned int i;
+	    bitmap_iterator bi;
+	    bool dead = true;
+
+	    /* See if STMT only stores to write-only variables and
+	       verify that there are no volatile operands.  tree-ssa-operands
+	       sets has_volatile_ops flag for all statements involving
+	       reads and writes when aliases are not built to prevent passes
+	       from removing them as dead.  The flag thus has no use for us
+	       and we need to look into all operands.  */
+	      
+	    EXECUTE_IF_SET_IN_BITMAP (gimple_stored_syms (stmt), 0, i, bi)
+	      {
+		tree var = referenced_var_lookup (i);
+		if (TREE_ADDRESSABLE (var)
+		    || is_global_var (var)
+		    || TREE_THIS_VOLATILE (var))
+		  dead = false;
+	      }
+
+	    if (dead && gimple_loaded_syms (stmt))
+	      EXECUTE_IF_SET_IN_BITMAP (gimple_loaded_syms (stmt), 0, i, bi)
+		if (TREE_THIS_VOLATILE (referenced_var_lookup (i)))
+		  dead = false;
+
+	    if (dead)
+	      FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_ALL_OPERANDS)
+		if (TREE_THIS_VOLATILE (op))
+		  dead = false;
+
+	    /* Look for possible occurrence var = indirect_ref (...) where
+	       indirect_ref itself is volatile.  */
+
+	    if (dead && is_gimple_assign (stmt)
+	        && TREE_THIS_VOLATILE (gimple_assign_rhs1 (stmt)))
+	      dead = false;
+
+	    if (dead)
+	      {
+		/* When LHS of var = call (); is dead, simplify it into
+		   call (); saving one operand.  */
+                if (is_gimple_call (stmt)
+                    && gimple_has_side_effects (stmt))
+		  {
+		    if (dump_file && (dump_flags & TDF_DETAILS))
+		      {
+			fprintf (dump_file, "Deleted LHS of call: ");
+			print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+			fprintf (dump_file, "\n");
+		      }
+		    push_stmt_changes (gsi_stmt_ptr (&gsi));
+                    gimple_call_set_lhs (stmt, NULL);
+		    pop_stmt_changes (gsi_stmt_ptr (&gsi));
+		  }
+		else
+		  {
+		    if (dump_file && (dump_flags & TDF_DETAILS))
+		      {
+			fprintf (dump_file, "  Deleted dead store '");
+			print_gimple_stmt (dump_file, stmt, 0, dump_flags);
+			fprintf (dump_file, "'\n");
+		      }
+		    removed = true;
+		    gsi_remove (&gsi, true);
+		    todo |= TODO_cleanup_cfg;
+		  }
+		todo |= TODO_remove_unused_locals | TODO_ggc_collect;
+	      }
+	  }
+	if (!removed)
+	  gsi_next (&gsi);
+      }
+  BITMAP_FREE (variables_loaded);
+  return todo;
+}
+
+struct gimple_opt_pass pass_simple_dse =
+{
+ {
+  GIMPLE_PASS,
+  "sdse",				/* name */
+  NULL,					/* gate */
+  execute_simple_dse,			/* execute */
+  NULL,					/* sub */
+  NULL,					/* next */
+  0,					/* static_pass_number */
+  0,					/* tv_id */
+  PROP_ssa,				/* properties_required */
+  0,					/* properties_provided */
+  0,					/* properties_destroyed */
+  0,					/* todo_flags_start */
+  TODO_dump_func          	        /* todo_flags_finish */
+ }
+};