GCC 4.2.0 release.

1 files changed, 2531 insertions, 0 deletions

diff --git a/contrib/gcc/tree-ssa-dom.c b/contrib/gcc/tree-ssa-dom.c
new file mode 100644
index 000000000000..88f7399edefb
--- /dev/null
+++ b/contrib/gcc/tree-ssa-dom.c
@@ -0,0 +1,2531 @@
+/* SSA Dominator optimizations for trees
+   Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006
+   Free Software Foundation, Inc.
+   Contributed by Diego Novillo <dnovillo@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, 51 Franklin Street, Fifth Floor,
+Boston, MA 02110-1301, USA.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "tree.h"
+#include "flags.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "ggc.h"
+#include "basic-block.h"
+#include "cfgloop.h"
+#include "output.h"
+#include "expr.h"
+#include "function.h"
+#include "diagnostic.h"
+#include "timevar.h"
+#include "tree-dump.h"
+#include "tree-flow.h"
+#include "domwalk.h"
+#include "real.h"
+#include "tree-pass.h"
+#include "tree-ssa-propagate.h"
+#include "langhooks.h"
+#include "params.h"
+
+/* This file implements optimizations on the dominator tree.  */
+
+
+/* Structure for recording edge equivalences as well as any pending
+   edge redirections during the dominator optimizer.
+
+   Computing and storing the edge equivalences instead of creating
+   them on-demand can save significant amounts of time, particularly
+   for pathological cases involving switch statements.  
+
+   These structures live for a single iteration of the dominator
+   optimizer in the edge's AUX field.  At the end of an iteration we
+   free each of these structures and update the AUX field to point
+   to any requested redirection target (the code for updating the
+   CFG and SSA graph for edge redirection expects redirection edge
+   targets to be in the AUX field for each edge.  */
+
+struct edge_info
+{
+  /* If this edge creates a simple equivalence, the LHS and RHS of
+     the equivalence will be stored here.  */
+  tree lhs;
+  tree rhs;
+
+  /* Traversing an edge may also indicate one or more particular conditions
+     are true or false.  The number of recorded conditions can vary, but
+     can be determined by the condition's code.  So we have an array
+     and its maximum index rather than use a varray.  */
+  tree *cond_equivalences;
+  unsigned int max_cond_equivalences;
+};
+
+
+/* Hash table with expressions made available during the renaming process.
+   When an assignment of the form X_i = EXPR is found, the statement is
+   stored in this table.  If the same expression EXPR is later found on the
+   RHS of another statement, it is replaced with X_i (thus performing
+   global redundancy elimination).  Similarly as we pass through conditionals
+   we record the conditional itself as having either a true or false value
+   in this table.  */
+static htab_t avail_exprs;
+
+/* Stack of available expressions in AVAIL_EXPRs.  Each block pushes any
+   expressions it enters into the hash table along with a marker entry
+   (null).  When we finish processing the block, we pop off entries and
+   remove the expressions from the global hash table until we hit the
+   marker.  */
+static VEC(tree,heap) *avail_exprs_stack;
+
+/* Stack of statements we need to rescan during finalization for newly
+   exposed variables.
+
+   Statement rescanning must occur after the current block's available
+   expressions are removed from AVAIL_EXPRS.  Else we may change the
+   hash code for an expression and be unable to find/remove it from
+   AVAIL_EXPRS.  */
+static VEC(tree,heap) *stmts_to_rescan;
+
+/* Structure for entries in the expression hash table.
+
+   This requires more memory for the hash table entries, but allows us
+   to avoid creating silly tree nodes and annotations for conditionals,
+   eliminates 2 global hash tables and two block local varrays.
+   
+   It also allows us to reduce the number of hash table lookups we
+   have to perform in lookup_avail_expr and finally it allows us to
+   significantly reduce the number of calls into the hashing routine
+   itself.  */
+
+struct expr_hash_elt
+{
+  /* The value (lhs) of this expression.  */
+  tree lhs;
+
+  /* The expression (rhs) we want to record.  */
+  tree rhs;
+
+  /* The stmt pointer if this element corresponds to a statement.  */
+  tree stmt;
+
+  /* The hash value for RHS/ann.  */
+  hashval_t hash;
+};
+
+/* Stack of dest,src pairs that need to be restored during finalization.
+
+   A NULL entry is used to mark the end of pairs which need to be
+   restored during finalization of this block.  */
+static VEC(tree,heap) *const_and_copies_stack;
+
+/* Track whether or not we have changed the control flow graph.  */
+static bool cfg_altered;
+
+/* Bitmap of blocks that have had EH statements cleaned.  We should
+   remove their dead edges eventually.  */
+static bitmap need_eh_cleanup;
+
+/* Statistics for dominator optimizations.  */
+struct opt_stats_d
+{
+  long num_stmts;
+  long num_exprs_considered;
+  long num_re;
+  long num_const_prop;
+  long num_copy_prop;
+};
+
+static struct opt_stats_d opt_stats;
+
+struct eq_expr_value
+{
+  tree src;
+  tree dst;
+};
+
+/* Local functions.  */
+static void optimize_stmt (struct dom_walk_data *, 
+			   basic_block bb,
+			   block_stmt_iterator);
+static tree lookup_avail_expr (tree, bool);
+static hashval_t avail_expr_hash (const void *);
+static hashval_t real_avail_expr_hash (const void *);
+static int avail_expr_eq (const void *, const void *);
+static void htab_statistics (FILE *, htab_t);
+static void record_cond (tree, tree);
+static void record_const_or_copy (tree, tree);
+static void record_equality (tree, tree);
+static void record_equivalences_from_phis (basic_block);
+static void record_equivalences_from_incoming_edge (basic_block);
+static bool eliminate_redundant_computations (tree);
+static void record_equivalences_from_stmt (tree, int, stmt_ann_t);
+static void dom_thread_across_edge (struct dom_walk_data *, edge);
+static void dom_opt_finalize_block (struct dom_walk_data *, basic_block);
+static void dom_opt_initialize_block (struct dom_walk_data *, basic_block);
+static void propagate_to_outgoing_edges (struct dom_walk_data *, basic_block);
+static void remove_local_expressions_from_table (void);
+static void restore_vars_to_original_value (void);
+static edge single_incoming_edge_ignoring_loop_edges (basic_block);
+
+
+/* Allocate an EDGE_INFO for edge E and attach it to E.
+   Return the new EDGE_INFO structure.  */
+
+static struct edge_info *
+allocate_edge_info (edge e)
+{
+  struct edge_info *edge_info;
+
+  edge_info = XCNEW (struct edge_info);
+
+  e->aux = edge_info;
+  return edge_info;
+}
+
+/* Free all EDGE_INFO structures associated with edges in the CFG.
+   If a particular edge can be threaded, copy the redirection
+   target from the EDGE_INFO structure into the edge's AUX field
+   as required by code to update the CFG and SSA graph for
+   jump threading.  */
+
+static void
+free_all_edge_infos (void)
+{
+  basic_block bb;
+  edge_iterator ei;
+  edge e;
+
+  FOR_EACH_BB (bb)
+    {
+      FOR_EACH_EDGE (e, ei, bb->preds)
+        {
+	 struct edge_info *edge_info = (struct edge_info *) e->aux;
+
+	  if (edge_info)
+	    {
+	      if (edge_info->cond_equivalences)
+		free (edge_info->cond_equivalences);
+	      free (edge_info);
+	      e->aux = NULL;
+	    }
+	}
+    }
+}
+
+/* Jump threading, redundancy elimination and const/copy propagation. 
+
+   This pass may expose new symbols that need to be renamed into SSA.  For
+   every new symbol exposed, its corresponding bit will be set in
+   VARS_TO_RENAME.  */
+
+static unsigned int
+tree_ssa_dominator_optimize (void)
+{
+  struct dom_walk_data walk_data;
+  unsigned int i;
+  struct loops loops_info;
+
+  memset (&opt_stats, 0, sizeof (opt_stats));
+
+  /* Create our hash tables.  */
+  avail_exprs = htab_create (1024, real_avail_expr_hash, avail_expr_eq, free);
+  avail_exprs_stack = VEC_alloc (tree, heap, 20);
+  const_and_copies_stack = VEC_alloc (tree, heap, 20);
+  stmts_to_rescan = VEC_alloc (tree, heap, 20);
+  need_eh_cleanup = BITMAP_ALLOC (NULL);
+
+  /* Setup callbacks for the generic dominator tree walker.  */
+  walk_data.walk_stmts_backward = false;
+  walk_data.dom_direction = CDI_DOMINATORS;
+  walk_data.initialize_block_local_data = NULL;
+  walk_data.before_dom_children_before_stmts = dom_opt_initialize_block;
+  walk_data.before_dom_children_walk_stmts = optimize_stmt;
+  walk_data.before_dom_children_after_stmts = propagate_to_outgoing_edges;
+  walk_data.after_dom_children_before_stmts = NULL;
+  walk_data.after_dom_children_walk_stmts = NULL;
+  walk_data.after_dom_children_after_stmts = dom_opt_finalize_block;
+  /* Right now we only attach a dummy COND_EXPR to the global data pointer.
+     When we attach more stuff we'll need to fill this out with a real
+     structure.  */
+  walk_data.global_data = NULL;
+  walk_data.block_local_data_size = 0;
+  walk_data.interesting_blocks = NULL;
+
+  /* Now initialize the dominator walker.  */
+  init_walk_dominator_tree (&walk_data);
+
+  calculate_dominance_info (CDI_DOMINATORS);
+
+  /* We need to know which edges exit loops so that we can
+     aggressively thread through loop headers to an exit
+     edge.  */
+  flow_loops_find (&loops_info);
+  mark_loop_exit_edges (&loops_info);
+  flow_loops_free (&loops_info);
+
+  /* Clean up the CFG so that any forwarder blocks created by loop
+     canonicalization are removed.  */
+  cleanup_tree_cfg ();
+  calculate_dominance_info (CDI_DOMINATORS);
+
+  /* We need accurate information regarding back edges in the CFG
+     for jump threading.  */
+  mark_dfs_back_edges ();
+
+  /* Recursively walk the dominator tree optimizing statements.  */
+  walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR);
+
+  {
+    block_stmt_iterator bsi;
+    basic_block bb;
+    FOR_EACH_BB (bb)
+      {
+	for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
+	  update_stmt_if_modified (bsi_stmt (bsi));
+      }
+  }
+
+  /* If we exposed any new variables, go ahead and put them into
+     SSA form now, before we handle jump threading.  This simplifies
+     interactions between rewriting of _DECL nodes into SSA form
+     and rewriting SSA_NAME nodes into SSA form after block
+     duplication and CFG manipulation.  */
+  update_ssa (TODO_update_ssa);
+
+  free_all_edge_infos ();
+
+  /* Thread jumps, creating duplicate blocks as needed.  */
+  cfg_altered |= thread_through_all_blocks ();
+
+  /* Removal of statements may make some EH edges dead.  Purge
+     such edges from the CFG as needed.  */
+  if (!bitmap_empty_p (need_eh_cleanup))
+    {
+      cfg_altered |= tree_purge_all_dead_eh_edges (need_eh_cleanup);
+      bitmap_zero (need_eh_cleanup);
+    }
+
+  if (cfg_altered)
+    free_dominance_info (CDI_DOMINATORS);
+
+  /* Finally, remove everything except invariants in SSA_NAME_VALUE.
+
+     Long term we will be able to let everything in SSA_NAME_VALUE
+     persist.  However, for now, we know this is the safe thing to do.  */
+  for (i = 0; i < num_ssa_names; i++)
+   {
+      tree name = ssa_name (i);
+      tree value;
+
+      if (!name)
+        continue;
+
+      value = SSA_NAME_VALUE (name);
+      if (value && !is_gimple_min_invariant (value))
+	SSA_NAME_VALUE (name) = NULL;
+    }
+
+  /* Debugging dumps.  */
+  if (dump_file && (dump_flags & TDF_STATS))
+    dump_dominator_optimization_stats (dump_file);
+
+  /* Delete our main hashtable.  */
+  htab_delete (avail_exprs);
+
+  /* And finalize the dominator walker.  */
+  fini_walk_dominator_tree (&walk_data);
+
+  /* Free asserted bitmaps and stacks.  */
+  BITMAP_FREE (need_eh_cleanup);
+  
+  VEC_free (tree, heap, avail_exprs_stack);
+  VEC_free (tree, heap, const_and_copies_stack);
+  VEC_free (tree, heap, stmts_to_rescan);
+  return 0;
+}
+
+static bool
+gate_dominator (void)
+{
+  return flag_tree_dom != 0;
+}
+
+struct tree_opt_pass pass_dominator = 
+{
+  "dom",				/* name */
+  gate_dominator,			/* gate */
+  tree_ssa_dominator_optimize,		/* execute */
+  NULL,					/* sub */
+  NULL,					/* next */
+  0,					/* static_pass_number */
+  TV_TREE_SSA_DOMINATOR_OPTS,		/* tv_id */
+  PROP_cfg | PROP_ssa | PROP_alias,	/* properties_required */
+  0,					/* properties_provided */
+  PROP_smt_usage,			/* properties_destroyed */
+  0,					/* todo_flags_start */
+  TODO_dump_func
+    | TODO_update_ssa
+    | TODO_cleanup_cfg
+    | TODO_verify_ssa	
+    | TODO_update_smt_usage,		/* todo_flags_finish */
+  0					/* letter */
+};
+
+
+/* Given a stmt CONDSTMT containing a COND_EXPR, canonicalize the
+   COND_EXPR into a canonical form.  */
+
+static void
+canonicalize_comparison (tree condstmt)
+{
+  tree cond = COND_EXPR_COND (condstmt);
+  tree op0;
+  tree op1;
+  enum tree_code code = TREE_CODE (cond);
+
+  if (!COMPARISON_CLASS_P (cond))
+    return;
+
+  op0 = TREE_OPERAND (cond, 0);
+  op1 = TREE_OPERAND (cond, 1);
+
+  /* If it would be profitable to swap the operands, then do so to
+     canonicalize the statement, enabling better optimization.
+
+     By placing canonicalization of such expressions here we
+     transparently keep statements in canonical form, even
+     when the statement is modified.  */
+  if (tree_swap_operands_p (op0, op1, false))
+    {
+      /* For relationals we need to swap the operands
+	 and change the code.  */
+      if (code == LT_EXPR
+	  || code == GT_EXPR
+	  || code == LE_EXPR
+	  || code == GE_EXPR)
+	{
+	  TREE_SET_CODE (cond, swap_tree_comparison (code));
+	  swap_tree_operands (condstmt,
+			      &TREE_OPERAND (cond, 0),
+			      &TREE_OPERAND (cond, 1));
+	  /* If one operand was in the operand cache, but the other is
+	     not, because it is a constant, this is a case that the
+	     internal updating code of swap_tree_operands can't handle
+	     properly.  */
+	  if (TREE_CODE_CLASS (TREE_CODE (op0)) 
+	      != TREE_CODE_CLASS (TREE_CODE (op1)))
+	    update_stmt (condstmt);
+	}
+    }
+}
+
+/* Initialize local stacks for this optimizer and record equivalences
+   upon entry to BB.  Equivalences can come from the edge traversed to
+   reach BB or they may come from PHI nodes at the start of BB.  */
+
+static void
+dom_opt_initialize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+			  basic_block bb)
+{
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    fprintf (dump_file, "\n\nOptimizing block #%d\n\n", bb->index);
+
+  /* Push a marker on the stacks of local information so that we know how
+     far to unwind when we finalize this block.  */
+  VEC_safe_push (tree, heap, avail_exprs_stack, NULL_TREE);
+  VEC_safe_push (tree, heap, const_and_copies_stack, NULL_TREE);
+
+  record_equivalences_from_incoming_edge (bb);
+
+  /* PHI nodes can create equivalences too.  */
+  record_equivalences_from_phis (bb);
+}
+
+/* Given an expression EXPR (a relational expression or a statement), 
+   initialize the hash table element pointed to by ELEMENT.  */
+
+static void
+initialize_hash_element (tree expr, tree lhs, struct expr_hash_elt *element)
+{
+  /* Hash table elements may be based on conditional expressions or statements.
+
+     For the former case, we have no annotation and we want to hash the
+     conditional expression.  In the latter case we have an annotation and
+     we want to record the expression the statement evaluates.  */
+  if (COMPARISON_CLASS_P (expr) || TREE_CODE (expr) == TRUTH_NOT_EXPR)
+    {
+      element->stmt = NULL;
+      element->rhs = expr;
+    }
+  else if (TREE_CODE (expr) == COND_EXPR)
+    {
+      element->stmt = expr;
+      element->rhs = COND_EXPR_COND (expr);
+    }
+  else if (TREE_CODE (expr) == SWITCH_EXPR)
+    {
+      element->stmt = expr;
+      element->rhs = SWITCH_COND (expr);
+    }
+  else if (TREE_CODE (expr) == RETURN_EXPR && TREE_OPERAND (expr, 0))
+    {
+      element->stmt = expr;
+      element->rhs = TREE_OPERAND (TREE_OPERAND (expr, 0), 1);
+    }
+  else if (TREE_CODE (expr) == GOTO_EXPR)
+    {
+      element->stmt = expr;
+      element->rhs = GOTO_DESTINATION (expr);
+    }
+  else
+    {
+      element->stmt = expr;
+      element->rhs = TREE_OPERAND (expr, 1);
+    }
+
+  element->lhs = lhs;
+  element->hash = avail_expr_hash (element);
+}
+
+/* Remove all the expressions in LOCALS from TABLE, stopping when there are
+   LIMIT entries left in LOCALs.  */
+
+static void
+remove_local_expressions_from_table (void)
+{
+  /* Remove all the expressions made available in this block.  */
+  while (VEC_length (tree, avail_exprs_stack) > 0)
+    {
+      struct expr_hash_elt element;
+      tree expr = VEC_pop (tree, avail_exprs_stack);
+
+      if (expr == NULL_TREE)
+	break;
+
+      initialize_hash_element (expr, NULL, &element);
+      htab_remove_elt_with_hash (avail_exprs, &element, element.hash);
+    }
+}
+
+/* Use the source/dest pairs in CONST_AND_COPIES_STACK to restore
+   CONST_AND_COPIES to its original state, stopping when we hit a
+   NULL marker.  */
+
+static void
+restore_vars_to_original_value (void)
+{
+  while (VEC_length (tree, const_and_copies_stack) > 0)
+    {
+      tree prev_value, dest;
+
+      dest = VEC_pop (tree, const_and_copies_stack);
+
+      if (dest == NULL)
+	break;
+
+      prev_value = VEC_pop (tree, const_and_copies_stack);
+      SSA_NAME_VALUE (dest) =  prev_value;
+    }
+}
+
+/* A trivial wrapper so that we can present the generic jump
+   threading code with a simple API for simplifying statements.  */
+static tree
+simplify_stmt_for_jump_threading (tree stmt, tree within_stmt ATTRIBUTE_UNUSED)
+{
+  return lookup_avail_expr (stmt, false);
+}
+
+/* Wrapper for common code to attempt to thread an edge.  For example,
+   it handles lazily building the dummy condition and the bookkeeping
+   when jump threading is successful.  */
+
+static void
+dom_thread_across_edge (struct dom_walk_data *walk_data, edge e)
+{
+  /* If we don't already have a dummy condition, build it now.  */
+  if (! walk_data->global_data)
+    {
+      tree dummy_cond = build2 (NE_EXPR, boolean_type_node,
+			        integer_zero_node, integer_zero_node);
+      dummy_cond = build3 (COND_EXPR, void_type_node, dummy_cond, NULL, NULL);
+      walk_data->global_data = dummy_cond;
+    }
+
+  thread_across_edge (walk_data->global_data, e, false,
+		      &const_and_copies_stack,
+		      simplify_stmt_for_jump_threading);
+}
+
+/* We have finished processing the dominator children of BB, perform
+   any finalization actions in preparation for leaving this node in
+   the dominator tree.  */
+
+static void
+dom_opt_finalize_block (struct dom_walk_data *walk_data, basic_block bb)
+{
+  tree last;
+
+
+  /* If we have an outgoing edge to a block with multiple incoming and
+     outgoing edges, then we may be able to thread the edge.  ie, we
+     may be able to statically determine which of the outgoing edges
+     will be traversed when the incoming edge from BB is traversed.  */
+  if (single_succ_p (bb)
+      && (single_succ_edge (bb)->flags & EDGE_ABNORMAL) == 0
+      && potentially_threadable_block (single_succ (bb)))
+    {
+      dom_thread_across_edge (walk_data, single_succ_edge (bb));
+    }
+  else if ((last = last_stmt (bb))
+	   && TREE_CODE (last) == COND_EXPR
+	   && (COMPARISON_CLASS_P (COND_EXPR_COND (last))
+	       || TREE_CODE (COND_EXPR_COND (last)) == SSA_NAME)
+	   && EDGE_COUNT (bb->succs) == 2
+	   && (EDGE_SUCC (bb, 0)->flags & EDGE_ABNORMAL) == 0
+	   && (EDGE_SUCC (bb, 1)->flags & EDGE_ABNORMAL) == 0)
+    {
+      edge true_edge, false_edge;
+
+      extract_true_false_edges_from_block (bb, &true_edge, &false_edge);
+
+      /* Only try to thread the edge if it reaches a target block with
+	 more than one predecessor and more than one successor.  */
+      if (potentially_threadable_block (true_edge->dest))
+	{
+	  struct edge_info *edge_info;
+	  unsigned int i;
+
+	  /* Push a marker onto the available expression stack so that we
+	     unwind any expressions related to the TRUE arm before processing
+	     the false arm below.  */
+	  VEC_safe_push (tree, heap, avail_exprs_stack, NULL_TREE);
+	  VEC_safe_push (tree, heap, const_and_copies_stack, NULL_TREE);
+
+	  edge_info = (struct edge_info *) true_edge->aux;
+
+	  /* If we have info associated with this edge, record it into
+	     our equivalency tables.  */
+	  if (edge_info)
+	    {
+	      tree *cond_equivalences = edge_info->cond_equivalences;
+	      tree lhs = edge_info->lhs;
+	      tree rhs = edge_info->rhs;
+
+	      /* If we have a simple NAME = VALUE equivalency record it.  */
+	      if (lhs && TREE_CODE (lhs) == SSA_NAME)
+		record_const_or_copy (lhs, rhs);
+
+	      /* If we have 0 = COND or 1 = COND equivalences, record them
+		 into our expression hash tables.  */
+	      if (cond_equivalences)
+		for (i = 0; i < edge_info->max_cond_equivalences; i += 2)
+		  {
+		    tree expr = cond_equivalences[i];
+		    tree value = cond_equivalences[i + 1];
+
+		    record_cond (expr, value);
+		  }
+	    }
+
+	  dom_thread_across_edge (walk_data, true_edge);
+
+	  /* And restore the various tables to their state before
+	     we threaded this edge.  */
+	  remove_local_expressions_from_table ();
+	}
+
+      /* Similarly for the ELSE arm.  */
+      if (potentially_threadable_block (false_edge->dest))
+	{
+	  struct edge_info *edge_info;
+	  unsigned int i;
+
+	  VEC_safe_push (tree, heap, const_and_copies_stack, NULL_TREE);
+	  edge_info = (struct edge_info *) false_edge->aux;
+
+	  /* If we have info associated with this edge, record it into
+	     our equivalency tables.  */
+	  if (edge_info)
+	    {
+	      tree *cond_equivalences = edge_info->cond_equivalences;
+	      tree lhs = edge_info->lhs;
+	      tree rhs = edge_info->rhs;
+
+	      /* If we have a simple NAME = VALUE equivalency record it.  */
+	      if (lhs && TREE_CODE (lhs) == SSA_NAME)
+		record_const_or_copy (lhs, rhs);
+
+	      /* If we have 0 = COND or 1 = COND equivalences, record them
+		 into our expression hash tables.  */
+	      if (cond_equivalences)
+		for (i = 0; i < edge_info->max_cond_equivalences; i += 2)
+		  {
+		    tree expr = cond_equivalences[i];
+		    tree value = cond_equivalences[i + 1];
+
+		    record_cond (expr, value);
+		  }
+	    }
+
+	  /* Now thread the edge.  */
+	  dom_thread_across_edge (walk_data, false_edge);
+
+	  /* No need to remove local expressions from our tables
+	     or restore vars to their original value as that will
+	     be done immediately below.  */
+	}
+    }
+
+  remove_local_expressions_from_table ();
+  restore_vars_to_original_value ();
+
+  /* If we queued any statements to rescan in this block, then
+     go ahead and rescan them now.  */
+  while (VEC_length (tree, stmts_to_rescan) > 0)
+    {
+      tree stmt = VEC_last (tree, stmts_to_rescan);
+      basic_block stmt_bb = bb_for_stmt (stmt);
+
+      if (stmt_bb != bb)
+	break;
+
+      VEC_pop (tree, stmts_to_rescan);
+      mark_new_vars_to_rename (stmt);
+    }
+}
+
+/* PHI nodes can create equivalences too.
+
+   Ignoring any alternatives which are the same as the result, if
+   all the alternatives are equal, then the PHI node creates an
+   equivalence.  */
+
+static void
+record_equivalences_from_phis (basic_block bb)
+{
+  tree phi;
+
+  for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
+    {
+      tree lhs = PHI_RESULT (phi);
+      tree rhs = NULL;
+      int i;
+
+      for (i = 0; i < PHI_NUM_ARGS (phi); i++)
+	{
+	  tree t = PHI_ARG_DEF (phi, i);
+
+	  /* Ignore alternatives which are the same as our LHS.  Since
+	     LHS is a PHI_RESULT, it is known to be a SSA_NAME, so we
+	     can simply compare pointers.  */
+	  if (lhs == t)
+	    continue;
+
+	  /* If we have not processed an alternative yet, then set
+	     RHS to this alternative.  */
+	  if (rhs == NULL)
+	    rhs = t;
+	  /* If we have processed an alternative (stored in RHS), then
+	     see if it is equal to this one.  If it isn't, then stop
+	     the search.  */
+	  else if (! operand_equal_for_phi_arg_p (rhs, t))
+	    break;
+	}
+
+      /* If we had no interesting alternatives, then all the RHS alternatives
+	 must have been the same as LHS.  */
+      if (!rhs)
+	rhs = lhs;
+
+      /* If we managed to iterate through each PHI alternative without
+	 breaking out of the loop, then we have a PHI which may create
+	 a useful equivalence.  We do not need to record unwind data for
+	 this, since this is a true assignment and not an equivalence
+	 inferred from a comparison.  All uses of this ssa name are dominated
+	 by this assignment, so unwinding just costs time and space.  */
+      if (i == PHI_NUM_ARGS (phi)
+	  && may_propagate_copy (lhs, rhs))
+	SSA_NAME_VALUE (lhs) = rhs;
+    }
+}
+
+/* Ignoring loop backedges, if BB has precisely one incoming edge then
+   return that edge.  Otherwise return NULL.  */
+static edge
+single_incoming_edge_ignoring_loop_edges (basic_block bb)
+{
+  edge retval = NULL;
+  edge e;
+  edge_iterator ei;
+
+  FOR_EACH_EDGE (e, ei, bb->preds)
+    {
+      /* A loop back edge can be identified by the destination of
+	 the edge dominating the source of the edge.  */
+      if (dominated_by_p (CDI_DOMINATORS, e->src, e->dest))
+	continue;
+
+      /* If we have already seen a non-loop edge, then we must have
+	 multiple incoming non-loop edges and thus we return NULL.  */
+      if (retval)
+	return NULL;
+
+      /* This is the first non-loop incoming edge we have found.  Record
+	 it.  */
+      retval = e;
+    }
+
+  return retval;
+}
+
+/* Record any equivalences created by the incoming edge to BB.  If BB
+   has more than one incoming edge, then no equivalence is created.  */
+
+static void
+record_equivalences_from_incoming_edge (basic_block bb)
+{
+  edge e;
+  basic_block parent;
+  struct edge_info *edge_info;
+
+  /* If our parent block ended with a control statement, then we may be
+     able to record some equivalences based on which outgoing edge from
+     the parent was followed.  */
+  parent = get_immediate_dominator (CDI_DOMINATORS, bb);
+
+  e = single_incoming_edge_ignoring_loop_edges (bb);
+
+  /* If we had a single incoming edge from our parent block, then enter
+     any data associated with the edge into our tables.  */
+  if (e && e->src == parent)
+    {
+      unsigned int i;
+
+      edge_info = (struct edge_info *) e->aux;
+
+      if (edge_info)
+	{
+	  tree lhs = edge_info->lhs;
+	  tree rhs = edge_info->rhs;
+	  tree *cond_equivalences = edge_info->cond_equivalences;
+
+	  if (lhs)
+	    record_equality (lhs, rhs);
+
+	  if (cond_equivalences)
+	    {
+	      for (i = 0; i < edge_info->max_cond_equivalences; i += 2)
+		{
+		  tree expr = cond_equivalences[i];
+		  tree value = cond_equivalences[i + 1];
+
+		  record_cond (expr, value);
+		}
+	    }
+	}
+    }
+}
+
+/* Dump SSA statistics on FILE.  */
+
+void
+dump_dominator_optimization_stats (FILE *file)
+{
+  long n_exprs;
+
+  fprintf (file, "Total number of statements:                   %6ld\n\n",
+	   opt_stats.num_stmts);
+  fprintf (file, "Exprs considered for dominator optimizations: %6ld\n",
+           opt_stats.num_exprs_considered);
+
+  n_exprs = opt_stats.num_exprs_considered;
+  if (n_exprs == 0)
+    n_exprs = 1;
+
+  fprintf (file, "    Redundant expressions eliminated:         %6ld (%.0f%%)\n",
+	   opt_stats.num_re, PERCENT (opt_stats.num_re,
+				      n_exprs));
+  fprintf (file, "    Constants propagated:                     %6ld\n",
+	   opt_stats.num_const_prop);
+  fprintf (file, "    Copies propagated:                        %6ld\n",
+	   opt_stats.num_copy_prop);
+
+  fprintf (file, "\nHash table statistics:\n");
+
+  fprintf (file, "    avail_exprs: ");
+  htab_statistics (file, avail_exprs);
+}
+
+
+/* Dump SSA statistics on stderr.  */
+
+void
+debug_dominator_optimization_stats (void)
+{
+  dump_dominator_optimization_stats (stderr);
+}
+
+
+/* Dump statistics for the hash table HTAB.  */
+
+static void
+htab_statistics (FILE *file, htab_t htab)
+{
+  fprintf (file, "size %ld, %ld elements, %f collision/search ratio\n",
+	   (long) htab_size (htab),
+	   (long) htab_elements (htab),
+	   htab_collisions (htab));
+}
+
+/* Enter a statement into the true/false expression hash table indicating
+   that the condition COND has the value VALUE.  */
+
+static void
+record_cond (tree cond, tree value)
+{
+  struct expr_hash_elt *element = XCNEW (struct expr_hash_elt);
+  void **slot;
+
+  initialize_hash_element (cond, value, element);
+
+  slot = htab_find_slot_with_hash (avail_exprs, (void *)element,
+				   element->hash, INSERT);
+  if (*slot == NULL)
+    {
+      *slot = (void *) element;
+      VEC_safe_push (tree, heap, avail_exprs_stack, cond);
+    }
+  else
+    free (element);
+}
+
+/* Build a new conditional using NEW_CODE, OP0 and OP1 and store
+   the new conditional into *p, then store a boolean_true_node
+   into *(p + 1).  */
+   
+static void
+build_and_record_new_cond (enum tree_code new_code, tree op0, tree op1, tree *p)
+{
+  *p = build2 (new_code, boolean_type_node, op0, op1);
+  p++;
+  *p = boolean_true_node;
+}
+
+/* Record that COND is true and INVERTED is false into the edge information
+   structure.  Also record that any conditions dominated by COND are true
+   as well.
+
+   For example, if a < b is true, then a <= b must also be true.  */
+
+static void
+record_conditions (struct edge_info *edge_info, tree cond, tree inverted)
+{
+  tree op0, op1;
+
+  if (!COMPARISON_CLASS_P (cond))
+    return;
+
+  op0 = TREE_OPERAND (cond, 0);
+  op1 = TREE_OPERAND (cond, 1);
+
+  switch (TREE_CODE (cond))
+    {
+    case LT_EXPR:
+    case GT_EXPR:
+      if (FLOAT_TYPE_P (TREE_TYPE (op0)))
+	{
+	  edge_info->max_cond_equivalences = 12;
+	  edge_info->cond_equivalences = XNEWVEC (tree, 12);
+	  build_and_record_new_cond (ORDERED_EXPR, op0, op1,
+				     &edge_info->cond_equivalences[8]);
+	  build_and_record_new_cond (LTGT_EXPR, op0, op1,
+				     &edge_info->cond_equivalences[10]);
+	}
+      else
+	{
+	  edge_info->max_cond_equivalences = 8;
+	  edge_info->cond_equivalences = XNEWVEC (tree, 8);
+	}
+
+      build_and_record_new_cond ((TREE_CODE (cond) == LT_EXPR
+				  ? LE_EXPR : GE_EXPR),
+				 op0, op1, &edge_info->cond_equivalences[4]);
+      build_and_record_new_cond (NE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[6]);
+      break;
+
+    case GE_EXPR:
+    case LE_EXPR:
+      if (FLOAT_TYPE_P (TREE_TYPE (op0)))
+	{
+	  edge_info->max_cond_equivalences = 6;
+	  edge_info->cond_equivalences = XNEWVEC (tree, 6);
+	  build_and_record_new_cond (ORDERED_EXPR, op0, op1,
+				     &edge_info->cond_equivalences[4]);
+	}
+      else
+	{
+	  edge_info->max_cond_equivalences = 4;
+	  edge_info->cond_equivalences = XNEWVEC (tree, 4);
+	}
+      break;
+
+    case EQ_EXPR:
+      if (FLOAT_TYPE_P (TREE_TYPE (op0)))
+	{
+	  edge_info->max_cond_equivalences = 10;
+	  edge_info->cond_equivalences = XNEWVEC (tree, 10);
+	  build_and_record_new_cond (ORDERED_EXPR, op0, op1,
+				     &edge_info->cond_equivalences[8]);
+	}
+      else
+	{
+	  edge_info->max_cond_equivalences = 8;
+	  edge_info->cond_equivalences = XNEWVEC (tree, 8);
+	}
+      build_and_record_new_cond (LE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[4]);
+      build_and_record_new_cond (GE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[6]);
+      break;
+
+    case UNORDERED_EXPR:
+      edge_info->max_cond_equivalences = 16;
+      edge_info->cond_equivalences = XNEWVEC (tree, 16);
+      build_and_record_new_cond (NE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[4]);
+      build_and_record_new_cond (UNLE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[6]);
+      build_and_record_new_cond (UNGE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[8]);
+      build_and_record_new_cond (UNEQ_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[10]);
+      build_and_record_new_cond (UNLT_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[12]);
+      build_and_record_new_cond (UNGT_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[14]);
+      break;
+
+    case UNLT_EXPR:
+    case UNGT_EXPR:
+      edge_info->max_cond_equivalences = 8;
+      edge_info->cond_equivalences = XNEWVEC (tree, 8);
+      build_and_record_new_cond ((TREE_CODE (cond) == UNLT_EXPR
+				  ? UNLE_EXPR : UNGE_EXPR),
+				 op0, op1, &edge_info->cond_equivalences[4]);
+      build_and_record_new_cond (NE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[6]);
+      break;
+
+    case UNEQ_EXPR:
+      edge_info->max_cond_equivalences = 8;
+      edge_info->cond_equivalences = XNEWVEC (tree, 8);
+      build_and_record_new_cond (UNLE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[4]);
+      build_and_record_new_cond (UNGE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[6]);
+      break;
+
+    case LTGT_EXPR:
+      edge_info->max_cond_equivalences = 8;
+      edge_info->cond_equivalences = XNEWVEC (tree, 8);
+      build_and_record_new_cond (NE_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[4]);
+      build_and_record_new_cond (ORDERED_EXPR, op0, op1,
+				 &edge_info->cond_equivalences[6]);
+      break;
+
+    default:
+      edge_info->max_cond_equivalences = 4;
+      edge_info->cond_equivalences = XNEWVEC (tree, 4);
+      break;
+    }
+
+  /* Now store the original true and false conditions into the first
+     two slots.  */
+  edge_info->cond_equivalences[0] = cond;
+  edge_info->cond_equivalences[1] = boolean_true_node;
+  edge_info->cond_equivalences[2] = inverted;
+  edge_info->cond_equivalences[3] = boolean_false_node;
+}
+
+/* A helper function for record_const_or_copy and record_equality.
+   Do the work of recording the value and undo info.  */
+
+static void
+record_const_or_copy_1 (tree x, tree y, tree prev_x)
+{
+  SSA_NAME_VALUE (x) = y;
+
+  VEC_reserve (tree, heap, const_and_copies_stack, 2);
+  VEC_quick_push (tree, const_and_copies_stack, prev_x);
+  VEC_quick_push (tree, const_and_copies_stack, x);
+}
+
+
+/* Return the loop depth of the basic block of the defining statement of X.
+   This number should not be treated as absolutely correct because the loop
+   information may not be completely up-to-date when dom runs.  However, it
+   will be relatively correct, and as more passes are taught to keep loop info
+   up to date, the result will become more and more accurate.  */
+
+int
+loop_depth_of_name (tree x)
+{
+  tree defstmt;
+  basic_block defbb;
+
+  /* If it's not an SSA_NAME, we have no clue where the definition is.  */
+  if (TREE_CODE (x) != SSA_NAME)
+    return 0;
+
+  /* Otherwise return the loop depth of the defining statement's bb.
+     Note that there may not actually be a bb for this statement, if the
+     ssa_name is live on entry.  */
+  defstmt = SSA_NAME_DEF_STMT (x);
+  defbb = bb_for_stmt (defstmt);
+  if (!defbb)
+    return 0;
+
+  return defbb->loop_depth;
+}
+
+
+/* Record that X is equal to Y in const_and_copies.  Record undo
+   information in the block-local vector.  */
+
+static void
+record_const_or_copy (tree x, tree y)
+{
+  tree prev_x = SSA_NAME_VALUE (x);
+
+  if (TREE_CODE (y) == SSA_NAME)
+    {
+      tree tmp = SSA_NAME_VALUE (y);
+      if (tmp)
+	y = tmp;
+    }
+
+  record_const_or_copy_1 (x, y, prev_x);
+}
+
+/* Similarly, but assume that X and Y are the two operands of an EQ_EXPR.
+   This constrains the cases in which we may treat this as assignment.  */
+
+static void
+record_equality (tree x, tree y)
+{
+  tree prev_x = NULL, prev_y = NULL;
+
+  if (TREE_CODE (x) == SSA_NAME)
+    prev_x = SSA_NAME_VALUE (x);
+  if (TREE_CODE (y) == SSA_NAME)
+    prev_y = SSA_NAME_VALUE (y);
+
+  /* If one of the previous values is invariant, or invariant in more loops
+     (by depth), then use that.
+     Otherwise it doesn't matter which value we choose, just so
+     long as we canonicalize on one value.  */
+  if (TREE_INVARIANT (y))
+    ;
+  else if (TREE_INVARIANT (x) || (loop_depth_of_name (x) <= loop_depth_of_name (y)))
+    prev_x = x, x = y, y = prev_x, prev_x = prev_y;
+  else if (prev_x && TREE_INVARIANT (prev_x))
+    x = y, y = prev_x, prev_x = prev_y;
+  else if (prev_y && TREE_CODE (prev_y) != VALUE_HANDLE)
+    y = prev_y;
+
+  /* After the swapping, we must have one SSA_NAME.  */
+  if (TREE_CODE (x) != SSA_NAME)
+    return;
+
+  /* For IEEE, -0.0 == 0.0, so we don't necessarily know the sign of a
+     variable compared against zero.  If we're honoring signed zeros,
+     then we cannot record this value unless we know that the value is
+     nonzero.  */
+  if (HONOR_SIGNED_ZEROS (TYPE_MODE (TREE_TYPE (x)))
+      && (TREE_CODE (y) != REAL_CST
+	  || REAL_VALUES_EQUAL (dconst0, TREE_REAL_CST (y))))
+    return;
+
+  record_const_or_copy_1 (x, y, prev_x);
+}
+
+/* Returns true when STMT is a simple iv increment.  It detects the
+   following situation:
+   
+   i_1 = phi (..., i_2)
+   i_2 = i_1 +/- ...  */
+
+static bool
+simple_iv_increment_p (tree stmt)
+{
+  tree lhs, rhs, preinc, phi;
+  unsigned i;
+
+  if (TREE_CODE (stmt) != MODIFY_EXPR)
+    return false;
+
+  lhs = TREE_OPERAND (stmt, 0);
+  if (TREE_CODE (lhs) != SSA_NAME)
+    return false;
+
+  rhs = TREE_OPERAND (stmt, 1);
+
+  if (TREE_CODE (rhs) != PLUS_EXPR
+      && TREE_CODE (rhs) != MINUS_EXPR)
+    return false;
+
+  preinc = TREE_OPERAND (rhs, 0);
+  if (TREE_CODE (preinc) != SSA_NAME)
+    return false;
+
+  phi = SSA_NAME_DEF_STMT (preinc);
+  if (TREE_CODE (phi) != PHI_NODE)
+    return false;
+
+  for (i = 0; i < (unsigned) PHI_NUM_ARGS (phi); i++)
+    if (PHI_ARG_DEF (phi, i) == lhs)
+      return true;
+
+  return false;
+}
+
+/* CONST_AND_COPIES is a table which maps an SSA_NAME to the current
+   known value for that SSA_NAME (or NULL if no value is known).  
+
+   Propagate values from CONST_AND_COPIES into the PHI nodes of the
+   successors of BB.  */
+
+static void
+cprop_into_successor_phis (basic_block bb)
+{
+  edge e;
+  edge_iterator ei;
+
+  FOR_EACH_EDGE (e, ei, bb->succs)
+    {
+      tree phi;
+      int indx;
+
+      /* If this is an abnormal edge, then we do not want to copy propagate
+	 into the PHI alternative associated with this edge.  */
+      if (e->flags & EDGE_ABNORMAL)
+	continue;
+
+      phi = phi_nodes (e->dest);
+      if (! phi)
+	continue;
+
+      indx = e->dest_idx;
+      for ( ; phi; phi = PHI_CHAIN (phi))
+	{
+	  tree new;
+	  use_operand_p orig_p;
+	  tree orig;
+
+	  /* The alternative may be associated with a constant, so verify
+	     it is an SSA_NAME before doing anything with it.  */
+	  orig_p = PHI_ARG_DEF_PTR (phi, indx);
+	  orig = USE_FROM_PTR (orig_p);
+	  if (TREE_CODE (orig) != SSA_NAME)
+	    continue;
+
+	  /* If we have *ORIG_P in our constant/copy table, then replace
+	     ORIG_P with its value in our constant/copy table.  */
+	  new = SSA_NAME_VALUE (orig);
+	  if (new
+	      && new != orig
+	      && (TREE_CODE (new) == SSA_NAME
+		  || is_gimple_min_invariant (new))
+	      && may_propagate_copy (orig, new))
+	    propagate_value (orig_p, new);
+	}
+    }
+}
+
+/* We have finished optimizing BB, record any information implied by
+   taking a specific outgoing edge from BB.  */
+
+static void
+record_edge_info (basic_block bb)
+{
+  block_stmt_iterator bsi = bsi_last (bb);
+  struct edge_info *edge_info;
+
+  if (! bsi_end_p (bsi))
+    {
+      tree stmt = bsi_stmt (bsi);
+
+      if (stmt && TREE_CODE (stmt) == SWITCH_EXPR)
+	{
+	  tree cond = SWITCH_COND (stmt);
+
+	  if (TREE_CODE (cond) == SSA_NAME)
+	    {
+	      tree labels = SWITCH_LABELS (stmt);
+	      int i, n_labels = TREE_VEC_LENGTH (labels);
+	      tree *info = XCNEWVEC (tree, last_basic_block);
+	      edge e;
+	      edge_iterator ei;
+
+	      for (i = 0; i < n_labels; i++)
+		{
+		  tree label = TREE_VEC_ELT (labels, i);
+		  basic_block target_bb = label_to_block (CASE_LABEL (label));
+
+		  if (CASE_HIGH (label)
+		      || !CASE_LOW (label)
+		      || info[target_bb->index])
+		    info[target_bb->index] = error_mark_node;
+		  else
+		    info[target_bb->index] = label;
+		}
+
+	      FOR_EACH_EDGE (e, ei, bb->succs)
+		{
+		  basic_block target_bb = e->dest;
+		  tree node = info[target_bb->index];
+
+		  if (node != NULL && node != error_mark_node)
+		    {
+		      tree x = fold_convert (TREE_TYPE (cond), CASE_LOW (node));
+		      edge_info = allocate_edge_info (e);
+		      edge_info->lhs = cond;
+		      edge_info->rhs = x;
+		    }
+		}
+	      free (info);
+	    }
+	}
+
+      /* A COND_EXPR may create equivalences too.  */
+      if (stmt && TREE_CODE (stmt) == COND_EXPR)
+	{
+	  tree cond = COND_EXPR_COND (stmt);
+	  edge true_edge;
+	  edge false_edge;
+
+	  extract_true_false_edges_from_block (bb, &true_edge, &false_edge);
+
+	  /* If the conditional is a single variable 'X', record 'X = 1'
+	     for the true edge and 'X = 0' on the false edge.  */
+	  if (SSA_VAR_P (cond))
+	    {
+	      struct edge_info *edge_info;
+
+	      edge_info = allocate_edge_info (true_edge);
+	      edge_info->lhs = cond;
+	      edge_info->rhs = constant_boolean_node (1, TREE_TYPE (cond));
+
+	      edge_info = allocate_edge_info (false_edge);
+	      edge_info->lhs = cond;
+	      edge_info->rhs = constant_boolean_node (0, TREE_TYPE (cond));
+	    }
+	  /* Equality tests may create one or two equivalences.  */
+	  else if (COMPARISON_CLASS_P (cond))
+	    {
+	      tree op0 = TREE_OPERAND (cond, 0);
+	      tree op1 = TREE_OPERAND (cond, 1);
+
+	      /* Special case comparing booleans against a constant as we
+		 know the value of OP0 on both arms of the branch.  i.e., we
+		 can record an equivalence for OP0 rather than COND.  */
+	      if ((TREE_CODE (cond) == EQ_EXPR || TREE_CODE (cond) == NE_EXPR)
+		  && TREE_CODE (op0) == SSA_NAME
+		  && TREE_CODE (TREE_TYPE (op0)) == BOOLEAN_TYPE
+		  && is_gimple_min_invariant (op1))
+		{
+		  if (TREE_CODE (cond) == EQ_EXPR)
+		    {
+		      edge_info = allocate_edge_info (true_edge);
+		      edge_info->lhs = op0;
+		      edge_info->rhs = (integer_zerop (op1)
+					    ? boolean_false_node
+					    : boolean_true_node);
+
+		      edge_info = allocate_edge_info (false_edge);
+		      edge_info->lhs = op0;
+		      edge_info->rhs = (integer_zerop (op1)
+					    ? boolean_true_node
+					    : boolean_false_node);
+		    }
+		  else
+		    {
+		      edge_info = allocate_edge_info (true_edge);
+		      edge_info->lhs = op0;
+		      edge_info->rhs = (integer_zerop (op1)
+					    ? boolean_true_node
+					    : boolean_false_node);
+
+		      edge_info = allocate_edge_info (false_edge);
+		      edge_info->lhs = op0;
+		      edge_info->rhs = (integer_zerop (op1)
+					    ? boolean_false_node
+					    : boolean_true_node);
+		    }
+		}
+
+	      else if (is_gimple_min_invariant (op0)
+		       && (TREE_CODE (op1) == SSA_NAME
+			   || is_gimple_min_invariant (op1)))
+		{
+		  tree inverted = invert_truthvalue (cond);
+		  struct edge_info *edge_info;
+
+		  edge_info = allocate_edge_info (true_edge);
+		  record_conditions (edge_info, cond, inverted);
+
+		  if (TREE_CODE (cond) == EQ_EXPR)
+		    {
+		      edge_info->lhs = op1;
+		      edge_info->rhs = op0;
+		    }
+
+		  edge_info = allocate_edge_info (false_edge);
+		  record_conditions (edge_info, inverted, cond);
+
+		  if (TREE_CODE (cond) == NE_EXPR)
+		    {
+		      edge_info->lhs = op1;
+		      edge_info->rhs = op0;
+		    }
+		}
+
+	      else if (TREE_CODE (op0) == SSA_NAME
+		       && (is_gimple_min_invariant (op1)
+			   || TREE_CODE (op1) == SSA_NAME))
+		{
+		  tree inverted = invert_truthvalue (cond);
+		  struct edge_info *edge_info;
+
+		  edge_info = allocate_edge_info (true_edge);
+		  record_conditions (edge_info, cond, inverted);
+
+		  if (TREE_CODE (cond) == EQ_EXPR)
+		    {
+		      edge_info->lhs = op0;
+		      edge_info->rhs = op1;
+		    }
+
+		  edge_info = allocate_edge_info (false_edge);
+		  record_conditions (edge_info, inverted, cond);
+
+		  if (TREE_CODE (cond) == NE_EXPR)
+		    {
+		      edge_info->lhs = op0;
+		      edge_info->rhs = op1;
+		    }
+		}
+	    }
+
+	  /* ??? TRUTH_NOT_EXPR can create an equivalence too.  */
+	}
+    }
+}
+
+/* Propagate information from BB to its outgoing edges.
+
+   This can include equivalency information implied by control statements
+   at the end of BB and const/copy propagation into PHIs in BB's
+   successor blocks.  */
+
+static void
+propagate_to_outgoing_edges (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+			     basic_block bb)
+{
+  record_edge_info (bb);
+  cprop_into_successor_phis (bb);
+}
+
+/* Search for redundant computations in STMT.  If any are found, then
+   replace them with the variable holding the result of the computation.
+
+   If safe, record this expression into the available expression hash
+   table.  */
+
+static bool
+eliminate_redundant_computations (tree stmt)
+{
+  tree *expr_p, def = NULL_TREE;
+  bool insert = true;
+  tree cached_lhs;
+  bool retval = false;
+  bool modify_expr_p = false;
+
+  if (TREE_CODE (stmt) == MODIFY_EXPR)
+    def = TREE_OPERAND (stmt, 0);
+
+  /* Certain expressions on the RHS can be optimized away, but can not
+     themselves be entered into the hash tables.  */
+  if (! def
+      || TREE_CODE (def) != SSA_NAME
+      || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def)
+      || !ZERO_SSA_OPERANDS (stmt, SSA_OP_VMAYDEF)
+      /* Do not record equivalences for increments of ivs.  This would create
+	 overlapping live ranges for a very questionable gain.  */
+      || simple_iv_increment_p (stmt))
+    insert = false;
+
+  /* Check if the expression has been computed before.  */
+  cached_lhs = lookup_avail_expr (stmt, insert);
+
+  opt_stats.num_exprs_considered++;
+
+  /* Get a pointer to the expression we are trying to optimize.  */
+  if (TREE_CODE (stmt) == COND_EXPR)
+    expr_p = &COND_EXPR_COND (stmt);
+  else if (TREE_CODE (stmt) == SWITCH_EXPR)
+    expr_p = &SWITCH_COND (stmt);
+  else if (TREE_CODE (stmt) == RETURN_EXPR && TREE_OPERAND (stmt, 0))
+    {
+      expr_p = &TREE_OPERAND (TREE_OPERAND (stmt, 0), 1);
+      modify_expr_p = true;
+    }
+  else
+    {
+      expr_p = &TREE_OPERAND (stmt, 1);
+      modify_expr_p = true;
+    }
+
+  /* It is safe to ignore types here since we have already done
+     type checking in the hashing and equality routines.  In fact
+     type checking here merely gets in the way of constant
+     propagation.  Also, make sure that it is safe to propagate
+     CACHED_LHS into *EXPR_P.  */
+  if (cached_lhs
+      && ((TREE_CODE (cached_lhs) != SSA_NAME
+	   && (modify_expr_p
+	       || tree_ssa_useless_type_conversion_1 (TREE_TYPE (*expr_p),
+						      TREE_TYPE (cached_lhs))))
+	  || may_propagate_copy (*expr_p, cached_lhs)))
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "  Replaced redundant expr '");
+	  print_generic_expr (dump_file, *expr_p, dump_flags);
+	  fprintf (dump_file, "' with '");
+	  print_generic_expr (dump_file, cached_lhs, dump_flags);
+	   fprintf (dump_file, "'\n");
+	}
+
+      opt_stats.num_re++;
+
+#if defined ENABLE_CHECKING
+      gcc_assert (TREE_CODE (cached_lhs) == SSA_NAME
+		  || is_gimple_min_invariant (cached_lhs));
+#endif
+
+      if (TREE_CODE (cached_lhs) == ADDR_EXPR
+	  || (POINTER_TYPE_P (TREE_TYPE (*expr_p))
+	      && is_gimple_min_invariant (cached_lhs)))
+	retval = true;
+      
+      if (modify_expr_p
+	  && !tree_ssa_useless_type_conversion_1 (TREE_TYPE (*expr_p),
+						  TREE_TYPE (cached_lhs)))
+	cached_lhs = fold_convert (TREE_TYPE (*expr_p), cached_lhs);
+
+      propagate_tree_value (expr_p, cached_lhs);
+      mark_stmt_modified (stmt);
+    }
+  return retval;
+}
+
+/* STMT, a MODIFY_EXPR, may create certain equivalences, in either
+   the available expressions table or the const_and_copies table.
+   Detect and record those equivalences.  */
+
+static void
+record_equivalences_from_stmt (tree stmt,
+			       int may_optimize_p,
+			       stmt_ann_t ann)
+{
+  tree lhs = TREE_OPERAND (stmt, 0);
+  enum tree_code lhs_code = TREE_CODE (lhs);
+
+  if (lhs_code == SSA_NAME)
+    {
+      tree rhs = TREE_OPERAND (stmt, 1);
+
+      /* Strip away any useless type conversions.  */
+      STRIP_USELESS_TYPE_CONVERSION (rhs);
+
+      /* If the RHS of the assignment is a constant or another variable that
+	 may be propagated, register it in the CONST_AND_COPIES table.  We
+	 do not need to record unwind data for this, since this is a true
+	 assignment and not an equivalence inferred from a comparison.  All
+	 uses of this ssa name are dominated by this assignment, so unwinding
+	 just costs time and space.  */
+      if (may_optimize_p
+	  && (TREE_CODE (rhs) == SSA_NAME
+	      || is_gimple_min_invariant (rhs)))
+	SSA_NAME_VALUE (lhs) = rhs;
+    }
+
+  /* A memory store, even an aliased store, creates a useful
+     equivalence.  By exchanging the LHS and RHS, creating suitable
+     vops and recording the result in the available expression table,
+     we may be able to expose more redundant loads.  */
+  if (!ann->has_volatile_ops
+      && (TREE_CODE (TREE_OPERAND (stmt, 1)) == SSA_NAME
+	  || is_gimple_min_invariant (TREE_OPERAND (stmt, 1)))
+      && !is_gimple_reg (lhs))
+    {
+      tree rhs = TREE_OPERAND (stmt, 1);
+      tree new;
+
+      /* FIXME: If the LHS of the assignment is a bitfield and the RHS
+         is a constant, we need to adjust the constant to fit into the
+         type of the LHS.  If the LHS is a bitfield and the RHS is not
+	 a constant, then we can not record any equivalences for this
+	 statement since we would need to represent the widening or
+	 narrowing of RHS.  This fixes gcc.c-torture/execute/921016-1.c
+	 and should not be necessary if GCC represented bitfields
+	 properly.  */
+      if (lhs_code == COMPONENT_REF
+	  && DECL_BIT_FIELD (TREE_OPERAND (lhs, 1)))
+	{
+	  if (TREE_CONSTANT (rhs))
+	    rhs = widen_bitfield (rhs, TREE_OPERAND (lhs, 1), lhs);
+	  else
+	    rhs = NULL;
+
+	  /* If the value overflowed, then we can not use this equivalence.  */
+	  if (rhs && ! is_gimple_min_invariant (rhs))
+	    rhs = NULL;
+	}
+
+      if (rhs)
+	{
+	  /* Build a new statement with the RHS and LHS exchanged.  */
+	  new = build2 (MODIFY_EXPR, TREE_TYPE (stmt), rhs, lhs);
+
+	  create_ssa_artficial_load_stmt (new, stmt);
+
+	  /* Finally enter the statement into the available expression
+	     table.  */
+	  lookup_avail_expr (new, true);
+	}
+    }
+}
+
+/* Replace *OP_P in STMT with any known equivalent value for *OP_P from
+   CONST_AND_COPIES.  */
+
+static bool
+cprop_operand (tree stmt, use_operand_p op_p)
+{
+  bool may_have_exposed_new_symbols = false;
+  tree val;
+  tree op = USE_FROM_PTR (op_p);
+
+  /* If the operand has a known constant value or it is known to be a
+     copy of some other variable, use the value or copy stored in
+     CONST_AND_COPIES.  */
+  val = SSA_NAME_VALUE (op);
+  if (val && val != op && TREE_CODE (val) != VALUE_HANDLE)
+    {
+      tree op_type, val_type;
+
+      /* Do not change the base variable in the virtual operand
+	 tables.  That would make it impossible to reconstruct
+	 the renamed virtual operand if we later modify this
+	 statement.  Also only allow the new value to be an SSA_NAME
+	 for propagation into virtual operands.  */
+      if (!is_gimple_reg (op)
+	  && (TREE_CODE (val) != SSA_NAME
+	      || is_gimple_reg (val)
+	      || get_virtual_var (val) != get_virtual_var (op)))
+	return false;
+
+      /* Do not replace hard register operands in asm statements.  */
+      if (TREE_CODE (stmt) == ASM_EXPR
+	  && !may_propagate_copy_into_asm (op))
+	return false;
+
+      /* Get the toplevel type of each operand.  */
+      op_type = TREE_TYPE (op);
+      val_type = TREE_TYPE (val);
+
+      /* While both types are pointers, get the type of the object
+	 pointed to.  */
+      while (POINTER_TYPE_P (op_type) && POINTER_TYPE_P (val_type))
+	{
+	  op_type = TREE_TYPE (op_type);
+	  val_type = TREE_TYPE (val_type);
+	}
+
+      /* Make sure underlying types match before propagating a constant by
+	 converting the constant to the proper type.  Note that convert may
+	 return a non-gimple expression, in which case we ignore this
+	 propagation opportunity.  */
+      if (TREE_CODE (val) != SSA_NAME)
+	{
+	  if (!lang_hooks.types_compatible_p (op_type, val_type))
+	    {
+	      val = fold_convert (TREE_TYPE (op), val);
+	      if (!is_gimple_min_invariant (val))
+		return false;
+	    }
+	}
+
+      /* Certain operands are not allowed to be copy propagated due
+	 to their interaction with exception handling and some GCC
+	 extensions.  */
+      else if (!may_propagate_copy (op, val))
+	return false;
+      
+      /* Do not propagate copies if the propagated value is at a deeper loop
+	 depth than the propagatee.  Otherwise, this may move loop variant
+	 variables outside of their loops and prevent coalescing
+	 opportunities.  If the value was loop invariant, it will be hoisted
+	 by LICM and exposed for copy propagation.  */
+      if (loop_depth_of_name (val) > loop_depth_of_name (op))
+	return false;
+
+      /* Dump details.  */
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "  Replaced '");
+	  print_generic_expr (dump_file, op, dump_flags);
+	  fprintf (dump_file, "' with %s '",
+		   (TREE_CODE (val) != SSA_NAME ? "constant" : "variable"));
+	  print_generic_expr (dump_file, val, dump_flags);
+	  fprintf (dump_file, "'\n");
+	}
+
+      /* If VAL is an ADDR_EXPR or a constant of pointer type, note
+	 that we may have exposed a new symbol for SSA renaming.  */
+      if (TREE_CODE (val) == ADDR_EXPR
+	  || (POINTER_TYPE_P (TREE_TYPE (op))
+	      && is_gimple_min_invariant (val)))
+	may_have_exposed_new_symbols = true;
+
+      if (TREE_CODE (val) != SSA_NAME)
+	opt_stats.num_const_prop++;
+      else
+	opt_stats.num_copy_prop++;
+
+      propagate_value (op_p, val);
+
+      /* And note that we modified this statement.  This is now
+	 safe, even if we changed virtual operands since we will
+	 rescan the statement and rewrite its operands again.  */
+      mark_stmt_modified (stmt);
+    }
+  return may_have_exposed_new_symbols;
+}
+
+/* CONST_AND_COPIES is a table which maps an SSA_NAME to the current
+   known value for that SSA_NAME (or NULL if no value is known).  
+
+   Propagate values from CONST_AND_COPIES into the uses, vuses and
+   v_may_def_ops of STMT.  */
+
+static bool
+cprop_into_stmt (tree stmt)
+{
+  bool may_have_exposed_new_symbols = false;
+  use_operand_p op_p;
+  ssa_op_iter iter;
+
+  FOR_EACH_SSA_USE_OPERAND (op_p, stmt, iter, SSA_OP_ALL_USES)
+    {
+      if (TREE_CODE (USE_FROM_PTR (op_p)) == SSA_NAME)
+	may_have_exposed_new_symbols |= cprop_operand (stmt, op_p);
+    }
+
+  return may_have_exposed_new_symbols;
+}
+
+
+/* Optimize the statement pointed to by iterator SI.
+   
+   We try to perform some simplistic global redundancy elimination and
+   constant propagation:
+
+   1- To detect global redundancy, we keep track of expressions that have
+      been computed in this block and its dominators.  If we find that the
+      same expression is computed more than once, we eliminate repeated
+      computations by using the target of the first one.
+
+   2- Constant values and copy assignments.  This is used to do very
+      simplistic constant and copy propagation.  When a constant or copy
+      assignment is found, we map the value on the RHS of the assignment to
+      the variable in the LHS in the CONST_AND_COPIES table.  */
+
+static void
+optimize_stmt (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+	       basic_block bb, block_stmt_iterator si)
+{
+  stmt_ann_t ann;
+  tree stmt, old_stmt;
+  bool may_optimize_p;
+  bool may_have_exposed_new_symbols = false;
+
+  old_stmt = stmt = bsi_stmt (si);
+  
+  if (TREE_CODE (stmt) == COND_EXPR)
+    canonicalize_comparison (stmt);
+  
+  update_stmt_if_modified (stmt);
+  ann = stmt_ann (stmt);
+  opt_stats.num_stmts++;
+  may_have_exposed_new_symbols = false;
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "Optimizing statement ");
+      print_generic_stmt (dump_file, stmt, TDF_SLIM);
+    }
+
+  /* Const/copy propagate into USES, VUSES and the RHS of V_MAY_DEFs.  */
+  may_have_exposed_new_symbols = cprop_into_stmt (stmt);
+
+  /* If the statement has been modified with constant replacements,
+     fold its RHS before checking for redundant computations.  */
+  if (ann->modified)
+    {
+      tree rhs;
+
+      /* Try to fold the statement making sure that STMT is kept
+	 up to date.  */
+      if (fold_stmt (bsi_stmt_ptr (si)))
+	{
+	  stmt = bsi_stmt (si);
+	  ann = stmt_ann (stmt);
+
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "  Folded to: ");
+	      print_generic_stmt (dump_file, stmt, TDF_SLIM);
+	    }
+	}
+
+      rhs = get_rhs (stmt);
+      if (rhs && TREE_CODE (rhs) == ADDR_EXPR)
+	recompute_tree_invariant_for_addr_expr (rhs);
+
+      /* Constant/copy propagation above may change the set of 
+	 virtual operands associated with this statement.  Folding
+	 may remove the need for some virtual operands.
+
+	 Indicate we will need to rescan and rewrite the statement.  */
+      may_have_exposed_new_symbols = true;
+    }
+
+  /* Check for redundant computations.  Do this optimization only
+     for assignments that have no volatile ops and conditionals.  */
+  may_optimize_p = (!ann->has_volatile_ops
+		    && ((TREE_CODE (stmt) == RETURN_EXPR
+			 && TREE_OPERAND (stmt, 0)
+			 && TREE_CODE (TREE_OPERAND (stmt, 0)) == MODIFY_EXPR
+			 && ! (TREE_SIDE_EFFECTS
+			       (TREE_OPERAND (TREE_OPERAND (stmt, 0), 1))))
+			|| (TREE_CODE (stmt) == MODIFY_EXPR
+			    && ! TREE_SIDE_EFFECTS (TREE_OPERAND (stmt, 1)))
+			|| TREE_CODE (stmt) == COND_EXPR
+			|| TREE_CODE (stmt) == SWITCH_EXPR));
+
+  if (may_optimize_p)
+    may_have_exposed_new_symbols |= eliminate_redundant_computations (stmt);
+
+  /* Record any additional equivalences created by this statement.  */
+  if (TREE_CODE (stmt) == MODIFY_EXPR)
+    record_equivalences_from_stmt (stmt,
+				   may_optimize_p,
+				   ann);
+
+  /* If STMT is a COND_EXPR and it was modified, then we may know
+     where it goes.  If that is the case, then mark the CFG as altered.
+
+     This will cause us to later call remove_unreachable_blocks and
+     cleanup_tree_cfg when it is safe to do so.  It is not safe to 
+     clean things up here since removal of edges and such can trigger
+     the removal of PHI nodes, which in turn can release SSA_NAMEs to
+     the manager.
+
+     That's all fine and good, except that once SSA_NAMEs are released
+     to the manager, we must not call create_ssa_name until all references
+     to released SSA_NAMEs have been eliminated.
+
+     All references to the deleted SSA_NAMEs can not be eliminated until
+     we remove unreachable blocks.
+
+     We can not remove unreachable blocks until after we have completed
+     any queued jump threading.
+
+     We can not complete any queued jump threads until we have taken
+     appropriate variables out of SSA form.  Taking variables out of
+     SSA form can call create_ssa_name and thus we lose.
+
+     Ultimately I suspect we're going to need to change the interface
+     into the SSA_NAME manager.  */
+
+  if (ann->modified)
+    {
+      tree val = NULL;
+
+      if (TREE_CODE (stmt) == COND_EXPR)
+	val = COND_EXPR_COND (stmt);
+      else if (TREE_CODE (stmt) == SWITCH_EXPR)
+	val = SWITCH_COND (stmt);
+
+      if (val && TREE_CODE (val) == INTEGER_CST && find_taken_edge (bb, val))
+	cfg_altered = true;
+
+      /* If we simplified a statement in such a way as to be shown that it
+	 cannot trap, update the eh information and the cfg to match.  */
+      if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt))
+	{
+	  bitmap_set_bit (need_eh_cleanup, bb->index);
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    fprintf (dump_file, "  Flagged to clear EH edges.\n");
+	}
+    }
+
+  if (may_have_exposed_new_symbols)
+    VEC_safe_push (tree, heap, stmts_to_rescan, bsi_stmt (si));
+}
+
+/* Search for an existing instance of STMT in the AVAIL_EXPRS table.  If
+   found, return its LHS. Otherwise insert STMT in the table and return
+   NULL_TREE.
+
+   Also, when an expression is first inserted in the AVAIL_EXPRS table, it
+   is also added to the stack pointed to by BLOCK_AVAIL_EXPRS_P, so that they
+   can be removed when we finish processing this block and its children.
+
+   NOTE: This function assumes that STMT is a MODIFY_EXPR node that
+   contains no CALL_EXPR on its RHS and makes no volatile nor
+   aliased references.  */
+
+static tree
+lookup_avail_expr (tree stmt, bool insert)
+{
+  void **slot;
+  tree lhs;
+  tree temp;
+  struct expr_hash_elt *element = XNEW (struct expr_hash_elt);
+
+  lhs = TREE_CODE (stmt) == MODIFY_EXPR ? TREE_OPERAND (stmt, 0) : NULL;
+
+  initialize_hash_element (stmt, lhs, element);
+
+  /* Don't bother remembering constant assignments and copy operations.
+     Constants and copy operations are handled by the constant/copy propagator
+     in optimize_stmt.  */
+  if (TREE_CODE (element->rhs) == SSA_NAME
+      || is_gimple_min_invariant (element->rhs))
+    {
+      free (element);
+      return NULL_TREE;
+    }
+
+  /* Finally try to find the expression in the main expression hash table.  */
+  slot = htab_find_slot_with_hash (avail_exprs, element, element->hash,
+				   (insert ? INSERT : NO_INSERT));
+  if (slot == NULL)
+    {
+      free (element);
+      return NULL_TREE;
+    }
+
+  if (*slot == NULL)
+    {
+      *slot = (void *) element;
+      VEC_safe_push (tree, heap, avail_exprs_stack,
+		     stmt ? stmt : element->rhs);
+      return NULL_TREE;
+    }
+
+  /* Extract the LHS of the assignment so that it can be used as the current
+     definition of another variable.  */
+  lhs = ((struct expr_hash_elt *)*slot)->lhs;
+
+  /* See if the LHS appears in the CONST_AND_COPIES table.  If it does, then
+     use the value from the const_and_copies table.  */
+  if (TREE_CODE (lhs) == SSA_NAME)
+    {
+      temp = SSA_NAME_VALUE (lhs);
+      if (temp && TREE_CODE (temp) != VALUE_HANDLE)
+	lhs = temp;
+    }
+
+  free (element);
+  return lhs;
+}
+
+/* Hashing and equality functions for AVAIL_EXPRS.  The table stores
+   MODIFY_EXPR statements.  We compute a value number for expressions using
+   the code of the expression and the SSA numbers of its operands.  */
+
+static hashval_t
+avail_expr_hash (const void *p)
+{
+  tree stmt = ((struct expr_hash_elt *)p)->stmt;
+  tree rhs = ((struct expr_hash_elt *)p)->rhs;
+  tree vuse;
+  ssa_op_iter iter;
+  hashval_t val = 0;
+
+  /* iterative_hash_expr knows how to deal with any expression and
+     deals with commutative operators as well, so just use it instead
+     of duplicating such complexities here.  */
+  val = iterative_hash_expr (rhs, val);
+
+  /* If the hash table entry is not associated with a statement, then we
+     can just hash the expression and not worry about virtual operands
+     and such.  */
+  if (!stmt || !stmt_ann (stmt))
+    return val;
+
+  /* Add the SSA version numbers of every vuse operand.  This is important
+     because compound variables like arrays are not renamed in the
+     operands.  Rather, the rename is done on the virtual variable
+     representing all the elements of the array.  */
+  FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, iter, SSA_OP_VUSE)
+    val = iterative_hash_expr (vuse, val);
+
+  return val;
+}
+
+static hashval_t
+real_avail_expr_hash (const void *p)
+{
+  return ((const struct expr_hash_elt *)p)->hash;
+}
+
+static int
+avail_expr_eq (const void *p1, const void *p2)
+{
+  tree stmt1 = ((struct expr_hash_elt *)p1)->stmt;
+  tree rhs1 = ((struct expr_hash_elt *)p1)->rhs;
+  tree stmt2 = ((struct expr_hash_elt *)p2)->stmt;
+  tree rhs2 = ((struct expr_hash_elt *)p2)->rhs;
+
+  /* If they are the same physical expression, return true.  */
+  if (rhs1 == rhs2 && stmt1 == stmt2)
+    return true;
+
+  /* If their codes are not equal, then quit now.  */
+  if (TREE_CODE (rhs1) != TREE_CODE (rhs2))
+    return false;
+
+  /* In case of a collision, both RHS have to be identical and have the
+     same VUSE operands.  */
+  if ((TREE_TYPE (rhs1) == TREE_TYPE (rhs2)
+       || lang_hooks.types_compatible_p (TREE_TYPE (rhs1), TREE_TYPE (rhs2)))
+      && operand_equal_p (rhs1, rhs2, OEP_PURE_SAME))
+    {
+      bool ret = compare_ssa_operands_equal (stmt1, stmt2, SSA_OP_VUSE);
+      gcc_assert (!ret || ((struct expr_hash_elt *)p1)->hash
+		  == ((struct expr_hash_elt *)p2)->hash);
+      return ret;
+    }
+
+  return false;
+}
+
+/* PHI-ONLY copy and constant propagation.  This pass is meant to clean
+   up degenerate PHIs created by or exposed by jump threading.  */
+
+/* Given PHI, return its RHS if the PHI is a degenerate, otherwise return
+   NULL.  */
+
+static tree
+degenerate_phi_result (tree phi)
+{
+  tree lhs = PHI_RESULT (phi);
+  tree val = NULL;
+  int i;
+
+  /* Ignoring arguments which are the same as LHS, if all the remaining
+     arguments are the same, then the PHI is a degenerate and has the
+     value of that common argument.  */
+  for (i = 0; i < PHI_NUM_ARGS (phi); i++)
+    {
+      tree arg = PHI_ARG_DEF (phi, i);
+
+      if (arg == lhs)
+	continue;
+      else if (!val)
+	val = arg;
+      else if (!operand_equal_p (arg, val, 0))
+	break;
+    }
+  return (i == PHI_NUM_ARGS (phi) ? val : NULL);
+}
+
+/* Given a tree node T, which is either a PHI_NODE or MODIFY_EXPR,
+   remove it from the IL.  */
+
+static void
+remove_stmt_or_phi (tree t)
+{
+  if (TREE_CODE (t) == PHI_NODE)
+    remove_phi_node (t, NULL);
+  else
+    {
+      block_stmt_iterator bsi = bsi_for_stmt (t);
+      bsi_remove (&bsi, true);
+    }
+}
+
+/* Given a tree node T, which is either a PHI_NODE or MODIFY_EXPR,
+   return the "rhs" of the node, in the case of a non-degenerate
+   PHI, NULL is returned.  */
+
+static tree
+get_rhs_or_phi_arg (tree t)
+{
+  if (TREE_CODE (t) == PHI_NODE)
+    return degenerate_phi_result (t);
+  else if (TREE_CODE (t) == MODIFY_EXPR)
+    return TREE_OPERAND (t, 1);
+  gcc_unreachable ();
+}
+
+
+/* Given a tree node T, which is either a PHI_NODE or a MODIFY_EXPR,
+   return the "lhs" of the node.  */
+
+static tree
+get_lhs_or_phi_result (tree t)
+{
+  if (TREE_CODE (t) == PHI_NODE)
+    return PHI_RESULT (t);
+  else if (TREE_CODE (t) == MODIFY_EXPR)
+    return TREE_OPERAND (t, 0);
+  gcc_unreachable ();
+}
+
+/* Propagate RHS into all uses of LHS (when possible).
+
+   RHS and LHS are derived from STMT, which is passed in solely so
+   that we can remove it if propagation is successful.
+
+   When propagating into a PHI node or into a statement which turns
+   into a trivial copy or constant initialization, set the
+   appropriate bit in INTERESTING_NAMEs so that we will visit those
+   nodes as well in an effort to pick up secondary optimization
+   opportunities.  */
+
+static void 
+propagate_rhs_into_lhs (tree stmt, tree lhs, tree rhs, bitmap interesting_names)
+{
+  /* First verify that propagation is valid and isn't going to move a
+     loop variant variable outside its loop.  */
+  if (! SSA_NAME_OCCURS_IN_ABNORMAL_PHI (lhs)
+      && (TREE_CODE (rhs) != SSA_NAME
+	  || ! SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs))
+      && may_propagate_copy (lhs, rhs)
+      && loop_depth_of_name (lhs) >= loop_depth_of_name (rhs))
+    {
+      use_operand_p use_p;
+      imm_use_iterator iter;
+      tree use_stmt;
+      bool all = true;
+
+      /* Dump details.  */
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "  Replacing '");
+	  print_generic_expr (dump_file, lhs, dump_flags);
+	  fprintf (dump_file, "' with %s '",
+	           (TREE_CODE (rhs) != SSA_NAME ? "constant" : "variable"));
+		   print_generic_expr (dump_file, rhs, dump_flags);
+	  fprintf (dump_file, "'\n");
+	}
+
+      /* Walk over every use of LHS and try to replace the use with RHS. 
+	 At this point the only reason why such a propagation would not
+	 be successful would be if the use occurs in an ASM_EXPR.  */
+      FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs)
+	{
+	
+	  /* It's not always safe to propagate into an ASM_EXPR.  */
+	  if (TREE_CODE (use_stmt) == ASM_EXPR
+	      && ! may_propagate_copy_into_asm (lhs))
+	    {
+	      all = false;
+	      continue;
+	    }
+
+	  /* Dump details.  */
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "    Original statement:");
+	      print_generic_expr (dump_file, use_stmt, dump_flags);
+	      fprintf (dump_file, "\n");
+	    }
+
+	  /* Propagate the RHS into this use of the LHS.  */
+	  FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
+	    propagate_value (use_p, rhs);
+
+	  /* Special cases to avoid useless calls into the folding
+	     routines, operand scanning, etc.
+
+	     First, propagation into a PHI may cause the PHI to become
+	     a degenerate, so mark the PHI as interesting.  No other
+	     actions are necessary.
+
+	     Second, if we're propagating a virtual operand and the
+	     propagation does not change the underlying _DECL node for
+	     the virtual operand, then no further actions are necessary.  */
+	  if (TREE_CODE (use_stmt) == PHI_NODE
+	      || (! is_gimple_reg (lhs)
+		  && TREE_CODE (rhs) == SSA_NAME
+		  && SSA_NAME_VAR (lhs) == SSA_NAME_VAR (rhs)))
+	    {
+	      /* Dump details.  */
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		{
+		  fprintf (dump_file, "    Updated statement:");
+		  print_generic_expr (dump_file, use_stmt, dump_flags);
+		  fprintf (dump_file, "\n");
+		}
+
+	      /* Propagation into a PHI may expose new degenerate PHIs,
+		 so mark the result of the PHI as interesting.  */
+	      if (TREE_CODE (use_stmt) == PHI_NODE)
+		{
+		  tree result = get_lhs_or_phi_result (use_stmt);
+		  bitmap_set_bit (interesting_names, SSA_NAME_VERSION (result));
+		}
+	      continue;
+	    }
+
+	  /* From this point onward we are propagating into a 
+	     real statement.  Folding may (or may not) be possible,
+	     we may expose new operands, expose dead EH edges,
+	     etc.  */
+	  fold_stmt_inplace (use_stmt);
+
+	  /* Sometimes propagation can expose new operands to the
+	     renamer.  Note this will call update_stmt at the 
+	     appropriate time.  */
+	  mark_new_vars_to_rename (use_stmt);
+
+	  /* Dump details.  */
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "    Updated statement:");
+	      print_generic_expr (dump_file, use_stmt, dump_flags);
+	      fprintf (dump_file, "\n");
+	    }
+
+	  /* If we replaced a variable index with a constant, then
+	     we would need to update the invariant flag for ADDR_EXPRs.  */
+	  if (TREE_CODE (use_stmt) == MODIFY_EXPR
+	      && TREE_CODE (TREE_OPERAND (use_stmt, 1)) == ADDR_EXPR)
+	    recompute_tree_invariant_for_addr_expr (TREE_OPERAND (use_stmt, 1));
+
+	  /* If we cleaned up EH information from the statement,
+	     mark its containing block as needing EH cleanups.  */
+	  if (maybe_clean_or_replace_eh_stmt (use_stmt, use_stmt))
+	    {
+	      bitmap_set_bit (need_eh_cleanup, bb_for_stmt (use_stmt)->index);
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		fprintf (dump_file, "  Flagged to clear EH edges.\n");
+	    }
+
+	  /* Propagation may expose new trivial copy/constant propagation
+	     opportunities.  */
+	  if (TREE_CODE (use_stmt) == MODIFY_EXPR
+	      && TREE_CODE (TREE_OPERAND (use_stmt, 0)) == SSA_NAME
+	      && (TREE_CODE (TREE_OPERAND (use_stmt, 1)) == SSA_NAME
+		  || is_gimple_min_invariant (TREE_OPERAND (use_stmt, 1))))
+	    {
+	      tree result = get_lhs_or_phi_result (use_stmt);
+	      bitmap_set_bit (interesting_names, SSA_NAME_VERSION (result));
+	    }
+
+	  /* Propagation into these nodes may make certain edges in
+	     the CFG unexecutable.  We want to identify them as PHI nodes
+	     at the destination of those unexecutable edges may become
+	     degenerates.  */
+	  else if (TREE_CODE (use_stmt) == COND_EXPR
+		   || TREE_CODE (use_stmt) == SWITCH_EXPR
+		   || TREE_CODE (use_stmt) == GOTO_EXPR)
+	    {
+	      tree val;
+
+	      if (TREE_CODE (use_stmt) == COND_EXPR)
+		val = COND_EXPR_COND (use_stmt);
+	      else if (TREE_CODE (use_stmt) == SWITCH_EXPR)
+		val = SWITCH_COND (use_stmt);
+	      else
+		val = GOTO_DESTINATION  (use_stmt);
+
+	      if (is_gimple_min_invariant (val))
+		{
+		  basic_block bb = bb_for_stmt (use_stmt);
+		  edge te = find_taken_edge (bb, val);
+		  edge_iterator ei;
+		  edge e;
+		  block_stmt_iterator bsi;
+
+		  /* Remove all outgoing edges except TE.  */
+		  for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei));)
+		    {
+		      if (e != te)
+			{
+			  tree phi;
+
+			  /* Mark all the PHI nodes at the destination of
+			     the unexecutable edge as interesting.  */
+			  for (phi = phi_nodes (e->dest);
+			       phi;
+			       phi = PHI_CHAIN (phi))
+			    {
+			      tree result = PHI_RESULT (phi);
+			      int version = SSA_NAME_VERSION (result);
+
+			      bitmap_set_bit (interesting_names, version);
+			    }
+
+			  te->probability += e->probability;
+
+			  te->count += e->count;
+			  remove_edge (e);
+			  cfg_altered = 1;
+			}
+		      else
+			ei_next (&ei);
+		    }
+
+		  bsi = bsi_last (bb_for_stmt (use_stmt));
+		  bsi_remove (&bsi, true);
+
+		  /* And fixup the flags on the single remaining edge.  */
+		  te->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
+		  te->flags &= ~EDGE_ABNORMAL;
+		  te->flags |= EDGE_FALLTHRU;
+		  if (te->probability > REG_BR_PROB_BASE)
+		    te->probability = REG_BR_PROB_BASE;
+	        }
+	    }
+	}
+
+      /* Ensure there is nothing else to do. */ 
+      gcc_assert (!all || has_zero_uses (lhs));
+
+      /* If we were able to propagate away all uses of LHS, then
+	 we can remove STMT.  */
+      if (all)
+	remove_stmt_or_phi (stmt);
+    }
+}
+
+/* T is either a PHI node (potentially a degenerate PHI node) or
+   a statement that is a trivial copy or constant initialization.
+
+   Attempt to eliminate T by propagating its RHS into all uses of
+   its LHS.  This may in turn set new bits in INTERESTING_NAMES
+   for nodes we want to revisit later.
+
+   All exit paths should clear INTERESTING_NAMES for the result
+   of T.  */
+
+static void
+eliminate_const_or_copy (tree t, bitmap interesting_names)
+{
+  tree lhs = get_lhs_or_phi_result (t);
+  tree rhs;
+  int version = SSA_NAME_VERSION (lhs);
+
+  /* If the LHS of this statement or PHI has no uses, then we can
+     just eliminate it.  This can occur if, for example, the PHI
+     was created by block duplication due to threading and its only
+     use was in the conditional at the end of the block which was
+     deleted.  */
+  if (has_zero_uses (lhs))
+    {
+      bitmap_clear_bit (interesting_names, version);
+      remove_stmt_or_phi (t);
+      return;
+    }
+
+  /* Get the RHS of the assignment or PHI node if the PHI is a
+     degenerate.  */
+  rhs = get_rhs_or_phi_arg (t);
+  if (!rhs)
+    {
+      bitmap_clear_bit (interesting_names, version);
+      return;
+    }
+
+  propagate_rhs_into_lhs (t, lhs, rhs, interesting_names);
+
+  /* Note that T may well have been deleted by now, so do
+     not access it, instead use the saved version # to clear
+     T's entry in the worklist.  */
+  bitmap_clear_bit (interesting_names, version);
+}
+
+/* The first phase in degenerate PHI elimination.
+
+   Eliminate the degenerate PHIs in BB, then recurse on the
+   dominator children of BB.  */
+
+static void
+eliminate_degenerate_phis_1 (basic_block bb, bitmap interesting_names)
+{
+  tree phi, next;
+  basic_block son;
+
+  for (phi = phi_nodes (bb); phi; phi = next)
+    {
+      next = PHI_CHAIN (phi);
+      eliminate_const_or_copy (phi, interesting_names);
+    }
+
+  /* Recurse into the dominator children of BB.  */
+  for (son = first_dom_son (CDI_DOMINATORS, bb);
+       son;
+       son = next_dom_son (CDI_DOMINATORS, son))
+    eliminate_degenerate_phis_1 (son, interesting_names);
+}
+
+
+/* A very simple pass to eliminate degenerate PHI nodes from the
+   IL.  This is meant to be fast enough to be able to be run several
+   times in the optimization pipeline.
+
+   Certain optimizations, particularly those which duplicate blocks
+   or remove edges from the CFG can create or expose PHIs which are
+   trivial copies or constant initializations.
+
+   While we could pick up these optimizations in DOM or with the
+   combination of copy-prop and CCP, those solutions are far too
+   heavy-weight for our needs.
+
+   This implementation has two phases so that we can efficiently
+   eliminate the first order degenerate PHIs and second order
+   degenerate PHIs.
+
+   The first phase performs a dominator walk to identify and eliminate
+   the vast majority of the degenerate PHIs.  When a degenerate PHI
+   is identified and eliminated any affected statements or PHIs
+   are put on a worklist.
+
+   The second phase eliminates degenerate PHIs and trivial copies
+   or constant initializations using the worklist.  This is how we
+   pick up the secondary optimization opportunities with minimal
+   cost.  */
+
+static unsigned int
+eliminate_degenerate_phis (void)
+{
+  bitmap interesting_names;
+  bitmap interesting_names1;
+
+  /* Bitmap of blocks which need EH information updated.  We can not
+     update it on-the-fly as doing so invalidates the dominator tree.  */
+  need_eh_cleanup = BITMAP_ALLOC (NULL);
+
+  /* INTERESTING_NAMES is effectively our worklist, indexed by
+     SSA_NAME_VERSION.
+
+     A set bit indicates that the statement or PHI node which
+     defines the SSA_NAME should be (re)examined to determine if
+     it has become a degenerate PHI or trivial const/copy propagation
+     opportunity. 
+
+     Experiments have show we generally get better compilation
+     time behavior with bitmaps rather than sbitmaps.  */
+  interesting_names = BITMAP_ALLOC (NULL);
+  interesting_names1 = BITMAP_ALLOC (NULL);
+
+  /* First phase.  Eliminate degenerate PHIs via a dominator
+     walk of the CFG.
+
+     Experiments have indicated that we generally get better
+     compile-time behavior by visiting blocks in the first
+     phase in dominator order.  Presumably this is because walking
+     in dominator order leaves fewer PHIs for later examination
+     by the worklist phase.  */
+  calculate_dominance_info (CDI_DOMINATORS);
+  eliminate_degenerate_phis_1 (ENTRY_BLOCK_PTR, interesting_names);
+
+  /* Second phase.  Eliminate second order degenerate PHIs as well
+     as trivial copies or constant initializations identified by
+     the first phase or this phase.  Basically we keep iterating
+     until our set of INTERESTING_NAMEs is empty.   */
+  while (!bitmap_empty_p (interesting_names))
+    {
+      unsigned int i;
+      bitmap_iterator bi;
+
+      /* EXECUTE_IF_SET_IN_BITMAP does not like its bitmap
+	 changed during the loop.  Copy it to another bitmap and
+	 use that.  */
+      bitmap_copy (interesting_names1, interesting_names);
+
+      EXECUTE_IF_SET_IN_BITMAP (interesting_names1, 0, i, bi)
+	{
+	  tree name = ssa_name (i);
+
+	  /* Ignore SSA_NAMEs that have been released because
+	     their defining statement was deleted (unreachable).  */
+	  if (name)
+	    eliminate_const_or_copy (SSA_NAME_DEF_STMT (ssa_name (i)),
+				     interesting_names);
+	}
+    }
+
+  /* Propagation of const and copies may make some EH edges dead.  Purge
+     such edges from the CFG as needed.  */
+  if (!bitmap_empty_p (need_eh_cleanup))
+    {
+      cfg_altered |= tree_purge_all_dead_eh_edges (need_eh_cleanup);
+      BITMAP_FREE (need_eh_cleanup);
+    }
+
+  BITMAP_FREE (interesting_names);
+  BITMAP_FREE (interesting_names1);
+  if (cfg_altered)
+    free_dominance_info (CDI_DOMINATORS);
+  return 0;
+}
+
+struct tree_opt_pass pass_phi_only_cprop =
+{
+  "phicprop",                           /* name */
+  gate_dominator,                       /* gate */
+  eliminate_degenerate_phis,            /* execute */
+  NULL,                                 /* sub */
+  NULL,                                 /* next */
+  0,                                    /* static_pass_number */
+  TV_TREE_PHI_CPROP,                    /* tv_id */
+  PROP_cfg | PROP_ssa | PROP_alias,     /* properties_required */
+  0,                                    /* properties_provided */
+  PROP_smt_usage,                       /* properties_destroyed */
+  0,                                    /* todo_flags_start */
+  TODO_cleanup_cfg | TODO_dump_func 
+    | TODO_ggc_collect | TODO_verify_ssa
+    | TODO_verify_stmts | TODO_update_smt_usage
+    | TODO_update_ssa, /* todo_flags_finish */
+  0                                     /* letter */
+};