--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/tree-cfgcleanup.c	Fri Jul 17 14:47:48 2009 +0900
@@ -0,0 +1,949 @@
+/* CFG cleanup for trees.
+   Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
+   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 "tree.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "hard-reg-set.h"
+#include "basic-block.h"
+#include "output.h"
+#include "toplev.h"
+#include "flags.h"
+#include "function.h"
+#include "expr.h"
+#include "ggc.h"
+#include "langhooks.h"
+#include "diagnostic.h"
+#include "tree-flow.h"
+#include "timevar.h"
+#include "tree-dump.h"
+#include "tree-pass.h"
+#include "toplev.h"
+#include "except.h"
+#include "cfgloop.h"
+#include "cfglayout.h"
+#include "hashtab.h"
+#include "tree-ssa-propagate.h"
+#include "tree-scalar-evolution.h"
+
+/* The set of blocks in that at least one of the following changes happened:
+   -- the statement at the end of the block was changed
+   -- the block was newly created
+   -- the set of the predecessors of the block changed
+   -- the set of the successors of the block changed
+   ??? Maybe we could track these changes separately, since they determine
+       what cleanups it makes sense to try on the block.  */
+bitmap cfgcleanup_altered_bbs;
+
+/* Remove any fallthru edge from EV.  Return true if an edge was removed.  */
+
+static bool
+remove_fallthru_edge (VEC(edge,gc) *ev)
+{
+  edge_iterator ei;
+  edge e;
+
+  FOR_EACH_EDGE (e, ei, ev)
+    if ((e->flags & EDGE_FALLTHRU) != 0)
+      {
+	remove_edge_and_dominated_blocks (e);
+	return true;
+      }
+  return false;
+}
+
+
+/* Disconnect an unreachable block in the control expression starting
+   at block BB.  */
+
+static bool
+cleanup_control_expr_graph (basic_block bb, gimple_stmt_iterator gsi)
+{
+  edge taken_edge;
+  bool retval = false;
+  gimple stmt = gsi_stmt (gsi);
+  tree val;
+
+  if (!single_succ_p (bb))
+    {
+      edge e;
+      edge_iterator ei;
+      bool warned;
+
+      fold_defer_overflow_warnings ();
+      val = gimple_fold (stmt);
+      taken_edge = find_taken_edge (bb, val);
+      if (!taken_edge)
+	{
+	  fold_undefer_and_ignore_overflow_warnings ();
+	  return false;
+	}
+
+      /* Remove all the edges except the one that is always executed.  */
+      warned = false;
+      for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
+	{
+	  if (e != taken_edge)
+	    {
+	      if (!warned)
+		{
+		  fold_undefer_overflow_warnings
+		    (true, stmt, WARN_STRICT_OVERFLOW_CONDITIONAL);
+		  warned = true;
+		}
+
+	      taken_edge->probability += e->probability;
+	      taken_edge->count += e->count;
+	      remove_edge_and_dominated_blocks (e);
+	      retval = true;
+	    }
+	  else
+	    ei_next (&ei);
+	}
+      if (!warned)
+	fold_undefer_and_ignore_overflow_warnings ();
+      if (taken_edge->probability > REG_BR_PROB_BASE)
+	taken_edge->probability = REG_BR_PROB_BASE;
+    }
+  else
+    taken_edge = single_succ_edge (bb);
+
+  bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
+  gsi_remove (&gsi, true);
+  taken_edge->flags = EDGE_FALLTHRU;
+
+  return retval;
+}
+
+/* Try to remove superfluous control structures in basic block BB.  Returns
+   true if anything changes.  */
+
+static bool
+cleanup_control_flow_bb (basic_block bb)
+{
+  gimple_stmt_iterator gsi;
+  bool retval = false;
+  gimple stmt;
+
+  /* If the last statement of the block could throw and now cannot,
+     we need to prune cfg.  */
+  retval |= gimple_purge_dead_eh_edges (bb);
+
+  gsi = gsi_last_bb (bb);
+  if (gsi_end_p (gsi))
+    return retval;
+
+  stmt = gsi_stmt (gsi);
+
+  if (gimple_code (stmt) == GIMPLE_COND
+      || gimple_code (stmt) == GIMPLE_SWITCH)
+    retval |= cleanup_control_expr_graph (bb, gsi);
+  else if (gimple_code (stmt) == GIMPLE_GOTO
+	   && TREE_CODE (gimple_goto_dest (stmt)) == ADDR_EXPR
+	   && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt), 0))
+	       == LABEL_DECL))
+    {
+      /* If we had a computed goto which has a compile-time determinable
+	 destination, then we can eliminate the goto.  */
+      edge e;
+      tree label;
+      edge_iterator ei;
+      basic_block target_block;
+
+      /* First look at all the outgoing edges.  Delete any outgoing
+	 edges which do not go to the right block.  For the one
+	 edge which goes to the right block, fix up its flags.  */
+      label = TREE_OPERAND (gimple_goto_dest (stmt), 0);
+      target_block = label_to_block (label);
+      for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
+	{
+	  if (e->dest != target_block)
+	    remove_edge_and_dominated_blocks (e);
+	  else
+	    {
+	      /* Turn off the EDGE_ABNORMAL flag.  */
+	      e->flags &= ~EDGE_ABNORMAL;
+
+	      /* And set EDGE_FALLTHRU.  */
+	      e->flags |= EDGE_FALLTHRU;
+	      ei_next (&ei);
+	    }
+	}
+
+      bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
+      bitmap_set_bit (cfgcleanup_altered_bbs, target_block->index);
+
+      /* Remove the GOTO_EXPR as it is not needed.  The CFG has all the
+	 relevant information we need.  */
+      gsi_remove (&gsi, true);
+      retval = true;
+    }
+
+  /* Check for indirect calls that have been turned into
+     noreturn calls.  */
+  else if (is_gimple_call (stmt)
+           && gimple_call_noreturn_p (stmt)
+           && remove_fallthru_edge (bb->succs))
+    retval = true;
+
+  return retval;
+}
+
+/* Return true if basic block BB does nothing except pass control
+   flow to another block and that we can safely insert a label at
+   the start of the successor block.
+
+   As a precondition, we require that BB be not equal to
+   ENTRY_BLOCK_PTR.  */
+
+static bool
+tree_forwarder_block_p (basic_block bb, bool phi_wanted)
+{
+  gimple_stmt_iterator gsi;
+  edge_iterator ei;
+  edge e, succ;
+  basic_block dest;
+
+  /* BB must have a single outgoing edge.  */
+  if (single_succ_p (bb) != 1
+      /* If PHI_WANTED is false, BB must not have any PHI nodes.
+	 Otherwise, BB must have PHI nodes.  */
+      || gimple_seq_empty_p (phi_nodes (bb)) == phi_wanted
+      /* BB may not be a predecessor of EXIT_BLOCK_PTR.  */
+      || single_succ (bb) == EXIT_BLOCK_PTR
+      /* Nor should this be an infinite loop.  */
+      || single_succ (bb) == bb
+      /* BB may not have an abnormal outgoing edge.  */
+      || (single_succ_edge (bb)->flags & EDGE_ABNORMAL))
+    return false;
+
+#if ENABLE_CHECKING
+  gcc_assert (bb != ENTRY_BLOCK_PTR);
+#endif
+
+  /* Now walk through the statements backward.  We can ignore labels,
+     anything else means this is not a forwarder block.  */
+  for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
+    {
+      gimple stmt = gsi_stmt (gsi);
+
+      switch (gimple_code (stmt))
+	{
+	case GIMPLE_LABEL:
+	  if (DECL_NONLOCAL (gimple_label_label (stmt)))
+	    return false;
+	  break;
+
+	default:
+	  return false;
+	}
+    }
+
+  if (find_edge (ENTRY_BLOCK_PTR, bb))
+    return false;
+
+  if (current_loops)
+    {
+      basic_block dest;
+      /* Protect loop latches, headers and preheaders.  */
+      if (bb->loop_father->header == bb)
+	return false;
+      dest = EDGE_SUCC (bb, 0)->dest;
+
+      if (dest->loop_father->header == dest)
+	return false;
+    }
+
+  /* If we have an EH edge leaving this block, make sure that the
+     destination of this block has only one predecessor.  This ensures
+     that we don't get into the situation where we try to remove two
+     forwarders that go to the same basic block but are handlers for
+     different EH regions.  */
+  succ = single_succ_edge (bb);
+  dest = succ->dest;
+  FOR_EACH_EDGE (e, ei, bb->preds)
+    {
+      if (e->flags & EDGE_EH)
+        {
+	  if (!single_pred_p (dest))
+	    return false;
+	}
+    }
+
+  return true;
+}
+
+/* Return true if BB has at least one abnormal incoming edge.  */
+
+static inline bool
+has_abnormal_incoming_edge_p (basic_block bb)
+{
+  edge e;
+  edge_iterator ei;
+
+  FOR_EACH_EDGE (e, ei, bb->preds)
+    if (e->flags & EDGE_ABNORMAL)
+      return true;
+
+  return false;
+}
+
+/* If all the PHI nodes in DEST have alternatives for E1 and E2 and
+   those alternatives are equal in each of the PHI nodes, then return
+   true, else return false.  */
+
+static bool
+phi_alternatives_equal (basic_block dest, edge e1, edge e2)
+{
+  int n1 = e1->dest_idx;
+  int n2 = e2->dest_idx;
+  gimple_stmt_iterator gsi;
+
+  for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
+    {
+      gimple phi = gsi_stmt (gsi);
+      tree val1 = gimple_phi_arg_def (phi, n1);
+      tree val2 = gimple_phi_arg_def (phi, n2);
+
+      gcc_assert (val1 != NULL_TREE);
+      gcc_assert (val2 != NULL_TREE);
+
+      if (!operand_equal_for_phi_arg_p (val1, val2))
+	return false;
+    }
+
+  return true;
+}
+
+/* Removes forwarder block BB.  Returns false if this failed.  */
+
+static bool
+remove_forwarder_block (basic_block bb)
+{
+  edge succ = single_succ_edge (bb), e, s;
+  basic_block dest = succ->dest;
+  gimple label;
+  edge_iterator ei;
+  gimple_stmt_iterator gsi, gsi_to;
+  bool seen_abnormal_edge = false;
+
+  /* We check for infinite loops already in tree_forwarder_block_p.
+     However it may happen that the infinite loop is created
+     afterwards due to removal of forwarders.  */
+  if (dest == bb)
+    return false;
+
+  /* If the destination block consists of a nonlocal label, do not merge
+     it.  */
+  label = first_stmt (dest);
+  if (label
+      && gimple_code (label) == GIMPLE_LABEL
+      && DECL_NONLOCAL (gimple_label_label (label)))
+    return false;
+
+  /* If there is an abnormal edge to basic block BB, but not into
+     dest, problems might occur during removal of the phi node at out
+     of ssa due to overlapping live ranges of registers.
+
+     If there is an abnormal edge in DEST, the problems would occur
+     anyway since cleanup_dead_labels would then merge the labels for
+     two different eh regions, and rest of exception handling code
+     does not like it.
+
+     So if there is an abnormal edge to BB, proceed only if there is
+     no abnormal edge to DEST and there are no phi nodes in DEST.  */
+  if (has_abnormal_incoming_edge_p (bb))
+    {
+      seen_abnormal_edge = true;
+
+      if (has_abnormal_incoming_edge_p (dest)
+	  || !gimple_seq_empty_p (phi_nodes (dest)))
+	return false;
+    }
+
+  /* If there are phi nodes in DEST, and some of the blocks that are
+     predecessors of BB are also predecessors of DEST, check that the
+     phi node arguments match.  */
+  if (!gimple_seq_empty_p (phi_nodes (dest)))
+    {
+      FOR_EACH_EDGE (e, ei, bb->preds)
+	{
+	  s = find_edge (e->src, dest);
+	  if (!s)
+	    continue;
+
+	  if (!phi_alternatives_equal (dest, succ, s))
+	    return false;
+	}
+    }
+
+  /* Redirect the edges.  */
+  for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
+    {
+      bitmap_set_bit (cfgcleanup_altered_bbs, e->src->index);
+
+      if (e->flags & EDGE_ABNORMAL)
+	{
+	  /* If there is an abnormal edge, redirect it anyway, and
+	     move the labels to the new block to make it legal.  */
+	  s = redirect_edge_succ_nodup (e, dest);
+	}
+      else
+	s = redirect_edge_and_branch (e, dest);
+
+      if (s == e)
+	{
+	  /* Create arguments for the phi nodes, since the edge was not
+	     here before.  */
+	  for (gsi = gsi_start_phis (dest);
+	       !gsi_end_p (gsi);
+	       gsi_next (&gsi))
+	    {
+	      gimple phi = gsi_stmt (gsi);
+	      add_phi_arg (phi, gimple_phi_arg_def (phi, succ->dest_idx), s);
+	    }
+	}
+    }
+
+  if (seen_abnormal_edge)
+    {
+      /* Move the labels to the new block, so that the redirection of
+	 the abnormal edges works.  */
+      gsi_to = gsi_start_bb (dest);
+      for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); )
+	{
+	  label = gsi_stmt (gsi);
+	  gcc_assert (gimple_code (label) == GIMPLE_LABEL);
+	  gsi_remove (&gsi, false);
+	  gsi_insert_before (&gsi_to, label, GSI_CONTINUE_LINKING);
+	}
+    }
+
+  bitmap_set_bit (cfgcleanup_altered_bbs, dest->index);
+
+  /* Update the dominators.  */
+  if (dom_info_available_p (CDI_DOMINATORS))
+    {
+      basic_block dom, dombb, domdest;
+
+      dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
+      domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
+      if (domdest == bb)
+	{
+	  /* Shortcut to avoid calling (relatively expensive)
+	     nearest_common_dominator unless necessary.  */
+	  dom = dombb;
+	}
+      else
+	dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
+
+      set_immediate_dominator (CDI_DOMINATORS, dest, dom);
+    }
+
+  /* And kill the forwarder block.  */
+  delete_basic_block (bb);
+
+  return true;
+}
+
+/* Split basic blocks on calls in the middle of a basic block that are now
+   known not to return, and remove the unreachable code.  */
+
+static bool
+split_bbs_on_noreturn_calls (void)
+{
+  bool changed = false;
+  gimple stmt;
+  basic_block bb;
+
+  /* Detect cases where a mid-block call is now known not to return.  */
+  if (cfun->gimple_df)
+    while (VEC_length (gimple, MODIFIED_NORETURN_CALLS (cfun)))
+      {
+	stmt = VEC_pop (gimple, MODIFIED_NORETURN_CALLS (cfun));
+	bb = gimple_bb (stmt);
+	/* BB might be deleted at this point, so verify first
+	   BB is present in the cfg.  */
+	if (bb == NULL
+	    || bb->index < NUM_FIXED_BLOCKS
+	    || bb->index >= n_basic_blocks
+	    || BASIC_BLOCK (bb->index) != bb
+	    || last_stmt (bb) == stmt
+	    || !gimple_call_noreturn_p (stmt))
+	  continue;
+
+	changed = true;
+	split_block (bb, stmt);
+	remove_fallthru_edge (bb->succs);
+      }
+
+  return changed;
+}
+
+/* If GIMPLE_OMP_RETURN in basic block BB is unreachable, remove it.  */
+
+static bool
+cleanup_omp_return (basic_block bb)
+{
+  gimple stmt = last_stmt (bb);
+  basic_block control_bb;
+
+  if (stmt == NULL
+      || gimple_code (stmt) != GIMPLE_OMP_RETURN
+      || !single_pred_p (bb))
+    return false;
+
+  control_bb = single_pred (bb);
+  stmt = last_stmt (control_bb);
+
+  if (gimple_code (stmt) != GIMPLE_OMP_SECTIONS_SWITCH)
+    return false;
+
+  /* The block with the control statement normally has two entry edges -- one
+     from entry, one from continue.  If continue is removed, return is
+     unreachable, so we remove it here as well.  */
+  if (EDGE_COUNT (control_bb->preds) == 2)
+    return false;
+
+  gcc_assert (EDGE_COUNT (control_bb->preds) == 1);
+  remove_edge_and_dominated_blocks (single_pred_edge (bb));
+  return true;
+}
+
+/* Tries to cleanup cfg in basic block BB.  Returns true if anything
+   changes.  */
+
+static bool
+cleanup_tree_cfg_bb (basic_block bb)
+{
+  bool retval = false;
+
+  if (cleanup_omp_return (bb))
+    return true;
+
+  retval = cleanup_control_flow_bb (bb);
+  
+  /* Forwarder blocks can carry line number information which is
+     useful when debugging, so we only clean them up when
+     optimizing.  */
+  if (optimize > 0
+      && tree_forwarder_block_p (bb, false)
+      && remove_forwarder_block (bb))
+    return true;
+
+  /* Merging the blocks may create new opportunities for folding
+     conditional branches (due to the elimination of single-valued PHI
+     nodes).  */
+  if (single_succ_p (bb)
+      && can_merge_blocks_p (bb, single_succ (bb)))
+    {
+      merge_blocks (bb, single_succ (bb));
+      return true;
+    }
+
+  return retval;
+}
+
+/* Iterate the cfg cleanups, while anything changes.  */
+
+static bool
+cleanup_tree_cfg_1 (void)
+{
+  bool retval = false;
+  basic_block bb;
+  unsigned i, n;
+
+  retval |= split_bbs_on_noreturn_calls ();
+
+  /* Prepare the worklists of altered blocks.  */
+  cfgcleanup_altered_bbs = BITMAP_ALLOC (NULL);
+
+  /* During forwarder block cleanup, we may redirect edges out of
+     SWITCH_EXPRs, which can get expensive.  So we want to enable
+     recording of edge to CASE_LABEL_EXPR.  */
+  start_recording_case_labels ();
+
+  /* Start by iterating over all basic blocks.  We cannot use FOR_EACH_BB,
+     since the basic blocks may get removed.  */
+  n = last_basic_block;
+  for (i = NUM_FIXED_BLOCKS; i < n; i++)
+    {
+      bb = BASIC_BLOCK (i);
+      if (bb)
+	retval |= cleanup_tree_cfg_bb (bb);
+    }
+
+  /* Now process the altered blocks, as long as any are available.  */
+  while (!bitmap_empty_p (cfgcleanup_altered_bbs))
+    {
+      i = bitmap_first_set_bit (cfgcleanup_altered_bbs);
+      bitmap_clear_bit (cfgcleanup_altered_bbs, i);
+      if (i < NUM_FIXED_BLOCKS)
+	continue;
+
+      bb = BASIC_BLOCK (i);
+      if (!bb)
+	continue;
+
+      retval |= cleanup_tree_cfg_bb (bb);
+
+      /* Rerun split_bbs_on_noreturn_calls, in case we have altered any noreturn
+	 calls.  */
+      retval |= split_bbs_on_noreturn_calls ();
+    }
+  
+  end_recording_case_labels ();
+  BITMAP_FREE (cfgcleanup_altered_bbs);
+  return retval;
+}
+
+
+/* Remove unreachable blocks and other miscellaneous clean up work.
+   Return true if the flowgraph was modified, false otherwise.  */
+
+static bool
+cleanup_tree_cfg_noloop (void)
+{
+  bool changed;
+
+  timevar_push (TV_TREE_CLEANUP_CFG);
+
+  /* Iterate until there are no more cleanups left to do.  If any
+     iteration changed the flowgraph, set CHANGED to true.
+
+     If dominance information is available, there cannot be any unreachable
+     blocks.  */
+  if (!dom_info_available_p (CDI_DOMINATORS))
+    {
+      changed = delete_unreachable_blocks ();
+      calculate_dominance_info (CDI_DOMINATORS);
+    }
+  else
+    {
+#ifdef ENABLE_CHECKING
+      verify_dominators (CDI_DOMINATORS);
+#endif
+      changed = false;
+    }
+
+  changed |= cleanup_tree_cfg_1 ();
+
+  gcc_assert (dom_info_available_p (CDI_DOMINATORS));
+  compact_blocks ();
+
+#ifdef ENABLE_CHECKING
+  verify_flow_info ();
+#endif
+
+  timevar_pop (TV_TREE_CLEANUP_CFG);
+
+  if (changed && current_loops)
+    loops_state_set (LOOPS_NEED_FIXUP);
+
+  return changed;
+}
+
+/* Repairs loop structures.  */
+
+static void
+repair_loop_structures (void)
+{
+  bitmap changed_bbs = BITMAP_ALLOC (NULL);
+  fix_loop_structure (changed_bbs);
+
+  /* This usually does nothing.  But sometimes parts of cfg that originally
+     were inside a loop get out of it due to edge removal (since they
+     become unreachable by back edges from latch).  */
+  if (loops_state_satisfies_p (LOOP_CLOSED_SSA))
+    rewrite_into_loop_closed_ssa (changed_bbs, TODO_update_ssa);
+
+  BITMAP_FREE (changed_bbs);
+
+#ifdef ENABLE_CHECKING
+  verify_loop_structure ();
+#endif
+  scev_reset ();
+
+  loops_state_clear (LOOPS_NEED_FIXUP);
+}
+
+/* Cleanup cfg and repair loop structures.  */
+
+bool
+cleanup_tree_cfg (void)
+{
+  bool changed = cleanup_tree_cfg_noloop ();
+
+  if (current_loops != NULL
+      && loops_state_satisfies_p (LOOPS_NEED_FIXUP))
+    repair_loop_structures ();
+
+  return changed;
+}
+
+/* Merge the PHI nodes at BB into those at BB's sole successor.  */
+
+static void
+remove_forwarder_block_with_phi (basic_block bb)
+{
+  edge succ = single_succ_edge (bb);
+  basic_block dest = succ->dest;
+  gimple label;
+  basic_block dombb, domdest, dom;
+
+  /* We check for infinite loops already in tree_forwarder_block_p.
+     However it may happen that the infinite loop is created
+     afterwards due to removal of forwarders.  */
+  if (dest == bb)
+    return;
+
+  /* If the destination block consists of a nonlocal label, do not
+     merge it.  */
+  label = first_stmt (dest);
+  if (label
+      && gimple_code (label) == GIMPLE_LABEL
+      && DECL_NONLOCAL (gimple_label_label (label)))
+    return;
+
+  /* Redirect each incoming edge to BB to DEST.  */
+  while (EDGE_COUNT (bb->preds) > 0)
+    {
+      edge e = EDGE_PRED (bb, 0), s;
+      gimple_stmt_iterator gsi;
+
+      s = find_edge (e->src, dest);
+      if (s)
+	{
+	  /* We already have an edge S from E->src to DEST.  If S and
+	     E->dest's sole successor edge have the same PHI arguments
+	     at DEST, redirect S to DEST.  */
+	  if (phi_alternatives_equal (dest, s, succ))
+	    {
+	      e = redirect_edge_and_branch (e, dest);
+	      redirect_edge_var_map_clear (e);
+	      continue;
+	    }
+
+	  /* PHI arguments are different.  Create a forwarder block by
+	     splitting E so that we can merge PHI arguments on E to
+	     DEST.  */
+	  e = single_succ_edge (split_edge (e));
+	}
+
+      s = redirect_edge_and_branch (e, dest);
+
+      /* redirect_edge_and_branch must not create a new edge.  */
+      gcc_assert (s == e);
+
+      /* Add to the PHI nodes at DEST each PHI argument removed at the
+	 destination of E.  */
+      for (gsi = gsi_start_phis (dest);
+	   !gsi_end_p (gsi);
+	   gsi_next (&gsi))
+	{
+	  gimple phi = gsi_stmt (gsi);
+	  tree def = gimple_phi_arg_def (phi, succ->dest_idx);
+
+	  if (TREE_CODE (def) == SSA_NAME)
+	    {
+	      edge_var_map_vector head;
+	      edge_var_map *vm;
+	      size_t i;
+
+	      /* If DEF is one of the results of PHI nodes removed during
+		 redirection, replace it with the PHI argument that used
+		 to be on E.  */
+	      head = redirect_edge_var_map_vector (e);
+	      for (i = 0; VEC_iterate (edge_var_map, head, i, vm); ++i)
+		{
+		  tree old_arg = redirect_edge_var_map_result (vm);
+		  tree new_arg = redirect_edge_var_map_def (vm);
+
+		  if (def == old_arg)
+		    {
+		      def = new_arg;
+		      break;
+		    }
+		}
+	    }
+
+	  add_phi_arg (phi, def, s);
+	}
+
+      redirect_edge_var_map_clear (e);
+    }
+
+  /* Update the dominators.  */
+  dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
+  domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
+  if (domdest == bb)
+    {
+      /* Shortcut to avoid calling (relatively expensive)
+	 nearest_common_dominator unless necessary.  */
+      dom = dombb;
+    }
+  else
+    dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
+
+  set_immediate_dominator (CDI_DOMINATORS, dest, dom);
+
+  /* Remove BB since all of BB's incoming edges have been redirected
+     to DEST.  */
+  delete_basic_block (bb);
+}
+
+/* This pass merges PHI nodes if one feeds into another.  For example,
+   suppose we have the following:
+
+  goto <bb 9> (<L9>);
+
+<L8>:;
+  tem_17 = foo ();
+
+  # tem_6 = PHI <tem_17(8), tem_23(7)>;
+<L9>:;
+
+  # tem_3 = PHI <tem_6(9), tem_2(5)>;
+<L10>:;
+
+  Then we merge the first PHI node into the second one like so:
+
+  goto <bb 9> (<L10>);
+
+<L8>:;
+  tem_17 = foo ();
+
+  # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
+<L10>:;
+*/
+
+static unsigned int
+merge_phi_nodes (void)
+{
+  basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks);
+  basic_block *current = worklist;
+  basic_block bb;
+
+  calculate_dominance_info (CDI_DOMINATORS);
+
+  /* Find all PHI nodes that we may be able to merge.  */
+  FOR_EACH_BB (bb)
+    {
+      basic_block dest;
+
+      /* Look for a forwarder block with PHI nodes.  */
+      if (!tree_forwarder_block_p (bb, true))
+	continue;
+
+      dest = single_succ (bb);
+
+      /* We have to feed into another basic block with PHI
+	 nodes.  */
+      if (!phi_nodes (dest)
+	  /* We don't want to deal with a basic block with
+	     abnormal edges.  */
+	  || has_abnormal_incoming_edge_p (bb))
+	continue;
+
+      if (!dominated_by_p (CDI_DOMINATORS, dest, bb))
+	{
+	  /* If BB does not dominate DEST, then the PHI nodes at
+	     DEST must be the only users of the results of the PHI
+	     nodes at BB.  */
+	  *current++ = bb;
+	}
+      else
+	{
+	  gimple_stmt_iterator gsi;
+	  unsigned int dest_idx = single_succ_edge (bb)->dest_idx;
+
+	  /* BB dominates DEST.  There may be many users of the PHI
+	     nodes in BB.  However, there is still a trivial case we
+	     can handle.  If the result of every PHI in BB is used
+	     only by a PHI in DEST, then we can trivially merge the
+	     PHI nodes from BB into DEST.  */
+	  for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
+	       gsi_next (&gsi))
+	    {
+	      gimple phi = gsi_stmt (gsi);
+	      tree result = gimple_phi_result (phi);
+	      use_operand_p imm_use;
+	      gimple use_stmt;
+
+	      /* If the PHI's result is never used, then we can just
+		 ignore it.  */
+	      if (has_zero_uses (result))
+		continue;
+
+	      /* Get the single use of the result of this PHI node.  */
+  	      if (!single_imm_use (result, &imm_use, &use_stmt)
+		  || gimple_code (use_stmt) != GIMPLE_PHI
+		  || gimple_bb (use_stmt) != dest
+		  || gimple_phi_arg_def (use_stmt, dest_idx) != result)
+		break;
+	    }
+
+	  /* If the loop above iterated through all the PHI nodes
+	     in BB, then we can merge the PHIs from BB into DEST.  */
+	  if (gsi_end_p (gsi))
+	    *current++ = bb;
+	}
+    }
+
+  /* Now let's drain WORKLIST.  */
+  while (current != worklist)
+    {
+      bb = *--current;
+      remove_forwarder_block_with_phi (bb);
+    }
+
+  free (worklist);
+  return 0;
+}
+
+static bool
+gate_merge_phi (void)
+{
+  return 1;
+}
+
+struct gimple_opt_pass pass_merge_phi = 
+{
+ {
+  GIMPLE_PASS,
+  "mergephi",			/* name */
+  gate_merge_phi,		/* gate */
+  merge_phi_nodes,		/* execute */
+  NULL,				/* sub */
+  NULL,				/* next */
+  0,				/* static_pass_number */
+  TV_TREE_MERGE_PHI,		/* tv_id */
+  PROP_cfg | PROP_ssa,		/* properties_required */
+  0,				/* properties_provided */
+  0,				/* properties_destroyed */
+  0,				/* todo_flags_start */
+  TODO_dump_func | TODO_ggc_collect	/* todo_flags_finish */
+  | TODO_verify_ssa
+ }
+};