re PR rtl-optimization/44374 (Hoist same instructions in different branches)

gcc/
	PR rtl-optimization/44374
	Reapply patch with fixes.
	* basic-block.h (enum bb_flags): Add BB_MODIFIED.
	* df-core.c (df_set_bb_dirty): Set it.
	* ifcvt.c (find_memory): Remove function.
	(dead_or_predicable): Use can_move_insns_across.
	* df.h (can_move_insns_across): Declare function.
	* cfgcleanup.c (block_was_dirty): New static variable.
	(flow_find_head_matching_sequence): Test for epilogue notes.
	(try_crossjump_bb, try_forward_edges): Test BB_MODIFIED flag rather
	than df_get_bb_dirty.
	(try_head_merge_bb): New static function.
	(try_optimize_cfg): Call it.  Call df_analyze if block_was_dirty
	is set.
	* df-problems.c: Include "target.h"
	(df_simulate_find_uses): New static function.
	(MEMREF_NORMAL, MEMREF_VOLATILE): New macros.
	(find_memory, find_memory_store): New static functions.
	(can_move_insns_across): New function.
	* Makefile.in (df-problems.o): Update dependencies.

gcc/testsuite/
	PR rtl-optimization/44374
	Reapply patch with fixes.
	* gcc.target/arm/headmerge-1.c: New test.
	* gcc.target/arm/headmerge-2.c: New test.
	* gcc.target/i386/headmerge-1.c: New test.
	* gcc.target/i386/headmerge-2.c: New test.

From-SVN: r167779

13 files changed, 817 insertions, 137 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index c832c34..8288373 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,26 @@
+2010-12-14  Bernd Schmidt  <bernds@codesourcery.com>
+
+	PR rtl-optimization/44374
+	Reapply patch with fixes.
+	* basic-block.h (enum bb_flags): Add BB_MODIFIED.
+	* df-core.c (df_set_bb_dirty): Set it.
+	* ifcvt.c (find_memory): Remove function.
+	(dead_or_predicable): Use can_move_insns_across.
+	* df.h (can_move_insns_across): Declare function.
+	* cfgcleanup.c (block_was_dirty): New static variable.
+	(flow_find_head_matching_sequence): Test for epilogue notes.
+	(try_crossjump_bb, try_forward_edges): Test BB_MODIFIED flag rather
+	than df_get_bb_dirty.
+	(try_head_merge_bb): New static function.
+	(try_optimize_cfg): Call it.  Call df_analyze if block_was_dirty
+	is set.
+	* df-problems.c: Include "target.h"
+	(df_simulate_find_uses): New static function.
+	(MEMREF_NORMAL, MEMREF_VOLATILE): New macros.
+	(find_memory, find_memory_store): New static functions.
+	(can_move_insns_across): New function.
+	* Makefile.in (df-problems.o): Update dependencies.
+
 2010-12-13  Joseph Myers  <joseph@codesourcery.com>
 
 	* config/xtensa/elf.h (SIZE_TYPE, PTRDIFF_TYPE): Define.
diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index ae195e3..f031630 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -3194,7 +3194,7 @@ df-core.o : df-core.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(RTL_H) \
 df-problems.o : df-problems.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) \
    $(RTL_H) insn-config.h $(RECOG_H) $(FUNCTION_H) $(REGS_H) alloc-pool.h \
    hard-reg-set.h $(BASIC_BLOCK_H) $(DF_H) $(BITMAP_H) sbitmap.h $(TIMEVAR_H) \
-   $(TM_P_H) $(FLAGS_H) output.h $(EXCEPT_H) dce.h vecprim.h
+   $(TM_P_H) $(TARGET_H) $(FLAGS_H) output.h $(EXCEPT_H) dce.h vecprim.h
 df-scan.o : df-scan.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(RTL_H) \
    insn-config.h $(RECOG_H) $(FUNCTION_H) $(REGS_H) alloc-pool.h \
    hard-reg-set.h $(BASIC_BLOCK_H) $(DF_H) $(BITMAP_H) sbitmap.h $(TIMEVAR_H) \
diff --git a/gcc/basic-block.h b/gcc/basic-block.h
index be0a1d1..3594eea 100644
--- a/gcc/basic-block.h
+++ b/gcc/basic-block.h
@@ -245,7 +245,13 @@ enum bb_flags
 
   /* Set on blocks that cannot be threaded through.
      Only used in cfgcleanup.c.  */
-  BB_NONTHREADABLE_BLOCK = 1 << 11
+  BB_NONTHREADABLE_BLOCK = 1 << 11,
+
+  /* Set on blocks that were modified in some way.  This bit is set in
+     df_set_bb_dirty, but not cleared by df_analyze, so it can be used
+     to test whether a block has been modified prior to a df_analyze
+     call.  */
+  BB_MODIFIED = 1 << 12
 };
 
 /* Dummy flag for convenience in the hot/cold partitioning code.  */
diff --git a/gcc/cfgcleanup.c b/gcc/cfgcleanup.c
index 78635d2..bf6ca45 100644
--- a/gcc/cfgcleanup.c
+++ b/gcc/cfgcleanup.c
@@ -65,6 +65,10 @@ static bool first_pass;
 /* Set to true if crossjumps occured in the latest run of try_optimize_cfg.  */
 static bool crossjumps_occured;
 
+/* Set to true if we couldn't run an optimization due to stale liveness
+   information; we should run df_analyze to enable more opportunities.  */
+static bool block_was_dirty;
+
 static bool try_crossjump_to_edge (int, edge, edge);
 static bool try_crossjump_bb (int, basic_block);
 static bool outgoing_edges_match (int, basic_block, basic_block);
@@ -431,7 +435,7 @@ try_forward_edges (int mode, basic_block b)
       int counter, goto_locus;
       bool threaded = false;
       int nthreaded_edges = 0;
-      bool may_thread = first_pass | df_get_bb_dirty (b);
+      bool may_thread = first_pass || (b->flags & BB_MODIFIED) != 0;
 
       /* Skip complex edges because we don't know how to update them.
 
@@ -466,7 +470,7 @@ try_forward_edges (int mode, basic_block b)
 	{
 	  basic_block new_target = NULL;
 	  bool new_target_threaded = false;
-	  may_thread |= df_get_bb_dirty (target);
+	  may_thread |= (target->flags & BB_MODIFIED) != 0;
 
 	  if (FORWARDER_BLOCK_P (target)
 	      && !(single_succ_edge (target)->flags & EDGE_CROSSING)
@@ -1184,12 +1188,20 @@ flow_find_head_matching_sequence (basic_block bb1, basic_block bb2, rtx *f1,
 
   while (true)
     {
-      /* Ignore notes.  */
+      /* Ignore notes, except NOTE_INSN_EPILOGUE_BEG.  */
       while (!NONDEBUG_INSN_P (i1) && i1 != BB_END (bb1))
-	i1 = NEXT_INSN (i1);
+	{
+	  if (NOTE_P (i1) && NOTE_KIND (i1) == NOTE_INSN_EPILOGUE_BEG)
+	    break;
+	  i1 = NEXT_INSN (i1);
+	}
 
       while (!NONDEBUG_INSN_P (i2) && i2 != BB_END (bb2))
-	i2 = NEXT_INSN (i2);
+	{
+	  if (NOTE_P (i2) && NOTE_KIND (i2) == NOTE_INSN_EPILOGUE_BEG)
+	    break;
+	  i2 = NEXT_INSN (i2);
+	}
 
       if ((i1 == BB_END (bb1) && !NONDEBUG_INSN_P (i1))
 	  || (i2 == BB_END (bb2) && !NONDEBUG_INSN_P (i2)))
@@ -1856,8 +1868,8 @@ try_crossjump_bb (int mode, basic_block bb)
 	  /* If nothing changed since the last attempt, there is nothing
 	     we can do.  */
 	  if (!first_pass
-	      && (!(df_get_bb_dirty (e->src))
-		  && !(df_get_bb_dirty (fallthru->src))))
+	      && !((e->src->flags & BB_MODIFIED)
+		   || (fallthru->src->flags & BB_MODIFIED)))
 	    continue;
 
 	  if (try_crossjump_to_edge (mode, e, fallthru))
@@ -1906,8 +1918,8 @@ try_crossjump_bb (int mode, basic_block bb)
 	  /* If nothing changed since the last attempt, there is nothing
 	     we can do.  */
 	  if (!first_pass
-	      && (!(df_get_bb_dirty (e->src))
-		  && !(df_get_bb_dirty (e2->src))))
+	      && !((e->src->flags & BB_MODIFIED)
+		   || (e2->src->flags & BB_MODIFIED)))
 	    continue;
 
 	  if (try_crossjump_to_edge (mode, e, e2))
@@ -1926,6 +1938,299 @@ try_crossjump_bb (int mode, basic_block bb)
   return changed;
 }
 
+/* Search the successors of BB for common insn sequences.  When found,
+   share code between them by moving it across the basic block
+   boundary.  Return true if any changes made.  */
+
+static bool
+try_head_merge_bb (basic_block bb)
+{
+  basic_block final_dest_bb = NULL;
+  int max_match = INT_MAX;
+  edge e0;
+  rtx *headptr, *currptr, *nextptr;
+  bool changed, moveall;
+  unsigned ix;
+  rtx e0_last_head, cond, move_before;
+  unsigned nedges = EDGE_COUNT (bb->succs);
+  rtx jump = BB_END (bb);
+  regset live, live_union;
+
+  /* Nothing to do if there is not at least two outgoing edges.  */
+  if (nedges < 2)
+    return false;
+
+  /* Don't crossjump if this block ends in a computed jump,
+     unless we are optimizing for size.  */
+  if (optimize_bb_for_size_p (bb)
+      && bb != EXIT_BLOCK_PTR
+      && computed_jump_p (BB_END (bb)))
+    return false;
+
+  cond = get_condition (jump, &move_before, true, false);
+  if (cond == NULL_RTX)
+    move_before = jump;
+
+  for (ix = 0; ix < nedges; ix++)
+    if (EDGE_SUCC (bb, ix)->dest == EXIT_BLOCK_PTR)
+      return false;
+
+  for (ix = 0; ix < nedges; ix++)
+    {
+      edge e = EDGE_SUCC (bb, ix);
+      basic_block other_bb = e->dest;
+
+      if (df_get_bb_dirty (other_bb))
+	{
+	  block_was_dirty = true;
+	  return false;
+	}
+
+      if (e->flags & EDGE_ABNORMAL)
+	return false;
+
+      /* Normally, all destination blocks must only be reachable from this
+	 block, i.e. they must have one incoming edge.
+
+	 There is one special case we can handle, that of multiple consecutive
+	 jumps where the first jumps to one of the targets of the second jump.
+	 This happens frequently in switch statements for default labels.
+	 The structure is as follows:
+	 FINAL_DEST_BB
+	 ....
+	 if (cond) jump A;
+	 fall through
+	 BB
+	 jump with targets A, B, C, D...
+	 A
+	 has two incoming edges, from FINAL_DEST_BB and BB
+
+	 In this case, we can try to move the insns through BB and into
+	 FINAL_DEST_BB.  */
+      if (EDGE_COUNT (other_bb->preds) != 1)
+	{
+	  edge incoming_edge, incoming_bb_other_edge;
+	  edge_iterator ei;
+
+	  if (final_dest_bb != NULL
+	      || EDGE_COUNT (other_bb->preds) != 2)
+	    return false;
+
+	  /* We must be able to move the insns across the whole block.  */
+	  move_before = BB_HEAD (bb);
+	  while (!NONDEBUG_INSN_P (move_before))
+	    move_before = NEXT_INSN (move_before);
+
+	  if (EDGE_COUNT (bb->preds) != 1)
+	    return false;
+	  incoming_edge = EDGE_PRED (bb, 0);
+	  final_dest_bb = incoming_edge->src;
+	  if (EDGE_COUNT (final_dest_bb->succs) != 2)
+	    return false;
+	  FOR_EACH_EDGE (incoming_bb_other_edge, ei, final_dest_bb->succs)
+	    if (incoming_bb_other_edge != incoming_edge)
+	      break;
+	  if (incoming_bb_other_edge->dest != other_bb)
+	    return false;
+	}
+    }
+
+  e0 = EDGE_SUCC (bb, 0);
+  e0_last_head = NULL_RTX;
+  changed = false;
+
+  for (ix = 1; ix < nedges; ix++)
+    {
+      edge e = EDGE_SUCC (bb, ix);
+      rtx e0_last, e_last;
+      int nmatch;
+
+      nmatch = flow_find_head_matching_sequence (e0->dest, e->dest,
+						 &e0_last, &e_last, 0);
+      if (nmatch == 0)
+	return false;
+
+      if (nmatch < max_match)
+	{
+	  max_match = nmatch;
+	  e0_last_head = e0_last;
+	}
+    }
+
+  /* If we matched an entire block, we probably have to avoid moving the
+     last insn.  */
+  if (max_match > 0
+      && e0_last_head == BB_END (e0->dest)
+      && (find_reg_note (e0_last_head, REG_EH_REGION, 0)
+	  || control_flow_insn_p (e0_last_head)))
+    {
+      max_match--;
+      if (max_match == 0)
+	return false;
+      do
+	e0_last_head = prev_real_insn (e0_last_head);
+      while (DEBUG_INSN_P (e0_last_head));
+    }
+
+  if (max_match == 0)
+    return false;
+
+  /* We must find a union of the live registers at each of the end points.  */
+  live = BITMAP_ALLOC (NULL);
+  live_union = BITMAP_ALLOC (NULL);
+
+  currptr = XNEWVEC (rtx, nedges);
+  headptr = XNEWVEC (rtx, nedges);
+  nextptr = XNEWVEC (rtx, nedges);
+
+  for (ix = 0; ix < nedges; ix++)
+    {
+      int j;
+      basic_block merge_bb = EDGE_SUCC (bb, ix)->dest;
+      rtx head = BB_HEAD (merge_bb);
+
+      while (!NONDEBUG_INSN_P (head))
+	head = NEXT_INSN (head);
+      headptr[ix] = head;
+      currptr[ix] = head;
+
+      /* Compute the end point and live information  */
+      for (j = 1; j < max_match; j++)
+	do
+	  head = NEXT_INSN (head);
+	while (!NONDEBUG_INSN_P (head));
+      simulate_backwards_to_point (merge_bb, live, head);
+      IOR_REG_SET (live_union, live);
+    }
+
+  /* If we're moving across two blocks, verify the validity of the
+     first move, then adjust the target and let the loop below deal
+     with the final move.  */
+  if (final_dest_bb != NULL)
+    {
+      rtx move_upto;
+
+      moveall = can_move_insns_across (currptr[0], e0_last_head, move_before,
+				       jump, e0->dest, live_union,
+				       NULL, &move_upto);
+      if (!moveall)
+	{
+	  if (move_upto == NULL_RTX)
+	    goto out;
+
+	  while (e0_last_head != move_upto)
+	    {
+	      df_simulate_one_insn_backwards (e0->dest, e0_last_head,
+					      live_union);
+	      e0_last_head = PREV_INSN (e0_last_head);
+	    }
+	}
+      if (e0_last_head == NULL_RTX)
+	goto out;
+
+      jump = BB_END (final_dest_bb);
+      cond = get_condition (jump, &move_before, true, false);
+      if (cond == NULL_RTX)
+	move_before = jump;
+    }
+
+  do
+    {
+      rtx move_upto;
+      moveall = can_move_insns_across (currptr[0], e0_last_head,
+				       move_before, jump, e0->dest, live_union,
+				       NULL, &move_upto);
+      if (!moveall && move_upto == NULL_RTX)
+	{
+	  if (jump == move_before)
+	    break;
+
+	  /* Try again, using a different insertion point.  */
+	  move_before = jump;
+
+#ifdef HAVE_cc0
+	  /* Don't try moving before a cc0 user, as that may invalidate
+	     the cc0.  */
+	  if (reg_mentioned_p (cc0_rtx, jump))
+	    break;
+#endif
+
+	  continue;
+	}
+
+      if (final_dest_bb && !moveall)
+	/* We haven't checked whether a partial move would be OK for the first
+	   move, so we have to fail this case.  */
+	break;
+
+      changed = true;
+      for (;;)
+	{
+	  if (currptr[0] == move_upto)
+	    break;
+	  for (ix = 0; ix < nedges; ix++)
+	    {
+	      rtx curr = currptr[ix];
+	      do
+		curr = NEXT_INSN (curr);
+	      while (!NONDEBUG_INSN_P (curr));
+	      currptr[ix] = curr;
+	    }
+	}
+
+      /* If we can't currently move all of the identical insns, remember
+	 each insn after the range that we'll merge.  */
+      if (!moveall)
+	for (ix = 0; ix < nedges; ix++)
+	  {
+	    rtx curr = currptr[ix];
+	    do
+	      curr = NEXT_INSN (curr);
+	    while (!NONDEBUG_INSN_P (curr));
+	    nextptr[ix] = curr;
+	  }
+
+      reorder_insns (headptr[0], currptr[0], PREV_INSN (move_before));
+      df_set_bb_dirty (EDGE_SUCC (bb, 0)->dest);
+      if (final_dest_bb != NULL)
+	df_set_bb_dirty (final_dest_bb);
+      df_set_bb_dirty (bb);
+      for (ix = 1; ix < nedges; ix++)
+	{
+	  df_set_bb_dirty (EDGE_SUCC (bb, ix)->dest);
+	  delete_insn_chain (headptr[ix], currptr[ix], false);
+	}
+      if (!moveall)
+	{
+	  if (jump == move_before)
+	    break;
+
+	  /* For the unmerged insns, try a different insertion point.  */
+	  move_before = jump;
+
+#ifdef HAVE_cc0
+	  /* Don't try moving before a cc0 user, as that may invalidate
+	     the cc0.  */
+	  if (reg_mentioned_p (cc0_rtx, jump))
+	    break;
+#endif
+
+	  for (ix = 0; ix < nedges; ix++)
+	    currptr[ix] = headptr[ix] = nextptr[ix];
+	}
+    }
+  while (!moveall);
+
+ out:
+  free (currptr);
+  free (headptr);
+  free (nextptr);
+
+  crossjumps_occured |= changed;
+
+  return changed;
+}
+
 /* Return true if BB contains just bb note, or bb note followed
    by only DEBUG_INSNs.  */
 
@@ -1971,6 +2276,7 @@ try_optimize_cfg (int mode)
 	 one predecessor, they may be combined.  */
       do
 	{
+	  block_was_dirty = false;
 	  changed = false;
 	  iterations++;
 
@@ -2170,6 +2476,13 @@ try_optimize_cfg (int mode)
 		  && try_crossjump_bb (mode, b))
 		changed_here = true;
 
+	      if ((mode & CLEANUP_CROSSJUMP)
+		  /* This can lengthen register lifetimes.  Do it only after
+		     reload.  */
+		  && reload_completed
+		  && try_head_merge_bb (b))
+		changed_here = true;
+
 	      /* Don't get confused by the index shift caused by
 		 deleting blocks.  */
 	      if (!changed_here)
@@ -2182,6 +2495,13 @@ try_optimize_cfg (int mode)
 	      && try_crossjump_bb (mode, EXIT_BLOCK_PTR))
 	    changed = true;
 
+	  if (block_was_dirty)
+	    {
+	      /* This should only be set by head-merging.  */
+	      gcc_assert (mode & CLEANUP_CROSSJUMP);
+	      df_analyze ();
+	    }
+
 #ifdef ENABLE_CHECKING
 	  if (changed)
 	    verify_flow_info ();
@@ -2366,8 +2686,7 @@ cleanup_cfg (int mode)
 	  if ((mode & CLEANUP_EXPENSIVE) && !reload_completed
 	      && !delete_trivially_dead_insns (get_insns (), max_reg_num ()))
 	    break;
-	  else if ((mode & CLEANUP_CROSSJUMP)
-		   && crossjumps_occured)
+	  if ((mode & CLEANUP_CROSSJUMP) && crossjumps_occured)
 	    run_fast_dce ();
 	}
       else
diff --git a/gcc/df-core.c b/gcc/df-core.c
index 06ff854..36270bf 100644
--- a/gcc/df-core.c
+++ b/gcc/df-core.c
@@ -1413,6 +1413,7 @@ df_get_bb_dirty (basic_block bb)
 void
 df_set_bb_dirty (basic_block bb)
 {
+  bb->flags |= BB_MODIFIED;
   if (df)
     {
       int p;
diff --git a/gcc/df-problems.c b/gcc/df-problems.c
index 559af91..d9fbc85 100644
--- a/gcc/df-problems.c
+++ b/gcc/df-problems.c
@@ -39,6 +39,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "basic-block.h"
 #include "sbitmap.h"
 #include "bitmap.h"
+#include "target.h"
 #include "timevar.h"
 #include "df.h"
 #include "except.h"
@@ -3541,6 +3542,27 @@ df_simulate_find_defs (rtx insn, bitmap defs)
     }
 }
 
+/* Find the set of uses for INSN.  This includes partial defs.  */
+
+static void
+df_simulate_find_uses (rtx insn, bitmap uses)
+{
+  df_ref *rec;
+  unsigned int uid = INSN_UID (insn);
+
+  for (rec = DF_INSN_UID_DEFS (uid); *rec; rec++)
+    {
+      df_ref def = *rec;
+      if (DF_REF_FLAGS (def) & (DF_REF_PARTIAL | DF_REF_CONDITIONAL))
+	bitmap_set_bit (uses, DF_REF_REGNO (def));
+    }
+  for (rec = DF_INSN_UID_USES (uid); *rec; rec++)
+    {
+      df_ref use = *rec;
+      bitmap_set_bit (uses, DF_REF_REGNO (use));
+    }
+}
+
 /* Find the set of real DEFs, which are not clobbers, for INSN.  */
 
 void
@@ -3768,7 +3790,303 @@ df_simulate_one_insn_forwards (basic_block bb, rtx insn, bitmap live)
     }
   df_simulate_fixup_sets (bb, live);
 }
+
+/* Used by the next two functions to encode information about the
+   memory references we found.  */
+#define MEMREF_NORMAL 1
+#define MEMREF_VOLATILE 2
+
+/* A subroutine of can_move_insns_across_p called through for_each_rtx.
+   Return either MEMREF_NORMAL or MEMREF_VOLATILE if a memory is found.  */
+
+static int
+find_memory (rtx *px, void *data ATTRIBUTE_UNUSED)
+{
+  rtx x = *px;
+
+  if (GET_CODE (x) == ASM_OPERANDS && MEM_VOLATILE_P (x))
+    return MEMREF_VOLATILE;
+
+  if (!MEM_P (x))
+    return 0;
+  if (MEM_VOLATILE_P (x))
+    return MEMREF_VOLATILE;
+  if (MEM_READONLY_P (x))
+    return 0;
+
+  return MEMREF_NORMAL;
+}
+
+/* A subroutine of can_move_insns_across_p called through note_stores.
+   DATA points to an integer in which we set either the bit for
+   MEMREF_NORMAL or the bit for MEMREF_VOLATILE if we find a MEM
+   of either kind.  */
+
+static void
+find_memory_stores (rtx x, const_rtx pat ATTRIBUTE_UNUSED,
+		    void *data ATTRIBUTE_UNUSED)
+{
+  int *pflags = (int *)data;
+  if (GET_CODE (x) == SUBREG)
+    x = XEXP (x, 0);
+  /* Treat stores to SP as stores to memory, this will prevent problems
+     when there are references to the stack frame.  */
+  if (x == stack_pointer_rtx)
+    *pflags |= MEMREF_VOLATILE;
+  if (!MEM_P (x))
+    return;
+  *pflags |= MEM_VOLATILE_P (x) ? MEMREF_VOLATILE : MEMREF_NORMAL;
+}
+
+/* Scan BB backwards, using df_simulate functions to keep track of
+   lifetimes, up to insn POINT.  The result is stored in LIVE.  */
+
+void
+simulate_backwards_to_point (basic_block bb, regset live, rtx point)
+{
+  rtx insn;
+  bitmap_copy (live, df_get_live_out (bb));
+  df_simulate_initialize_backwards (bb, live);
+
+  /* Scan and update life information until we reach the point we're
+     interested in.  */
+  for (insn = BB_END (bb); insn != point; insn = PREV_INSN (insn))
+    df_simulate_one_insn_backwards (bb, insn, live);
+}
+
+/* Return true if it is safe to move a group of insns, described by
+   the range FROM to TO, backwards across another group of insns,
+   described by ACROSS_FROM to ACROSS_TO.  It is assumed that there
+   are no insns between ACROSS_TO and FROM, but they may be in
+   different basic blocks; MERGE_BB is the block from which the
+   insns will be moved.  The caller must pass in a regset MERGE_LIVE
+   which specifies the registers live after TO.
+
+   This function may be called in one of two cases: either we try to
+   move identical instructions from all successor blocks into their
+   predecessor, or we try to move from only one successor block.  If
+   OTHER_BRANCH_LIVE is nonnull, it indicates that we're dealing with
+   the second case.  It should contain a set of registers live at the
+   end of ACROSS_TO which must not be clobbered by moving the insns.
+   In that case, we're also more careful about moving memory references
+   and trapping insns.
+
+   We return false if it is not safe to move the entire group, but it
+   may still be possible to move a subgroup.  PMOVE_UPTO, if nonnull,
+   is set to point at the last moveable insn in such a case.  */
 
+bool
+can_move_insns_across (rtx from, rtx to, rtx across_from, rtx across_to,
+		       basic_block merge_bb, regset merge_live,
+		       regset other_branch_live, rtx *pmove_upto)
+{
+  rtx insn, next, max_to;
+  bitmap merge_set, merge_use, local_merge_live;
+  bitmap test_set, test_use;
+  unsigned i, fail = 0;
+  bitmap_iterator bi;
+  int memrefs_in_across = 0;
+  int mem_sets_in_across = 0;
+  bool trapping_insns_in_across = false;
+
+  if (pmove_upto != NULL)
+    *pmove_upto = NULL_RTX;
+
+  /* Find real bounds, ignoring debug insns.  */
+  while (!NONDEBUG_INSN_P (from) && from != to)
+    from = NEXT_INSN (from);
+  while (!NONDEBUG_INSN_P (to) && from != to)
+    to = PREV_INSN (to);
+
+  for (insn = across_to; ; insn = next)
+    {
+      if (NONDEBUG_INSN_P (insn))
+	{
+	  memrefs_in_across |= for_each_rtx (&PATTERN (insn), find_memory,
+					     NULL);
+	  note_stores (PATTERN (insn), find_memory_stores,
+		       &mem_sets_in_across);
+	  /* This is used just to find sets of the stack pointer.  */
+	  memrefs_in_across |= mem_sets_in_across;
+	  trapping_insns_in_across |= may_trap_p (PATTERN (insn));
+	}
+      next = PREV_INSN (insn);
+      if (insn == across_from)
+	break;
+    }
+
+  /* Collect:
+     MERGE_SET = set of registers set in MERGE_BB
+     MERGE_USE = set of registers used in MERGE_BB and live at its top
+     MERGE_LIVE = set of registers live at the point inside the MERGE
+     range that we've reached during scanning
+     TEST_SET = set of registers set between ACROSS_FROM and ACROSS_END.
+     TEST_USE = set of registers used between ACROSS_FROM and ACROSS_END,
+     and live before ACROSS_FROM.  */
+
+  merge_set = BITMAP_ALLOC (&reg_obstack);
+  merge_use = BITMAP_ALLOC (&reg_obstack);
+  local_merge_live = BITMAP_ALLOC (&reg_obstack);
+  test_set = BITMAP_ALLOC (&reg_obstack);
+  test_use = BITMAP_ALLOC (&reg_obstack);
+
+  /* Compute the set of registers set and used in the ACROSS range.  */
+  if (other_branch_live != NULL)
+    bitmap_copy (test_use, other_branch_live);
+  df_simulate_initialize_backwards (merge_bb, test_use);
+  for (insn = across_to; ; insn = next)
+    {
+      if (NONDEBUG_INSN_P (insn))
+	{
+	  df_simulate_find_defs (insn, test_set);
+	  df_simulate_defs (insn, test_use);
+	  df_simulate_uses (insn, test_use);
+	}
+      next = PREV_INSN (insn);
+      if (insn == across_from)
+	break;
+    }
+
+  /* Compute an upper bound for the amount of insns moved, by finding
+     the first insn in MERGE that sets a register in TEST_USE, or uses
+     a register in TEST_SET.  We also check for calls, trapping operations,
+     and memory references.  */
+  max_to = NULL_RTX;
+  for (insn = from; ; insn = next)
+    {
+      if (CALL_P (insn))
+	break;
+      if (NOTE_P (insn) && NOTE_KIND (insn) == NOTE_INSN_EPILOGUE_BEG)
+	break;
+      if (NONDEBUG_INSN_P (insn))
+	{
+	  if (may_trap_p (PATTERN (insn))
+	      && (trapping_insns_in_across || other_branch_live != NULL))
+	    break;
+
+	  /* We cannot move memory stores past each other, or move memory
+	     reads past stores, at least not without tracking them and
+	     calling true_dependence on every pair.
+
+	     If there is no other branch and no memory references or
+	     sets in the ACROSS range, we can move memory references
+	     freely, even volatile ones.
+
+	     Otherwise, the rules are as follows: volatile memory
+	     references and stores can't be moved at all, and any type
+	     of memory reference can't be moved if there are volatile
+	     accesses or stores in the ACROSS range.  That leaves
+	     normal reads, which can be moved, as the trapping case is
+	     dealt with elsewhere.  */
+	  if (other_branch_live != NULL || memrefs_in_across != 0)
+	    {
+	      int mem_ref_flags = 0;
+	      int mem_set_flags = 0;
+	      note_stores (PATTERN (insn), find_memory_stores, &mem_set_flags);
+	      mem_ref_flags = for_each_rtx (&PATTERN (insn), find_memory,
+					    NULL);
+	      /* Catch sets of the stack pointer.  */
+	      mem_ref_flags |= mem_set_flags;
+
+	      if ((mem_ref_flags | mem_set_flags) & MEMREF_VOLATILE)
+		break;
+	      if ((memrefs_in_across & MEMREF_VOLATILE) && mem_ref_flags != 0)
+		break;
+	      if (mem_set_flags != 0
+		  || (mem_sets_in_across != 0 && mem_ref_flags != 0))
+		break;
+	    }
+	  df_simulate_find_uses (insn, merge_use);
+	  /* We're only interested in uses which use a value live at
+	     the top, not one previously set in this block.  */
+	  bitmap_and_compl_into (merge_use, merge_set);
+	  df_simulate_find_defs (insn, merge_set);
+	  if (bitmap_intersect_p (merge_set, test_use)
+	      || bitmap_intersect_p (merge_use, test_set))
+	    break;
+	  max_to = insn;
+	}
+      next = NEXT_INSN (insn);
+      if (insn == to)
+	break;
+    }
+  if (max_to != to)
+    fail = 1;
+
+  if (max_to == NULL_RTX || (fail && pmove_upto == NULL))
+    goto out;
+
+  /* Now, lower this upper bound by also taking into account that
+     a range of insns moved across ACROSS must not leave a register
+     live at the end that will be clobbered in ACROSS.  We need to
+     find a point where TEST_SET & LIVE == 0.
+
+     Insns in the MERGE range that set registers which are also set
+     in the ACROSS range may still be moved as long as we also move
+     later insns which use the results of the set, and make the
+     register dead again.  This is verified by the condition stated
+     above.  We only need to test it for registers that are set in
+     the moved region.
+
+     MERGE_LIVE is provided by the caller and holds live registers after
+     TO.  */
+  bitmap_copy (local_merge_live, merge_live);
+  for (insn = to; insn != max_to; insn = PREV_INSN (insn))
+    df_simulate_one_insn_backwards (merge_bb, insn, local_merge_live);
+
+  /* We're not interested in registers that aren't set in the moved
+     region at all.  */
+  bitmap_and_into (local_merge_live, merge_set);
+  for (;;)
+    {
+      if (NONDEBUG_INSN_P (insn))
+	{
+	  if (!bitmap_intersect_p (test_set, local_merge_live))
+	    {
+	      max_to = insn;
+	      break;
+	    }
+
+	  df_simulate_one_insn_backwards (merge_bb, insn,
+					  local_merge_live);
+	}
+      if (insn == from)
+	{
+	  fail = 1;
+	  goto out;
+	}
+      insn = PREV_INSN (insn);
+    }
+
+  if (max_to != to)
+    fail = 1;
+
+  if (pmove_upto)
+    *pmove_upto = max_to;
+
+  /* For small register class machines, don't lengthen lifetimes of
+     hard registers before reload.  */
+  if (! reload_completed
+      && targetm.small_register_classes_for_mode_p (VOIDmode))
+    {
+      EXECUTE_IF_SET_IN_BITMAP (merge_set, 0, i, bi)
+	{
+	  if (i < FIRST_PSEUDO_REGISTER
+	      && ! fixed_regs[i]
+	      && ! global_regs[i])
+	    fail = 1;
+	}
+    }
+
+ out:
+  BITMAP_FREE (merge_set);
+  BITMAP_FREE (merge_use);
+  BITMAP_FREE (local_merge_live);
+  BITMAP_FREE (test_set);
+  BITMAP_FREE (test_use);
+
+  return !fail;
+}
 
 
 /*----------------------------------------------------------------------------
diff --git a/gcc/df.h b/gcc/df.h
index a9bc366..684b06d 100644
--- a/gcc/df.h
+++ b/gcc/df.h
@@ -970,7 +970,9 @@ extern void df_simulate_one_insn_backwards (basic_block, rtx, bitmap);
 extern void df_simulate_finalize_backwards (basic_block, bitmap);
 extern void df_simulate_initialize_forwards (basic_block, bitmap);
 extern void df_simulate_one_insn_forwards (basic_block, rtx, bitmap);
-
+extern void simulate_backwards_to_point (basic_block, regset, rtx);
+extern bool can_move_insns_across (rtx, rtx, rtx, rtx, basic_block, regset,
+				   regset, rtx *);
 /* Functions defined in df-scan.c.  */
 
 extern void df_scan_alloc (bitmap);
diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index e5a8835..eee5cc7 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -102,7 +102,6 @@ static int noce_find_if_block (basic_block, edge, edge, int);
 static int cond_exec_find_if_block (ce_if_block_t *);
 static int find_if_case_1 (basic_block, edge, edge);
 static int find_if_case_2 (basic_block, edge, edge);
-static int find_memory (rtx *, void *);
 static int dead_or_predicable (basic_block, basic_block, basic_block,
 			       basic_block, int);
 static void noce_emit_move_insn (rtx, rtx);
@@ -3975,15 +3974,6 @@ find_if_case_2 (basic_block test_bb, edge then_edge, edge else_edge)
   return TRUE;
 }
 
-/* A subroutine of dead_or_predicable called through for_each_rtx.
-   Return 1 if a memory is found.  */
-
-static int
-find_memory (rtx *px, void *data ATTRIBUTE_UNUSED)
-{
-  return MEM_P (*px);
-}
-
 /* Used by the code above to perform the actual rtl transformations.
    Return TRUE if successful.
 
@@ -3997,7 +3987,7 @@ dead_or_predicable (basic_block test_bb, basic_block merge_bb,
 		    basic_block other_bb, basic_block new_dest, int reversep)
 {
   rtx head, end, jump, earliest = NULL_RTX, old_dest, new_label = NULL_RTX;
-  bitmap merge_set = NULL, merge_set_noclobber = NULL;
+  bitmap merge_set = NULL;
   /* Number of pending changes.  */
   int n_validated_changes = 0;
 
@@ -4087,129 +4077,46 @@ dead_or_predicable (basic_block test_bb, basic_block merge_bb,
     }
 #endif
 
+  /* If we allocated new pseudos (e.g. in the conditional move
+     expander called from noce_emit_cmove), we must resize the
+     array first.  */
+  if (max_regno < max_reg_num ())
+    max_regno = max_reg_num ();
+
   /* Try the NCE path if the CE path did not result in any changes.  */
   if (n_validated_changes == 0)
     {
+      rtx cond, insn;
+      regset live;
+      bool success;
+
       /* In the non-conditional execution case, we have to verify that there
 	 are no trapping operations, no calls, no references to memory, and
 	 that any registers modified are dead at the branch site.  */
 
-      rtx insn, cond, prev;
-      bitmap test_live, test_set;
-      bool intersect = false;
-
-      /* Check for no calls or trapping operations.  */
-      for (insn = head; ; insn = NEXT_INSN (insn))
-	{
-	  if (CALL_P (insn))
-	    return FALSE;
-	  if (NONDEBUG_INSN_P (insn))
-	    {
-	      if (may_trap_p (PATTERN (insn)))
-		return FALSE;
-
-	      /* ??? Even non-trapping memories such as stack frame
-		 references must be avoided.  For stores, we collect
-		 no lifetime info; for reads, we'd have to assert
-		 true_dependence false against every store in the
-		 TEST range.  */
-	      if (for_each_rtx (&PATTERN (insn), find_memory, NULL))
-		return FALSE;
-	    }
-	  if (insn == end)
-	    break;
-	}
-
-      if (! any_condjump_p (jump))
+      if (!any_condjump_p (jump))
 	return FALSE;
 
       /* Find the extent of the conditional.  */
       cond = noce_get_condition (jump, &earliest, false);
-      if (! cond)
+      if (!cond)
 	return FALSE;
 
-      /* Collect:
-	   MERGE_SET = set of registers set in MERGE_BB
-	   MERGE_SET_NOCLOBBER = like MERGE_SET, but only includes registers
-	     that are really set, not just clobbered.
-	   TEST_LIVE = set of registers live at EARLIEST
-	   TEST_SET = set of registers set between EARLIEST and the
-	     end of the block.  */
+      live = BITMAP_ALLOC (&reg_obstack);
+      simulate_backwards_to_point (merge_bb, live, end);
+      success = can_move_insns_across (head, end, earliest, jump,
+				       merge_bb, live,
+				       df_get_live_in (other_bb), NULL);
+      BITMAP_FREE (live);
+      if (!success)
+	return FALSE;
 
+      /* Collect the set of registers set in MERGE_BB.  */
       merge_set = BITMAP_ALLOC (&reg_obstack);
-      merge_set_noclobber = BITMAP_ALLOC (&reg_obstack);
-
-      /* If we allocated new pseudos (e.g. in the conditional move
-	 expander called from noce_emit_cmove), we must resize the
-	 array first.  */
-      if (max_regno < max_reg_num ())
-	max_regno = max_reg_num ();
 
       FOR_BB_INSNS (merge_bb, insn)
-	{
-	  if (NONDEBUG_INSN_P (insn))
-	    {
-	      df_simulate_find_defs (insn, merge_set);
-	      df_simulate_find_noclobber_defs (insn, merge_set_noclobber);
-	    }
-	}
-
-      /* For small register class machines, don't lengthen lifetimes of
-	 hard registers before reload.  */
-      if (! reload_completed
-	  && targetm.small_register_classes_for_mode_p (VOIDmode))
-	{
-	  unsigned i;
-	  bitmap_iterator bi;
-
-          EXECUTE_IF_SET_IN_BITMAP (merge_set_noclobber, 0, i, bi)
-	    {
-	      if (i < FIRST_PSEUDO_REGISTER
-		  && ! fixed_regs[i]
-		  && ! global_regs[i])
-		goto fail;
-	    }
-	}
-
-      /* For TEST, we're interested in a range of insns, not a whole block.
-	 Moreover, we're interested in the insns live from OTHER_BB.  */
-      test_live = BITMAP_ALLOC (&reg_obstack);
-      test_set = BITMAP_ALLOC (&reg_obstack);
-
-      /* The loop below takes the set of live registers
-         after JUMP, and calculates the live set before EARLIEST. */
-      bitmap_copy (test_live, df_get_live_in (other_bb));
-      df_simulate_initialize_backwards (test_bb, test_live);
-      for (insn = jump; ; insn = prev)
-	{
-	  if (INSN_P (insn))
-	    {
-	      df_simulate_find_defs (insn, test_set);
-	      df_simulate_one_insn_backwards (test_bb, insn, test_live);
-	    }
-	  prev = PREV_INSN (insn);
-	  if (insn == earliest)
-	    break;
-	}
-
-      /* We can perform the transformation if
-	   MERGE_SET_NOCLOBBER & TEST_SET
-	 and
-	   MERGE_SET & TEST_LIVE
-	 and
-	   TEST_SET & DF_LIVE_IN (merge_bb)
-	 are empty.  */
-
-      if (bitmap_intersect_p (merge_set_noclobber, test_set)
-	  || bitmap_intersect_p (merge_set, test_live)
-	  || bitmap_intersect_p (test_set, df_get_live_in (merge_bb)))
-	intersect = true;
-
-      BITMAP_FREE (test_live);
-      BITMAP_FREE (test_set);
-
-      if (intersect)
-	goto fail;
+	if (NONDEBUG_INSN_P (insn))
+	  df_simulate_find_defs (insn, merge_set);
     }
 
  no_body:
@@ -4288,7 +4195,6 @@ dead_or_predicable (basic_block test_bb, basic_block merge_bb,
 	    remove_reg_equal_equiv_notes_for_regno (i);
 
 	  BITMAP_FREE (merge_set);
-	  BITMAP_FREE (merge_set_noclobber);
 	}
 
       reorder_insns (head, end, PREV_INSN (earliest));
@@ -4307,12 +4213,10 @@ dead_or_predicable (basic_block test_bb, basic_block merge_bb,
 
  cancel:
   cancel_changes (0);
- fail:
+
   if (merge_set)
-    {
-      BITMAP_FREE (merge_set);
-      BITMAP_FREE (merge_set_noclobber);
-    }
+    BITMAP_FREE (merge_set);
+
   return FALSE;
 }
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index a9ed2f8..8c4d838 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,12 @@
+2010-12-14  Bernd Schmidt  <bernds@codesourcery.com>
+
+	PR rtl-optimization/44374
+	Reapply patch with fixes.
+	* gcc.target/arm/headmerge-1.c: New test.
+	* gcc.target/arm/headmerge-2.c: New test.
+	* gcc.target/i386/headmerge-1.c: New test.
+	* gcc.target/i386/headmerge-2.c: New test.
+
 2010-12-13  Jason Merrill  <jason@redhat.com>
 
 	PR c++/46873
diff --git a/gcc/testsuite/gcc.target/arm/headmerge-1.c b/gcc/testsuite/gcc.target/arm/headmerge-1.c
new file mode 100644
index 0000000..218c6a2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/headmerge-1.c
@@ -0,0 +1,14 @@
+/* { dg-do compile }  */
+/* { dg-options "-O2" }  */
+/* { dg-final { scan-assembler-times "#120" 1 } } */
+
+extern void foo1 (int);
+extern void foo2 (int);
+
+void t (int x, int y)
+{
+  if (y < 5)
+    foo1 (120);
+  else
+    foo2 (120);
+}
diff --git a/gcc/testsuite/gcc.target/arm/headmerge-2.c b/gcc/testsuite/gcc.target/arm/headmerge-2.c
new file mode 100644
index 0000000..36637a6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/headmerge-2.c
@@ -0,0 +1,35 @@
+/* { dg-do compile }  */
+/* { dg-options "-O2" }  */
+/* { dg-final { scan-assembler-times "120" 1 } } */
+
+extern void foo1 (int);
+extern void foo2 (int);
+extern void foo3 (int);
+extern void foo4 (int);
+extern void foo5 (int);
+extern void foo6 (int);
+
+void t (int x, int y)
+{
+  switch (y)
+    {
+    case 1:
+      foo1 (120);
+      break;
+    case 5:
+      foo2 (120);
+      break;
+    case 7:
+      foo3 (120);
+      break;
+    case 10:
+      foo4 (120);
+      break;
+    case 13:
+      foo5 (120);
+      break;
+    default:
+      foo6 (120);
+      break;
+    }
+}
diff --git a/gcc/testsuite/gcc.target/i386/headmerge-1.c b/gcc/testsuite/gcc.target/i386/headmerge-1.c
new file mode 100644
index 0000000..941028c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/headmerge-1.c
@@ -0,0 +1,14 @@
+/* { dg-do compile }  */
+/* { dg-options "-O2" }  */
+/* { dg-final { scan-assembler-times "120" 1 } } */
+
+extern void foo1 (int);
+extern void foo2 (int);
+
+void t (int x, int y)
+{
+  if (y < 5)
+    foo1 (120);
+  else
+    foo2 (120);
+}
diff --git a/gcc/testsuite/gcc.target/i386/headmerge-2.c b/gcc/testsuite/gcc.target/i386/headmerge-2.c
new file mode 100644
index 0000000..36637a6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/headmerge-2.c
@@ -0,0 +1,35 @@
+/* { dg-do compile }  */
+/* { dg-options "-O2" }  */
+/* { dg-final { scan-assembler-times "120" 1 } } */
+
+extern void foo1 (int);
+extern void foo2 (int);
+extern void foo3 (int);
+extern void foo4 (int);
+extern void foo5 (int);
+extern void foo6 (int);
+
+void t (int x, int y)
+{
+  switch (y)
+    {
+    case 1:
+      foo1 (120);
+      break;
+    case 5:
+      foo2 (120);
+      break;
+    case 7:
+      foo3 (120);
+      break;
+    case 10:
+      foo4 (120);
+      break;
+    case 13:
+      foo5 (120);
+      break;
+    default:
+      foo6 (120);
+      break;
+    }
+}