From 97ad7daba75127b0d09ce9d64753f8e29eebd091 Mon Sep 17 00:00:00 2001
From: amodra <amodra@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Sat, 15 Oct 2011 10:36:00 +0000
Subject: [PATCH] 	* ifcvt.c (dead_or_predicable): Disable if-conversion
 when 	doing so is likely to kill a shrink-wrapping opportunity.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@180028 138bc75d-0d04-0410-961f-82ee72b054a4
---
 gcc/ChangeLog |  3 +++
 gcc/ifcvt.c   | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 960b79b..8a0f6ef 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,8 @@
 2011-10-15  Alan Modra  <amodra@gmail.com>
 
+	* ifcvt.c (dead_or_predicable): Disable if-conversion when
+	doing so is likely to kill a shrink-wrapping opportunity.
+
 	PR rtl-optimization/49941
 	* jump.c (mark_jump_label_1): Set JUMP_LABEL for simple_return jumps.
 
diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index 272cbb7..fee3532 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -4166,6 +4166,64 @@ dead_or_predicable (basic_block test_bb, basic_block merge_bb,
       FOR_BB_INSNS (merge_bb, insn)
 	if (NONDEBUG_INSN_P (insn))
 	  df_simulate_find_defs (insn, merge_set);
+
+      /* If shrink-wrapping, disable this optimization when test_bb is
+	 the first basic block and merge_bb exits.  The idea is to not
+	 move code setting up a return register as that may clobber a
+	 register used to pass function parameters, which then must be
+	 saved in caller-saved regs.  A caller-saved reg requires the
+	 prologue, killing a shrink-wrap opportunity.  */
+      if ((flag_shrink_wrap && HAVE_simple_return && !epilogue_completed)
+	  && ENTRY_BLOCK_PTR->next_bb == test_bb
+	  && single_succ_p (new_dest)
+	  && single_succ (new_dest) == EXIT_BLOCK_PTR
+	  && bitmap_intersect_p (df_get_live_in (new_dest), merge_set))
+	{
+	  regset return_regs;
+	  unsigned int i;
+
+	  return_regs = BITMAP_ALLOC (&reg_obstack);
+
+	  /* Start off with the intersection of regs used to pass
+	     params and regs used to return values.  */
+	  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+	    if (FUNCTION_ARG_REGNO_P (i)
+		&& targetm.calls.function_value_regno_p (i))
+	      bitmap_set_bit (return_regs, INCOMING_REGNO (i));
+
+	  bitmap_and_into (return_regs, df_get_live_out (ENTRY_BLOCK_PTR));
+	  bitmap_and_into (return_regs, df_get_live_in (EXIT_BLOCK_PTR));
+	  if (!bitmap_empty_p (return_regs))
+	    {
+	      FOR_BB_INSNS_REVERSE (new_dest, insn)
+		if (NONDEBUG_INSN_P (insn))
+		  {
+		    df_ref *def_rec;
+		    unsigned int uid = INSN_UID (insn);
+
+		    /* If this insn sets any reg in return_regs..  */
+		    for (def_rec = DF_INSN_UID_DEFS (uid); *def_rec; def_rec++)
+		      {
+			df_ref def = *def_rec;
+			unsigned r = DF_REF_REGNO (def);
+
+			if (bitmap_bit_p (return_regs, r))
+			  break;
+		      }
+		    /* ..then add all reg uses to the set of regs
+		       we're interested in.  */
+		    if (*def_rec)
+		      df_simulate_uses (insn, return_regs);
+		  }
+	      if (bitmap_intersect_p (merge_set, return_regs))
+		{
+		  BITMAP_FREE (return_regs);
+		  BITMAP_FREE (merge_set);
+		  return FALSE;
+		}
+	    }
+	  BITMAP_FREE (return_regs);
+	}
     }
 
  no_body:
-- 
2.7.4