From patchwork Thu Oct  6 16:01:39 2011
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Subject: Initial shrink-wrapping patch
Date: Thu, 06 Oct 2011 06:01:39 -0000
From: Bernd Schmidt <bernds@codesourcery.com>
X-Patchwork-Id: 118119
Message-Id: <4E8DD0E3.5010106@codesourcery.com>
To: Ian Lance Taylor <iant@google.com>
Cc: Richard Henderson <rth@redhat.com>,
 Richard Guenther <richard.guenther@gmail.com>,
 GCC Patches <gcc-patches@gcc.gnu.org>, richard.sandiford@linaro.org

On 10/06/11 17:57, Ian Lance Taylor wrote:
> There is absolutely no reason to try to shrink wrap that code.  It will
> never help.  That code always has to be first.  It especially has to be
> first because the gold linker recognizes the prologue specially when a
> split-stack function calls a non-split-stack function, in order to
> request a larger stack.

Urgh, ok.

> Therefore, it seems to me that we should apply shrink wrapping to the
> function as it exists *before* the split-stack prologue is created.  The
> flag_split_stack bit should be moved after the flag_shrink_wrap bit.

Sounds like we just need to always emit the split prologue on the
original entry edge then. Can you test the following with Go?


Bernd
* function.c (thread_prologue_and_epilogue_insns): Emit split
	prologue on the orig_entry_edge. Don't account for it in
	prologue_clobbered.


Index: gcc/function.c
===================================================================
--- gcc/function.c	(revision 179619)
+++ gcc/function.c	(working copy)
@@ -5602,10 +5602,6 @@ thread_prologue_and_epilogue_insns (void
 	  note_stores (PATTERN (p_insn), record_hard_reg_sets,
 		       &prologue_clobbered);
 	}
-      for (p_insn = split_prologue_seq; p_insn; p_insn = NEXT_INSN (p_insn))
-	if (NONDEBUG_INSN_P (p_insn))
-	  note_stores (PATTERN (p_insn), record_hard_reg_sets,
-		       &prologue_clobbered);
 
       bitmap_initialize (&bb_antic_flags, &bitmap_default_obstack);
       bitmap_initialize (&bb_on_list, &bitmap_default_obstack);
@@ -5758,7 +5754,7 @@ thread_prologue_and_epilogue_insns (void
 
   if (split_prologue_seq != NULL_RTX)
     {
-      insert_insn_on_edge (split_prologue_seq, entry_edge);
+      insert_insn_on_edge (split_prologue_seq, orig_entry_edge);
       inserted = true;
     }
   if (prologue_seq != NULL_RTX)