[backport gcc-4.8/trunk r196478, ChangeLogs were committed
 as part of the unrelated r196479 <mikpe@it.uu.se>]
 
Date: Tue, 5 Mar 2013 17:26:46 +0100
From: Jakub Jelinek <jakub at redhat dot com>
Subject: [PATCH] Avoid extending lifetime of likely spilled hard regs in ifcvt before reload (PR rtl-optimization/56484)
List-Archive: <http://gcc.gnu.org/ml/gcc-patches/>

Hi!

Without this patch, ifcvt extends lifetime of %eax hard register,
which causes reload/LRA ICE later on.  Combiner and other passes try hard
not to do that, even ifcvt has code for it if x is a hard register a few
lines below it, but in this case the hard register is SET_SRC (set_b).

With this patch we just use the pseudo (x) which has been initialized
from the hard register before the conditional.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

gcc/

2013-03-05  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/56484
	* ifcvt.c (noce_process_if_block): If else_bb is NULL, avoid extending
	lifetimes of hard registers on small register class machines.

gcc/testsuite/

2013-03-05  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/56484
	* gcc.c-torture/compile/pr56484.c: New test.

--- gcc-4.7.2/gcc/ifcvt.c.~1~	2012-02-27 15:30:44.000000000 +0100
+++ gcc-4.7.2/gcc/ifcvt.c	2013-03-09 12:59:47.690492428 +0100
@@ -2495,6 +2495,12 @@ noce_process_if_block (struct noce_if_in
 	  || ! noce_operand_ok (SET_SRC (set_b))
 	  || reg_overlap_mentioned_p (x, SET_SRC (set_b))
 	  || modified_between_p (SET_SRC (set_b), insn_b, jump)
+	  /* Avoid extending the lifetime of hard registers on small
+	     register class machines.  */
+	  || (REG_P (SET_SRC (set_b))
+	      && HARD_REGISTER_P (SET_SRC (set_b))
+	      && targetm.small_register_classes_for_mode_p
+		   (GET_MODE (SET_SRC (set_b))))
 	  /* Likewise with X.  In particular this can happen when
 	     noce_get_condition looks farther back in the instruction
 	     stream than one might expect.  */
--- gcc-4.7.2/gcc/testsuite/gcc.c-torture/compile/pr56484.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.2/gcc/testsuite/gcc.c-torture/compile/pr56484.c	2013-03-09 12:59:47.690492428 +0100
@@ -0,0 +1,17 @@
+/* PR rtl-optimization/56484 */
+
+unsigned char b[4096];
+int bar (void);
+
+int
+foo (void)
+{
+  int a = 0;
+  while (bar ())
+    {
+      int c = bar ();
+      a = a < 0 ? a : c;
+      __builtin_memset (b, 0, sizeof b);
+    }
+  return a;
+}