[backport gcc-4.8/trunk r192439 <mikpe@it.uu.se>]

gcc/

2012-10-14  Steven Bosscher  <steven@gcc.gnu.org>

	PR rtl-optimization/54919
	* loop-unroll.c (struct var_to_expand): Remove accum_pos field.
	(analyze_insn_to_expand_var): Do not record accum_pos.
	(expand_var_during_unrolling): Use validate_replace_rtx_group to
	perform replacement of all references to SET_DEST (set) with the
	new register, including references in REG_EQUAL notes.
	(insert_var_expansion_initialization): Insert initializatio insns
	at the bottom of the pre-header of the loop.

gcc/testsuite/

2012-10-14  Steven Bosscher  <steven@gcc.gnu.org>

	PR rtl-optimization/54919
	* gcc.dg/pr54919.c: New testcase.

--- gcc-4.7.3/gcc/loop-unroll.c.~1~	2011-12-01 17:57:07.000000000 +0100
+++ gcc-4.7.3/gcc/loop-unroll.c	2013-05-19 17:17:55.998064786 +0200
@@ -101,10 +101,6 @@ struct var_to_expand
                                       the accumulator.  If REUSE_EXPANSION is 0 reuse
                                       the original accumulator.  Else use
                                       var_expansions[REUSE_EXPANSION - 1].  */
-  unsigned accum_pos;              /* The position in which the accumulator is placed in
-                                      the insn src.  For example in x = x + something
-                                      accum_pos is 0 while in x = something + x accum_pos
-                                      is 1.  */
 };
 
 /* Information about optimization applied in
@@ -1723,7 +1719,6 @@ analyze_insn_to_expand_var (struct loop
   ves->op = GET_CODE (src);
   ves->expansion_count = 0;
   ves->reuse_expansion = 0;
-  ves->accum_pos = accum_pos;
   return ves;
 }
 
@@ -2083,9 +2078,7 @@ expand_var_during_unrolling (struct var_
   else
     new_reg = get_expansion (ve);
 
-  validate_change (insn, &SET_DEST (set), new_reg, 1);
-  validate_change (insn, &XEXP (SET_SRC (set), ve->accum_pos), new_reg, 1);
-
+  validate_replace_rtx_group (SET_DEST (set), new_reg, insn);
   if (apply_change_group ())
     if (really_new_expansion)
       {
@@ -2125,7 +2118,7 @@ static void
 insert_var_expansion_initialization (struct var_to_expand *ve,
 				     basic_block place)
 {
-  rtx seq, var, zero_init, insn;
+  rtx seq, var, zero_init;
   unsigned i;
   enum machine_mode mode = GET_MODE (ve->reg);
   bool honor_signed_zero_p = HONOR_SIGNED_ZEROS (mode);
@@ -2165,11 +2158,7 @@ insert_var_expansion_initialization (str
   seq = get_insns ();
   end_sequence ();
 
-  insn = BB_HEAD (place);
-  while (!NOTE_INSN_BASIC_BLOCK_P (insn))
-    insn = NEXT_INSN (insn);
-
-  emit_insn_after (seq, insn);
+  emit_insn_after (seq, BB_END (place));
 }
 
 /* Combine the variable expansions at the loop exit.  PLACE is the
--- gcc-4.7.3/gcc/testsuite/gcc.dg/pr54919.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.3/gcc/testsuite/gcc.dg/pr54919.c	2013-05-19 17:17:55.998064786 +0200
@@ -0,0 +1,27 @@
+/* PR tree-optimization/54919 */
+/* Testcase by Zdenek Sojka <zsojka@seznam.cz> */
+
+/* { dg-do run } */
+/* { dg-options "-O3 -ffast-math -funroll-loops -fvariable-expansion-in-unroller" } */
+
+int a[10];
+extern void abort(void) __attribute__((noreturn));
+
+int __attribute__((__noinline__, __noclone__))
+foo (void)
+{
+  double d;
+  int i;
+  for (i = 0, d = 0; i < 64; i++)
+    d--;
+  return (int) d;
+}
+
+int
+main (void)
+{
+  if (foo () != -64)
+    abort ();
+  return 0;
+}
+