2013-02-11  Jakub Jelinek  <jakub@redhat.com>
	    Steven Bosscher   <steven@gcc.gnu.org>

	PR rtl-optimization/56151
	* optabs.c (add_equal_note): Don't return 0 if target is a MEM,
	equal to op0 or op1, and last_insn pattern is CODE operation
	with MEM dest and one of the operands matches that MEM.

	* gcc.target/i386/pr56151.c: New test.

--- gcc/optabs.c.jj	2013-01-16 08:30:10.000000000 +0100
+++ gcc/optabs.c	2013-02-11 15:28:16.543839881 +0100
@@ -190,17 +190,34 @@ add_equal_note (rtx insns, rtx target, e
   if (GET_CODE (target) == ZERO_EXTRACT)
     return 1;
 
-  /* If TARGET is in OP0 or OP1, punt.  We'd end up with a note referencing
-     a value changing in the insn, so the note would be invalid for CSE.  */
-  if (reg_overlap_mentioned_p (target, op0)
-      || (op1 && reg_overlap_mentioned_p (target, op1)))
-    return 0;
-
   for (last_insn = insns;
        NEXT_INSN (last_insn) != NULL_RTX;
        last_insn = NEXT_INSN (last_insn))
     ;
 
+  /* If TARGET is in OP0 or OP1, punt.  We'd end up with a note referencing
+     a value changing in the insn, so the note would be invalid for CSE.  */
+  if (reg_overlap_mentioned_p (target, op0)
+      || (op1 && reg_overlap_mentioned_p (target, op1)))
+    {
+      if (MEM_P (target)
+	  && (rtx_equal_p (target, op0)
+	      || (op1 && rtx_equal_p (target, op1))))
+	{
+	  /* For MEM target, with MEM = MEM op X, prefer no REG_EQUAL note
+	     over expanding it as temp = MEM op X, MEM = temp.  See PR56151. */
+	  set = single_set (last_insn);
+	  if (set
+	      && GET_CODE (SET_SRC (set)) == code
+	      && MEM_P (SET_DEST (set))
+	      && (rtx_equal_p (SET_DEST (set), XEXP (SET_SRC (set), 0))
+		  || (op1 && rtx_equal_p (SET_DEST (set),
+					  XEXP (SET_SRC (set), 1)))))
+	    return 1;
+	}
+      return 0;
+    }
+
   set = single_set (last_insn);
   if (set == NULL_RTX)
     return 1;
--- gcc/testsuite/gcc.target/i386/pr56151.c.jj	2013-02-11 16:20:51.459752951 +0100
+++ gcc/testsuite/gcc.target/i386/pr56151.c	2013-02-11 16:23:10.590964710 +0100
@@ -0,0 +1,17 @@
+/* PR rtl-optimization/56151 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int vara, varb;
+
+void
+foo (int i, int j)
+{
+  vara = varb | vara;
+}
+
+/* Verify the above is compiled into movl varb, %reg; orl %reg, vara instead
+   of longer movl vara, %reg; orl varb, %reg; movl %reg, vara.  */
+/* { dg-final { scan-assembler-not "mov\[^\n\r]*vara" { target nonpic } } } */
+/* { dg-final { scan-assembler-times "mov\[^\n\r]*varb" 1 { target nonpic } } } */
+/* { dg-final { scan-assembler-times "or\[^\n\r]*vara" 1 { target nonpic } } } */