re PR rtl-optimization/56151 (Performance degradation after r194054 on x86 Atom.)

	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.

Co-Authored-By: Steven Bosscher <steven@gcc.gnu.org>

From-SVN: r195972

4 files changed, 59 insertions, 6 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 360514e..d959c9c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2013-02-12  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.
+
 2013-02-11  Sriraman Tallam  <tmsriramgoogle.com>
 
 	* doc/extend.texi: Document Function Multiversioning and "default"
diff --git a/gcc/optabs.c b/gcc/optabs.c
index 8a3d3a9..c1dacf4 100644
--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -190,17 +190,40 @@ add_equal_note (rtx insns, rtx target, enum rtx_code code, rtx op0, rtx op1)
   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.  If the target
+	     supports MEM = MEM op X instructions, it is sometimes too hard
+	     to reconstruct that form later, especially if X is also a memory,
+	     and due to multiple occurrences of addresses the address might
+	     be forced into register unnecessarily.
+	     Note that not emitting the REG_EQUIV note might inhibit
+	     CSE in some cases.  */
+	  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;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 4aa1b4c..e9ab329 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2013-02-12  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/56151
+	* gcc.target/i386/pr56151.c: New test.
+
 2013-02-11  Sriraman Tallam  <tmsriramgoogle.com>
 
 	* g++.dg/ext/mv12.C: New test.
diff --git a/gcc/testsuite/gcc.target/i386/pr56151.c b/gcc/testsuite/gcc.target/i386/pr56151.c
new file mode 100644
index 0000000..24a1b8a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr56151.c
@@ -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 } } } */