RFA: PR62208: const0_rtx used for vectors in simplify-rtx.c

[Richard Sandiford]

This PR is about a case where an XOR+EQ sequence can legitimately
be simplified.  The problem was that the sequence was operating on
vectors while the simplified version used a 0 CONST_INT (const0_rtx).

The code seems to have been like that for a long time but presumably
the bug has been latent until now.  I suppose normally we'd want
earlier optimisations to catch this.

Tested on x86_64-linux-gnu.  OK to install?

Thanks,
Richard


gcc/
        PR rtl-optimization/62208
        * simplify-rtx.c (simplify_relational_operation_1): Use CONST0_RTX
        rather than const0_rtx in eq/ne-xor simplifications.

gcc/testsuite/
        * gcc.target/i386/pr62208.c: New test.

Index: gcc/simplify-rtx.c
===================================================================
--- gcc/simplify-rtx.c  2014-09-06 11:05:20.859563557 +0100
+++ gcc/simplify-rtx.c  2014-09-06 11:05:20.935564244 +0100
@@ -4480,16 +4480,16 @@ simplify_relational_operation_1 (enum rt
       && op0code == XOR
       && rtx_equal_p (XEXP (op0, 0), op1)
       && !side_effects_p (XEXP (op0, 0)))
-    return simplify_gen_relational (code, mode, cmp_mode,
-                                   XEXP (op0, 1), const0_rtx);
+    return simplify_gen_relational (code, mode, cmp_mode, XEXP (op0, 1),
+                                   CONST0_RTX (mode));
 
   /* Likewise (eq/ne (xor x y) y) simplifies to (eq/ne x 0).  */
   if ((code == EQ || code == NE)
       && op0code == XOR
       && rtx_equal_p (XEXP (op0, 1), op1)
       && !side_effects_p (XEXP (op0, 1)))
-    return simplify_gen_relational (code, mode, cmp_mode,
-                                   XEXP (op0, 0), const0_rtx);
+    return simplify_gen_relational (code, mode, cmp_mode, XEXP (op0, 0),
+                                   CONST0_RTX (mode));
 
   /* (eq/ne (xor x C1) C2) simplifies to (eq/ne x (C1^C2)).  */
   if ((code == EQ || code == NE)
Index: gcc/testsuite/gcc.target/i386/pr62208.c
===================================================================
--- /dev/null   2014-09-03 21:33:59.721983712 +0100
+++ gcc/testsuite/gcc.target/i386/pr62208.c     2014-09-06 11:09:18.220708443 
+0100
@@ -0,0 +1,23 @@
+/* { dg-options "-O3 -fwhole-program -march=x86-64" } */
+
+int *a;
+unsigned int b;
+
+void fn2 ()
+{
+  int t[9];
+  for (; b; b++)
+    *a ^= (~t[b] != t[b]);
+}
+
+int fn1 ()
+{
+  fn2 (); 
+  return 0; 
+}
+
+int main ()
+{
+  fn1 (); 
+  return 0;
+}