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

Richard Biener richard.guenther@gmail.com
Sat Sep 6 14:06:00 GMT 2014


On September 6, 2014 12:28:29 PM CEST, Richard Sandiford <rdsandiford@googlemail.com> wrote:
>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?

OK.

Thanks,
Richard.

>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;
>+}




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