[PATCH] match.pd: Optimize (x < 0) ^ (y < 0) to (x ^ y) < 0 etc. [PR96681]

[Richard Biener]

On January 15, 2021 7:25:33 PM GMT+01:00, Jakub Jelinek <jakub@redhat.com> wrote:
>Hi!
>
>This patch simplifies comparisons that test the sign bit xored
>together.
>If the comparisons are both < 0 or both >= 0, then we should xor the
>operands
>together and compare the result to < 0, if the comparisons are
>different,
>we should compare to >= 0.
>
>Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Ok. 

Thanks, 
Richard. 

>2021-01-15  Jakub Jelinek  <jakub@redhat.com>
>
>	PR tree-optimization/96681
>	* match.pd ((x < 0) ^ (y < 0) to (x ^ y) < 0): New simplification.
>	((x >= 0) ^ (y >= 0) to (x ^ y) < 0): Likewise.
>	((x < 0) ^ (y >= 0) to (x ^ y) >= 0): Likewise.
>	((x >= 0) ^ (y < 0) to (x ^ y) >= 0): Likewise.
>
>	* gcc.dg/tree-ssa/pr96681.c: New test.
>
>--- gcc/match.pd.jj	2021-01-15 13:12:11.232019067 +0100
>+++ gcc/match.pd	2021-01-15 14:00:21.567135280 +0100
>@@ -3993,6 +3993,24 @@ (define_operator_list COND_TERNARY
>    (if (single_use (@2))
>     (cmp @0 @1)))))
> 
>+/* Simplify (x < 0) ^ (y < 0) to (x ^ y) < 0 and
>+   (x >= 0) ^ (y >= 0) to (x ^ y) < 0.  */
>+(for cmp (lt ge)
>+ (simplify
>+  (bit_xor (cmp:s @0 integer_zerop) (cmp:s @1 integer_zerop))
>+   (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
>+	&& !TYPE_UNSIGNED (TREE_TYPE (@0))
>+	&& types_match (TREE_TYPE (@0), TREE_TYPE (@1)))
>+    (lt (bit_xor @0 @1) { build_zero_cst (TREE_TYPE (@0)); }))))
>+/* Simplify (x < 0) ^ (y >= 0) to (x ^ y) >= 0 and
>+   (x >= 0) ^ (y < 0) to (x ^ y) >= 0.  */
>+(simplify
>+ (bit_xor:c (lt:s @0 integer_zerop) (ge:s @1 integer_zerop))
>+  (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
>+       && !TYPE_UNSIGNED (TREE_TYPE (@0))
>+       && types_match (TREE_TYPE (@0), TREE_TYPE (@1)))
>+   (ge (bit_xor @0 @1) { build_zero_cst (TREE_TYPE (@0)); })))
>+
> /* Transform comparisons of the form X * C1 CMP 0 to X CMP 0 in the
>    signed arithmetic case.  That form is created by the compiler
>    often enough for folding it to be of value.  One example is in
>--- gcc/testsuite/gcc.dg/tree-ssa/pr96681.c.jj	2021-01-15
>14:16:25.254366911 +0100
>+++ gcc/testsuite/gcc.dg/tree-ssa/pr96681.c	2021-01-15
>14:18:30.618941775 +0100
>@@ -0,0 +1,35 @@
>+/* PR tree-optimization/96681 */
>+/* { dg-do compile } */
>+/* { dg-options "-O2 -fdump-tree-optimized" } */
>+/* { dg-final { scan-tree-dump-times " \\^ " 5 "optimized" } } */
>+/* { dg-final { scan-tree-dump-times " (?:<|>=) 0" 5 "optimized" } }
>*/
>+
>+int
>+foo (int x, int y)
>+{
>+  return (x < 0) ^ (y < 0);
>+}
>+
>+int
>+bar (int x, int y)
>+{
>+  return (x > -1) ^ (y > -1);
>+}
>+
>+int
>+baz (int x, int y)
>+{
>+  return (x ^ y) < 0;
>+}
>+
>+int
>+qux (int x, int y)
>+{
>+  return (x ^ y) >= 0;
>+}
>+
>+int
>+corge (int x, int y)
>+{
>+  return (x >= 0) ^ (y < 0);
>+}
>
>	Jakub