[PATCH] match.pd: Optimize ((cst << x) & 1) [PR96669]

[Richard Biener]

On January 16, 2021 1:59:50 AM GMT+01:00, Jakub Jelinek <jakub@redhat.com> wrote:
>On Fri, Jan 15, 2021 at 09:21:07PM +0100, Richard Biener wrote:
>> >BTW, I've tried to also fix what the PR wanted primarily by adding
>> >/* Simplify (CST << x) & 1 to 0 if CST is even or to x == 0 if it is
>> >odd.  /
>> >(simplify
>> > (bit_and (lshift INTEGER_CST@1 @0) integer_onep)
>> >  (if ((wi::to_wide (@1) & 1) != 0)
>> >   (eq @0 { build_zero_cst (TREE_TYPE (@0)); })
>> >   ({ build_zero_cst (type); })))
>> >simplifier before this one, but genmatch.c doesn't seem to put it
>into
>> >the
>> >resulting files.  Is there a way to figure out what is going on?
>
>Actually, it was a PEBKAC, it helps when the comment termination is */
>rather than just / alone.
>
>The following works fine, no need to stick it into an unrelated
>pattern.
>
>Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Ok. 

Richard. 

>2021-01-15  Jakub Jelinek  <jakub@redhat.com>
>
>	PR tree-optimization/96669
>	* match.pd ((CST << x) & 1 -> x == 0): New simplification.
>
>	* gcc.dg/tree-ssa/pr96669-1.c: Adjust regexp.
>	* gcc.dg/tree-ssa/pr96669-2.c: New test.
>
>--- gcc/match.pd.jj	2021-01-15 21:12:07.656060308 +0100
>+++ gcc/match.pd	2021-01-15 23:51:34.038119715 +0100
>@@ -3117,6 +3117,13 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>       (op @0 { build_int_cst (TREE_TYPE (@1), low); })))))))
> 
> 
>+/* Simplify (CST << x) & 1 to 0 if CST is even or to x == 0 if it is
>odd.  */
>+(simplify
>+ (bit_and (lshift INTEGER_CST@1 @0) integer_onep)
>+  (if ((wi::to_wide (@1) & 1) != 0)
>+   (convert (eq:boolean_type_node @0 { build_zero_cst (TREE_TYPE
>(@0)); }))
>+   { build_zero_cst (type); }))
>+
>/* Simplify ((C << x) & D) != 0 where C and D are power of two
>constants,
>    either to false if D is smaller (unsigned comparison) than C, or to
>    x == log2 (D) - log2 (C).  Similarly for right shifts.  */
>--- gcc/testsuite/gcc.dg/tree-ssa/pr96669-1.c.jj	2021-01-15
>22:03:18.089279035 +0100
>+++ gcc/testsuite/gcc.dg/tree-ssa/pr96669-1.c	2021-01-16
>01:55:42.800379400 +0100
>@@ -1,7 +1,7 @@
> /* PR tree-optimization/96669 */
> /* { dg-do compile } */
> /* { dg-options "-O2 -fdump-tree-original" } */
>-/* { dg-final { scan-tree-dump "return a == 0;" "original" } } */
>+/* { dg-final { scan-tree-dump "a == 0" "original" } } */
> /* { dg-final { scan-tree-dump "return 1;" "original" } } */
> /* { dg-final { scan-tree-dump "return c == 3;" "original" } } */
> /* { dg-final { scan-tree-dump "return d != 1;" "original" } } */
>--- gcc/testsuite/gcc.dg/tree-ssa/pr96669-2.c.jj	2021-01-15
>22:03:47.075951818 +0100
>+++ gcc/testsuite/gcc.dg/tree-ssa/pr96669-2.c	2021-01-16
>01:56:02.859156051 +0100
>@@ -0,0 +1,30 @@
>+/* PR tree-optimization/96669 */
>+/* { dg-do compile } */
>+/* { dg-options "-O2 -fdump-tree-original" } */
>+/* { dg-final { scan-tree-dump "a == 0" "original" } } */
>+/* { dg-final { scan-tree-dump-times "return 0;" 2 "original" } } */
>+/* { dg-final { scan-tree-dump "c == 0" "original" } } */
>+
>+int
>+f1 (int a)
>+{
>+  return ((1 << a) & 1);
>+}
>+
>+int
>+f2 (int b)
>+{
>+  return ((2 << b) & 1);
>+}
>+
>+int
>+f3 (int c)
>+{
>+  return ((35 << c) & 1);
>+}
>+
>+int
>+f4 (int d)
>+{
>+  return ((42 << d) & 1);
>+}
>
>
>	Jakub