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

[Jakub Jelinek <jakub@redhat.com>]

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?

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