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

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While we had a ((1 << x) & 1) != 0 to x == 0 optimization already,
this patch adds ((cst << x) & 1) optimization too, this time the
second constant must be 1 though, not some power of two, but the first
one can be any constant.  If it is even, the result is false, if it is
odd, the result is x == 0.

2021-01-16  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.
This commit is contained in:
Jakub Jelinek 2021-01-16 09:21:52 +01:00
parent b673e7547f
commit e2559c3945
3 changed files with 38 additions and 1 deletions
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7
gcc/match.pd
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@ -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. */

2
gcc/testsuite/gcc.dg/tree-ssa/pr96669-1.c
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@ -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" } } */

30
gcc/testsuite/gcc.dg/tree-ssa/pr96669-2.c Normal file
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@ -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);
}