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match.pd: Optimize X / bool_range_Y to X [PR96094]

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When the divisor is bool or has [0, 1] range, as division by
0 is UB, the only remaining option in valid programs is division by 1,
so we can optimize X / bool_range_Y into X.

2020-12-15  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/96094
	* match.pd (X / bool_range_Y -> X): New simplification.

	* gcc.dg/tree-ssa/pr96094.c: New test.
This commit is contained in:
Jakub Jelinek 2020-12-15 22:43:46 +01:00
parent 36c9a3fe3f
commit d41b097350
2 changed files with 43 additions and 4 deletions
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13
gcc/match.pd
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@ -348,11 +348,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
/* But not for 0 / 0 so that we can get the proper warnings and errors. */
(if (!integer_zerop (@1))
@0))
/* X / -1 is -X. */
/* X / -1 is -X. */
(simplify
(div @0 integer_minus_onep@1)
(if (!TYPE_UNSIGNED (type))
(negate @0)))
(div @0 integer_minus_onep@1)
(if (!TYPE_UNSIGNED (type))
(negate @0)))
/* X / bool_range_Y is X. */
(simplify
(div @0 SSA_NAME@1)
(if (INTEGRAL_TYPE_P (type) && ssa_name_has_boolean_range (@1))
@0))
/* X / X is one. */
(simplify
(div @0 @0)

34
gcc/testsuite/gcc.dg/tree-ssa/pr96094.c Normal file
View File

@ -0,0 +1,34 @@
/* PR tree-optimization/96094 */
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-optimized" } */
/* { dg-final { scan-tree-dump-times "return 34;" 2 "optimized" } } */
/* { dg-final { scan-tree-dump-times "return y_\[0-9]*\\\(D\\\);" 2 "optimized" } } */
/* { dg-final { scan-tree-dump-times "return \[^\n\r;]*;" 4 "optimized" } } */
int
foo (int x)
{
if (x >= 2U)
return 34;
return 34 / x;
}
int
bar (int x, int y)
{
if (x >= 2U)
return y;
return y / x;
}
int
baz (_Bool x)
{
return 34 / x;
}
int
qux (_Bool x, int y)
{
return y / x;
}