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match.pd: Optimize __builtin_mul_overflow_p (x, cst, (utype)0) to x > ~(utype)0 / cst [PR30314]

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A comparison with a constant is most likely always faster than
.MUL_OVERFLOW from which we only check whether it overflowed and not the
multiplication result, and even if not, it is simpler operation on GIMPLE
and even if a target exists where such multiplications with overflow checking
are cheaper than comparisons, because comparisons are so much more common
than overflow checking multiplications, it would be nice if it simply
arranged for comparisons to be emitted like those multiplications on its
own...

2022-06-01  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/30314
	* match.pd (__builtin_mul_overflow_p (x, cst, (utype) 0) ->
	x > ~(utype)0 / cst): New simplification.

	* gcc.dg/tree-ssa/pr30314.c: New test.
This commit is contained in:
Jakub Jelinek 2022-06-01 17:54:39 +02:00
parent 289f860fe6
commit cf78d8411d
2 changed files with 29 additions and 0 deletions
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11
gcc/match.pd
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@ -5969,6 +5969,17 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
&& (!TYPE_UNSIGNED (TREE_TYPE (@2)) || TYPE_UNSIGNED (TREE_TYPE (@0))))
(ovf @1 @0))))
/* Optimize __builtin_mul_overflow_p (x, cst, (utype) 0) if all 3 types
are unsigned to x > (umax / cst). */
(simplify
(imagpart (IFN_MUL_OVERFLOW:cs@2 @0 integer_nonzerop@1))
(if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
&& TYPE_UNSIGNED (TREE_TYPE (@0))
&& TYPE_MAX_VALUE (TREE_TYPE (@0))
&& types_match (TREE_TYPE (@0), TREE_TYPE (TREE_TYPE (@2)))
&& int_fits_type_p (@1, TREE_TYPE (@0)))
(convert (gt @0 (trunc_div! { TYPE_MAX_VALUE (TREE_TYPE (@0)); } @1)))))
/* Simplification of math builtins. These rules must all be optimizations
as well as IL simplifications. If there is a possibility that the new
form could be a pessimization, the rule should go in the canonicalization

18
gcc/testsuite/gcc.dg/tree-ssa/pr30314.c Normal file
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@ -0,0 +1,18 @@
/* PR middle-end/30314 */
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-optimized" } */
/* { dg-final { scan-tree-dump-not "\.MUL_OVERFLOW " "optimized" } } */
/* { dg-final { scan-tree-dump " > 122713351" "optimized" { target int32 } } } */
/* { dg-final { scan-tree-dump " > 527049830677415760" "optimized" { target lp64 } } } */
int
foo (unsigned int x)
{
return __builtin_mul_overflow_p (x, 35U, 0U);
}
int
bar (unsigned long int x)
{
return __builtin_mul_overflow_p (x, 35UL, 0UL);
}