On Wed, 1 Jun 2022, Jakub Jelinek wrote:
> Hi!
>
> 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...
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2022-06-01 Jakub Jelinek <ja...@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.
>
> --- gcc/match.pd.jj 2022-06-01 13:54:32.000654151 +0200
> +++ gcc/match.pd 2022-06-01 15:13:35.473084402 +0200
> @@ -5969,6 +5969,17 @@ (define_operator_list SYNC_FETCH_AND_AND
> && (!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))
does :c work here? I think it is at least ignored, possibly diagnostic
in genmatch is missing ...
> + (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
> --- gcc/testsuite/gcc.dg/tree-ssa/pr30314.c.jj 2022-06-01
> 15:22:53.201271365 +0200
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr30314.c 2022-06-01 15:13:24.725196482
> +0200
> @@ -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);
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
