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

[Richard Biener <rguenther@suse.de>]

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  <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.
> 
> --- 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 <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
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