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Date: Thu, 2 Jun 2022 09:58:31 +0000 (UTC)
From: Richard Biener <rguenther@suse.de>
To: Jakub Jelinek <jakub@redhat.com>
cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] match.pd: Optimize __builtin_mul_overflow_p (x, cst,
 (utype)0) to x > ~(utype)0 / cst [PR30314]
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On Thu, 2 Jun 2022, Jakub Jelinek wrote:

> On Thu, Jun 02, 2022 at 08:36:42AM +0000, Richard Biener wrote:
> > > --- 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 ...
> 
> I saw it used in another pattern, so thought it will work fine:
>   (cmp:c (realpart (IFN_ADD_OVERFLOW:c@2 @0 @1)) @0)
> 
> And looking at the generated source, I think it does work:
>               case CFN_MUL_OVERFLOW:
>                 if (gimple_call_num_args (_c1) == 2)
>                   {
>                     tree _q20 = gimple_call_arg (_c1, 0);
>                     _q20 = do_valueize (valueize, _q20);
>                     tree _q21 = gimple_call_arg (_c1, 1);
>                     _q21 = do_valueize (valueize, _q21);
>                     if (integer_nonzerop (_q21))
>                       {
>                         {
> /* #line 5976 "../../gcc/match.pd" */
>                           tree captures[3] ATTRIBUTE_UNUSED = { _p0, _q20, _q21 };
>                           if (gimple_simplify_256 (res_op, seq, valueize, type, captures))
>                             return true;
>                         }
>                       }
>                     if (integer_nonzerop (_q20))
>                       {
>                         {
> /* #line 5976 "../../gcc/match.pd" */
>                           tree captures[3] ATTRIBUTE_UNUSED = { _p0, _q21, _q20 };
>                           if (gimple_simplify_256 (res_op, seq, valueize, type, captures))
>                             return true;
>                         }
>                       }
>                   }
> Though, sure, I should test it in the testcase too.

Ah yeah, we simply trust :c on functions with two arguments (and
explicitely handle CFN_FMA).

Richard.