Re: [PATCH] phiopt: Drop SSA_NAME_RANGE_INFO in maybe equal case [PR108166]

[Aldy Hernandez <aldyh@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 3642 bytes --]

On Thu, Dec 22, 2022, 12:33 Richard Biener <rguenther@suse.de> wrote:

> On Thu, 22 Dec 2022, Jakub Jelinek wrote:
>
> > Hi!
> >
> > The following place in value_replacement is after proving that
> > x == cst1 ? cst2 : x
> > phi result is only used in a comparison with constant which doesn't
> > care if it compares cst1 or cst2 and replaces it with x.
> > The testcase is miscompiled because we have after the replacement
> > incorrect range info for the phi result, we would need to
> > effectively union the phi result range with cst1 (oarg in the code)
> > because previously that constant might be missing in the range, but
> > newly it can appear (we've just verified that the single use stmt
> > of the phi result doesn't care about that value in particular).
> >
> > The following patch just resets the info, bootstrapped/regtested
> > on x86_64-linux and i686-linux, ok for trunk?
>
> OK.
>
> > Aldy/Andrew, how would one instead union the SSA_NAME_RANGE_INFO
> > with some INTEGER_CST and store it back into SSA_NAME_RANGE_INFO
> > (including adjusting non-zero bits and the like)?
>
> There's no get_range_info on SSA_NAMEs (anymore?) but you can
> construct a value_range from the


This is my fault. When we added get_global_range_query, I removed
get_range_info. I should've left that entry point. I'll look into adding it
next cycle for readability's sake


 INTEGER_CST singleton and
> union that into the SSA_NAMEs range and then do set_range_info
> with the altered range I guess.
>

Note that set_range_info is an intersect operation. It should really be
called update_range_info. Up to now, there were no users that wanted to
clobber old ranges completely.

Aldy


> Richard.
>
> > 2022-12-22  Jakub Jelinek  <jakub@redhat.com>
> >
> >       PR tree-optimization/108166
> >       * tree-ssa-phiopt.cc (value_replacement): For the maybe_equal_p
> >       case turned into equal_p reset SSA_NAME_RANGE_INFO of phi result.
> >
> >       * g++.dg/torture/pr108166.C: New test.
> >
> > --- gcc/tree-ssa-phiopt.cc.jj 2022-10-28 11:00:53.970243821 +0200
> > +++ gcc/tree-ssa-phiopt.cc    2022-12-21 14:27:58.118326548 +0100
> > @@ -1491,6 +1491,12 @@ value_replacement (basic_block cond_bb,
> >                 default:
> >                   break;
> >                 }
> > +           if (equal_p)
> > +             /* After the optimization PHI result can have value
> > +                which it couldn't have previously.
> > +                We could instead of resetting it union the range
> > +                info with oarg.  */
> > +             reset_flow_sensitive_info (gimple_phi_result (phi));
> >             if (equal_p && MAY_HAVE_DEBUG_BIND_STMTS)
> >               {
> >                 imm_use_iterator imm_iter;
> > --- gcc/testsuite/g++.dg/torture/pr108166.C.jj        2022-12-21
> 14:31:02.638661322 +0100
> > +++ gcc/testsuite/g++.dg/torture/pr108166.C   2022-12-21
> 14:30:45.441909725 +0100
> > @@ -0,0 +1,26 @@
> > +// PR tree-optimization/108166
> > +// { dg-do run }
> > +
> > +bool a, b;
> > +int d, c;
> > +
> > +const int &
> > +foo (const int &f, const int &g)
> > +{
> > +  return !f ? f : g;
> > +}
> > +
> > +__attribute__((noipa)) void
> > +bar (int)
> > +{
> > +}
> > +
> > +int
> > +main ()
> > +{
> > +  c = foo (b, 0) > ((b ? d : b) ?: 8);
> > +  a = b ? d : b;
> > +  bar (a);
> > +  if (a != 0)
> > +    __builtin_abort ();
> > +}
> >
> >       Jakub
> >
> >
>
> --
> Richard Biener <rguenther@suse.de>
> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
> Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
> HRB 36809 (AG Nuernberg)
>
>