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From: "tnfchris at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/113287] wrong code with
 __builtin_mul_overflow_p() and _BitInt() with -O3 -msse4
Date: Tue, 09 Jan 2024 14:29:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113287

Tamar Christina <tnfchris at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |tnfchris at gcc dot=
 gnu.org
   Last reconfirmed|                            |2024-01-09
     Ever confirmed|0                           |1

--- Comment #3 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
I'll take it. Thanks :)

The key difference between the loop that aborts and the one that doesn't is
this:

The one that doesn't abort generates:

  mask_patt_21.17_45 =3D vect__5.16_43 !=3D vect_cst__44;
  if (mask_patt_21.17_45 !=3D { 0, 0, 0, 0 })
    goto <bb 19>; [5.50%]

and the one that does genertaes:

  mask_patt_72.30_100 =3D vect_cst__101 !=3D vect__48.29_102;
  if (mask_patt_72.30_100 =3D=3D { -1, -1, -1, -1 })
    goto <bb 23>; [20.00%]

This happens when the CFG in the loop is flipped, so the vectorizer is inst=
ead
asking for the target to check that all values are true instead of any.

Looking at ix86_expand_branch only one part of the branch does a XOR to acc=
ount
for the difference.

So I'll first start looking whether the generated assembly is as expected.=