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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114635] OpenMP reductions fail dependency
 analysis
Date: Mon, 08 Apr 2024 12:19:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114635

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |openmp
             Blocks|                            |53947
                 CC|                            |rguenth at gcc dot gnu.org,
                   |                            |rsandifo at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
We have

(compute_affine_dependence
  ref_a: D.5604[_33], stmt_a: _65 =3D D.5604[_33];
  ref_b: D.5604[_33], stmt_b: D.5604[_33] =3D _ifc__144;
) -> dependence analysis failed

but of course safelen should apply here, but we likely hit

  if (max_vf !=3D MAX_VECTORIZATION_FACTOR
      && maybe_lt (max_vf, min_vf))
    return opt_result::failure_at (vect_location, "bad data dependence.\n");

we have max_vf =3D=3D 16 but min_vf is {4, 4} with E_VNx4SFmode.  Maybe
safelen (and thus max_vf) needs to be poly-int?  Maybe somehow safelen
needs to be ensured by additional masking with SVE?


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations=