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From: "juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/111401] New: Middle-end: Missed optimization of
 MASK_LEN_FOLD_LEFT_PLUS
Date: Wed, 13 Sep 2023 09:31:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111401

            Bug ID: 111401
           Summary: Middle-end: Missed optimization of
                    MASK_LEN_FOLD_LEFT_PLUS
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: juzhe.zhong at rivai dot ai
  Target Milestone: ---

There is a case I think I missed the optimization in the loop vectorizer:

https://godbolt.org/z/x5sjdenhM

double
foo2 (double *__restrict a,
     double init,
     int *__restrict cond,
     int n)
{
    for (int i =3D 0; i < n; i++)
      if (cond[i])
        init +=3D a[i];
    return init;
}

It generate the GIMPLE IR as follows:

_60 =3D .SELECT_VL (ivtmp_58, 4);
...
vect__ifc__35.14_56 =3D .VCOND_MASK (mask__23.10_50, vect__8.13_54, { 0.0, =
0.0,
0.0, 0.0 });
  _36 =3D .MASK_LEN_FOLD_LEFT_PLUS (init_20, vect__ifc__35.14_56, { -1, -1,=
 -1,
-1 }, _60, 0);

The mask of MASK_LEN_FOLD_LEFT_PLUS is the dummy mask {-1.-1,...-1}
I think we should forward the mask of VCOND_MASK into the
MASK_LEN_FOLD_LEFT_PLUS.

Then we can eliminate the VCOND_MASK.


I don't where is the optimal place to do the optimization.

Should be the match.pd ? or the loop vectorizer code?

Thanks.=