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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/112742] New: missed vectorization with
 src[a*b+i] where a*b is not int rather than same percission as size_type
Date: Tue, 28 Nov 2023 07:43:16 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112742

            Bug ID: 112742
           Summary: missed vectorization with src[a*b+i] where a*b is not
                    int rather than same percission as size_type
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
            Blocks: 53947
  Target Milestone: ---
            Target: x86_64-*-* aarch64-*-*

Take:
```
void f(unsigned char * __restrict src,=20
      unsigned stride, int h, int row)
{
  unsigned char *src1 =3D src+row*stride;
  for(int col =3D 0; col < h; col++)
    {
        src1[col]=3Dsrc1[col] + 1;
    }
}

void f1(unsigned char * __restrict src, unsigned rs,
      unsigned cs, unsigned stride, int h, int row)
{
  for(int col =3D 0; col < h; col++)
    {
        src[row*stride+col]=3Dsrc[row*stride+col] + 1;
    }
}
```

These 2 function should be vectorized. But f1 does not. If we use -m32 (or
-mabi=3Dilp32 on aarch64) f1 does now get vectorized.
Note LLVM is able to vectorize f1 for both aarch64 and x86_64.


Referenced Bugs:

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