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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/111762] New: `(a | 3) ^ 1` and `(a & ~1) | 2`
 should produce the same code
Date: Tue, 10 Oct 2023 19:25:22 +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: internal-improvement
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=3D111762

            Bug ID: 111762
           Summary: `(a | 3) ^ 1` and `(a & ~1) | 2` should produce the
                    same code
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: internal-improvement
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
int f(int in) {
  in =3D in | 3;
  in =3D in ^ 1;
  return in;
}

int f1(int in) {
  in =3D (in & ~(unsigned long)1);
  in =3D in | 2;
  return in;
}
```

These 2 functions produce the same result but the code generated is differe=
nt.

I noticed this while writing the patch for PR 111282 and noticing that
`gcc.dg/tree-ssa/and-1.c` testcase now fails (test needs to be fixed).

LLVM/clang looks like canonicalizes to f1. I suspect xor is harder to optim=
ize
when dealing with reassociation so doing f1 is better.=