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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/115086] New: bic is not used when the non-not part is a
 constant
Date: Tue, 14 May 2024 09:45:01 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 15.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115086

            Bug ID: 115086
           Summary: bic is not used when the non-not part is a constant
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64

Take:
```
int g2(int a,int c)
{
  int b =3D 4 & ~c;
  return b;
}
```

Currently GCC produces:
```
g2:
        mvn     w0, w1
        and     w0, w0, 4
        ret
```
But producing bic is better for most (if not all) modern cores due to the
instruction that generates the constant would be "free". That is GCC should
produce:
```
g2:
        mov     w8, 4
        bic     w0, w8, w1
        ret
```

Which is what clang/LLVM produces.=