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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/114684] New: `-(int)(unsigned:1)signed:1`
 could just be `(int)signed:1`
Date: Wed, 10 Apr 2024 20:49:29 +0000
X-Bugzilla-Reason: CC
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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=3D114684

            Bug ID: 114684
           Summary: `-(int)(unsigned:1)signed:1` could just be
                    `(int)signed:1`
           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
  Target Milestone: ---

Take:
```
struct t{
  signed s1 : 1;
  unsigned u1 : 1;
} b =3D {-1};

int f()
{
  struct t tt =3D b;
  return tt.s1;
}
int f1()
{
  struct t tt =3D b;
  tt.u1 =3D tt.s1;
  int ttt =3D tt.u1;
  return -ttt;
}
```

These 2 functions should produce the same code. (For aarch64 it almost does,
there is an extra sign extend in f). I noticed this while fixing PR 114666.=
 It
is also related to PR 101955. Note this only works for 1bit signed values.=