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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/109862] New: IV-OPTs could use int but still
 uses smaller sized for IV
Date: Mon, 15 May 2023 16:24:54 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
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=3D109862

            Bug ID: 109862
           Summary: IV-OPTs could use int but still uses smaller sized for
                    IV
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64, riscv32, riscv64

Take:
```
int f(char a)
{
        unsigned char t;
        unsigned short t1 =3D a;
        for(t =3D 0; t < 8; t ++)
        {
                t1 >>=3D1;
                t1 +=3D a;
        }
        return t1;
}
int f1(char a)
{
        unsigned int t;
        unsigned short t1 =3D a;
        for(t =3D 0; t < 8; t ++)
        {
                t1 >>=3D1;
                t1 +=3D a;
        }
        return t1;
}

```
f1 produces better code as there is no extra zero-extend (anding) inside the
loop for the IV of t.

Note this shows up in coremarks in the crc functions (if not unrolling).=