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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/109657] New: (a ? -1 : 0) | b could be optimized better
 for aarch64
Date: Thu, 27 Apr 2023 22:47:15 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109657

            Bug ID: 109657
           Summary: (a ? -1 : 0) | b could be optimized better for aarch64
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: pinskia at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64-*-*

Take (at -O2):
```
unsigned b(unsigned a, unsigned b){
    if(b){
        return -1;
    }
    return a;
}
unsigned b1(unsigned a, unsigned b){
    unsigned t =3D b ? -1 : 0;
    return a | t;
}
```
Right now we produce:
```
b:
        cmp     w1, 0
        csinv   w0, w0, wzr, eq
        ret
b1:
        cmp     w1, 0
        csetm   w1, ne
        orr     w0, w1, w0
        ret
```

We can help combine here by adding a pattern for:
(set (reg/i:SI 0 x0)
    (ior:SI (neg:SI (ne:SI (reg:CC 66 cc)
                (const_int 0 [0])))
        (reg:SI 102)))

Which is the same as=20
(set (reg/i:SI 0 x0)
    (if_then_else:SI (eq (reg:CC 66 cc)
            (const_int 0 [0]))
        (reg:SI 97)
        (const_int -1 [0xffffffffffffffff])))
pattern.

I suspect both are considered canonical too.=