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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/111167] New: swapping around duplicated
 conditionals can produce better code
Date: Sat, 26 Aug 2023 19:39:51 +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=3D111167

            Bug ID: 111167
           Summary: swapping around duplicated conditionals can produce
                    better code
           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: ---

Take reduced from GCC's sources for lookup_attribute:
```
void f(int);
inline void canonicalize_attr_name(const char *&s, int l) {
  if (l > 4 && s[0] =3D=3D '_' && s[l - 1] =3D=3D '_' )=20
    s +=3D 2;
}
void lookup_attribute(const char *attr_ns, int list, int t) {
  if (attr_ns && attr_ns[0] !=3D '_') {
    canonicalize_attr_name(attr_ns, 5);
  }
  if (list =3D=3D 0)
  {
    short attr_ns_len =3D attr_ns ? t : 0;
    f(attr_ns_len);
  }
}

```

In optimized we have:
```
  if (attr_ns_25(D) !=3D 0B)
    goto <bb 4>; [70.00%]
  else
    goto <bb 3>; [30.00%]

  <bb 3> [local count: 322122543]:
  if (list_10(D) =3D=3D 0)
    goto <bb 6>; [50.00%]
  else
    goto <bb 7>; [50.00%]

  <bb 4> [local count: 751619279]:
  if (list_10(D) =3D=3D 0)
    goto <bb 5>; [50.00%]
  else
    goto <bb 7>; [50.00%]

```

But we should really just have:
if (list_10(D) =3D=3D 0) goto bb7;
if (attr_ns_25(D) !=3D 0B) goto bb5; else bb6;=