Bug 115547 - `(a ^ c) & (a | c)` -> `a ^ c` not done on the gimple/tree level
Summary: `(a ^ c) & (a | c)` -> `a ^ c` not done on the gimple/tree level
Status: NEW
Alias: None
Product: gcc
Classification: Unclassified
Component: tree-optimization (show other bugs)
Version: 15.0
: P3 enhancement
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords: easyhack, missed-optimization, TREE
Depends on:
Blocks:
 
Reported: 2024-06-19 05:56 UTC by Drea Pinski
Modified: 2026-04-16 13:02 UTC (History)
1 user (show)

See Also:
Host:
Target:
Build:
Known to work:
Known to fail:
Last reconfirmed: 2026-03-24 00:00:00

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Description Drea Pinski 2024-06-19 05:56:47 UTC 
Take:
```
bool fn5(bool a, bool c) {
    return a != c && (a || c);
}
int fn6(int a, int c) {
    return (a ^ c) & (a | c);
}
```

these 2 are optimized to (a^c) on the RTL level only (well fn5 is not done for aarch64). We should be able to optimize them on the gimple level too.
Comment 1 Drea Pinski 2024-06-19 06:00:26 UTC 
Note sometimes it can get complex for bool case:
```
bool fn1(bool a, bool b, bool c) {
    return a != c && (b || (c || a));
}

bool fn2(bool a, bool b, bool c) {
    return a != c && (b || c || a);
}
bool fn3(bool a, bool b, bool c) {
    return a != c && (a || b || c);
}
bool fn4(bool a, bool b, bool c) {
    return a != c && (a || c || b);
}
```

The above is from https://github.com/llvm/llvm-project/issues/95946 .

For those we have:
```
  <bb 2> [local count: 1073741824]:
  if (a_3(D) != c_4(D))
    goto <bb 3>; [66.00%]
  else
    goto <bb 4>; [34.00%]

  <bb 3> [local count: 708669600]:
  _8 = c_4(D) | b_5(D);
  _7 = a_3(D) | _8;

  <bb 4> [local count: 1073741824]:
  # iftmp.0_2 = PHI <_7(3), 0(2)>
  return iftmp.0_2;
```

Which really we know that (a|c) will be 1. But maybe that is a different issue all together.
Comment 2 Drea Pinski 2026-03-24 06:53:19 UTC 
Another testcase:
```
bool test1(bool a, bool b)
{
    return (a | b) ? (a ^ b) : (a & b);
}
```

Right now I am not worried about comment #1 though.