https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111108
Bug ID: 111108
Summary: (a|c) == (a|c) should be convert into (a&~c) ==
(a&~c) IFF ~c simplifies
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:
```
#define C 0x1
unsigned g(unsigned X, unsigned Y)
{
return (X | C) == (Y | C);
}
unsigned g1(unsigned X, unsigned Y)
{
return (X & ~C) == (Y & ~C);
}
unsigned g2(unsigned X, unsigned Y)
{
return ((X | C) & ~C) == ((Y | C) & ~C);
}
```
These all functions are the same as (X|C) == (Y|C) is saying the only bits of X
and Y which you want to compare is ~C.
Note I suspect we could also do this for non-constant C but that would normally
produce worse code but maybe we could see if both X & ~C and Y & ~C simplifies
(due to non-zero bits ...).
