[Bug tree-optimization/115055] New: reassociation should use match-and-simplify

[Bug tree-optimization/115055] New: reassociation should use match-and-simplify

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115055

            Bug ID: 115055
           Summary: reassociation should use match-and-simplify
           Product: gcc
           Version: 15.0
            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:
```
int f(int a, int c)
{
        int b = a & c;
        return (a == 0) & b;
}
```

This should be optimized to 0 but currently does not. 

There is a match pattern (via PR 111431) which is able to handle `a & (a == 0)`
into `0`. reassociation knows how to handle `a & a` but it seems like if while
doing reassociation, we should be to try to use match-and-simplify to simplify
the f here.

[Bug tree-optimization/115055] reassociation should use match-and-simplify

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115055

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-05-13
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
  b_5 = a_3(D) & c_4(D);
  _1 = a_3(D) == 0;
  _2 = (int) _1;
  _6 = b_5 & _2;
  return _6;

I believe reassoc doesn't see that a and (int)(a == 0) are "related" when
ranking ops of the AND, so it fails to appropriately order them and thus
trigger the simplification.  We definitely want to avoid doing n^2
matching combos of all AND operands.

So confirmed, but not necessarily confirming the proposed solution.