[Bug tree-optimization/126311] New: (t * u) / v can be reduced if gcd (u, v) > 1

[kaelfandrew at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126311

            Bug ID: 126311
           Summary: (t * u) / v can be reduced if gcd (u, v) > 1
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kaelfandrew at gmail dot com
  Target Milestone: ---

https://godbolt.org/z/hzxdP9EEP

```
int
src (short tt)
{
  int t = tt;
  return (t * (2 * 3)) / (2 * 5);
}

int
tgt (short tt)
{
  int t = tt;
  return (t * 3) / 5;
}
```

With -O2, src () should optimize to tgt ()

gcc/match.pd has this pattern to implement this PR:

 /* Simplify (t * u) / v -> t * (u / v) if u is multiple of v.  */
 (simplify
  (div (mult@3 @0 INTEGER_CST@1) INTEGER_CST@2)
  (if (INTEGRAL_TYPE_P (type)