[Bug tree-optimization/116823] New: phiprop should ignore clobbers

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116823

            Bug ID: 116823
           Summary: phiprop should ignore clobbers
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: pinskia at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
const int &c(const int &d, const int &e) {
  if (d < e)
    return e;
  return d;
}

int g(int i, struct f *ff)
{
  const int &a = c(i, 10);
  return a;
}
```

Even though this is undefined code because the lifetime of the temp for 10 is
not extended, we could have phiprop ignore the clobber and optimize like it was
extended.