[Bug tree-optimization/125793] New: phi_opt should factor out calls

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125793

            Bug ID: 125793
           Summary: phi_opt should factor out calls
           Product: gcc
           Version: 16.0
            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
        Depends on: 123113
            Blocks: 89018
  Target Milestone: ---

Take:
```

long transform(long);

long transform_max(long a, long b, long c) {
    if (c)
    {
      return (a >= b) ? transform(a) : transform(b);
    }
    return a+b;
}
```

This should be converted into:
```
long transform_max1(long a, long b, long c) {
    if (c)
      return transform((a >= b) ? a : b);
    return a+b;
}
```

This is partly why phiopt needs to do the factoring besides just sink.

Note LLVM does not handle this either because their factoring only happens in a
similar pass to sink where all phi operands need to be happening.
This is what PR 123113 is there to solve.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89018
[Bug 89018] common subexpression present in both branches of condition is not
factored out
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123113
[Bug 123113] factor_out_conditional_operation could be improved to handle
`EDGE_COUNT (merge->preds) != 2`