[Bug tree-optimization/127053] New: cselim_limited could be improved to skip over one clobber on either branch

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127053

            Bug ID: 127053
           Summary: cselim_limited could be improved to skip over one
                    clobber on either branch
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: pinskia at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

This shows up with std::optional:

```
#include <optional>

void func(std::optional<int> &x) {
    x.reset();
}
```


In phiopt1 we have:
```
  if (_4 != 0)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> :
  MEM[(struct _Optional_payload_base *)x_2(D)]._M_engaged = 0;
  MEM[(int *)x_2(D)] ={v} {CLOBBER(eob)};
  goto <bb 5>; [100.00%]

  <bb 4> :
  MEM[(struct _Optional_payload_base *)x_2(D)]._M_engaged = 0;

  <bb 5> :
```

Only the DR based cselim handles this currently because of the clobber.