[Bug tree-optimization/126580] New: missing cselim at phiopt1

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126580

            Bug ID: 126580
           Summary: missing cselim at phiopt1
           Product: gcc
           Version: 17.0
            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
            Blocks: 125909
  Target Milestone: ---

Take:
```
int *sink(int*);
void f(int a, int c, int d, int *e)
{
  e = sink(&a);
  a = d;
  c = *e;
  c += a;
  if (c)
    a = d|c;
  sink(&a);
}
```

This can be optimized at `-O2 -fallow-store-data-races` to just:
```
  a = d_6(D);
  c_8 = *e_5;
  c_9 = d_6(D) + c_8;
  _1 = d_6(D) | c_9;
  MEM <int> [(void *)&a] = _1;
```

In phiopt1.

But currently it takes until phiopt2 which is after cselim.
The reason is because cond_store_replacement_limited rejects `case 1` because
it wants to delete the store. But for allowing store data races you don't need
to delete the store, you can keep it around and let the rest of the compiler
take care of it.


The same is true of:
```
void f1(int *a, int c, int d, int *e)
{
  *a = d;
  c = *e;
  c += *a;
  int t = d|c;
  if (c)
    *a = t;
}
```


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125909
[Bug 125909] cselim should be removed