[llvm] [MachinePipeliner] Fix store-store dependences (#72508) (PR #72575)

[via llvm-commits]

bcahoon wrote:

The first case is most similar to the one in the bug report (though, without the load), https://github.com/llvm/llvm-project/issues/72508
```
for (int i=0; i<n; i++) {
  /* S0 */ a[i] = 1;
  /* S1 */ int tmp = a[x];  // To prevent optimization
  /* S2 */ a[i] = tmp;
}
```
Perhaps the bug report is missing some details about why the second store cannot be scheduled in a later stage.

https://github.com/llvm/llvm-project/pull/72575