[clang] [llvm] [OpenMP] Diagnostic check for imperfect loop collapse (PR #96087)

[Alexey Bataev via cfe-commits]

alexey-bataev wrote:


> FWIW, I don't think there's a reasonable, safe way to collapse loops like this and maintain parallel semantics, but ICBW.

I think, there is a proper way. Just annotate these instructions with something like:
```
if (first inner loop iteration) {
  arr[i][i] = ...;
}
```
and it should be correct

https://github.com/llvm/llvm-project/pull/96087