[polly] [Polly] Data flow reduction detection to cover more cases (PR #84901)

[Michael Kruse via llvm-commits]

https://github.com/Meinersbur requested changes to this pull request.

Thanks for the patch. I really appreciate the good code comments.

Could you add a test that checks two independent reductions in the same loop, e.g.:
```
for (int i = 0; i < n; ++i) {
  *sum += A[i];
  *prod += B[i];
}
```
`ScopBuilder::buildEqivClassBlockStmts` should create two ScopStmts for the same BasicBlock here.

https://github.com/llvm/llvm-project/pull/84901