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

[Alexey Bataev via cfe-commits]

alexey-bataev wrote:

I suggest defining the canonical (pessimistic in performance, but optimistic in correctness) form of the loop and emit it in the frontend. Later OpenMPOpt pass can optimize this "canonical" (slow but correct) form to better (but still correct) form, if possible (dropping critical section, for example, if it is proved it is safe).

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