[clang] [clang][OpenMP] Diagnose badly-formed collapsed imperfect loop nests (#60678) (PR #101305)

[Julian Brown via cfe-commits]

jtb20 wrote:

> > OpenMPIterationSpaceChecker is still passed a pointer to CollapsedLoopDecls, because one caller passes a nullptr, and we don't want to do the analysis in that case.
> 
> Still pass by reference, just pass empty where it is not required

So the new pushed version does that, sort of -- but I'm not sure it's unambiguously better. (The "empty" member is a predicate for SmallPtrSet, not a value representing an empty set. Did you mean something else?)

Otherwise, std::optional might be a possibility, but it can't be used with references, IIUC.

https://github.com/llvm/llvm-project/pull/101305