[flang][OpenMP] Add semantic check for close nesting of `master` regions

[arnamoy10]

Summary

This patch implements the following semantic check:

A master region may not be closely nested inside a work-sharing, loop, atomic, task, or taskloop region.

Adds a test case and also modifies a couple of existing test cases to include the check.

[kiranchandramohan]

flang/lib/Semantics/check-omp-structure.cpp

504

Nit: Can we check whether it is the master construct before calling the check function?

flang/lib/Semantics/check-omp-structure.h

91

Not for this patch. It will be good to generate these Sets from the OMP.td file.

92

Why is parallelSet here? Master is allowed inside parallel.

[arnamoy10]

Addressing reviewers comments.

flang/lib/Semantics/check-omp-structure.cpp

504

Done, thanks!

flang/lib/Semantics/check-omp-structure.h

92

Good catch, updated the code and removed it. Now the set is inspired from here

[kiranchandramohan]

flang/lib/Semantics/check-omp-structure.h

92

Can you add all those combined constructs also. Those combined constructs which will lead to a nested master violating this constraint, like parallel do.

[arnamoy10]

flang/lib/Semantics/check-omp-structure.h

92

Can you please review this patch? Then I should be able to use the combined constructs for worksharing from the patch here.

[kiranchandramohan]

flang/lib/Semantics/check-omp-structure.h

92

Apologies, I missed it completely.

[arnamoy10]

Updating the patch to use the recent merged workShareSet (that included tests for combined constructs for worksharing loops).

[kiranchandramohan]

flang/lib/Semantics/check-omp-structure.h

98

Is a master construct not allowed in a master construct?

[arnamoy10]

Removing master construct from the error set.

flang/lib/Semantics/check-omp-structure.h

98

Thanks for the catch, just updated the code.

[kiranchandramohan]

LGTM.