[flang][OpenMP] Add semantic check for teams nesting

[peixin]

Summary

This patch implements the following check for TEAMS construct:

OpenMP Version 5.0 Teams construct restriction: A teams region can
only be strictly nested within the implicit parallel region or a target
region. If a teams construct is nested within a target construct, that
target construct must contain no statements, declarations or directives
outside of the teams construct.

Also add one test case for the check.

[peixin]

Fix errors info in related test cases.

[clementval]

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

206

This is only for OpenMP so it should be moved to check-omp-structure.h. Same for the two functions below. The check-directive-structure.h is meant to be shared bewteen OpenMP and OpenACC.

flang/test/Semantics/omp-firstprivate01.f90

15

Which statement is outside?

flang/test/Semantics/omp-nested-master.f90

90

parallel region instead of parallelregion

106

Missing a space here as well.

122

Missing space

139

Missing space

flang/test/Semantics/omp-nested-simd.f90

45

Missing space

[peixin]

@clementval Thanks for the review.

Moved two sets of functions and counters to check-omp-structure.h and merged them. Also fix the errors info in the test cases.

[peixin]

flang/test/Semantics/omp-firstprivate01.f90

15

This target directive has two teams construct nested inside and both of teams construct contain statements. Change the error info by replacing statements by statements or directives, which should be more reasonable.

[kiranchandramohan]

Looks OK. Have two questions.

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

632

Is the parent teams check required?

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

255

Nit: Can we add a LastType at the end of the enum and use it as the size of the directiveNest_ array?

[peixin]

@kiranchandramohan Thanks for the review. Fixed the patch according to your comments.

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

632

The restriction for two strictly nested teams has already been checked with the error info of distribute and parallel region only allowed strictly nested inside teams region. Rethink about it and reporting one more error here is more reasonable. Deleted the check of parent teams and added the error info in test case omp-nested-teams.f90.

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

255

Good idea. Added it.

[peixin]

Change directiveNest_[2] to directiveNest_[3] since one more element LastType was added.

[kiranchandramohan]

LGTM.

@clementval do you have further comments?

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

254

Nit: Sorry, I meant can you move this below the enum and use LastType (with SIMDNest =1 ) or LastType +1 as the size of the directiveNest_array?

enum directiveNestType { SIMDNest, TargetBlockOnlyTeams, LastType };
int directiveNest_[LastType+1] = {0};

[peixin]

@kiranchandramohan Thanks for the suggestions, which prevents from using magic number. Replaced directiveNest_[3] with directiveNest_[LastType+1].

[clementval]

LGTM as well. Sorry for the delay in reviewing the change to the patch. You can go ahead and land it.