[flang][OpenMP] Enhance parser support for taskwait construct to OpenMP 5.0

[kiranktp]

Summary

This patch enhances parser support for taskwait construct to OpenMP 5.0.

2.17.5 taskwait Construct
!$omp taskwait [clause[ [,] clause] ... ]

		where clause is one of the following:
		depend([depend-modifier,]dependence-type : locator-list)

The patch includes code changes and testcase modifications.

[kiranktp]

Corrected the section number to 2.17.5 [from OpenMP 5.0] for taskwait construct

[kiranktp]

Lint: Pre-merge checks

/mnt/disks/ssd0/agent/llvm-project/flang/lib/Semantics/check-omp-structure.cpp:671:18: warning: invalid case style for variable 'allowed' [readability-identifier-naming]

OmpClauseSet allowed{OmpClause::DEPEND};
             ^~~~~~~
             Allowed

I think I can neglect this warning as i have used the correct naming convention for the variable.
Local variables names should start with lower case. The same has been used in multiple places in the same file.

[kiranchandramohan]

This looks OK but needs a rebase after @clementval's changes.

[kiranktp]

In D82255#2149511, @kiranchandramohan wrote:

This looks OK but needs a rebase after @clementval's changes.

Thanks Kiran. I will rebase this patch and submit again.

[kiranktp]

Rebasing after @clementval's patch and adding appropriate changes needed.

[kiranchandramohan]

LGTM.

Please wait for approval from @clementval.

[clementval]

Minor comment but LGTM.

llvm/include/llvm/Frontend/OpenMP/OMP.td

317 ↗

(On Diff #278098)

Is it allowed from 5.0 or before? If it is allowed from 5.0 you can specify it like VersionedClause<OMPC_Depend, 50> so it will be accepted (in clang so far) from 5.0 and later. This feature is not used in Flang for the moment.

[kiranktp]

In D82255#2153074, @clementval wrote:

Minor comment but LGTM.

Thanks for the review @clementval. This is allowed from OpenMP 5.0 and later.
I will do the modification.

[kiranktp]

taskwait has depend clause from OpenMP 5.0 and later.

[clementval]

Still LGTM

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

void OmpStructureChecker::Enter(
     const parser::OpenMPSimpleStandaloneConstruct &x) {
   const auto &dir{std::get<parser::OmpSimpleStandaloneDirective>(x.t)};
   switch (dir.v) {
   case parser::OmpSimpleStandaloneDirective::Directive::Barrier: {
     // 2.13.3 barrier
     PushContext(dir.source, OmpDirective::BARRIER);
   } break;
   case parser::OmpSimpleStandaloneDirective::Directive::Taskwait: {
-    // 2.13.4 taskwait
+    // 2.17.5 taskwait [OpenMP 5.0]
     PushContext(dir.source, OmpDirective::TASKWAIT);
+    OmpClauseSet allowed{OmpClause::DEPEND};
+    SetContextAllowed(allowed);
   } break;
   case parser::OmpSimpleStandaloneDirective::Directive::Taskyield: {
     // 2.9.4 taskyield
     PushContext(dir.source, OmpDirective::TASKYIELD);
   } break;
   case parser::OmpSimpleStandaloneDirective::Directive::TargetEnterData: {
     // 2.10.2 target-enter-data-clause -> if-clause |
     //                                    device-clause |

flang/test/Semantics/omp-clause-validity01.f90

! 2.13.1 master
   !$omp end master
   !$omp end parallel
 
 ! Standalone Directives (basic)
 
   !$omp taskyield
   !$omp barrier
   !$omp taskwait
+  !$omp taskwait depend(source)
+  !ERROR: Internal: no symbol found for 'i'
+  !$omp taskwait depend(sink:i-1)
   ! !$omp target enter data map(to:arrayA) map(alloc:arrayB)
   ! !$omp target update from(arrayA) to(arrayB)
   ! !$omp target exit data map(from:arrayA) map(delete:arrayB)
   !$omp ordered depend(source)
   !ERROR: Internal: no symbol found for 'i'
   !$omp ordered depend(sink:i-1)
   !$omp flush (c)
   !$omp cancel DO