[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.

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

protected:
   void SetContextClauseInfo(C type) {
     GetContext().clauseInfo.emplace(type, GetContext().clause);
   }
 
   void AddClauseToCrtContext(C type) {
     GetContext().actualClauses.push_back(type);
   }
 
-  void EnterSIMDNest() { simdNest_++; }
-
-  void ExitSIMDNest() { simdNest_--; }
-
-  int GetSIMDNest() { return simdNest_; }
-
   // Check if the given clause is present in the current context
   const PC *FindClause(C type) {
     auto it{GetContext().clauseInfo.find(type)};
     if (it != GetContext().clauseInfo.end()) {
       return it->second;
     }
     return nullptr;
   }
 
protected:
   virtual llvm::StringRef getDirectiveName(D directive) { return ""; };
 
   SemanticsContext &context_;
   std::vector<DirectiveContext> dirContext_; // used as a stack
   std::unordered_map<D, DirectiveClauses<C, ClauseEnumSize>>
       directiveClausesMap_;
 
   std::string ClauseSetToString(const common::EnumSet<C, ClauseEnumSize> set);
-  int simdNest_{0};
 };
 
 template <typename D, typename C, typename PC, std::size_t ClauseEnumSize>
 void DirectiveStructureChecker<D, C, PC, ClauseEnumSize>::CheckNoBranching(
     const parser::Block &block, D directive,
     const parser::CharBlock &directiveSource) {
   NoBranchingEnforce<D> noBranchingEnforce{
       context_, directiveSource, directive, ContextDirectiveAsFortran()};

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

private:
   void GetSymbolsInObjectList(const parser::OmpObjectList &, SymbolSourceMap &);
   void CheckDefinableObjects(SymbolSourceMap &, const llvm::omp::Clause);
   void CheckPrivateSymbolsInOuterCxt(
       SymbolSourceMap &, DirectivesClauseTriple &, const llvm::omp::Clause);
   const parser::Name GetLoopIndex(const parser::DoConstruct *x);
   void SetLoopInfo(const parser::OpenMPLoopConstruct &x);
   void CheckIsLoopIvPartOfClause(
       llvmOmpClause clause, const parser::OmpObjectList &ompObjectList);
+  bool CheckTargetBlockOnlyTeams(const parser::Block &);
   void CheckWorkshareBlockStmts(const parser::Block &, parser::CharBlock);
 
   void CheckLoopItrVariableIsInt(const parser::OpenMPLoopConstruct &x);
   void CheckDoWhile(const parser::OpenMPLoopConstruct &x);
   void CheckCycleConstraints(const parser::OpenMPLoopConstruct &x);
   void CheckDistLinear(const parser::OpenMPLoopConstruct &x);
   void CheckSIMDNest(const parser::OpenMPConstruct &x);
   std::int64_t GetOrdCollapseLevel(const parser::OpenMPLoopConstruct &x);
private:
   void CheckMultipleAppearanceAcrossContext(
       const parser::OmpObjectList &ompObjectList);
   const parser::OmpObjectList *GetOmpObjectList(const parser::OmpClause &);
   void CheckPredefinedAllocatorRestriction(const parser::CharBlock &source,
       const parser::OmpObjectList &ompObjectList);
   void CheckPredefinedAllocatorRestriction(
       const parser::CharBlock &source, const parser::Name &name);
   bool isPredefinedAllocator{false};
+  void EnterDirectiveNest(const int index) { directiveNest_[index]++; }
+  void ExitDirectiveNest(const int index) { directiveNest_[index]--; }
+  int GetDirectiveNest(const int index) { return directiveNest_[index]; }
+
+  enum directiveNestType { SIMDNest, TargetBlockOnlyTeams, LastType };
+  int directiveNest_[LastType + 1] = {0};
 };
 } // namespace Fortran::semantics
 #endif // FORTRAN_SEMANTICS_CHECK_OMP_STRUCTURE_H_

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

 
 void OmpStructureChecker::Enter(const parser::OpenMPConstruct &x) {
   // Simd Construct with Ordered Construct Nesting check
   // We cannot use CurrentDirectiveIsNested() here because
   // PushContextAndClauseSets() has not been called yet, it is
   // called individually for each construct.  Therefore a
   // dirContext_ size `1` means the current construct is nested
   if (dirContext_.size() >= 1) {
-    if (GetSIMDNest() > 0) {
+    if (GetDirectiveNest(SIMDNest) > 0) {
       CheckSIMDNest(x);
     }
   }
 }
 
 void OmpStructureChecker::Enter(const parser::OpenMPLoopConstruct &x) {
   const auto &beginLoopDir{std::get<parser::OmpBeginLoopDirective>(x.t)};
   const auto &beginDir{std::get<parser::OmpLoopDirective>(beginLoopDir.t)};
 
   // check matching, End directive is optional
   if (const auto &endLoopDir{
           std::get<std::optional<parser::OmpEndLoopDirective>>(x.t)}) {
     const auto &endDir{
         std::get<parser::OmpLoopDirective>(endLoopDir.value().t)};
 
     CheckMatching<parser::OmpLoopDirective>(beginDir, endDir);
   }
 
   PushContextAndClauseSets(beginDir.source, beginDir.v);
   if (llvm::omp::simdSet.test(GetContext().directive)) {
-    EnterSIMDNest();
+    EnterDirectiveNest(SIMDNest);
   }
 
   if (beginDir.v == llvm::omp::Directive::OMPD_do) {
     // 2.7.1 do-clause -> private-clause |
     //                    firstprivate-clause |
     //                    lastprivate-clause |
     //                    linear-clause |
     //                    reduction-clause |
for (auto var : indexVars) {
           "Variable '%s' not allowed in `LINEAR` clause, only loop iterator can be specified in `LINEAR` clause of a construct combined with `DISTRIBUTE`"_err_en_US,
           root.name());
     }
   }
 }
 
 void OmpStructureChecker::Leave(const parser::OpenMPLoopConstruct &) {
   if (llvm::omp::simdSet.test(GetContext().directive)) {
-    ExitSIMDNest();
+    ExitDirectiveNest(SIMDNest);
   }
   dirContext_.pop_back();
 }
 
 void OmpStructureChecker::Enter(const parser::OmpEndLoopDirective &x) {
   const auto &dir{std::get<parser::OmpLoopDirective>(x.t)};
   ResetPartialContext(dir.source);
   switch (dir.v) {
void OmpStructureChecker::Enter(const parser::OpenMPBlockConstruct &x) {
   if (CurrentDirectiveIsNested()) {
     CheckIfDoOrderedClause(beginDir);
     if (llvm::omp::teamSet.test(GetContextParent().directive)) {
       HasInvalidTeamsNesting(beginDir.v, beginDir.source);
     }
     if (GetContext().directive == llvm::omp::Directive::OMPD_master) {
       CheckMasterNesting(x);
     }
+    // A teams region can only be strictly nested within the implicit parallel
+    // region or a target region.
+    if (GetContext().directive == llvm::omp::Directive::OMPD_teams &&
+        GetContextParent().directive != llvm::omp::Directive::OMPD_target) {
+      context_.Say(parser::FindSourceLocation(x),
+          "%s region can only be strictly nested within the implicit parallel "
+          "region or TARGET region"_err_en_US,
+          ContextDirectiveAsFortran());
+    }
+    // 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.
+    if (GetContext().directive == llvm::omp::Directive::OMPD_teams &&
+        GetContextParent().directive == llvm::omp::Directive::OMPD_target &&
+        !GetDirectiveNest(TargetBlockOnlyTeams)) {
+      context_.Say(GetContextParent().directiveSource,
+          "TARGET construct with nested TEAMS region contains statements or "
+          "directives outside of the TEAMS construct"_err_en_US);
+    }
   }
 
   CheckNoBranching(block, beginDir.v, beginDir.source);
 
   switch (beginDir.v) {
+  case llvm::omp::Directive::OMPD_target:
+    if (CheckTargetBlockOnlyTeams(block)) {
+      EnterDirectiveNest(TargetBlockOnlyTeams);
+    }
+    break;
   case llvm::omp::OMPD_workshare:
   case llvm::omp::OMPD_parallel_workshare:
     CheckWorkshareBlockStmts(block, beginDir.source);
     HasInvalidWorksharingNesting(
         beginDir.source, llvm::omp::nestedWorkshareErrSet);
     break;
   case llvm::omp::Directive::OMPD_single:
     // TODO: This check needs to be extended while implementing nesting of
else if (IsCloselyNestedRegion(llvm::omp::nestedOrderedErrSet)) {
       context_.Say(blkDirective.source,
           "`ORDERED` region may not be closely nested inside of "
           "`CRITICAL`, `ORDERED`, explicit `TASK` or `TASKLOOP` region."_err_en_US);
     }
   }
 }
 
 void OmpStructureChecker::Leave(const parser::OpenMPBlockConstruct &) {
+  if (GetDirectiveNest(TargetBlockOnlyTeams)) {
+    ExitDirectiveNest(TargetBlockOnlyTeams);
+  }
   dirContext_.pop_back();
 }
 
 void OmpStructureChecker::Enter(const parser::OpenMPSectionsConstruct &x) {
   const auto &beginSectionsDir{
       std::get<parser::OmpBeginSectionsDirective>(x.t)};
   const auto &endSectionsDir{std::get<parser::OmpEndSectionsDirective>(x.t)};
   const auto &beginDir{
if (auto *enclosingContext{GetEnclosingContextWithDir(enclosingDir)}) {
               parser::ToUpperCaseLetters(getClauseName(currClause).str()),
               symbol->name());
         }
       }
     }
   }
 }
 
+bool OmpStructureChecker::CheckTargetBlockOnlyTeams(
+    const parser::Block &block) {
+  bool nestedTeams{false};
+  auto it{block.begin()};
+
+  if (const auto *ompConstruct{parser::Unwrap<parser::OpenMPConstruct>(*it)}) {
+    if (const auto *ompBlockConstruct{
+            std::get_if<parser::OpenMPBlockConstruct>(&ompConstruct->u)}) {
+      const auto &beginBlockDir{
+          std::get<parser::OmpBeginBlockDirective>(ompBlockConstruct->t)};
+      const auto &beginDir{
+          std::get<parser::OmpBlockDirective>(beginBlockDir.t)};
+      if (beginDir.v == llvm::omp::Directive::OMPD_teams) {
+        nestedTeams = true;
+      }
+    }
+  }
+
+  if (nestedTeams && ++it == block.end()) {
+    return true;
+  }
+  return false;
+}
+
 void OmpStructureChecker::CheckWorkshareBlockStmts(
     const parser::Block &block, parser::CharBlock source) {
   OmpWorkshareBlockChecker ompWorkshareBlockChecker{context_, source};
 
   for (auto it{block.begin()}; it != block.end(); ++it) {
     if (parser::Unwrap<parser::AssignmentStmt>(*it) ||
         parser::Unwrap<parser::ForallStmt>(*it) ||
         parser::Unwrap<parser::ForallConstruct>(*it) ||

flang/test/Semantics/omp-firstprivate01.f90

 ! RUN: %S/test_errors.sh %s %t %flang_fc1 -fopenmp
 ! REQUIRES: shell
 ! OpenMP Version 4.5
 ! 2.15.3.4 firstprivate Clause
 ! Variables that appear in a firstprivate clause on a distribute or
 ! worksharing constructs must not appear in the private or
 ! reduction clause in a teams or parallel constructs in the outer context
 
 program omp_firstprivate
   integer :: i, a(10), b(10), c(10)
 
   a = 10
   b = 20
 
+  !ERROR: TARGET construct with nested TEAMS region contains statements or directives outside of the TEAMS construct
   !$omp target
   !$omp teams private(a, b)
   !ERROR: FIRSTPRIVATE variable 'a' is PRIVATE in outer context
   !$omp distribute firstprivate(a)
   do i = 1, 10
     a(i) = a(i) + b(i) - i
   end do
   !$omp end distribute

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

do i = 1, 10
     !$omp master
     j = j -1
     !$omp end master
   end do
   !$omp end ordered
 
   !$omp ordered
   do i = 1, 10
+    !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
     !$omp teams
     !$omp distribute
     do k =1, 10
       print *, "hello"
       !$omp master
       j = j -1
       !$omp end master
     end do
     !$omp end distribute
     !$omp end teams
   end do
   !$omp end ordered
 
   !$omp critical
   do i = 1, 10
+    !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
     !$omp teams
     !$omp distribute
     do k =1, 10
       print *, "hello"
       !$omp master
       j = j -1
       !$omp end master
     end do
     !$omp end distribute
     !$omp end teams
   end do
   !$omp end critical
 
   !$omp taskloop
   do i = 1, 10
+    !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
     !$omp teams
     !$omp distribute
     do k =1, 10
       print *, "hello"
       !ERROR: `MASTER` region may not be closely nested inside of `WORKSHARING`, `LOOP`, `TASK`, `TASKLOOP`, or `ATOMIC` region.
       !$omp master
       j = j -1
       !$omp end master
     end do
     !$omp end distribute
     !$omp end teams
   end do
   !$omp end taskloop
 
   !$omp task
   do i = 1, 10
+    !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
     !$omp teams
     !$omp distribute
     do k =1, 10
       print *, "hello"
       !ERROR: `MASTER` region may not be closely nested inside of `WORKSHARING`, `LOOP`, `TASK`, `TASKLOOP`, or `ATOMIC` region.
       !$omp master
       j = j -1
       !$omp end master
     end do
     !$omp end distribute
     !$omp end teams
   end do
   !$omp end task
 
 end program omp_nest_master

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

SUBROUTINE NESTED_BAD(N)
 
   !$OMP SIMD
   DO I = 1,N
     IF (I <= 10) THEN
       !$OMP ORDERED SIMD
       DO J = 1,N
         print *, "Hi"
         !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+        !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
         !$omp teams 
          DO K = 1,N
         print *, 'Hello'
         END DO
         !$omp end teams
       END DO
       !$OMP END ORDERED
     ENDIF
   END DO
   !$OMP END SIMD
 
   !$OMP SIMD
   DO I = 1,N
     !$OMP ATOMIC
     K =  K + 1
     IF (I <= 10) THEN
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp task 
       do J = 1, N
         K = 2
       end do
       !$omp end task
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
-      !$omp teams 
-      do J = 1, N
-        K = 2
-      end do
-      !$omp end teams
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp target 
       do J = 1, N
         K = 2
       end do
       !$omp end target
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$OMP DO
       DO J = 1,N
DO I = 1,N
     IF (I <= 10) THEN
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp task 
       do J = 1, N
         K = 2
       end do
       !$omp end task
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
-      !$omp teams 
-      do J = 1, N
-        K = 2
-      end do
-      !$omp end teams
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp target 
       do J = 1, N
         K = 2
       end do
       !$omp end target
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
       !$OMP DO
DO I = 1,N
     IF (I <= 10) THEN
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp task 
       do J = 1, N
         K = 2
       end do
       !$omp end task
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
-      !$omp teams 
-      do J = 1, N
-        K = 2
-      end do
-      !$omp end teams
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp target 
       do J = 1, N
         K = 2
       end do
       !$omp end target
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
       !$OMP DO
DO I = 1,N
     IF (I <= 10) THEN
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp task 
       do J = 1, N
         K = 2
       end do
       !$omp end task
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
-      !$omp teams 
-      do J = 1, N
-        K = 2
-      end do
-      !$omp end teams
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp target 
       do J = 1, N
         K = 2
       end do
       !$omp end target
       !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
       !$OMP DO
       DO J = 1,N

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

+! RUN: %S/test_errors.sh %s %t %flang -fopenmp
+! REQUIRES: shell
+
+! OpenMP Version 5.0
+! Check OpenMP construct validity for the following directives:
+! 2.7 Teams Construct
+
+program main
+  integer :: i, j, N = 10
+  real :: a, b, c
+
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+
+  !$omp target
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  !$omp end target
+
+  !$omp target
+  !$omp parallel
+  !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  !$omp end parallel
+  !$omp end target
+
+  !$omp parallel
+  !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  !$omp end parallel
+
+  !$omp do
+  do i = 1, N
+  !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  end do
+
+  !$omp master
+  !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  !$omp end master
+
+  !$omp target parallel
+  !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  !$omp end target parallel
+
+  !$omp target
+  !$omp teams
+  !ERROR: Only `DISTRIBUTE` or `PARALLEL` regions are allowed to be strictly nested inside `TEAMS` region.
+  !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  !$omp end teams
+  !$omp end target
+
+  !$omp target teams
+  !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  !$omp end target teams
+
+  !ERROR: TARGET construct with nested TEAMS region contains statements or directives outside of the TEAMS construct
+  !$omp target
+  do i = 1, N
+    !$omp teams
+    a = 3.14
+    !$omp end teams
+  enddo
+  !$omp end target
+
+  !ERROR: TARGET construct with nested TEAMS region contains statements or directives outside of the TEAMS construct
+  !$omp target
+  if (i .GT. 1) then
+    if (j .GT. 1) then
+      !$omp teams
+      a = 3.14
+      !$omp end teams
+    end if
+  end if
+  !$omp end target
+
+  !ERROR: TARGET construct with nested TEAMS region contains statements or directives outside of the TEAMS construct
+  !$omp target
+  b = 3.14
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  !$omp end target
+
+  !ERROR: TARGET construct with nested TEAMS region contains statements or directives outside of the TEAMS construct
+  !$omp target
+  !$omp teams
+  a = 3.14
+  !$omp end teams
+  c = 3.14
+  !$omp end target
+
+end program main