check-omp-structure.h

//===-- lib/Semantics/check-omp-structure.h ---------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
 
// OpenMP structure validity check list
//    1. invalid clauses on directive
//    2. invalid repeated clauses on directive
//    3. TODO: invalid nesting of regions
 
#ifndef FORTRAN_SEMANTICS_CHECK_OMP_STRUCTURE_H_
#define FORTRAN_SEMANTICS_CHECK_OMP_STRUCTURE_H_
 
#include "check-directive-structure.h"
#include "flang/Common/enum-set.h"
#include "flang/Parser/parse-tree.h"
#include "flang/Semantics/openmp-directive-sets.h"
#include "flang/Semantics/semantics.h"
 
using OmpClauseSet =
    Fortran::common::EnumSet<llvm::omp::Clause, llvm::omp::Clause_enumSize>;
 
#define GEN_FLANG_DIRECTIVE_CLAUSE_SETS
#include "llvm/Frontend/OpenMP/OMP.inc"
 
namespace llvm {
namespace omp {
static OmpClauseSet privateSet{
    Clause::OMPC_private, Clause::OMPC_firstprivate, Clause::OMPC_lastprivate};
static OmpClauseSet privateReductionSet{
    OmpClauseSet{Clause::OMPC_reduction} | privateSet};
// omp.td cannot differentiate allowed/not allowed clause list for few
// directives for fortran. nowait is not allowed on begin directive clause list
// for below list of directives. Directives with conflicting list of clauses are
// included in below list.
static const OmpDirectiveSet noWaitClauseNotAllowedSet{
    Directive::OMPD_do,
    Directive::OMPD_do_simd,
    Directive::OMPD_sections,
    Directive::OMPD_single,
    Directive::OMPD_workshare,
};
} // namespace omp
} // namespace llvm
 
namespace Fortran::semantics {
struct AnalyzedCondStmt;
 
namespace omp {
struct LoopSequence;
}
 
// Mapping from 'Symbol' to 'Source' to keep track of the variables
// used in multiple clauses
using SymbolSourceMap = std::multimap<const Symbol *, parser::CharBlock>;
// Multimap to check the triple <current_dir, enclosing_dir, enclosing_clause>
using DirectivesClauseTriple = std::multimap<llvm::omp::Directive,
    std::pair<llvm::omp::Directive, const OmpClauseSet>>;
 
using OmpStructureCheckerBase = DirectiveStructureChecker<llvm::omp::Directive,
    llvm::omp::Clause, parser::OmpClause, llvm::omp::Clause_enumSize>;
 
class OmpStructureChecker : public OmpStructureCheckerBase {
public:
  using Base = OmpStructureCheckerBase;
 
  OmpStructureChecker(SemanticsContext &context);
 
  using llvmOmpClause = const llvm::omp::Clause;
 
  bool Enter(const parser::MainProgram &);
  void Leave(const parser::MainProgram &);
  bool Enter(const parser::BlockData &);
  void Leave(const parser::BlockData &);
  bool Enter(const parser::Module &);
  void Leave(const parser::Module &);
  bool Enter(const parser::Submodule &);
  void Leave(const parser::Submodule &);
  bool Enter(const parser::SubroutineStmt &);
  bool Enter(const parser::EndSubroutineStmt &);
  bool Enter(const parser::FunctionStmt &);
  bool Enter(const parser::EndFunctionStmt &);
  bool Enter(const parser::BlockConstruct &);
  void Leave(const parser::BlockConstruct &);
  void Enter(const parser::InternalSubprogram &);
  void Enter(const parser::ModuleSubprogram &);
 
  void Enter(const parser::SpecificationPart &);
  void Leave(const parser::SpecificationPart &);
  void Enter(const parser::ExecutionPart &);
  void Leave(const parser::ExecutionPart &);
 
  void Enter(const parser::OpenMPConstruct &);
  void Leave(const parser::OpenMPConstruct &);
  void Enter(const parser::OpenMPDeclarativeConstruct &);
  void Leave(const parser::OpenMPDeclarativeConstruct &);
 
  void Enter(const parser::OpenMPMisplacedEndDirective &);
  void Leave(const parser::OpenMPMisplacedEndDirective &);
  void Enter(const parser::OpenMPInvalidDirective &);
  void Leave(const parser::OpenMPInvalidDirective &);
 
  void Enter(const parser::OpenMPLoopConstruct &);
  void Leave(const parser::OpenMPLoopConstruct &);
 
  void Enter(const parser::OpenMPAssumeConstruct &);
  void Leave(const parser::OpenMPAssumeConstruct &);
  void Enter(const parser::OpenMPDeclarativeAssumes &);
  void Leave(const parser::OpenMPDeclarativeAssumes &);
  void Enter(const parser::OpenMPInteropConstruct &);
  void Leave(const parser::OpenMPInteropConstruct &);
  void Enter(const parser::OmpBlockConstruct &);
  void Leave(const parser::OmpBlockConstruct &);
  void Leave(const parser::OmpBeginDirective &);
  void Enter(const parser::OmpEndDirective &);
  void Leave(const parser::OmpEndDirective &);
 
  void Enter(const parser::OpenMPSectionsConstruct &);
  void Leave(const parser::OpenMPSectionsConstruct &);
  void Enter(const parser::OmpEndSectionsDirective &);
  void Leave(const parser::OmpEndSectionsDirective &);
 
  void Enter(const parser::OmpDeclareVariantDirective &);
  void Leave(const parser::OmpDeclareVariantDirective &);
  void Enter(const parser::OpenMPDeclareSimdConstruct &);
  void Leave(const parser::OpenMPDeclareSimdConstruct &);
  void Enter(const parser::OmpAllocateDirective &);
  void Leave(const parser::OmpAllocateDirective &);
  void Enter(const parser::OpenMPDeclareMapperConstruct &);
  void Leave(const parser::OpenMPDeclareMapperConstruct &);
  void Enter(const parser::OpenMPDeclareReductionConstruct &);
  void Leave(const parser::OpenMPDeclareReductionConstruct &);
  void Enter(const parser::OpenMPDeclareTargetConstruct &);
  void Leave(const parser::OpenMPDeclareTargetConstruct &);
  void Enter(const parser::OpenMPDepobjConstruct &);
  void Leave(const parser::OpenMPDepobjConstruct &);
  void Enter(const parser::OpenMPDispatchConstruct &);
  void Leave(const parser::OpenMPDispatchConstruct &);
  void Enter(const parser::OmpErrorDirective &);
  void Leave(const parser::OmpErrorDirective &);
  void Enter(const parser::OmpNothingDirective &);
  void Leave(const parser::OmpNothingDirective &);
  void Enter(const parser::OpenMPAllocatorsConstruct &);
  void Leave(const parser::OpenMPAllocatorsConstruct &);
  void Enter(const parser::OpenMPRequiresConstruct &);
  void Leave(const parser::OpenMPRequiresConstruct &);
  void Enter(const parser::OpenMPGroupprivate &);
  void Leave(const parser::OpenMPGroupprivate &);
  void Enter(const parser::OpenMPThreadprivate &);
  void Leave(const parser::OpenMPThreadprivate &);
 
  void Enter(const parser::OpenMPSimpleStandaloneConstruct &);
  void Leave(const parser::OpenMPSimpleStandaloneConstruct &);
  void Enter(const parser::OpenMPFlushConstruct &);
  void Leave(const parser::OpenMPFlushConstruct &);
  void Enter(const parser::OpenMPCancelConstruct &);
  void Leave(const parser::OpenMPCancelConstruct &);
  void Enter(const parser::OpenMPCancellationPointConstruct &);
  void Leave(const parser::OpenMPCancellationPointConstruct &);
  void Enter(const parser::OpenMPCriticalConstruct &);
  void Leave(const parser::OpenMPCriticalConstruct &);
  void Enter(const parser::OpenMPAtomicConstruct &);
  void Leave(const parser::OpenMPAtomicConstruct &);
 
  void Leave(const parser::OmpClauseList &);
  void Enter(const parser::OmpClause &);
 
  void Enter(const parser::DoConstruct &);
  void Leave(const parser::DoConstruct &);
 
  void Enter(const parser::OmpDirectiveSpecification &);
  void Leave(const parser::OmpDirectiveSpecification &);
 
  void Enter(const parser::OmpMetadirectiveDirective &);
  void Leave(const parser::OmpMetadirectiveDirective &);
 
  void Enter(const parser::OmpContextSelector &);
  void Leave(const parser::OmpContextSelector &);
 
  template <typename A> void Enter(const parser::Statement<A> &);
  void Leave(const parser::GotoStmt &);
  void Leave(const parser::ComputedGotoStmt &);
  void Leave(const parser::ArithmeticIfStmt &);
  void Leave(const parser::AssignedGotoStmt &);
  void Leave(const parser::AltReturnSpec &);
  void Leave(const parser::ErrLabel &);
  void Leave(const parser::EndLabel &);
  void Leave(const parser::EorLabel &);
 
#define GEN_FLANG_CLAUSE_CHECK_ENTER
#include "llvm/Frontend/OpenMP/OMP.inc"
 
private:
  using LoopOrConstruct = std::variant<const parser::DoConstruct *,
      const parser::OpenMPConstruct *>;
 
  // Most of these functions are defined in check-omp-structure.cpp, but
  // some groups have their own files.
 
  // check-omp-atomic.cpp
  void CheckStorageOverlap(const evaluate::Expr<evaluate::SomeType> &,
      llvm::ArrayRef<evaluate::Expr<evaluate::SomeType>>, parser::CharBlock);
  void ErrorShouldBeVariable(const MaybeExpr &expr, parser::CharBlock source);
  void CheckAtomicType(SymbolRef sym, parser::CharBlock source,
      std::string_view name, bool checkTypeOnPointer = true);
  void CheckAtomicVariable(const evaluate::Expr<evaluate::SomeType> &,
      parser::CharBlock, bool checkTypeOnPointer = true);
  std::pair<const parser::ExecutionPartConstruct *,
      const parser::ExecutionPartConstruct *>
  CheckUpdateCapture(const parser::ExecutionPartConstruct *ec1,
      const parser::ExecutionPartConstruct *ec2, parser::CharBlock source);
  void CheckAtomicCaptureAssignment(const evaluate::Assignment &capture,
      const SomeExpr &atom, parser::CharBlock source);
  void CheckAtomicReadAssignment(
      const evaluate::Assignment &read, parser::CharBlock source);
  void CheckAtomicWriteAssignment(
      const evaluate::Assignment &write, parser::CharBlock source);
  std::optional<evaluate::Assignment> CheckAtomicUpdateAssignment(
      const evaluate::Assignment &update, parser::CharBlock source);
  std::pair<bool, bool> CheckAtomicUpdateAssignmentRhs(const SomeExpr &atom,
      const SomeExpr &rhs, parser::CharBlock source, bool suppressDiagnostics);
  void CheckAtomicConditionalUpdateAssignment(const SomeExpr &cond,
      parser::CharBlock condSource, const evaluate::Assignment &assign,
      parser::CharBlock assignSource);
  void CheckAtomicConditionalUpdateStmt(
      const AnalyzedCondStmt &update, parser::CharBlock source);
  void CheckAtomicUpdateOnly(const parser::OpenMPAtomicConstruct &x,
      const parser::Block &body, parser::CharBlock source);
  void CheckAtomicConditionalUpdate(const parser::OpenMPAtomicConstruct &x,
      const parser::Block &body, parser::CharBlock source);
  void CheckAtomicUpdateCapture(const parser::OpenMPAtomicConstruct &x,
      const parser::Block &body, parser::CharBlock source);
  void CheckAtomicConditionalUpdateCapture(
      const parser::OpenMPAtomicConstruct &x, const parser::Block &body,
      parser::CharBlock source);
  void CheckAtomicRead(const parser::OpenMPAtomicConstruct &x);
  void CheckAtomicWrite(const parser::OpenMPAtomicConstruct &x);
  void CheckAtomicUpdate(const parser::OpenMPAtomicConstruct &x);
 
  // check-omp-loop.cpp
  void HasInvalidDistributeNesting(const parser::OpenMPLoopConstruct &x);
  void HasInvalidLoopBinding(const parser::OpenMPLoopConstruct &x);
  void CheckSIMDNest(const parser::OpenMPConstruct &x);
  void CheckRectangularNest(const parser::OmpDirectiveSpecification &spec,
      const omp::LoopSequence &nest);
  void CheckNestedConstruct(const parser::OpenMPLoopConstruct &x);
  const parser::Name GetLoopIndex(const parser::DoConstruct *x);
  void SetLoopInfo(const parser::OpenMPLoopConstruct &x);
  void CheckIterationVariableType(const parser::OpenMPLoopConstruct &x);
  std::int64_t GetOrdCollapseLevel(const parser::OpenMPLoopConstruct &x);
  void CheckAssociatedLoopConstraints(const parser::OpenMPLoopConstruct &x);
  void CheckScanModifier(const parser::OmpClause::Reduction &x);
  void CheckDistLinear(const parser::OpenMPLoopConstruct &x);
 
  // check-omp-metadirective.cpp
  const std::list<parser::OmpTraitProperty> &GetTraitPropertyList(
      const parser::OmpTraitSelector &);
  std::optional<llvm::omp::Clause> GetClauseFromProperty(
      const parser::OmpTraitProperty &);
 
  void CheckTraitSelectorList(const std::list<parser::OmpTraitSelector> &);
  void CheckTraitSetSelector(const parser::OmpTraitSetSelector &);
  void CheckTraitScore(const parser::OmpTraitScore &);
  bool VerifyTraitPropertyLists(
      const parser::OmpTraitSetSelector &, const parser::OmpTraitSelector &);
  void CheckTraitSelector(
      const parser::OmpTraitSetSelector &, const parser::OmpTraitSelector &);
  void CheckTraitADMO(
      const parser::OmpTraitSetSelector &, const parser::OmpTraitSelector &);
  void CheckTraitCondition(
      const parser::OmpTraitSetSelector &, const parser::OmpTraitSelector &);
  void CheckTraitDeviceNum(
      const parser::OmpTraitSetSelector &, const parser::OmpTraitSelector &);
  void CheckTraitRequires(
      const parser::OmpTraitSetSelector &, const parser::OmpTraitSelector &);
  void CheckTraitSimd(
      const parser::OmpTraitSetSelector &, const parser::OmpTraitSelector &);
 
  // check-omp-structure.cpp
  bool IsAllowedClause(llvm::omp::Clause clauseId);
  bool CheckAllowedClause(llvmOmpClause clause);
  void CheckVariableListItem(const SymbolSourceMap &symbols);
  void CheckDirectiveSpelling(
      parser::CharBlock spelling, llvm::omp::Directive id);
  void CheckDirectiveDeprecation(const parser::OpenMPConstruct &x);
  void AnalyzeObject(const parser::OmpObject &object);
  void AnalyzeObjects(const parser::OmpObjectList &objects);
 
  const parser::OpenMPConstruct *GetCurrentConstruct() const;
  void CheckSourceLabel(const parser::Label &);
  void CheckLabelContext(const parser::CharBlock, const parser::CharBlock,
      const parser::OpenMPConstruct *, const parser::OpenMPConstruct *);
  void ClearLabels();
  void CheckMultipleOccurrence(semantics::UnorderedSymbolSet &listVars,
      const std::list<parser::Name> &nameList, const parser::CharBlock &item,
      const std::string &clauseName);
  void CheckMultListItems();
  void CheckStructureComponent(
      const parser::OmpObjectList &objects, llvm::omp::Clause clauseId);
  bool HasInvalidWorksharingNesting(
      const parser::OmpDirectiveName &name, const OmpDirectiveSet &);
 
  bool IsCloselyNestedRegion(const OmpDirectiveSet &set);
  bool IsNestedInDirective(llvm::omp::Directive directive);
  bool IsCombinedParallelWorksharing(llvm::omp::Directive directive) const;
  bool InTargetRegion();
  void HasInvalidTeamsNesting(
      const llvm::omp::Directive &dir, const parser::CharBlock &source);
  bool HasRequires(llvm::omp::Clause req);
  void CheckAllowedMapTypes(
      parser::OmpMapType::Value, llvm::ArrayRef<parser::OmpMapType::Value>);
 
  llvm::StringRef getClauseName(llvm::omp::Clause clause) override;
  llvm::StringRef getDirectiveName(llvm::omp::Directive directive) override;
 
  template < //
      typename LessTy, typename RangeTy,
      typename IterTy = decltype(std::declval<RangeTy>().begin())>
  std::optional<IterTy> FindDuplicate(RangeTy &&);
 
  void CheckDependList(const parser::DataRef &);
  void CheckDoacross(const parser::OmpDoacross &doa);
  void CheckDimsModifier(parser::CharBlock source, size_t numValues,
      const parser::OmpDimsModifier &x);
  bool IsDataRefTypeParamInquiry(const parser::DataRef *dataRef);
  void CheckVarIsNotPartOfAnotherVar(const parser::CharBlock &source,
      const parser::OmpObject &obj, llvm::StringRef clause = "");
  void CheckVarIsNotPartOfAnotherVar(const parser::CharBlock &source,
      const parser::OmpObjectList &objList, llvm::StringRef clause = "");
  void CheckThreadprivateOrDeclareTargetVar(const parser::Designator &);
  void CheckThreadprivateOrDeclareTargetVar(const parser::Name &);
  void CheckThreadprivateOrDeclareTargetVar(const parser::OmpObject &);
  void CheckThreadprivateOrDeclareTargetVar(const parser::OmpObjectList &);
  void CheckSymbolName(
      const parser::CharBlock &source, const parser::OmpObject &object);
  void CheckSymbolNames(
      const parser::CharBlock &source, const parser::OmpObjectList &objList);
  void CheckIntentInPointer(SymbolSourceMap &, const llvm::omp::Clause);
  void CheckAssumedSizeArray(SymbolSourceMap &, const llvm::omp::Clause);
  void CheckProcedurePointer(SymbolSourceMap &, const llvm::omp::Clause);
  void CheckCrayPointee(const parser::OmpObjectList &objectList,
      llvm::StringRef clause, bool suggestToUseCrayPointer = true);
  void GetSymbolsInObjectList(const parser::OmpObjectList &, SymbolSourceMap &);
  void CheckDefinableObjects(SymbolSourceMap &, const llvm::omp::Clause);
  void CheckCopyingPolymorphicAllocatable(
      SymbolSourceMap &, const llvm::omp::Clause);
  void CheckPrivateSymbolsInOuterCxt(
      SymbolSourceMap &, DirectivesClauseTriple &, const llvm::omp::Clause);
  void CheckIsLoopIvPartOfClause(
      llvmOmpClause clause, const parser::OmpObjectList &ompObjectList);
  bool CheckTargetBlockOnlyTeams(const parser::Block &);
  void CheckWorkshareBlockStmts(const parser::Block &, parser::CharBlock);
  void CheckWorkdistributeBlockStmts(const parser::Block &, parser::CharBlock);
  void CheckIndividualAllocateDirective(
      const parser::OmpAllocateDirective &x, bool isExecutable);
  void CheckExecutableAllocateDirective(const parser::OmpAllocateDirective &x);
 
  void CheckIteratorRange(const parser::OmpIteratorSpecifier &x);
  void CheckIteratorModifier(const parser::OmpIterator &x);
 
  void CheckTargetNest(const parser::OpenMPConstruct &x);
  void CheckTargetUpdate();
  void CheckTaskgraph(const parser::OmpBlockConstruct &x);
  void CheckDependenceType(const parser::OmpDependenceType::Value &x);
  void CheckTaskDependenceType(const parser::OmpTaskDependenceType::Value &x);
  std::optional<llvm::omp::Directive> GetCancelType(
      llvm::omp::Directive cancelDir, const parser::CharBlock &cancelSource,
      const std::optional<parser::OmpClauseList> &maybeClauses);
  void CheckCancellationNest(
      const parser::CharBlock &source, llvm::omp::Directive type);
  void CheckReductionObjects(
      const parser::OmpObjectList &objects, llvm::omp::Clause clauseId);
  bool CheckReductionOperator(const parser::OmpReductionIdentifier &ident,
      parser::CharBlock source, llvm::omp::Clause clauseId);
  void CheckReductionObjectTypes(const parser::OmpObjectList &objects,
      const parser::OmpReductionIdentifier &ident);
  void CheckReductionModifier(const parser::OmpReductionModifier &);
  void CheckLastprivateModifier(const parser::OmpLastprivateModifier &);
  void CheckMasterNesting(const parser::OmpBlockConstruct &x);
  void ChecksOnOrderedAsBlock();
  void CheckBarrierNesting(const parser::OpenMPSimpleStandaloneConstruct &x);
  void CheckScan(const parser::OpenMPSimpleStandaloneConstruct &x);
  void ChecksOnOrderedAsStandalone();
  void CheckOrderedDependClause(std::optional<std::int64_t> orderedValue);
  void CheckReductionArraySection(
      const parser::OmpObjectList &ompObjectList, llvm::omp::Clause clauseId);
  void CheckArraySection(const parser::ArrayElement &arrayElement,
      const parser::Name &name, const llvm::omp::Clause clause);
  void CheckLastPartRefForArraySection(
      const parser::Designator &designator, llvm::omp::Clause clauseId);
  void CheckSharedBindingInOuterContext(
      const parser::OmpObjectList &ompObjectList);
  void CheckIfContiguous(const parser::OmpObject &object);
  const parser::Name *GetObjectName(const parser::OmpObject &object);
  void CheckInitOnDepobj(const parser::OpenMPDepobjConstruct &depobj,
      const parser::OmpClause &initClause);
  void CheckAllowedRequiresClause(llvmOmpClause clause);
  void AddEndDirectiveClauses(const parser::OmpClauseList &clauses);
 
  void EnterDirectiveNest(const int index) { directiveNest_[index]++; }
  void ExitDirectiveNest(const int index) { directiveNest_[index]--; }
  int GetDirectiveNest(const int index) { return directiveNest_[index]; }
 
  bool deviceConstructFound_{false};
  enum directiveNestType : int {
    SIMDNest,
    TargetBlockOnlyTeams,
    TargetNest,
    DeclarativeNest,
    ContextSelectorNest,
    MetadirectiveNest,
    LastType = MetadirectiveNest,
  };
  int directiveNest_[LastType + 1] = {0};
 
  int allocateDirectiveLevel_{0};
  parser::CharBlock visitedAtomicSource_;
  SymbolSourceMap deferredNonVariables_;
 
  // Stack of nested DO loops and OpenMP constructs.
  // This is used to verify DO loop nest for DOACROSS, and branches into
  // and out of OpenMP constructs.
  std::vector<LoopOrConstruct> constructStack_;
  // Scopes for scoping units.
  std::vector<const Scope *> scopeStack_;
  // Stack of directive specifications (except for SECTION).
  // This is to allow visitor functions to see all specified clauses, since
  // they are only recorded in DirectiveContext as they are processed.
  std::vector<const parser::OmpDirectiveSpecification *> dirStack_;
 
  enum class PartKind : int {
    // There are also other "parts", such as internal-subprogram-part, etc,
    // but we're keeping track of these two for now.
    SpecificationPart,
    ExecutionPart,
  };
  std::vector<PartKind> partStack_;
 
  std::multimap<const parser::Label,
      std::pair<parser::CharBlock, const parser::OpenMPConstruct *>>
      sourceLabels_;
  std::map<const parser::Label,
      std::pair<parser::CharBlock, const parser::OpenMPConstruct *>>
      targetLabels_;
  parser::CharBlock currentStatementSource_;
};
 
template <typename A>
void OmpStructureChecker::Enter(const parser::Statement<A> &statement) {
  currentStatementSource_ = statement.source;
  // Keep track of the labels in all the labelled statements
  if (statement.label) {
    auto label{statement.label.value()};
    // Get the context to check if the labelled statement is in an
    // enclosing OpenMP construct
    auto *thisConstruct{GetCurrentConstruct()};
    targetLabels_.emplace(
        label, std::make_pair(currentStatementSource_, thisConstruct));
    // Check if a statement that causes a jump to the 'label'
    // has already been encountered
    auto range{sourceLabels_.equal_range(label)};
    for (auto it{range.first}; it != range.second; ++it) {
      // Check if both the statement with 'label' and the statement that
      // causes a jump to the 'label' are in the same scope
      CheckLabelContext(it->second.first, currentStatementSource_,
          it->second.second, thisConstruct);
    }
  }
}

template <typename LessTy, typename RangeTy, typename IterTy>
std::optional<IterTy> OmpStructureChecker::FindDuplicate(RangeTy &&range) {
  // Deal with iterators, since the actual elements may be rvalues (i.e.
  // have no addresses), for example with custom-constructed ranges that
  // are not simple c.begin()..c.end().
  std::set<IterTy, LessTy> uniq;
  for (auto it{range.begin()}, end{range.end()}; it != end; ++it) {
    if (!uniq.insert(it).second) {
      return it;
    }
  }
  return std::nullopt;
}
 
} // namespace Fortran::semantics
#endif // FORTRAN_SEMANTICS_CHECK_OMP_STRUCTURE_H_