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

#include "check-omp-structure.h"

#include "check-directive-structure.h"
#include "definable.h"
#include "resolve-names-utils.h"

#include "flang/Common/idioms.h"
#include "flang/Common/indirection.h"
#include "flang/Common/visit.h"
#include "flang/Evaluate/fold.h"
#include "flang/Evaluate/tools.h"
#include "flang/Evaluate/type.h"
#include "flang/Parser/char-block.h"
#include "flang/Parser/characters.h"
#include "flang/Parser/message.h"
#include "flang/Parser/openmp-utils.h"
#include "flang/Parser/parse-tree-visitor.h"
#include "flang/Parser/parse-tree.h"
#include "flang/Parser/tools.h"
#include "flang/Semantics/expression.h"
#include "flang/Semantics/openmp-directive-sets.h"
#include "flang/Semantics/openmp-modifiers.h"
#include "flang/Semantics/openmp-utils.h"
#include "flang/Semantics/scope.h"
#include "flang/Semantics/semantics.h"
#include "flang/Semantics/symbol.h"
#include "flang/Semantics/tools.h"
#include "flang/Semantics/type.h"
#include "flang/Support/Fortran-features.h"

#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Frontend/OpenMP/OMP.h"

#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iterator>
#include <list>
#include <map>
#include <optional>
#include <set>
#include <string>
#include <tuple>
#include <type_traits>
#include <utility>
#include <variant>

namespace Fortran::semantics {

using namespace Fortran::semantics::omp;
using namespace Fortran::parser::omp;

OmpStructureChecker::OmpStructureChecker(SemanticsContext &context)
    : DirectiveStructureChecker(context,
#define GEN_FLANG_DIRECTIVE_CLAUSE_MAP
#include "llvm/Frontend/OpenMP/OMP.inc"
      ) {
  scopeStack_.push_back(&context.globalScope());
}

bool OmpStructureChecker::Enter(const parser::MainProgram &x) {
  using StatementProgramStmt = parser::Statement<parser::ProgramStmt>;
  if (auto &stmt{std::get<std::optional<StatementProgramStmt>>(x.t)}) {
    scopeStack_.push_back(stmt->statement.v.symbol->scope());
  } else {
    for (const Scope &scope : context_.globalScope().children()) {
      // There can only be one main program.
      if (scope.kind() == Scope::Kind::MainProgram) {
        scopeStack_.push_back(&scope);
        break;
      }
    }
  }
  return true;
}

void OmpStructureChecker::Leave(const parser::MainProgram &x) {
  scopeStack_.pop_back();
}

bool OmpStructureChecker::Enter(const parser::BlockData &x) {
  // The BLOCK DATA name is optional, so we need to look for the
  // corresponding scope in the global scope.
  auto &stmt{std::get<parser::Statement<parser::BlockDataStmt>>(x.t)};
  if (auto &name{stmt.statement.v}) {
    scopeStack_.push_back(name->symbol->scope());
  } else {
    for (const Scope &scope : context_.globalScope().children()) {
      if (scope.kind() == Scope::Kind::BlockData) {
        if (auto *s{scope.symbol()}; !s || s->name().empty()) {
          scopeStack_.push_back(&scope);
          break;
        }
      }
    }
  }
  return true;
}

void OmpStructureChecker::Leave(const parser::BlockData &x) {
  scopeStack_.pop_back();
}

bool OmpStructureChecker::Enter(const parser::Module &x) {
  auto &stmt{std::get<parser::Statement<parser::ModuleStmt>>(x.t)};
  const Symbol *sym{stmt.statement.v.symbol};
  scopeStack_.push_back(sym->scope());
  return true;
}

void OmpStructureChecker::Leave(const parser::Module &x) {
  scopeStack_.pop_back();
}

bool OmpStructureChecker::Enter(const parser::Submodule &x) {
  auto &stmt{std::get<parser::Statement<parser::SubmoduleStmt>>(x.t)};
  const Symbol *sym{std::get<parser::Name>(stmt.statement.t).symbol};
  scopeStack_.push_back(sym->scope());
  return true;
}

void OmpStructureChecker::Leave(const parser::Submodule &x) {
  scopeStack_.pop_back();
}

// Function/subroutine subprogram nodes don't appear in INTERFACEs, but
// the subprogram/end statements do.
bool OmpStructureChecker::Enter(const parser::SubroutineStmt &x) {
  const Symbol *sym{std::get<parser::Name>(x.t).symbol};
  scopeStack_.push_back(sym->scope());
  return true;
}

bool OmpStructureChecker::Enter(const parser::EndSubroutineStmt &x) {
  scopeStack_.pop_back();
  return true;
}

bool OmpStructureChecker::Enter(const parser::FunctionStmt &x) {
  const Symbol *sym{std::get<parser::Name>(x.t).symbol};
  scopeStack_.push_back(sym->scope());
  return true;
}

bool OmpStructureChecker::Enter(const parser::EndFunctionStmt &x) {
  scopeStack_.pop_back();
  return true;
}

bool OmpStructureChecker::Enter(const parser::BlockConstruct &x) {
  auto &specPart{std::get<parser::BlockSpecificationPart>(x.t)};
  auto &execPart{std::get<parser::Block>(x.t)};
  if (auto &&source{parser::GetSource(specPart)}) {
    scopeStack_.push_back(&context_.FindScope(*source));
  } else if (auto &&source{parser::GetSource(execPart)}) {
    scopeStack_.push_back(&context_.FindScope(*source));
  }
  return true;
}

void OmpStructureChecker::Leave(const parser::BlockConstruct &x) {
  auto &specPart{std::get<parser::BlockSpecificationPart>(x.t)};
  auto &execPart{std::get<parser::Block>(x.t)};
  if (auto &&source{parser::GetSource(specPart)}) {
    scopeStack_.push_back(&context_.FindScope(*source));
  } else if (auto &&source{parser::GetSource(execPart)}) {
    scopeStack_.push_back(&context_.FindScope(*source));
  }
}

void OmpStructureChecker::Enter(const parser::SpecificationPart &) {
  partStack_.push_back(PartKind::SpecificationPart);
}

void OmpStructureChecker::Leave(const parser::SpecificationPart &) {
  partStack_.pop_back();
}

void OmpStructureChecker::Enter(const parser::ExecutionPart &) {
  partStack_.push_back(PartKind::ExecutionPart);
}

void OmpStructureChecker::Leave(const parser::ExecutionPart &) {
  partStack_.pop_back();
}

// 'OmpWorkshareBlockChecker' is used to check the validity of the assignment
// statements and the expressions enclosed in an OpenMP Workshare construct
class OmpWorkshareBlockChecker {
public:
  OmpWorkshareBlockChecker(SemanticsContext &context, parser::CharBlock source)
      : context_{context}, source_{source} {}

  template <typename T> bool Pre(const T &) { return true; }
  template <typename T> void Post(const T &) {}

  bool Pre(const parser::AssignmentStmt &assignment) {
    const auto &var{std::get<parser::Variable>(assignment.t)};
    const auto &expr{std::get<parser::Expr>(assignment.t)};
    const auto *lhs{GetExpr(context_, var)};
    const auto *rhs{GetExpr(context_, expr)};
    if (lhs && rhs) {
      Tristate isDefined{semantics::IsDefinedAssignment(
          lhs->GetType(), lhs->Rank(), rhs->GetType(), rhs->Rank())};
      if (isDefined == Tristate::Yes) {
        context_.Say(expr.source,
            "Defined assignment statement is not "
            "allowed in a WORKSHARE construct"_err_en_US);
      }
    }
    return true;
  }

  bool Pre(const parser::Expr &expr) {
    if (const auto *e{GetExpr(context_, expr)}) {
      for (const Symbol &symbol : evaluate::CollectSymbols(*e)) {
        const Symbol &root{GetAssociationRoot(symbol)};
        if (IsFunction(root)) {
          std::string attrs{""};
          if (!IsElementalProcedure(root)) {
            attrs = " non-ELEMENTAL";
          }
          if (root.attrs().test(Attr::IMPURE)) {
            if (attrs != "") {
              attrs = "," + attrs;
            }
            attrs = " IMPURE" + attrs;
          }
          if (attrs != "") {
            context_.Say(expr.source,
                "User defined%s function '%s' is not allowed in a "
                "WORKSHARE construct"_err_en_US,
                attrs, root.name());
          }
        }
      }
    }
    return false;
  }

private:
  SemanticsContext &context_;
  parser::CharBlock source_;
};

// 'OmpWorkdistributeBlockChecker' is used to check the validity of the
// assignment statements and the expressions enclosed in an OpenMP
// WORKDISTRIBUTE construct
class OmpWorkdistributeBlockChecker {
public:
  OmpWorkdistributeBlockChecker(
      SemanticsContext &context, parser::CharBlock source)
      : context_{context}, source_{source} {}

  template <typename T> bool Pre(const T &) { return true; }
  template <typename T> void Post(const T &) {}

  bool Pre(const parser::AssignmentStmt &assignment) {
    const auto &var{std::get<parser::Variable>(assignment.t)};
    const auto &expr{std::get<parser::Expr>(assignment.t)};
    const auto *lhs{GetExpr(context_, var)};
    const auto *rhs{GetExpr(context_, expr)};
    if (lhs && rhs) {
      Tristate isDefined{semantics::IsDefinedAssignment(
          lhs->GetType(), lhs->Rank(), rhs->GetType(), rhs->Rank())};
      if (isDefined == Tristate::Yes) {
        context_.Say(expr.source,
            "Defined assignment statement is not allowed in a WORKDISTRIBUTE construct"_err_en_US);
      }
    }
    return true;
  }

  bool Pre(const parser::Expr &expr) {
    if (const auto *e{GetExpr(context_, expr)}) {
      if (!e)
        return false;
      for (const Symbol &symbol : evaluate::CollectSymbols(*e)) {
        const Symbol &root{GetAssociationRoot(symbol)};
        if (IsFunction(root)) {
          std::vector<std::string> attrs;
          if (!IsElementalProcedure(root)) {
            attrs.push_back("non-ELEMENTAL");
          }
          if (root.attrs().test(Attr::IMPURE)) {
            attrs.push_back("IMPURE");
          }
          std::string attrsStr =
              attrs.empty() ? "" : " " + llvm::join(attrs, ", ");
          context_.Say(expr.source,
              "User defined%s function '%s' is not allowed in a WORKDISTRIBUTE construct"_err_en_US,
              attrsStr, root.name());
        }
      }
    }
    return false;
  }

private:
  SemanticsContext &context_;
  parser::CharBlock source_;
};

// `OmpUnitedTaskDesignatorChecker` is used to check if the designator
// can appear within the TASK construct
class OmpUnitedTaskDesignatorChecker {
public:
  OmpUnitedTaskDesignatorChecker(SemanticsContext &context)
      : context_{context} {}

  template <typename T> bool Pre(const T &) { return true; }
  template <typename T> void Post(const T &) {}

  bool Pre(const parser::Name &name) {
    if (name.symbol->test(Symbol::Flag::OmpThreadprivate)) {
      // OpenMP 5.2: 5.2 threadprivate directive restriction
      context_.Say(name.source,
          "A THREADPRIVATE variable `%s` cannot appear in an UNTIED TASK region"_err_en_US,
          name.source);
    }
    return true;
  }

private:
  SemanticsContext &context_;
};

bool OmpStructureChecker::IsAllowedClause(llvm::omp::Clause clauseId) {
  // Do not do clause checks while processing METADIRECTIVE.
  // See comment in CheckAllowedClause.
  if (GetDirectiveNest(ContextSelectorNest) > 0) {
    return true;
  }
  return llvm::omp::isAllowedClauseForDirective(
      GetContext().directive, clauseId, context_.langOptions().OpenMPVersion);
}

bool OmpStructureChecker::CheckAllowedClause(llvmOmpClause clause) {
  // Do not do clause checks while processing METADIRECTIVE.
  // Context selectors can contain clauses that are not given as a part
  // of a construct, but as trait properties. Testing whether they are
  // valid or not is deferred to the checks of the context selectors.
  // As it stands now, these clauses would appear as if they were present
  // on METADIRECTIVE, leading to incorrect diagnostics.
  if (GetDirectiveNest(ContextSelectorNest) > 0) {
    return true;
  }

  unsigned version{context_.langOptions().OpenMPVersion};
  DirectiveContext &dirCtx = GetContext();
  llvm::omp::Directive dir{dirCtx.directive};

  if (!llvm::omp::isAllowedClauseForDirective(dir, clause, version)) {
    unsigned allowedInVersion{[&] {
      for (unsigned v : llvm::omp::getOpenMPVersions()) {
        if (v <= version) {
          continue;
        }
        if (llvm::omp::isAllowedClauseForDirective(dir, clause, v)) {
          return v;
        }
      }
      return 0u;
    }()};

    // Only report it if there is a later version that allows it.
    // If it's not allowed at all, it will be reported by CheckAllowed.
    if (allowedInVersion != 0) {
      context_.Say(dirCtx.clauseSource,
          "%s clause is not allowed on directive %s in %s, %s"_err_en_US,
          parser::omp::GetUpperName(clause, version),
          parser::omp::GetUpperName(dir, version), ThisVersion(version),
          TryVersion(allowedInVersion));
    }
  }
  return CheckAllowed(clause);
}

void OmpStructureChecker::AnalyzeObject(const parser::OmpObject &object) {
  if (std::holds_alternative<parser::Name>(object.u) ||
      std::holds_alternative<parser::OmpObject::Invalid>(object.u)) {
    // Do not analyze common block names. The analyzer will flag an error
    // on those.
    return;
  }
  if (auto *symbol{GetObjectSymbol(object)}) {
    // Eliminate certain kinds of symbols before running the analyzer to
    // avoid confusing error messages. The analyzer assumes that the context
    // of the object use is an expression, and some diagnostics are tailored
    // to that.
    if (symbol->has<DerivedTypeDetails>() || symbol->has<MiscDetails>()) {
      // Type names, construct names, etc.
      return;
    }
    if (auto *typeSpec{symbol->GetType()}) {
      if (typeSpec->category() == DeclTypeSpec::Category::Character) {
        // Don't pass character objects to the analyzer, it can emit somewhat
        // cryptic errors (e.g. "'obj' is not an array"). Substrings are
        // checked elsewhere in OmpStructureChecker.
        return;
      }
    }
  }
  evaluate::ExpressionAnalyzer ea{context_};
  auto restore{ea.AllowWholeAssumedSizeArray(true)};
  common::visit( //
      common::visitors{
          [&](auto &&s) { ea.Analyze(s); },
          [&](const parser::OmpObject::Invalid &invalid) {},
      },
      object.u);
}

void OmpStructureChecker::AnalyzeObjects(const parser::OmpObjectList &objects) {
  for (const parser::OmpObject &object : objects.v) {
    AnalyzeObject(object);
  }
}

bool OmpStructureChecker::IsCloselyNestedRegion(const OmpDirectiveSet &set) {
  // Definition of close nesting:
  //
  // `A region nested inside another region with no parallel region nested
  // between them`
  //
  // Examples:
  //   non-parallel construct 1
  //    non-parallel construct 2
  //      parallel construct
  //        construct 3
  // In the above example, construct 3 is NOT closely nested inside construct 1
  // or 2
  //
  //   non-parallel construct 1
  //    non-parallel construct 2
  //        construct 3
  // In the above example, construct 3 is closely nested inside BOTH construct 1
  // and 2
  //
  // Algorithm:
  // Starting from the parent context, Check in a bottom-up fashion, each level
  // of the context stack. If we have a match for one of the (supplied)
  // violating directives, `close nesting` is satisfied. If no match is there in
  // the entire stack, `close nesting` is not satisfied. If at any level, a
  // `parallel` region is found, `close nesting` is not satisfied.

  if (CurrentDirectiveIsNested()) {
    int index = dirContext_.size() - 2;
    while (index != -1) {
      if (set.test(dirContext_[index].directive)) {
        return true;
      } else if (llvm::omp::allParallelSet.test(dirContext_[index].directive)) {
        return false;
      }
      index--;
    }
  }
  return false;
}

bool OmpStructureChecker::IsNestedInDirective(llvm::omp::Directive directive) {
  if (dirContext_.size() >= 1) {
    for (size_t i = dirContext_.size() - 1; i > 0; --i) {
      if (dirContext_[i - 1].directive == directive) {
        return true;
      }
    }
  }
  return false;
}

bool OmpStructureChecker::InTargetRegion() {
  if (IsNestedInDirective(llvm::omp::Directive::OMPD_target)) {
    // Return true even for device_type(host).
    return true;
  }
  for (const Scope *scope : llvm::reverse(scopeStack_)) {
    if (const auto *symbol{scope->symbol()}) {
      if (symbol->test(Symbol::Flag::OmpDeclareTarget)) {
        return true;
      }
    }
  }
  return false;
}

bool OmpStructureChecker::HasRequires(llvm::omp::Clause req) {
  const Scope &unit{GetProgramUnit(*scopeStack_.back())};
  return common::visit(
      [&](const auto &details) {
        if constexpr (std::is_convertible_v<decltype(details),
                          const WithOmpDeclarative &>) {
          if (auto *reqs{details.ompRequires()}) {
            return reqs->test(req);
          }
        }
        return false;
      },
      DEREF(unit.symbol()).details());
}

void OmpStructureChecker::CheckVariableListItem(
    const SymbolSourceMap &symbols) {
  for (auto &[symbol, source] : symbols) {
    if (!IsVariableListItem(*symbol)) {
      context_.SayWithDecl(
          *symbol, source, "'%s' must be a variable"_err_en_US, symbol->name());
    }
  }
}

void OmpStructureChecker::CheckDirectiveSpelling(
    parser::CharBlock spelling, llvm::omp::Directive id) {
  // Directive names that contain spaces can be spelled in the source without
  // any of the spaces. Because of that getOpenMPKind* is not guaranteed to
  // work with the source spelling as the argument.
  //
  // To verify the source spellings, we have to get the spelling for a given
  // version, remove spaces and compare it with the source spelling (also
  // with spaces removed).
  auto removeSpaces = [](llvm::StringRef s) {
    std::string n{s.str()};
    for (size_t idx{n.size()}; idx > 0; --idx) {
      if (isspace(n[idx - 1])) {
        n.erase(idx - 1, 1);
      }
    }
    return n;
  };

  std::string lowerNoWS{removeSpaces(
      parser::ToLowerCaseLetters({spelling.begin(), spelling.size()}))};
  llvm::StringRef ref(lowerNoWS);
  if (ref.starts_with("end")) {
    ref = ref.drop_front(3);
  }

  unsigned version{context_.langOptions().OpenMPVersion};

  // For every "future" version v, check if the check if the corresponding
  // spelling of id was introduced later than the current version. If so,
  // and if that spelling matches the source spelling, issue a warning.
  for (unsigned v : llvm::omp::getOpenMPVersions()) {
    if (v <= version) {
      continue;
    }
    llvm::StringRef name{llvm::omp::getOpenMPDirectiveName(id, v)};
    auto [kind, versions]{llvm::omp::getOpenMPDirectiveKindAndVersions(name)};
    assert(kind == id && "Directive kind mismatch");

    if (static_cast<int>(version) >= versions.Min) {
      continue;
    }
    if (ref == removeSpaces(name)) {
      context_.Say(spelling,
          "Directive spelling '%s' is introduced in a later OpenMP version, %s"_warn_en_US,
          parser::ToUpperCaseLetters(ref), TryVersion(versions.Min));
      break;
    }
  }
}

void OmpStructureChecker::CheckDirectiveDeprecation(
    const parser::OpenMPConstruct &x) {
  parser::OmpDirectiveName dirName{GetOmpDirectiveName(x)};
  unsigned version{context_.langOptions().OpenMPVersion};
  // We only want to emit the warning when the version being used has the
  // directive deprecated
  if (version >= 52) {
    // Check MASTER.
    llvm::SmallVector<llvm::omp::Directive> leafs{
        llvm::omp::getLeafConstructsOrSelf(dirName.v)};
    if (llvm::is_contained(leafs, llvm::omp::Directive::OMPD_master)) {
      for (auto &id : leafs) {
        if (id == llvm::omp::Directive::OMPD_master) {
          id = llvm::omp::Directive::OMPD_masked;
        }
      }

      auto preferredId{llvm::omp::getCompoundConstruct(leafs)};
      context_.Warn(common::UsageWarning::OpenMPUsage, dirName.source,
          "OpenMP directive %s has been deprecated, please use %s instead"_warn_en_US,
          GetUpperName(dirName.v, version), GetUpperName(preferredId, version));
    }
  }

  // Executable allocate is checked separately because these can be nested in
  // one another, but only the top-level directive should cause a warning.
}

void OmpStructureChecker::CheckMultipleOccurrence(
    semantics::UnorderedSymbolSet &listVars,
    const std::list<parser::Name> &nameList, const parser::CharBlock &item,
    const std::string &clauseName) {
  for (auto const &var : nameList) {
    if (llvm::is_contained(listVars, *(var.symbol))) {
      context_.Say(item,
          "List item '%s' present at multiple %s clauses"_err_en_US,
          var.ToString(), clauseName);
    }
    listVars.insert(*(var.symbol));
  }
}

void OmpStructureChecker::CheckMultListItems() {
  semantics::UnorderedSymbolSet listVars;

  // Aligned clause
  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_aligned)) {
    const auto &alignedClause{std::get<parser::OmpClause::Aligned>(clause->u)};
    const auto &alignedList{std::get<0>(alignedClause.v.t)};
    std::list<parser::Name> alignedNameList;
    for (const auto &ompObject : alignedList.v) {
      if (const auto *name{parser::Unwrap<parser::Name>(ompObject)}) {
        if (name->symbol) {
          if (FindCommonBlockContaining(*(name->symbol))) {
            context_.Say(clause->source,
                "'%s' is a common block name and can not appear in an "
                "ALIGNED clause"_err_en_US,
                name->ToString());
          } else if (!(IsBuiltinCPtr(*(name->symbol)) ||
                         IsAllocatableOrObjectPointer(
                             &name->symbol->GetUltimate()))) {
            context_.Say(clause->source,
                "'%s' in ALIGNED clause must be of type C_PTR, POINTER or "
                "ALLOCATABLE"_err_en_US,
                name->ToString());
          } else {
            alignedNameList.push_back(*name);
          }
        } else {
          // The symbol is null, return early
          return;
        }
      }
    }
    CheckMultipleOccurrence(
        listVars, alignedNameList, clause->source, "ALIGNED");
  }

  // Nontemporal clause
  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_nontemporal)) {
    const auto &nontempClause{
        std::get<parser::OmpClause::Nontemporal>(clause->u)};
    const auto &nontempNameList{nontempClause.v};
    CheckMultipleOccurrence(
        listVars, nontempNameList, clause->source, "NONTEMPORAL");
  }

  // Linear clause
  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_linear)) {
    std::list<parser::Name> nameList;
    SymbolSourceMap symbols;
    GetSymbolsInObjectList(*GetOmpObjectList(*clause), symbols);
    llvm::transform(symbols, std::back_inserter(nameList), [&](auto &&pair) {
      return parser::Name{pair.second, const_cast<Symbol *>(pair.first)};
    });
    CheckMultipleOccurrence(listVars, nameList, clause->source, "LINEAR");
  }
}
bool OmpStructureChecker::IsCombinedParallelWorksharing(
    llvm::omp::Directive directive) const {
  // Combined parallel-worksharing constructs create their own parallel region
  // They should not be subject to worksharing nesting restrictions
  switch (directive) {
  case llvm::omp::OMPD_parallel_do:
  case llvm::omp::OMPD_parallel_do_simd:
  case llvm::omp::OMPD_parallel_sections:
  case llvm::omp::OMPD_parallel_workshare:
    return true;
  default:
    return false;
  }
}

bool OmpStructureChecker::HasInvalidWorksharingNesting(
    const parser::OmpDirectiveName &name, const OmpDirectiveSet &set) {
  // set contains all the invalid closely nested directives
  // for the given directive (`source` here)
  if (IsCombinedParallelWorksharing(name.v)) {
    return false;
  }
  if (IsCloselyNestedRegion(set)) {
    context_.Say(name.source,
        "A worksharing region may not be closely nested inside a "
        "worksharing, explicit task, taskloop, critical, ordered, atomic, or "
        "master region"_err_en_US);
    return true;
  }
  return false;
}

void OmpStructureChecker::HasInvalidTeamsNesting(
    const llvm::omp::Directive &dir, const parser::CharBlock &source) {
  if (!llvm::omp::nestedTeamsAllowedSet.test(dir)) {
    context_.Say(source,
        "Only `DISTRIBUTE`, `PARALLEL`, or `LOOP` regions are allowed to be "
        "strictly nested inside `TEAMS` region."_err_en_US);
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Hint &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_hint);
  auto &dirCtx{GetContext()};

  if (std::optional<int64_t> maybeVal{GetIntValue(x.v.v)}) {
    int64_t val{*maybeVal};
    if (val >= 0) {
      // Check contradictory values.
      if ((val & 0xC) == 0xC || // omp_sync_hint_speculative and nonspeculative
          (val & 0x3) == 0x3) { // omp_sync_hint_contended and uncontended
        context_.Say(dirCtx.clauseSource,
            "The synchronization hint is not valid"_err_en_US);
      }
    } else {
      context_.Say(dirCtx.clauseSource,
          "Synchronization hint must be non-negative"_err_en_US);
    }
  } else {
    context_.Say(dirCtx.clauseSource,
        "Synchronization hint must be a constant integer value"_err_en_US);
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::DynGroupprivate &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_dyn_groupprivate);
  parser::CharBlock source{GetContext().clauseSource};

  OmpVerifyModifiers(x.v, llvm::omp::OMPC_dyn_groupprivate, source, context_);
}

void OmpStructureChecker::Enter(const parser::OmpDirectiveSpecification &x) {
  // OmpDirectiveSpecification exists on its own only in METADIRECTIVE.
  // In other cases it's a part of other constructs that handle directive
  // context stack by themselves.
  if (GetDirectiveNest(MetadirectiveNest)) {
    PushContextAndClauseSets(
        std::get<parser::OmpDirectiveName>(x.t).source, x.DirId());
  }
}

void OmpStructureChecker::Leave(const parser::OmpDirectiveSpecification &) {
  if (GetDirectiveNest(MetadirectiveNest)) {
    dirContext_.pop_back();
  }
}

template <typename Checker> struct DirectiveSpellingVisitor {
  using Directive = llvm::omp::Directive;

  DirectiveSpellingVisitor(Checker &&checker) : checker_(std::move(checker)) {}

  template <typename T> bool Pre(const T &) { return true; }
  template <typename T> void Post(const T &) {}

  template <typename... Ts>
  static const parser::OmpDirectiveName &GetDirName(
      const std::tuple<Ts...> &t) {
    return std::get<parser::OmpBeginDirective>(t).DirName();
  }

  bool Pre(const parser::OpenMPDispatchConstruct &x) {
    checker_(GetDirName(x.t).source, Directive::OMPD_dispatch);
    return false;
  }
  bool Pre(const parser::OpenMPAllocatorsConstruct &x) {
    checker_(GetDirName(x.t).source, Directive::OMPD_allocators);
    return false;
  }
  bool Pre(const parser::OpenMPGroupprivate &x) {
    checker_(x.v.DirName().source, Directive::OMPD_groupprivate);
    return false;
  }
  bool Pre(const parser::OmpBeginDirective &x) {
    checker_(x.DirName().source, x.DirId());
    return false;
  }
  bool Pre(const parser::OmpEndDirective &x) {
    checker_(x.DirName().source, x.DirId());
    return false;
  }

  bool Pre(const parser::OmpDirectiveSpecification &x) {
    auto &name = std::get<parser::OmpDirectiveName>(x.t);
    checker_(name.source, name.v);
    return false;
  }

private:
  Checker checker_;
};

template <typename T>
DirectiveSpellingVisitor(T &&) -> DirectiveSpellingVisitor<T>;

void OmpStructureChecker::Enter(const parser::OpenMPConstruct &x) {
  DirectiveSpellingVisitor visitor(
      [this](parser::CharBlock source, llvm::omp::Directive id) {
        return CheckDirectiveSpelling(source, id);
      });
  parser::Walk(x, visitor);
  if (GetOmpDirectiveName(x).v != llvm::omp::Directive::OMPD_section) {
    dirStack_.push_back(&GetOmpDirectiveSpecification(x));
  }

  CheckDirectiveDeprecation(x);

  if (GetOmpDirectiveName(x).v != llvm::omp::Directive::OMPD_section) {
    dirStack_.push_back(&GetOmpDirectiveSpecification(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 (GetDirectiveNest(SIMDNest) > 0) {
      CheckSIMDNest(x);
    }
    if (GetDirectiveNest(TargetNest) > 0) {
      CheckTargetNest(x);
    }
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPConstruct &x) {
  for (const auto &[sym, source] : deferredNonVariables_) {
    context_.SayWithDecl(
        *sym, source, "'%s' must be a variable"_err_en_US, sym->name());
  }
  deferredNonVariables_.clear();
  if (GetOmpDirectiveName(x).v != llvm::omp::Directive::OMPD_section) {
    dirStack_.pop_back();
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPDeclarativeConstruct &x) {
  DirectiveSpellingVisitor visitor(
      [this](parser::CharBlock source, llvm::omp::Directive id) {
        return CheckDirectiveSpelling(source, id);
      });
  parser::Walk(x, visitor);

  dirStack_.push_back(&GetOmpDirectiveSpecification(x));
  EnterDirectiveNest(DeclarativeNest);
}

void OmpStructureChecker::Leave(const parser::OpenMPDeclarativeConstruct &x) {
  ExitDirectiveNest(DeclarativeNest);
  dirStack_.pop_back();
}

void OmpStructureChecker::AddEndDirectiveClauses(
    const parser::OmpClauseList &clauses) {
  for (const parser::OmpClause &clause : clauses.v) {
    GetContext().endDirectiveClauses.push_back(clause.Id());
  }
}

void OmpStructureChecker::CheckIteratorRange(
    const parser::OmpIteratorSpecifier &x) {
  // Check:
  // 1. Whether begin/end are present.
  // 2. Whether the step value is non-zero.
  // 3. If the step has a known sign, whether the lower/upper bounds form
  // a proper interval.
  const auto &[begin, end, step]{std::get<parser::SubscriptTriplet>(x.t).t};
  if (!begin || !end) {
    context_.Say(x.source,
        "The begin and end expressions in iterator range-specification are "
        "mandatory"_err_en_US);
  }
  // [5.2:67:19] In a range-specification, if the step is not specified its
  // value is implicitly defined to be 1.
  if (auto stepv{step ? GetIntValue(*step) : std::optional<int64_t>{1}}) {
    if (*stepv == 0) {
      context_.Say(
          x.source, "The step value in the iterator range is 0"_warn_en_US);
    } else if (begin && end) {
      std::optional<int64_t> beginv{GetIntValue(*begin)};
      std::optional<int64_t> endv{GetIntValue(*end)};
      if (beginv && endv) {
        if (*stepv > 0 && *beginv > *endv) {
          context_.Say(x.source,
              "The begin value is greater than the end value in iterator "
              "range-specification with a positive step"_warn_en_US);
        } else if (*stepv < 0 && *beginv < *endv) {
          context_.Say(x.source,
              "The begin value is less than the end value in iterator "
              "range-specification with a negative step"_warn_en_US);
        }
      }
    }
  }
}

void OmpStructureChecker::CheckIteratorModifier(const parser::OmpIterator &x) {
  // Check if all iterator variables have integer type.
  for (auto &&iterSpec : x.v) {
    bool isInteger{true};
    auto &typeDecl{std::get<parser::TypeDeclarationStmt>(iterSpec.t)};
    auto &typeSpec{std::get<parser::DeclarationTypeSpec>(typeDecl.t)};
    if (!std::holds_alternative<parser::IntrinsicTypeSpec>(typeSpec.u)) {
      isInteger = false;
    } else {
      auto &intrinType{std::get<parser::IntrinsicTypeSpec>(typeSpec.u)};
      if (!std::holds_alternative<parser::IntegerTypeSpec>(intrinType.u)) {
        isInteger = false;
      }
    }
    if (!isInteger) {
      context_.Say(iterSpec.source,
          "The iterator variable must be of integer type"_err_en_US);
    }
    CheckIteratorRange(iterSpec);
  }
}

void OmpStructureChecker::CheckTargetNest(const parser::OpenMPConstruct &c) {
  // 2.12.5 Target Construct Restriction
  bool eligibleTarget{true};
  llvm::omp::Directive ineligibleTargetDir;
  parser::CharBlock source;
  common::visit(
      common::visitors{
          [&](const parser::OmpBlockConstruct &c) {
            const parser::OmpDirectiveName &beginName{c.BeginDir().DirName()};
            source = beginName.source;
            if (beginName.v == llvm::omp::Directive::OMPD_target_data) {
              eligibleTarget = false;
              ineligibleTargetDir = beginName.v;
            }
          },
          [&](const parser::OpenMPStandaloneConstruct &c) {
            common::visit(
                common::visitors{
                    [&](const parser::OpenMPSimpleStandaloneConstruct &c) {
                      source = c.v.DirName().source;
                      switch (llvm::omp::Directive dirId{c.v.DirId()}) {
                      case llvm::omp::Directive::OMPD_target_update:
                      case llvm::omp::Directive::OMPD_target_enter_data:
                      case llvm::omp::Directive::OMPD_target_exit_data:
                        eligibleTarget = false;
                        ineligibleTargetDir = dirId;
                        break;
                      default:
                        break;
                      }
                    },
                    [&](const auto &c) {},
                },
                c.u);
          },
          [&](const parser::OpenMPLoopConstruct &c) {
            const parser::OmpDirectiveName &beginName{c.BeginDir().DirName()};
            source = beginName.source;
            if (llvm::omp::allTargetSet.test(beginName.v)) {
              eligibleTarget = false;
              ineligibleTargetDir = beginName.v;
            }
          },
          [&](const auto &c) {},
      },
      c.u);
  if (!eligibleTarget) {
    unsigned version{context_.langOptions().OpenMPVersion};
    context_.Warn(common::UsageWarning::OpenMPUsage, source,
        "If %s directive is nested inside TARGET region, the behaviour is unspecified"_port_en_US,
        parser::omp::GetUpperName(ineligibleTargetDir, version));
  }
}

void OmpStructureChecker::Enter(const parser::OmpBlockConstruct &x) {
  const parser::OmpDirectiveSpecification &beginSpec{x.BeginDir()};
  const std::optional<parser::OmpEndDirective> &endSpec{x.EndDir()};
  const parser::Block &block{std::get<parser::Block>(x.t)};
  unsigned version{context_.langOptions().OpenMPVersion};

  PushContextAndClauseSets(beginSpec.DirName().source, beginSpec.DirId());

  // Missing mandatory end block: this is checked in semantics because that
  // makes it easier to control the error messages.
  // The end block is mandatory when the construct is not applied to a strictly
  // structured block (aka it is applied to a loosely structured block).
  if (!endSpec && !IsStrictlyStructuredBlock(block)) {
    llvm::omp::Directive dirId{beginSpec.DirId()};
    auto &msg{context_.Say(beginSpec.source,
        "Expected OpenMP END %s directive"_err_en_US,
        parser::omp::GetUpperName(dirId, version))};
    // ORDERED has two variants, so be explicit about which variant we think
    // this is.
    if (dirId == llvm::omp::Directive::OMPD_ordered) {
      msg.Attach(
          beginSpec.source, "The ORDERED directive is block-associated"_en_US);
    }
  }

  if (llvm::omp::allTargetSet.test(GetContext().directive)) {
    EnterDirectiveNest(TargetNest);
  }

  if (CurrentDirectiveIsNested()) {
    if (llvm::omp::bottomTeamsSet.test(GetContextParent().directive)) {
      HasInvalidTeamsNesting(beginSpec.DirId(), beginSpec.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(x.BeginDir().DirName().source,
          "%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);
    }
    if (GetContext().directive == llvm::omp::Directive::OMPD_workdistribute &&
        GetContextParent().directive != llvm::omp::Directive::OMPD_teams) {
      context_.Say(x.BeginDir().DirName().source,
          "%s region can only be strictly nested within TEAMS region"_err_en_US,
          ContextDirectiveAsFortran());
    }
  }

  CheckNoBranching(block, beginSpec.DirId(), beginSpec.source);

  // Target block constructs are target device constructs. Keep track of
  // whether any such construct has been visited to later check that REQUIRES
  // directives for target-related options don't appear after them.
  if (llvm::omp::allTargetSet.test(beginSpec.DirId())) {
    deviceConstructFound_ = true;
  }

  if (GetContext().directive == llvm::omp::Directive::OMPD_single) {
    std::set<Symbol *> singleCopyprivateSyms;
    std::set<Symbol *> endSingleCopyprivateSyms;
    bool foundNowait{false};
    parser::CharBlock NowaitSource;

    auto catchCopyPrivateNowaitClauses = [&](const auto &dirSpec, bool isEnd) {
      for (auto &clause : dirSpec.Clauses().v) {
        if (clause.Id() == llvm::omp::Clause::OMPC_copyprivate) {
          for (const auto &ompObject : GetOmpObjectList(clause)->v) {
            const auto *name{parser::Unwrap<parser::Name>(ompObject)};
            if (Symbol * symbol{name->symbol}) {
              if (singleCopyprivateSyms.count(symbol)) {
                if (isEnd) {
                  context_.Warn(common::UsageWarning::OpenMPUsage, name->source,
                      "The COPYPRIVATE clause with '%s' is already used on the SINGLE directive"_warn_en_US,
                      name->ToString());
                } else {
                  context_.Say(name->source,
                      "'%s' appears in more than one COPYPRIVATE clause on the SINGLE directive"_err_en_US,
                      name->ToString());
                }
              } else if (endSingleCopyprivateSyms.count(symbol)) {
                context_.Say(name->source,
                    "'%s' appears in more than one COPYPRIVATE clause on the END SINGLE directive"_err_en_US,
                    name->ToString());
              } else {
                if (isEnd) {
                  endSingleCopyprivateSyms.insert(symbol);
                } else {
                  singleCopyprivateSyms.insert(symbol);
                }
              }
            }
          }
        } else if (clause.Id() == llvm::omp::Clause::OMPC_nowait) {
          if (foundNowait) {
            context_.Say(clause.source,
                "At most one NOWAIT clause can appear on the SINGLE directive"_err_en_US);
          } else {
            foundNowait = !isEnd;
          }
          if (!NowaitSource.ToString().size()) {
            NowaitSource = clause.source;
          }
        }
      }
    };
    catchCopyPrivateNowaitClauses(beginSpec, false);
    if (endSpec) {
      catchCopyPrivateNowaitClauses(*endSpec, true);
    }
    unsigned version{context_.langOptions().OpenMPVersion};
    if (version <= 52 && NowaitSource.ToString().size() &&
        (singleCopyprivateSyms.size() || endSingleCopyprivateSyms.size())) {
      context_.Say(NowaitSource,
          "NOWAIT clause must not be used with COPYPRIVATE clause on the SINGLE directive"_err_en_US);
    }
  }

  switch (beginSpec.DirId()) {
  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, beginSpec.source);
    HasInvalidWorksharingNesting(
        std::get<parser::OmpDirectiveName>(beginSpec.t),
        llvm::omp::nestedWorkshareErrSet);
    break;
  case llvm::omp::OMPD_workdistribute:
    if (!CurrentDirectiveIsNested()) {
      context_.Say(beginSpec.source,
          "A WORKDISTRIBUTE region must be nested inside TEAMS region only."_err_en_US);
    }
    CheckWorkdistributeBlockStmts(block, beginSpec.source);
    break;
  case llvm::omp::OMPD_teams_workdistribute:
  case llvm::omp::OMPD_target_teams_workdistribute:
    CheckWorkdistributeBlockStmts(block, beginSpec.source);
    break;
  case llvm::omp::Directive::OMPD_scope:
  case llvm::omp::Directive::OMPD_single:
    // TODO: This check needs to be extended while implementing nesting of
    // regions checks.
    HasInvalidWorksharingNesting(
        std::get<parser::OmpDirectiveName>(beginSpec.t),
        llvm::omp::nestedWorkshareErrSet);
    break;
  case llvm::omp::Directive::OMPD_task:
    for (const auto &clause : beginSpec.Clauses().v) {
      if (std::get_if<parser::OmpClause::Untied>(&clause.u)) {
        OmpUnitedTaskDesignatorChecker check{context_};
        parser::Walk(block, check);
      }
    }
    break;
  default:
    break;
  }
}

void OmpStructureChecker::CheckMasterNesting(
    const parser::OmpBlockConstruct &x) {
  // A MASTER region may not be `closely nested` inside a worksharing, loop,
  // task, taskloop, or atomic region.
  // TODO:  Expand the check to include `LOOP` construct as well when it is
  // supported.
  if (IsCloselyNestedRegion(llvm::omp::nestedMasterErrSet)) {
    context_.Say(x.BeginDir().source,
        "`MASTER` region may not be closely nested inside of `WORKSHARING`, "
        "`LOOP`, `TASK`, `TASKLOOP`,"
        " or `ATOMIC` region."_err_en_US);
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPAssumeConstruct &x) {
  PushContextAndClauseSets(x.source, llvm::omp::Directive::OMPD_assume);
}

void OmpStructureChecker::Leave(const parser::OpenMPAssumeConstruct &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OpenMPDeclarativeAssumes &x) {
  PushContextAndClauseSets(x.source, llvm::omp::Directive::OMPD_assumes);
}

void OmpStructureChecker::Leave(const parser::OpenMPDeclarativeAssumes &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Leave(const parser::OmpBlockConstruct &x) {
  if (GetContext().directive == llvm::omp::Directive::OMPD_taskgraph) {
    CheckTaskgraph(x);
  }
  if (GetDirectiveNest(TargetBlockOnlyTeams)) {
    ExitDirectiveNest(TargetBlockOnlyTeams);
  }
  if (llvm::omp::allTargetSet.test(GetContext().directive)) {
    ExitDirectiveNest(TargetNest);
  }
  dirContext_.pop_back();
}

void OmpStructureChecker::ChecksOnOrderedAsBlock() {
  if (FindClause(llvm::omp::Clause::OMPC_depend)) {
    context_.Say(GetContext().clauseSource,
        "DEPEND clauses are not allowed when ORDERED construct is a block construct with an ORDERED region"_err_en_US);
    return;
  }

  bool isNestedInDo{false};
  bool isNestedInDoSIMD{false};
  bool isNestedInSIMD{false};
  bool noOrderedClause{false};
  bool isOrderedClauseWithPara{false};
  bool isCloselyNestedRegion{true};
  if (CurrentDirectiveIsNested()) {
    for (int i = (int)dirContext_.size() - 2; i >= 0; i--) {
      if (llvm::omp::nestedOrderedErrSet.test(dirContext_[i].directive)) {
        context_.Say(GetContext().directiveSource,
            "`ORDERED` region may not be closely nested inside of `CRITICAL`, "
            "`ORDERED`, explicit `TASK` or `TASKLOOP` region."_err_en_US);
        break;
      } else if (llvm::omp::allDoSet.test(dirContext_[i].directive)) {
        isNestedInDo = true;
        isNestedInDoSIMD =
            llvm::omp::allDoSimdSet.test(dirContext_[i].directive);
        if (const auto *clause{
                FindClause(dirContext_[i], llvm::omp::Clause::OMPC_ordered)}) {
          const auto &orderedClause{
              std::get<parser::OmpClause::Ordered>(clause->u)};
          const auto orderedValue{GetIntValue(orderedClause.v)};
          isOrderedClauseWithPara = orderedValue > 0;
        } else {
          noOrderedClause = true;
        }
        break;
      } else if (llvm::omp::allSimdSet.test(dirContext_[i].directive)) {
        isNestedInSIMD = true;
        break;
      } else if (llvm::omp::nestedOrderedParallelErrSet.test(
                     dirContext_[i].directive)) {
        isCloselyNestedRegion = false;
        break;
      }
    }
  }

  if (!isCloselyNestedRegion) {
    context_.Say(GetContext().directiveSource,
        "An ORDERED directive without the DEPEND clause must be closely nested "
        "in a SIMD, worksharing-loop, or worksharing-loop SIMD "
        "region"_err_en_US);
  } else {
    if (CurrentDirectiveIsNested() &&
        FindClause(llvm::omp::Clause::OMPC_simd) &&
        (!isNestedInDoSIMD && !isNestedInSIMD)) {
      context_.Say(GetContext().directiveSource,
          "An ORDERED directive with SIMD clause must be closely nested in a "
          "SIMD or worksharing-loop SIMD region"_err_en_US);
    }
    if (isNestedInDo && (noOrderedClause || isOrderedClauseWithPara)) {
      context_.Say(GetContext().directiveSource,
          "An ORDERED directive without the DEPEND clause must be closely "
          "nested in a worksharing-loop (or worksharing-loop SIMD) region with "
          "ORDERED clause without the parameter"_err_en_US);
    }
  }
}

void OmpStructureChecker::Leave(const parser::OmpBeginDirective &) {
  switch (GetContext().directive) {
  case llvm::omp::Directive::OMPD_ordered:
    // [5.1] 2.19.9 Ordered Construct Restriction
    ChecksOnOrderedAsBlock();
    break;
  default:
    break;
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPSectionsConstruct &x) {
  const parser::OmpDirectiveSpecification &beginSpec{x.BeginDir()};
  const parser::OmpDirectiveName &beginName{beginSpec.DirName()};
  const auto &endSpec{x.EndDir()};
  PushContextAndClauseSets(beginName.source, beginName.v);

  if (!endSpec) {
    context_.Say(
        beginName.source, "Expected OpenMP END SECTIONS directive"_err_en_US);
    // Following code assumes the option is present.
    return;
  }

  CheckMatching<parser::OmpDirectiveName>(beginName, endSpec->DirName());

  AddEndDirectiveClauses(endSpec->Clauses());

  const auto &sectionBlocks{std::get<std::list<parser::OpenMPConstruct>>(x.t)};
  for (const parser::OpenMPConstruct &construct : sectionBlocks) {
    auto &section{std::get<parser::OpenMPSectionConstruct>(construct.u)};
    CheckNoBranching(
        std::get<parser::Block>(section.t), beginName.v, beginName.source);
  }
  HasInvalidWorksharingNesting(std::get<parser::OmpDirectiveName>(beginSpec.t),
      llvm::omp::nestedWorkshareErrSet);
}

void OmpStructureChecker::Leave(const parser::OpenMPSectionsConstruct &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OmpEndSectionsDirective &x) {
  const parser::OmpDirectiveName &dirName{x.DirName()};
  ResetPartialContext(dirName.source);
  switch (dirName.v) {
    // 2.7.2 end-sections -> END SECTIONS [nowait-clause]
  case llvm::omp::Directive::OMPD_sections:
    PushContextAndClauseSets(
        dirName.source, llvm::omp::Directive::OMPD_end_sections);
    break;
  default:
    // no clauses are allowed
    break;
  }
}

// TODO: Verify the popping of dirContext requirement after nowait
// implementation, as there is an implicit barrier at the end of the worksharing
// constructs unless a nowait clause is specified. Only OMPD_end_sections is
// popped becuase it is pushed while entering the EndSectionsDirective.
void OmpStructureChecker::Leave(const parser::OmpEndSectionsDirective &x) {
  if (GetContext().directive == llvm::omp::Directive::OMPD_end_sections) {
    dirContext_.pop_back();
  }
}

void OmpStructureChecker::CheckThreadprivateOrDeclareTargetVar(
    const parser::Designator &designator) {
  auto *name{parser::Unwrap<parser::Name>(designator)};
  // If the symbol is null, return early, CheckSymbolNames
  // should have already reported the missing symbol as a
  // diagnostic error
  if (!name || !name->symbol) {
    return;
  }

  llvm::omp::Directive directive{GetContext().directive};

  if (name->symbol->GetUltimate().IsSubprogram()) {
    if (directive == llvm::omp::Directive::OMPD_threadprivate)
      context_.Say(name->source,
          "The procedure name cannot be in a %s directive"_err_en_US,
          ContextDirectiveAsFortran());
    // TODO: Check for procedure name in declare target directive.
  } else if (name->symbol->attrs().test(Attr::PARAMETER)) {
    if (directive == llvm::omp::Directive::OMPD_threadprivate)
      context_.Say(name->source,
          "The entity with PARAMETER attribute cannot be in a %s directive"_err_en_US,
          ContextDirectiveAsFortran());
    else if (directive == llvm::omp::Directive::OMPD_declare_target)
      context_.Warn(common::UsageWarning::OpenMPUsage, name->source,
          "The entity with PARAMETER attribute is used in a %s directive"_warn_en_US,
          ContextDirectiveAsFortran());
  } else if (FindCommonBlockContaining(*name->symbol)) {
    context_.Say(name->source,
        "A variable in a %s directive cannot be an element of a common block"_err_en_US,
        ContextDirectiveAsFortran());
  } else if (FindEquivalenceSet(*name->symbol)) {
    context_.Say(name->source,
        "A variable in a %s directive cannot appear in an EQUIVALENCE statement"_err_en_US,
        ContextDirectiveAsFortran());
  } else if (name->symbol->test(Symbol::Flag::OmpThreadprivate) &&
      directive == llvm::omp::Directive::OMPD_declare_target) {
    context_.Say(name->source,
        "A THREADPRIVATE variable cannot appear in a %s directive"_err_en_US,
        ContextDirectiveAsFortran());
  } else {
    const semantics::Scope &useScope{
        context_.FindScope(GetContext().directiveSource)};
    const semantics::Scope &curScope = name->symbol->GetUltimate().owner();
    if (!curScope.IsTopLevel()) {
      const semantics::Scope &declScope =
          GetProgramUnitOrBlockConstructContaining(curScope);
      const semantics::Symbol *sym{
          declScope.parent().FindSymbol(name->symbol->name())};
      if (sym &&
          (sym->has<MainProgramDetails>() || sym->has<ModuleDetails>())) {
        context_.Say(name->source,
            "The module name cannot be in a %s directive"_err_en_US,
            ContextDirectiveAsFortran());
      } else if (!IsSaved(*name->symbol) &&
          declScope.kind() != Scope::Kind::MainProgram &&
          declScope.kind() != Scope::Kind::Module &&
          !name->symbol->attrs().test(Attr::EXTERNAL)) {
        context_.Say(name->source,
            "A variable that appears in a %s directive must be declared in the scope of a module or have the SAVE attribute, either explicitly or implicitly"_err_en_US,
            ContextDirectiveAsFortran());
      } else if (useScope != declScope) {
        context_.Say(name->source,
            "The %s directive and the common block or variable in it must appear in the same declaration section of a scoping unit"_err_en_US,
            ContextDirectiveAsFortran());
      }
    }
  }
}

void OmpStructureChecker::CheckThreadprivateOrDeclareTargetVar(
    const parser::Name &name) {
  if (!name.symbol) {
    return;
  }

  if (auto *cb{name.symbol->detailsIf<CommonBlockDetails>()}) {
    llvm::omp::Directive directive{GetContext().directive};
    for (const auto &obj : cb->objects()) {
      if (FindEquivalenceSet(*obj)) {
        if (directive == llvm::omp::Directive::OMPD_threadprivate) {
          context_.Warn(common::LanguageFeature::OpenMPThreadprivateEquivalence,
              name.source,
              "A variable in a %s directive used in an EQUIVALENCE statement is an OpenMP extension (variable '%s' from common block '/%s/')"_warn_en_US,
              ContextDirectiveAsFortran(), obj->name(), name.symbol->name());
        } else {
          context_.Say(name.source,
              "A variable in a %s directive cannot appear in an EQUIVALENCE statement (variable '%s' from common block '/%s/')"_err_en_US,
              ContextDirectiveAsFortran(), obj->name(), name.symbol->name());
        }
      }
    }
  }
}

void OmpStructureChecker::CheckThreadprivateOrDeclareTargetVar(
    const parser::OmpObject &object) {
  common::visit( //
      common::visitors{
          [&](auto &&s) { CheckThreadprivateOrDeclareTargetVar(s); },
          [&](const parser::OmpObject::Invalid &invalid) {},
      },
      object.u);
}

void OmpStructureChecker::CheckThreadprivateOrDeclareTargetVar(
    const parser::OmpObjectList &objList) {
  for (const auto &ompObject : objList.v) {
    CheckThreadprivateOrDeclareTargetVar(ompObject);
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPGroupprivate &x) {
  PushContextAndClauseSets(
      x.v.DirName().source, llvm::omp::Directive::OMPD_groupprivate);

  for (const parser::OmpArgument &arg : x.v.Arguments().v) {
    auto *locator{std::get_if<parser::OmpLocator>(&arg.u)};
    const Symbol *sym{GetArgumentSymbol(arg)};

    if (!locator || !sym ||
        (!IsVariableListItem(*sym) && !IsCommonBlock(*sym))) {
      context_.Say(arg.source,
          "GROUPPRIVATE argument should be a variable or a named common block"_err_en_US);
      continue;
    }

    if (sym->has<AssocEntityDetails>()) {
      context_.SayWithDecl(*sym, arg.source,
          "GROUPPRIVATE argument cannot be an ASSOCIATE name"_err_en_US);
      continue;
    }
    if (auto *obj{sym->detailsIf<ObjectEntityDetails>()}) {
      if (obj->IsCoarray()) {
        context_.Say(
            arg.source, "GROUPPRIVATE argument cannot be a coarray"_err_en_US);
        continue;
      }
      if (obj->init()) {
        context_.SayWithDecl(*sym, arg.source,
            "GROUPPRIVATE argument cannot be declared with an initializer"_err_en_US);
        continue;
      }
    }
    if (sym->test(Symbol::Flag::InCommonBlock)) {
      context_.Say(arg.source,
          "GROUPPRIVATE argument cannot be a member of a common block"_err_en_US);
      continue;
    }
    if (!IsCommonBlock(*sym)) {
      const Scope &thisScope{context_.FindScope(x.v.source)};
      if (thisScope != sym->owner()) {
        context_.SayWithDecl(*sym, arg.source,
            "GROUPPRIVATE argument variable must be declared in the same scope as the construct on which it appears"_err_en_US);
        continue;
      } else if (!thisScope.IsModule() && !sym->attrs().test(Attr::SAVE)) {
        context_.SayWithDecl(*sym, arg.source,
            "GROUPPRIVATE argument variable must be declared in the module scope or have SAVE attribute"_err_en_US);
        continue;
      }
    }
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPGroupprivate &x) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OpenMPThreadprivate &x) {
  const parser::OmpDirectiveName &dirName{x.v.DirName()};
  PushContextAndClauseSets(dirName.source, dirName.v);
}

void OmpStructureChecker::Leave(const parser::OpenMPThreadprivate &x) {
  const parser::OmpDirectiveSpecification &dirSpec{x.v};
  for (const parser::OmpArgument &arg : x.v.Arguments().v) {
    if (auto *object{GetArgumentObject(arg)}) {
      CheckSymbolName(dirSpec.source, *object);
      CheckVarIsNotPartOfAnotherVar(dirSpec.source, *object);
      CheckThreadprivateOrDeclareTargetVar(*object);
    }
  }
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OpenMPDeclareSimdConstruct &x) {
  const parser::OmpDirectiveName &dirName{x.v.DirName()};
  PushContextAndClauseSets(dirName.source, dirName.v);

  const Scope &containingScope = context_.FindScope(dirName.source);
  const Scope &progUnitScope = GetProgramUnitContaining(containingScope);

  for (const parser::OmpClause &clause : x.v.Clauses().v) {
    const auto *u = std::get_if<parser::OmpClause::Uniform>(&clause.u);
    if (!u) {
      continue;
    }
    assert(clause.Id() == llvm::omp::Clause::OMPC_uniform);

    for (const parser::Name &name : u->v) {
      const Symbol *sym{name.symbol};
      if (!sym || !IsDummy(*sym) ||
          &GetProgramUnitContaining(sym->owner()) != &progUnitScope) {
        context_.Say(name.source,
            "Variable '%s' in UNIFORM clause must be a dummy argument of the "
            "enclosing procedure"_err_en_US,
            name.ToString());
      }
    }
  }

  const parser::OmpArgumentList &args{x.v.Arguments()};
  if (args.v.empty()) {
    return;
  } else if (args.v.size() > 1) {
    context_.Say(args.source,
        "DECLARE_SIMD directive should have at most one argument"_err_en_US);
    return;
  }

  auto isValidSymbol{[](const Symbol *sym) {
    if (IsProcedure(*sym) || IsFunction(*sym)) {
      return true;
    }
    if (const Symbol *owner{GetScopingUnit(sym->owner()).symbol()}) {
      return IsProcedure(*owner) || IsFunction(*owner);
    }
    return false;
  }};

  const parser::OmpArgument &arg{args.v.front()};
  if (auto *sym{GetArgumentSymbol(arg)}) {
    if (!isValidSymbol(sym)) {
      auto &msg{context_.Say(arg.source,
          "The name '%s' should refer to a procedure"_err_en_US, sym->name())};
      if (sym->test(Symbol::Flag::Implicit)) {
        msg.Attach(arg.source,
            "The name '%s' has been implicitly declared"_en_US, sym->name());
      }
    }
  } else {
    context_.Say(arg.source,
        "The argument to the DECLARE_SIMD directive should be a procedure name"_err_en_US);
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPDeclareSimdConstruct &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OmpDeclareVariantDirective &x) {
  const parser::OmpDirectiveName &dirName{x.v.DirName()};
  PushContextAndClauseSets(dirName.source, dirName.v);

  const parser::OmpArgumentList &args{x.v.Arguments()};
  if (args.v.size() != 1) {
    context_.Say(args.source,
        "DECLARE_VARIANT directive should have a single argument"_err_en_US);
    return;
  }

  auto InvalidArgument{[&](parser::CharBlock source) {
    context_.Say(source,
        "The argument to the DECLARE_VARIANT directive should be [base-name:]variant-name"_err_en_US);
  }};

  auto CheckSymbol{[&](const Symbol *sym, parser::CharBlock source) {
    if (sym) {
      if (!IsProcedure(*sym) && !IsFunction(*sym)) {
        auto &msg{context_.Say(source,
            "The name '%s' should refer to a procedure"_err_en_US,
            sym->name())};
        if (sym->test(Symbol::Flag::Implicit)) {
          msg.Attach(source, "The name '%s' has been implicitly declared"_en_US,
              sym->name());
        }
      }
    } else {
      InvalidArgument(source);
    }
  }};

  const parser::OmpArgument &arg{args.v.front()};
  common::visit( //
      common::visitors{
          [&](const parser::OmpBaseVariantNames &y) {
            CheckSymbol(GetObjectSymbol(std::get<0>(y.t)), arg.source);
            CheckSymbol(GetObjectSymbol(std::get<1>(y.t)), arg.source);
          },
          [&](const parser::OmpLocator &y) {
            CheckSymbol(GetArgumentSymbol(arg), arg.source);
          },
          [&](auto &&y) { InvalidArgument(arg.source); },
      },
      arg.u);
}

void OmpStructureChecker::Leave(const parser::OmpDeclareVariantDirective &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::CheckInitOnDepobj(
    const parser::OpenMPDepobjConstruct &depobj,
    const parser::OmpClause &initClause) {
  const parser::OmpDirectiveSpecification &dirSpec{depobj.v};
  const parser::OmpArgumentList &args{dirSpec.Arguments()};
  const parser::OmpInitClause &init{
      std::get<parser::OmpClause::Init>(initClause.u).v};

  if (!args.v.empty()) {
    context_.Say(args.source,
        "The INIT clause is not allowed when the DEPOBJ directive has an argument"_err_en_US);
  }

  if (!OmpVerifyModifiers(
          init, llvm::omp::Clause::OMPC_init, initClause.source, context_)) {
    return;
  }

  auto &modifiers{OmpGetModifiers(init)};
  if (auto *depInfo{
          OmpGetUniqueModifier<parser::OmpDepinfoModifier>(modifiers)}) {
    auto depKind{std::get<common::OmpDependenceKind>(depInfo->t)};
    if (depKind == common::OmpDependenceKind::Depobj) {
      auto &desc{OmpGetDescriptor<parser::OmpDepinfoModifier>()};
      context_.Say(OmpGetModifierSource(modifiers, depInfo),
          "'%s' is not an allowed value of the '%s' modifier"_err_en_US,
          parser::ToUpperCaseLetters(EnumToString(depKind)), desc.name.str());
    }
  } else {
    auto &desc{OmpGetDescriptor<parser::OmpDepinfoModifier>()};
    context_.Say(initClause.source,
        "The '%s' modifier is required on a DEPOBJ construct"_err_en_US,
        desc.name.str());
  }
  if (auto *prefType{OmpGetUniqueModifier<parser::OmpPreferType>(modifiers)}) {
    auto &desc{OmpGetDescriptor<parser::OmpPreferType>()};
    context_.Say(OmpGetModifierSource(modifiers, prefType),
        "The '%s' modifier is not allowed on a DEPOBJ construct"_err_en_US,
        desc.name.str());
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPDepobjConstruct &x) {
  const auto &dirName{std::get<parser::OmpDirectiveName>(x.v.t)};
  PushContextAndClauseSets(dirName.source, llvm::omp::Directive::OMPD_depobj);
  unsigned version{context_.langOptions().OpenMPVersion};

  const parser::OmpArgumentList &arguments{x.v.Arguments()};
  const parser::OmpClauseList &clauses{x.v.Clauses()};

  // Ref: [6.0:505-506]

  if (version < 60) {
    if (arguments.v.size() != 1) {
      parser::CharBlock source(
          arguments.v.empty() ? dirName.source : arguments.source);
      context_.Say(
          source, "The DEPOBJ directive requires a single argument"_err_en_US);
    }
  }
  if (clauses.v.size() != 1) {
    context_.Say(
        x.source, "The DEPOBJ construct requires a single clause"_err_en_US);
    return;
  }

  if (version >= 60 && arguments.v.empty()) {
    context_.Say(x.source,
        "DEPOBJ syntax with no argument is not handled yet"_err_en_US);
  }

  auto getObjSymbol{[&](const parser::OmpObject &obj) {
    return common::visit( //
        common::visitors{
            [&](auto &&s) { return GetLastName(s).symbol; },
            [&](const parser::OmpObject::Invalid &invalid) {
              return static_cast<Symbol *>(nullptr);
            },
        },
        obj.u);
  }};
  auto getArgSymbol{[&](const parser::OmpArgument &arg) {
    if (auto *locator{std::get_if<parser::OmpLocator>(&arg.u)}) {
      if (auto *object{std::get_if<parser::OmpObject>(&locator->u)}) {
        return getObjSymbol(*object);
      }
    }
    return static_cast<Symbol *>(nullptr);
  }};

  for (auto &clause : clauses.v) {
    llvm::omp::Clause clauseId{clause.Id()};

    if (clauseId == llvm::omp::Clause::OMPC_init) {
      CheckInitOnDepobj(x, clause);
    } else if (clauseId == llvm::omp::Clause::OMPC_destroy) {
      // [5.2:73:27-28]
      // If the destroy clause appears on a depobj construct, destroy-var must
      // refer to the same depend object as the depobj argument of the
      // construct.
      auto &wrapper{std::get<parser::OmpClause::Destroy>(clause.u)};
      if (const std::optional<parser::OmpDestroyClause> &destroy{wrapper.v}) {
        const Symbol *constrSym{getArgSymbol(arguments.v.front())};
        const Symbol *clauseSym{getObjSymbol(destroy->v)};
        if (constrSym && clauseSym && constrSym != clauseSym) {
          context_.Say(x.source,
              "The DESTROY clause must refer to the same object as the "
              "DEPOBJ construct"_err_en_US);
        }
      }
    }
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPDepobjConstruct &x) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OpenMPRequiresConstruct &x) {
  const auto &dirName{x.v.DirName()};
  PushContextAndClauseSets(dirName.source, dirName.v);
  unsigned version{context_.langOptions().OpenMPVersion};

  for (const parser::OmpClause &clause : x.v.Clauses().v) {
    llvm::omp::Clause id{clause.Id()};
    if (id == llvm::omp::Clause::OMPC_atomic_default_mem_order) {
      if (!visitedAtomicSource_.empty()) {
        parser::MessageFormattedText txt(
            "REQUIRES directive with '%s' clause found lexically after atomic operation without a memory order clause"_err_en_US,
            parser::omp::GetUpperName(id, version));
        parser::Message message(clause.source, txt);
        message.Attach(visitedAtomicSource_, "Previous atomic construct"_en_US);
        context_.Say(std::move(message));
      }
    } else {
      bool hasArgument{common::visit(
          [&](auto &&s) {
            using TypeS = llvm::remove_cvref_t<decltype(s)>;
            if constexpr ( //
                std::is_same_v<TypeS, parser::OmpClause::DeviceSafesync> ||
                std::is_same_v<TypeS, parser::OmpClause::DynamicAllocators> ||
                std::is_same_v<TypeS, parser::OmpClause::ReverseOffload> ||
                std::is_same_v<TypeS, parser::OmpClause::SelfMaps> ||
                std::is_same_v<TypeS, parser::OmpClause::UnifiedAddress> ||
                std::is_same_v<TypeS, parser::OmpClause::UnifiedSharedMemory>) {
              return s.v.has_value();
            } else {
              return false;
            }
          },
          clause.u)};
      if (version < 60 && hasArgument) {
        context_.Say(clause.source,
            "An argument to %s is an %s feature, %s"_warn_en_US,
            parser::omp::GetUpperName(clause.Id(), version), ThisVersion(60),
            TryVersion(60));
      }
    }
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPRequiresConstruct &) {
  dirContext_.pop_back();
}

static std::pair<const parser::AllocateStmt *, parser::CharBlock>
getAllocateStmtAndSource(const parser::ExecutionPartConstruct *epc) {
  if (SourcedActionStmt as{GetActionStmt(epc)}) {
    using IndirectionAllocateStmt = common::Indirection<parser::AllocateStmt>;
    if (auto *indirect{std::get_if<IndirectionAllocateStmt>(&as.stmt()->u)}) {
      return {&indirect->value(), as.source};
    }
  }
  return {nullptr, ""};
}

// Collect symbols that correspond to non-component objects on the
// ALLOCATE statement.
static UnorderedSymbolSet GetNonComponentSymbols(
    const parser::AllocateStmt &stmt) {
  UnorderedSymbolSet symbols;
  for (auto &alloc : std::get<std::list<parser::Allocation>>(stmt.t)) {
    auto &object{std::get<parser::AllocateObject>(alloc.t)};
    if (auto *name{std::get_if<parser::Name>(&object.u)}) {
      if (name->symbol) {
        symbols.insert(name->symbol->GetUltimate());
      }
    }
  }
  return symbols;
}

void OmpStructureChecker::CheckIndividualAllocateDirective(
    const parser::OmpAllocateDirective &x, bool isExecutable) {
  const parser::OmpDirectiveSpecification &beginSpec{x.BeginDir()};
  const parser::OmpDirectiveName &dirName{beginSpec.DirName()};

  const Scope &thisScope{context_.FindScope(dirName.source)};

  auto maybeHasPredefinedAllocator{[&](const parser::OmpClause *calloc) {
    // Return "true" if the ALLOCATOR clause was provided with an argument
    // that is either a prefdefined allocator, or a run-time value.
    // Otherwise return "false".
    if (!calloc) {
      return false;
    }
    auto *allocator{std::get_if<parser::OmpClause::Allocator>(&calloc->u)};
    if (auto val{ToInt64(GetEvaluateExpr(DEREF(allocator).v))}) {
      // Predefined allocators (defined in OpenMP 6.0 20.8.1):
      //   omp_null_allocator = 0,
      //   omp_default_mem_alloc = 1,
      //   omp_large_cap_mem_alloc = 2,
      //   omp_const_mem_alloc = 3,
      //   omp_high_bw_mem_alloc = 4,
      //   omp_low_lat_mem_alloc = 5,
      //   omp_cgroup_mem_alloc = 6,
      //   omp_pteam_mem_alloc = 7,
      //   omp_thread_mem_alloc = 8
      return *val >= 0 && *val <= 8;
    }
    return true;
  }};

  const auto *allocator{
      parser::omp::FindClause(beginSpec, llvm::omp::Clause::OMPC_allocator)};

  if (InTargetRegion()) {
    bool hasDynAllocators{
        HasRequires(llvm::omp::Clause::OMPC_dynamic_allocators)};
    if (!allocator && !hasDynAllocators) {
      context_.Say(dirName.source,
          "An ALLOCATE directive in a TARGET region must specify an ALLOCATOR clause or REQUIRES(DYNAMIC_ALLOCATORS) must be specified"_err_en_US);
    }
  }

  auto maybePredefined{maybeHasPredefinedAllocator(allocator)};

  unsigned version{context_.langOptions().OpenMPVersion};
  std::string condStr{version == 50
          ? "a named common block, has SAVE attribute or is declared in the "
            "scope of a module"
          : "a named common block or has SAVE attribute"};

  auto checkSymbol{[&](const Symbol &symbol, parser::CharBlock source) {
    if (!isExecutable) {
      // For structure members, the scope is the derived type, which is
      // never "this" scope. Ignore this check for members, they will be
      // flagged anyway.
      if (symbol.owner() != thisScope && !IsStructureComponent(symbol)) {
        context_.Say(source,
            "A list item on a declarative ALLOCATE must be declared in the same scope in which the directive appears"_err_en_US);
      }
      if (IsPointer(symbol) || IsAllocatable(symbol)) {
        context_.Say(source,
            "A list item in a declarative ALLOCATE cannot have the ALLOCATABLE or POINTER attribute"_err_en_US);
      }
    }
    if (symbol.GetUltimate().has<AssocEntityDetails>()) {
      context_.Say(source,
          "A list item in a declarative ALLOCATE cannot be an associate name"_err_en_US);
    }
    bool inModule{
        version == 50 && symbol.owner().kind() == Scope::Kind::Module};
    if (symbol.attrs().test(Attr::SAVE) || IsCommonBlock(symbol) || inModule) {
      if (!allocator) {
        context_.Say(source,
            "If a list item is %s, an ALLOCATOR clause must be present with a predefined allocator"_err_en_US,
            condStr);
      } else if (!maybePredefined) {
        context_.Say(source,
            "If a list item is %s, only a predefined allocator may be used on the ALLOCATOR clause"_err_en_US,
            condStr);
      }
    }
    if (FindCommonBlockContaining(symbol)) {
      context_.Say(source,
          "A variable that is part of a common block may not be specified as a list item in an ALLOCATE directive, except implicitly via the named common block"_err_en_US);
    }
  }};

  for (const parser::OmpArgument &arg : beginSpec.Arguments().v) {
    const parser::OmpObject *object{GetArgumentObject(arg)};
    if (!object) {
      context_.Say(arg.source,
          "An argument to ALLOCATE directive must be a variable list item"_err_en_US);
      continue;
    }

    if (const Symbol *symbol{GetObjectSymbol(*object)}) {
      if (!IsTypeParamInquiry(*symbol)) {
        checkSymbol(*symbol, arg.source);
      }
      CheckVarIsNotPartOfAnotherVar(dirName.source, *object);
    }
  }
}

void OmpStructureChecker::CheckExecutableAllocateDirective(
    const parser::OmpAllocateDirective &x) {
  parser::omp::OmpAllocateInfo info{SplitOmpAllocate(x)};

  auto [allocStmt, allocSource]{getAllocateStmtAndSource(info.body)};
  if (!allocStmt) {
    // This has been diagnosed already.
    return;
  }

  UnorderedSymbolSet allocateSyms{GetNonComponentSymbols(*allocStmt)};
  SymbolSourceMap directiveSyms;
  bool hasEmptyList{false};

  for (const parser::OmpAllocateDirective *ompAlloc : info.dirs) {
    const parser::OmpDirectiveSpecification &spec{DEREF(ompAlloc).BeginDir()};
    if (spec.Arguments().v.empty()) {
      if (hasEmptyList && info.dirs.size() > 1) {
        context_.Say(spec.DirName().source,
            "If multiple directives are present in an executable ALLOCATE directive, at most one of them may specify no list items"_err_en_US);
      }
      hasEmptyList = true;
    }
    for (const parser::OmpArgument &arg : spec.Arguments().v) {
      if (auto *sym{GetArgumentSymbol(arg)}) {
        // Ignore these checks for structure members. They are not allowed
        // in the first place, so don't tell the users that they need to
        // be specified somewhere,
        if (IsStructureComponent(*sym)) {
          continue;
        }
        if (auto f{directiveSyms.find(sym)}; f != directiveSyms.end()) {
          parser::MessageFormattedText txt(
              "A list item on an executable ALLOCATE may only be specified once"_err_en_US);
          parser::Message message(arg.source, txt);
          message.Attach(f->second, "The list item was specified here"_en_US);
          context_.Say(std::move(message));
        } else {
          directiveSyms.insert(std::make_pair(sym, arg.source));
        }

        if (auto f{allocateSyms.find(*sym)}; f == allocateSyms.end()) {
          context_
              .Say(arg.source,
                  "A list item on an executable ALLOCATE must be specified on the associated ALLOCATE statement"_err_en_US)
              .Attach(allocSource, "The ALLOCATE statement"_en_US);
        }
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpAllocateDirective &x) {
  const parser::OmpDirectiveSpecification &beginSpec{x.BeginDir()};
  const parser::OmpDirectiveName &dirName{beginSpec.DirName()};
  PushContextAndClauseSets(dirName.source, dirName.v);
  ++allocateDirectiveLevel_;

  bool isExecutable{partStack_.back() == PartKind::ExecutionPart};

  unsigned version{context_.langOptions().OpenMPVersion};
  if (isExecutable && allocateDirectiveLevel_ == 1 && version >= 52) {
    context_.Warn(common::UsageWarning::OpenMPUsage, dirName.source,
        "The executable form of the OpenMP ALLOCATE directive has been deprecated, please use ALLOCATORS instead"_warn_en_US);
  }

  CheckIndividualAllocateDirective(x, isExecutable);

  if (isExecutable) {
    auto isOmpAllocate{[](const parser::ExecutionPartConstruct &epc) {
      if (auto *omp{GetOmp(epc)}) {
        auto odn{GetOmpDirectiveName(*omp)};
        return odn.v == llvm::omp::Directive::OMPD_allocate;
      }
      return false;
    }};

    auto &body{std::get<parser::Block>(x.t)};
    // The parser should put at most one statement in the body.
    assert(body.size() <= 1 && "Multiple statements in allocate");
    if (body.empty()) {
      context_.Say(dirName.source,
          "An executable ALLOCATE directive must be associated with an ALLOCATE statement"_err_en_US);
    } else {
      const parser::ExecutionPartConstruct &first{body.front()};
      auto [allocStmt, _]{getAllocateStmtAndSource(&body.front())};
      if (!isOmpAllocate(first) && !allocStmt) {
        parser::CharBlock source{[&]() {
          if (auto &&maybeSource{parser::GetSource(first)}) {
            return *maybeSource;
          }
          return dirName.source;
        }()};
        context_.Say(source,
            "The statement associated with executable ALLOCATE directive must be an ALLOCATE statement"_err_en_US);
      }
    }
  }
}

void OmpStructureChecker::Leave(const parser::OmpAllocateDirective &x) {
  bool isExecutable{partStack_.back() == PartKind::ExecutionPart};
  if (isExecutable && allocateDirectiveLevel_ == 1) {
    CheckExecutableAllocateDirective(x);
  }

  --allocateDirectiveLevel_;
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OmpClause::Allocator &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_allocator);
  RequiresPositiveParameter(llvm::omp::Clause::OMPC_allocator, x.v);
}

void OmpStructureChecker::Enter(const parser::OmpClause::Allocate &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_allocate);
  if (OmpVerifyModifiers(
          x.v, llvm::omp::OMPC_allocate, GetContext().clauseSource, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    if (auto *align{
            OmpGetUniqueModifier<parser::OmpAlignModifier>(modifiers)}) {
      if (const auto &v{GetIntValue(align->v)}; !v || *v <= 0) {
        context_.Say(OmpGetModifierSource(modifiers, align),
            "The alignment value should be a constant positive integer"_err_en_US);
      }
    }
  }

  // If the clause is not allowed, don't diagnose specific problems with it.
  if (!IsAllowedClause(llvm::omp::Clause::OMPC_allocate)) {
    return;
  }

  llvm::omp::Directive dirId{GetContext().directive};
  // For any list item that is specified in the allocate clause on a directive
  // other than the allocators directive, a data-sharing attribute clause that
  // may create a private copy of that list item must be specified on the same
  // directive.
  if (dirId != llvm::omp::Directive::OMPD_allocators &&
      dirId != llvm::omp::Directive::OMPD_section) {
    static llvm::omp::Clause privatizingDSAClauses[] = {
        llvm::omp::Clause::OMPC_private,
        llvm::omp::Clause::OMPC_firstprivate,
        llvm::omp::Clause::OMPC_lastprivate,
        llvm::omp::Clause::OMPC_is_device_ptr,
        llvm::omp::Clause::OMPC_use_device_ptr,
    };
    const parser::OmpDirectiveSpecification &spec{*dirStack_.back()};

    std::set<const Symbol *> privatized;
    for (auto dsaClause : privatizingDSAClauses) {
      if (auto *found{parser::omp::FindClause(spec, dsaClause)}) {
        for (auto &object : GetOmpObjectList(*found)->v) {
          if (auto *symbol{GetObjectSymbol(object)}) {
            privatized.insert(symbol);
          }
        }
      }
    }

    for (auto &object : GetOmpObjectList(x)->v) {
      if (auto *symbol{GetObjectSymbol(object)}) {
        if (!privatized.count(symbol)) {
          context_.Say(
              GetObjectSource(object).value_or(GetContext().clauseSource),
              "The ALLOCATE clause requires that '%s' must be listed in a private data-sharing attribute clause on the same directive"_err_en_US,
              symbol->name());
        }
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPDeclareMapperConstruct &x) {
  const parser::OmpDirectiveName &dirName{x.v.DirName()};
  PushContextAndClauseSets(dirName.source, dirName.v);

  const parser::OmpArgumentList &args{x.v.Arguments()};
  if (args.v.size() != 1) {
    context_.Say(args.source,
        "DECLARE_MAPPER directive should have a single argument"_err_en_US);
    return;
  }

  const parser::OmpArgument &arg{args.v.front()};
  if (auto *spec{std::get_if<parser::OmpMapperSpecifier>(&arg.u)}) {
    const auto &type = std::get<parser::TypeSpec>(spec->t);
    if (!std::get_if<parser::DerivedTypeSpec>(&type.u)) {
      context_.Say(arg.source, "Type is not a derived type"_err_en_US);
    }
  } else {
    context_.Say(arg.source,
        "The argument to the DECLARE_MAPPER directive should be a mapper-specifier"_err_en_US);
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPDeclareMapperConstruct &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(
    const parser::OpenMPDeclareReductionConstruct &x) {
  const parser::OmpDirectiveName &dirName{x.v.DirName()};
  PushContextAndClauseSets(dirName.source, dirName.v);

  const parser::OmpArgumentList &args{x.v.Arguments()};
  if (args.v.size() != 1) {
    context_.Say(args.source,
        "DECLARE_REDUCTION directive should have a single argument"_err_en_US);
    return;
  }

  const parser::OmpArgument &arg{args.v.front()};
  if (!std::holds_alternative<parser::OmpReductionSpecifier>(arg.u)) {
    context_.Say(arg.source,
        "The argument to the DECLARE_REDUCTION directive should be a reduction-specifier"_err_en_US);
  }
}

void OmpStructureChecker::Leave(
    const parser::OpenMPDeclareReductionConstruct &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::CheckSymbolName(
    const parser::CharBlock &source, const parser::OmpObject &object) {
  common::visit(
      common::visitors{
          [&](const parser::Designator &designator) {
            if (const auto *name{parser::Unwrap<parser::Name>(object)}) {
              if (!name->symbol) {
                context_.Say(source,
                    "The given %s directive clause has an invalid argument"_err_en_US,
                    ContextDirectiveAsFortran());
              }
            }
          },
          [&](const parser::Name &name) {
            if (!name.symbol) {
              context_.Say(source,
                  "The given %s directive clause has an invalid argument"_err_en_US,
                  ContextDirectiveAsFortran());
            }
          },
          [&](const parser::OmpObject::Invalid &invalid) {},
      },
      object.u);
}

void OmpStructureChecker::CheckSymbolNames(
    const parser::CharBlock &source, const parser::OmpObjectList &objList) {
  for (const auto &ompObject : objList.v) {
    CheckSymbolName(source, ompObject);
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPDeclareTargetConstruct &x) {
  const parser::OmpDirectiveName &dirName{x.v.DirName()};
  PushContext(dirName.source, dirName.v);

  // Check if arguments are extended-list-items.
  for (const parser::OmpArgument &arg : x.v.Arguments().v) {
    const Symbol *symbol{GetArgumentSymbol(arg)};
    if (!symbol) {
      context_.Say(arg.source,
          "An argument to the DECLARE TARGET directive should be an extended-list-item"_err_en_US);
      continue;
    }
    const GenericDetails *genericDetails = symbol->detailsIf<GenericDetails>();
    if (genericDetails) {
      context_.Say(arg.source,
          "The procedure '%s' in DECLARE TARGET construct cannot be a generic name."_err_en_US,
          symbol->name());
      genericDetails->specific();
    }
    if (IsProcedurePointer(*symbol)) {
      context_.Say(arg.source,
          "The procedure '%s' in DECLARE TARGET construct cannot be a procedure pointer."_err_en_US,
          symbol->name());
    }
    const SubprogramDetails *entryDetails =
        symbol->detailsIf<SubprogramDetails>();
    if (entryDetails && entryDetails->entryScope()) {
      context_.Say(arg.source,
          "The procedure '%s' in DECLARE TARGET construct cannot be an entry name."_err_en_US,
          symbol->name());
    }
    if (IsStmtFunction(*symbol)) {
      context_.Say(arg.source,
          "The procedure '%s' in DECLARE TARGET construct cannot be a statement function."_err_en_US,
          symbol->name());
    }
  }

  // Check if there are arguments or clauses, but not both.
  if (!x.v.Clauses().v.empty()) {
    if (!x.v.Arguments().v.empty()) {
      context_.Say(x.source,
          "DECLARE TARGET directive can have argument or clauses, but not both"_err_en_US);
    }
    SetClauseSets(llvm::omp::Directive::OMPD_declare_target);
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPDeclareTargetConstruct &x) {
  const parser::OmpDirectiveName &dirName{x.v.DirName()};

  // Handle both forms of DECLARE TARGET.
  // - Extended list: It behaves as if there was an ENTER/TO clause with the
  //   list of objects as argument. It accepts no explicit clauses.
  // - With clauses.
  for (const parser::OmpArgument &arg : x.v.Arguments().v) {
    if (auto *object{GetArgumentObject(arg)}) {
      deviceConstructFound_ = true;
      CheckSymbolName(dirName.source, *object);
      CheckVarIsNotPartOfAnotherVar(dirName.source, *object);
      CheckThreadprivateOrDeclareTargetVar(*object);
    }
  }

  if (!x.v.Clauses().v.empty()) {
    const parser::OmpClause *enterClause =
        FindClause(llvm::omp::Clause::OMPC_enter);
    const parser::OmpClause *toClause = FindClause(llvm::omp::Clause::OMPC_to);
    const parser::OmpClause *linkClause =
        FindClause(llvm::omp::Clause::OMPC_link);
    const parser::OmpClause *indirectClause =
        FindClause(llvm::omp::Clause::OMPC_indirect);
    if (!enterClause && !toClause && !linkClause) {
      context_.Say(x.source,
          "If the DECLARE TARGET directive has a clause, it must contain at least one ENTER clause or LINK clause"_err_en_US);
    }
    if (indirectClause && !enterClause) {
      context_.Say(x.source,
          "The INDIRECT clause cannot be used without the ENTER clause with the DECLARE TARGET directive."_err_en_US);
    }
    unsigned version{context_.langOptions().OpenMPVersion};
    if (toClause && version >= 52) {
      context_.Warn(common::UsageWarning::OpenMPUsage, toClause->source,
          "The usage of TO clause on DECLARE TARGET directive has been deprecated. Use ENTER clause instead."_warn_en_US);
    }
    if (indirectClause) {
      CheckAllowedClause(llvm::omp::Clause::OMPC_indirect);
    }
  }

  bool toClauseFound{false};
  bool deviceTypeClauseFound{false};
  bool enterClauseFound{false};
  for (const parser::OmpClause &clause : x.v.Clauses().v) {
    common::visit(
        common::visitors{
            [&](const auto &c) {
              using TypeC = llvm::remove_cvref_t<decltype(c)>;
              if constexpr ( //
                  std::is_same_v<TypeC, parser::OmpClause::Enter> ||
                  std::is_same_v<TypeC, parser::OmpClause::Link> ||
                  std::is_same_v<TypeC, parser::OmpClause::To>) {
                auto &objList{*GetOmpObjectList(c)};
                CheckSymbolNames(dirName.source, objList);
                CheckVarIsNotPartOfAnotherVar(dirName.source, objList);
                CheckThreadprivateOrDeclareTargetVar(objList);
              }
              if constexpr (std::is_same_v<TypeC, parser::OmpClause::Enter>) {
                enterClauseFound = true;
              }
              if constexpr (std::is_same_v<TypeC, parser::OmpClause::To>) {
                toClauseFound = true;
              }
            },
            [&](const parser::OmpClause::DeviceType &deviceTypeClause) {
              deviceTypeClauseFound = true;
              if (deviceTypeClause.v.v !=
                  parser::OmpDeviceTypeClause::DeviceTypeDescription::Host) {
                // Function / subroutine explicitly marked as runnable by the
                // target device.
                deviceConstructFound_ = true;
              }
            },
        },
        clause.u);

    if ((toClauseFound || enterClauseFound) && !deviceTypeClauseFound) {
      deviceConstructFound_ = true;
    }
  }

  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OmpErrorDirective &x) {
  const parser::OmpDirectiveName &dirName{x.v.DirName()};
  PushContextAndClauseSets(dirName.source, dirName.v);
}

void OmpStructureChecker::Enter(const parser::OmpNothingDirective &x) {
  const parser::OmpDirectiveName &dirName{x.v.DirName()};
  PushContextAndClauseSets(dirName.source, dirName.v);
}

void OmpStructureChecker::Leave(const parser::OmpNothingDirective &x) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OpenMPDispatchConstruct &x) {
  const parser::OmpDirectiveSpecification &dirSpec{x.BeginDir()};
  const auto &block{std::get<parser::Block>(x.t)};
  PushContextAndClauseSets(
      dirSpec.DirName().source, llvm::omp::Directive::OMPD_dispatch);

  if (block.empty()) {
    context_.Say(x.source,
        "The DISPATCH construct should contain a single function or subroutine call"_err_en_US);
    return;
  }

  bool passChecks{false};
  omp::SourcedActionStmt action{omp::GetActionStmt(block)};
  if (const auto *assignStmt{
          parser::Unwrap<parser::AssignmentStmt>(*action.stmt())}) {
    if (parser::Unwrap<parser::FunctionReference>(assignStmt->t)) {
      passChecks = true;
    }
  } else if (parser::Unwrap<parser::CallStmt>(*action.stmt())) {
    passChecks = true;
  }

  if (!passChecks) {
    context_.Say(action.source,
        "The body of the DISPATCH construct should be a function or a subroutine call"_err_en_US);
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPDispatchConstruct &x) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Leave(const parser::OmpErrorDirective &x) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OmpClause::At &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_at);
  if (GetDirectiveNest(DeclarativeNest) > 0) {
    if (x.v.v == parser::OmpAtClause::ActionTime::Execution) {
      context_.Say(GetContext().clauseSource,
          "The ERROR directive with AT(EXECUTION) cannot appear in the specification part"_err_en_US);
    }
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPAllocatorsConstruct &x) {
  const parser::OmpDirectiveSpecification &beginSpec{x.BeginDir()};
  const parser::OmpDirectiveName &dirName{beginSpec.DirName()};
  PushContextAndClauseSets(
      dirName.source, llvm::omp::Directive::OMPD_allocators);

  for (const auto &clause : beginSpec.Clauses().v) {
    auto *alloc{std::get_if<parser::OmpClause::Allocate>(&clause.u)};
    if (!alloc) {
      continue;
    }
    using OmpAllocatorSimpleModifier = parser::OmpAllocatorSimpleModifier;
    using OmpAllocatorComplexModifier = parser::OmpAllocatorComplexModifier;

    if (InTargetRegion()) {
      auto &modifiers{OmpGetModifiers(alloc->v)};
      bool hasAllocator{
          OmpGetUniqueModifier<OmpAllocatorSimpleModifier>(modifiers) ||
          OmpGetUniqueModifier<OmpAllocatorComplexModifier>(modifiers)};
      bool hasDynAllocators{
          HasRequires(llvm::omp::Clause::OMPC_dynamic_allocators)};
      if (!hasAllocator && !hasDynAllocators) {
        context_.Say(clause.source,
            "An ALLOCATE clause in a TARGET region must specify an allocator or REQUIRES(DYNAMIC_ALLOCATORS) must be specified"_err_en_US);
      }
    }
  }

  auto &body{std::get<parser::Block>(x.t)};
  // The parser should put at most one statement in the body.
  assert(body.size() <= 1 && "Malformed body in allocators");
  if (body.empty()) {
    context_.Say(dirName.source,
        "The body of an ALLOCATORS construct should be an ALLOCATE statement"_err_en_US);
    return;
  }

  auto [allocStmt, allocSource]{getAllocateStmtAndSource(&body.front())};
  if (!allocStmt) {
    parser::CharBlock source{[&]() {
      if (auto &&maybeSource{parser::GetSource(body.front())}) {
        return *maybeSource;
      }
      return dirName.source;
    }()};
    context_.Say(source,
        "The body of an ALLOCATORS construct should be an ALLOCATE statement"_err_en_US);
    return;
  }

  UnorderedSymbolSet allocateSyms{GetNonComponentSymbols(*allocStmt)};
  for (const auto &clause : beginSpec.Clauses().v) {
    auto *alloc{std::get_if<parser::OmpClause::Allocate>(&clause.u)};
    if (!alloc) {
      continue;
    }
    for (auto &object : DEREF(GetOmpObjectList(clause)).v) {
      CheckVarIsNotPartOfAnotherVar(dirName.source, object);
      if (auto *symbol{GetObjectSymbol(object)}) {
        if (IsStructureComponent(*symbol)) {
          continue;
        }
        parser::CharBlock source{[&]() {
          if (auto &&objectSource{GetObjectSource(object)}) {
            return *objectSource;
          }
          return clause.source;
        }()};
        if (!IsTypeParamInquiry(*symbol)) {
          if (auto f{allocateSyms.find(*symbol)}; f == allocateSyms.end()) {
            context_
                .Say(source,
                    "A list item in an ALLOCATORS construct must be specified on the associated ALLOCATE statement"_err_en_US)
                .Attach(allocSource, "The ALLOCATE statement"_en_US);
          }
        }
      }
    }
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPAllocatorsConstruct &x) {
  dirContext_.pop_back();
}

void OmpStructureChecker::CheckScan(
    const parser::OpenMPSimpleStandaloneConstruct &x) {
  if (x.v.Clauses().v.size() != 1) {
    context_.Say(x.source,
        "Exactly one of EXCLUSIVE or INCLUSIVE clause is expected"_err_en_US);
  }
  if (!CurrentDirectiveIsNested() ||
      !llvm::omp::scanParentAllowedSet.test(GetContextParent().directive)) {
    context_.Say(x.source,
        "Orphaned SCAN directives are prohibited; perhaps you forgot "
        "to enclose the directive in to a WORKSHARING LOOP, a WORKSHARING "
        "LOOP SIMD or a SIMD directive."_err_en_US);
  }
}

void OmpStructureChecker::CheckBarrierNesting(
    const parser::OpenMPSimpleStandaloneConstruct &x) {
  // A barrier region may not be `closely nested` inside a worksharing, loop,
  // task, taskloop, critical, ordered, atomic, or master region.
  // TODO:  Expand the check to include `LOOP` construct as well when it is
  // supported.
  if (IsCloselyNestedRegion(llvm::omp::nestedBarrierErrSet)) {
    context_.Say(x.v.DirName().source,
        "`BARRIER` region may not be closely nested inside of `WORKSHARING`, "
        "`LOOP`, `TASK`, `TASKLOOP`,"
        "`CRITICAL`, `ORDERED`, `ATOMIC` or `MASTER` region."_err_en_US);
  }
}

void OmpStructureChecker::ChecksOnOrderedAsStandalone() {
  if (FindClause(llvm::omp::Clause::OMPC_threads) ||
      FindClause(llvm::omp::Clause::OMPC_simd)) {
    context_.Say(GetContext().clauseSource,
        "THREADS and SIMD clauses are not allowed when ORDERED construct is a standalone construct with no ORDERED region"_err_en_US);
  }

  int dependSinkCount{0}, dependSourceCount{0};
  bool exclusiveShown{false}, duplicateSourceShown{false};

  auto visitDoacross{[&](const parser::OmpDoacross &doa,
                         const parser::CharBlock &src) {
    common::visit(
        common::visitors{
            [&](const parser::OmpDoacross::Source &) { dependSourceCount++; },
            [&](const parser::OmpDoacross::Sink &) { dependSinkCount++; }},
        doa.u);
    if (!exclusiveShown && dependSinkCount > 0 && dependSourceCount > 0) {
      exclusiveShown = true;
      context_.Say(src,
          "The SINK and SOURCE dependence types are mutually exclusive"_err_en_US);
    }
    if (!duplicateSourceShown && dependSourceCount > 1) {
      duplicateSourceShown = true;
      context_.Say(src,
          "At most one SOURCE dependence type can appear on the ORDERED directive"_err_en_US);
    }
  }};

  // Visit the DEPEND and DOACROSS clauses.
  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_depend)) {
    const auto &dependClause{std::get<parser::OmpClause::Depend>(clause->u)};
    if (auto *doAcross{std::get_if<parser::OmpDoacross>(&dependClause.v.u)}) {
      visitDoacross(*doAcross, clause->source);
    } else {
      context_.Say(clause->source,
          "Only SINK or SOURCE dependence types are allowed when ORDERED construct is a standalone construct with no ORDERED region"_err_en_US);
    }
  }
  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_doacross)) {
    auto &doaClause{std::get<parser::OmpClause::Doacross>(clause->u)};
    visitDoacross(doaClause.v.v, clause->source);
  }

  bool isNestedInDoOrderedWithPara{false};
  if (CurrentDirectiveIsNested() &&
      llvm::omp::nestedOrderedDoAllowedSet.test(GetContextParent().directive)) {
    if (const auto *clause{
            FindClause(GetContextParent(), llvm::omp::Clause::OMPC_ordered)}) {
      const auto &orderedClause{
          std::get<parser::OmpClause::Ordered>(clause->u)};
      const auto orderedValue{GetIntValue(orderedClause.v)};
      if (orderedValue > 0) {
        isNestedInDoOrderedWithPara = true;
        CheckOrderedDependClause(orderedValue);
      }
    }
  }

  if (FindClause(llvm::omp::Clause::OMPC_depend) &&
      !isNestedInDoOrderedWithPara) {
    context_.Say(GetContext().clauseSource,
        "An ORDERED construct with the DEPEND clause must be closely nested "
        "in a worksharing-loop (or parallel worksharing-loop) construct with "
        "ORDERED clause with a parameter"_err_en_US);
  }
}

void OmpStructureChecker::CheckOrderedDependClause(
    std::optional<int64_t> orderedValue) {
  auto visitDoacross{[&](const parser::OmpDoacross &doa,
                         const parser::CharBlock &src) {
    if (auto *sinkVector{std::get_if<parser::OmpDoacross::Sink>(&doa.u)}) {
      int64_t numVar = sinkVector->v.v.size();
      if (orderedValue != numVar) {
        context_.Say(src,
            "The number of variables in the SINK iteration vector does not match the parameter specified in ORDERED clause"_err_en_US);
      }
    }
  }};
  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_depend)) {
    auto &dependClause{std::get<parser::OmpClause::Depend>(clause->u)};
    if (auto *doAcross{std::get_if<parser::OmpDoacross>(&dependClause.v.u)}) {
      visitDoacross(*doAcross, clause->source);
    }
  }
  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_doacross)) {
    auto &doaClause{std::get<parser::OmpClause::Doacross>(clause->u)};
    visitDoacross(doaClause.v.v, clause->source);
  }
}

void OmpStructureChecker::CheckTargetUpdate() {
  const parser::OmpClause *toWrapper{FindClause(llvm::omp::Clause::OMPC_to)};
  const parser::OmpClause *fromWrapper{
      FindClause(llvm::omp::Clause::OMPC_from)};
  if (!toWrapper && !fromWrapper) {
    context_.Say(GetContext().directiveSource,
        "At least one motion-clause (TO/FROM) must be specified on "
        "TARGET UPDATE construct."_err_en_US);
  }
  if (toWrapper && fromWrapper) {
    SymbolSourceMap toSymbols, fromSymbols;
    GetSymbolsInObjectList(*GetOmpObjectList(*fromWrapper), fromSymbols);
    GetSymbolsInObjectList(*GetOmpObjectList(*toWrapper), toSymbols);

    for (auto &[symbol, source] : toSymbols) {
      auto fromSymbol{fromSymbols.find(symbol)};
      if (fromSymbol != fromSymbols.end()) {
        context_.Say(source,
            "A list item ('%s') can only appear in a TO or FROM clause, but not in both."_err_en_US,
            symbol->name());
        context_.Say(source, "'%s' appears in the TO clause."_because_en_US,
            symbol->name());
        context_.Say(fromSymbol->second,
            "'%s' appears in the FROM clause."_because_en_US,
            fromSymbol->first->name());
      }
    }
  }
}

namespace {
struct TaskgraphVisitor {
  TaskgraphVisitor(SemanticsContext &context) : context_(context) {}

  template <typename T> bool Pre(const T &) { return true; }
  template <typename T> void Post(const T &) {}

  bool Pre(const parser::OpenMPConstruct &x) {
    parser::OmpDirectiveName name{GetOmpDirectiveName(x)};
    llvm::ArrayRef<llvm::omp::Directive> leafs{getLeafConstructsOrSelf(name.v)};

    if (!IsTaskGenerating(leafs)) {
      context_.Say(name.source,
          "Only task-generating constructs are allowed inside TASKGRAPH region"_err_en_US);
      // Only visit top-level constructs.
      return false;
    }

    const parser::OmpDirectiveSpecification &dirSpec{GetDirSpec(x)};

    // Most restrictions apply to replayable constructs. All constructs are
    // replayable unless REPLAYABLE(false) is present.
    bool isReplayable{IsReplayable(dirSpec)};
    const parser::OmpClause *nogroup{nullptr};

    for (const parser::OmpClause &clause : dirSpec.Clauses().v) {
      switch (clause.Id()) {
      case llvm::omp::Clause::OMPC_transparent:
        if (isReplayable) {
          CheckTransparent(clause);
        }
        break;
      case llvm::omp::Clause::OMPC_detach:
        if (isReplayable) {
          context_.Say(clause.source,
              "Detachable replayable tasks are not allowed in a TASKGRAPH region"_err_en_US);
        }
        break;
      case llvm::omp::Clause::OMPC_if:
        if (isReplayable) {
          CheckIf(clause, leafs);
        }
        break;
      case llvm::omp::Clause::OMPC_nogroup:
        nogroup = &clause;
        break;
      default:
        break;
      }
    }

    unsigned version{context_.langOptions().OpenMPVersion};
    bool allowsNogroup{llvm::omp::isAllowedClauseForDirective(
        leafs[0], llvm::omp::Clause::OMPC_nogroup, version)};

    if (allowsNogroup) {
      if (!nogroup) {
        context_.Say(dirSpec.source,
            "The NOGROUP clause must be specified on every construct in a TASKGRAPH region that could be enclosed in an implicit TASKGROUP"_err_en_US);
      }
    }

    // Only visit top-level constructs.
    return false;
  }

private:
  const parser::OmpDirectiveSpecification &GetDirSpec(
      const parser::OpenMPConstruct &x) const {
    return common::visit(
        common::visitors{
            [&](const parser::OmpBlockConstruct &y)
                -> const parser::OmpDirectiveSpecification & {
              return y.BeginDir();
            },
            [&](const parser::OpenMPLoopConstruct &y)
                -> const parser::OmpDirectiveSpecification & {
              return y.BeginDir();
            },
            [&](const parser::OpenMPStandaloneConstruct &y)
                -> const parser::OmpDirectiveSpecification & {
              return std::get<parser::OpenMPSimpleStandaloneConstruct>(y.u).v;
            },
            [&](const auto &) -> const parser::OmpDirectiveSpecification & {
              llvm_unreachable("Invalid construct");
            },
        },
        x.u);
  }

  bool IsTaskGenerating(llvm::ArrayRef<llvm::omp::Directive> leafs) const {
    const static llvm::omp::Directive taskGen[] = {
        llvm::omp::Directive::OMPD_target,
        llvm::omp::Directive::OMPD_target_data,
        llvm::omp::Directive::OMPD_target_enter_data,
        llvm::omp::Directive::OMPD_target_exit_data,
        llvm::omp::Directive::OMPD_target_update,
        llvm::omp::Directive::OMPD_task,
        llvm::omp::Directive::OMPD_taskloop,
    };
    return llvm::all_of(leafs,
        [](llvm::omp::Directive d) { return llvm::is_contained(taskGen, d); });
  }

  bool IsReplayable(const parser::OmpDirectiveSpecification &dirSpec) const {
    for (const parser::OmpClause &clause : dirSpec.Clauses().v) {
      if (clause.Id() != llvm::omp::Clause::OMPC_replayable) {
        continue;
      }
      if (auto &repl{std::get<parser::OmpClause::Replayable>(clause.u).v}) {
        // Scalar<Logical<Constant<indirection<Expr>>>>
        const auto &parserExpr{parser::UnwrapRef<parser::Expr>(repl)};
        if (auto &&expr{GetEvaluateExpr(parserExpr)}) {
          return GetLogicalValue(*expr).value_or(true);
        }
      }
      break;
    }
    return true;
  }

  void CheckTransparent(const parser::OmpClause &clause) const {
    bool isTransparent{true};
    if (auto &transp{std::get<parser::OmpClause::Transparent>(clause.u).v}) {
      // Scalar<Integer<indirection<Expr>>>
      const auto &parserExpr{parser::UnwrapRef<parser::Expr>(transp)};
      if (auto &&expr{GetEvaluateExpr(parserExpr)}) {
        // If the argument is omp_not_impex (defined as 0), then
        // the task is not transparent, otherwise it is.
        const int64_t omp_not_impex{0};
        if (auto &&val{evaluate::ToInt64(*expr)}) {
          isTransparent = *val != omp_not_impex;
        }
      }
    }
    if (isTransparent) {
      context_.Say(clause.source,
          "Transparent replayable tasks are not allowed in a TASKGRAPH region"_err_en_US);
    }
  }

  void CheckIf(const parser::OmpClause &clause,
      llvm::ArrayRef<llvm::omp::Directive> leafs) const {
    // The only constructs that can generate undeferred tasks (via IF clause)
    // are TASK and TASKLOOP.
    if (leafs[0] != llvm::omp::Directive::OMPD_task &&
        leafs[0] != llvm::omp::Directive::OMPD_taskloop) {
      return;
    }

    auto &&ifc{std::get<parser::OmpClause::If>(clause.u)};
    // Check if there is a directive-name-modifier first.
    auto &modifiers{OmpGetModifiers(ifc.v)};
    if (auto *dnm{OmpGetUniqueModifier<parser::OmpDirectiveNameModifier>(
            modifiers)}) {
      llvm::omp::Directive sub{dnm->v};
      auto subLeafs{llvm::omp::getLeafConstructsOrSelf(sub)};
      // Only interested in the outermost constructs. The body of the created
      // task is not a part of the TASKGRAPH region.
      if (subLeafs[0] != leafs[0]) {
        return;
      }
    }
    // Scalar<Logical<indirection<Expr>>>
    const auto &parserExpr{parser::UnwrapRef<parser::Expr>(
        std::get<parser::ScalarLogicalExpr>(ifc.v.t))};
    if (auto &&expr{GetEvaluateExpr(parserExpr)}) {
      // If the value is known to be false, an undeferred task will be
      // generated.
      if (!GetLogicalValue(*expr).value_or(true)) {
        context_.Say(clause.source,
            "Undeferred replayable tasks are not allowed in a TASKGRAPH region"_err_en_US);
      }
    }
  }

  SemanticsContext &context_;
};
} // namespace

void OmpStructureChecker::CheckTaskgraph(const parser::OmpBlockConstruct &x) {
  const parser::Block &block{std::get<parser::Block>(x.t)};

  TaskgraphVisitor visitor{context_};
  parser::Walk(block, visitor);
}

void OmpStructureChecker::CheckTaskDependenceType(
    const parser::OmpTaskDependenceType::Value &x) {
  // Common checks for task-dependence-type (DEPEND and UPDATE clauses).
  unsigned version{context_.langOptions().OpenMPVersion};
  unsigned since{0};

  switch (x) {
  case parser::OmpTaskDependenceType::Value::In:
  case parser::OmpTaskDependenceType::Value::Out:
  case parser::OmpTaskDependenceType::Value::Inout:
    break;
  case parser::OmpTaskDependenceType::Value::Mutexinoutset:
  case parser::OmpTaskDependenceType::Value::Depobj:
    since = 50;
    break;
  case parser::OmpTaskDependenceType::Value::Inoutset:
    since = 52;
    break;
  }

  if (version < since) {
    context_.Say(GetContext().clauseSource,
        "%s task dependence type is not supported in %s, %s"_warn_en_US,
        parser::ToUpperCaseLetters(EnumToString(x)), ThisVersion(version),
        TryVersion(since));
  }
}

void OmpStructureChecker::CheckDependenceType(
    const parser::OmpDependenceType::Value &x) {
  // Common checks for dependence-type (DEPEND and UPDATE clauses).
  unsigned version{context_.langOptions().OpenMPVersion};
  unsigned deprecatedIn{~0u};

  switch (x) {
  case parser::OmpDependenceType::Value::Source:
  case parser::OmpDependenceType::Value::Sink:
    deprecatedIn = 52;
    break;
  }

  if (version >= deprecatedIn) {
    context_.Say(GetContext().clauseSource,
        "%s dependence type is deprecated in %s"_warn_en_US,
        parser::ToUpperCaseLetters(parser::OmpDependenceType::EnumToString(x)),
        ThisVersion(deprecatedIn));
  }
}

void OmpStructureChecker::Enter(
    const parser::OpenMPSimpleStandaloneConstruct &x) {
  const auto &dir{std::get<parser::OmpDirectiveName>(x.v.t)};
  PushContextAndClauseSets(dir.source, dir.v);
  switch (dir.v) {
  case llvm::omp::Directive::OMPD_barrier:
    CheckBarrierNesting(x);
    break;
  case llvm::omp::Directive::OMPD_scan:
    CheckScan(x);
    break;
  default:
    break;
  }
}

void OmpStructureChecker::Leave(
    const parser::OpenMPSimpleStandaloneConstruct &x) {
  switch (GetContext().directive) {
  case llvm::omp::Directive::OMPD_ordered:
    // [5.1] 2.19.9 Ordered Construct Restriction
    ChecksOnOrderedAsStandalone();
    break;
  case llvm::omp::Directive::OMPD_target_update:
    CheckTargetUpdate();
    break;
  default:
    break;
  }
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OpenMPFlushConstruct &x) {
  const auto &dirName{std::get<parser::OmpDirectiveName>(x.v.t)};
  PushContextAndClauseSets(dirName.source, llvm::omp::Directive::OMPD_flush);
}

void OmpStructureChecker::Leave(const parser::OpenMPFlushConstruct &x) {
  auto &flushList{std::get<std::optional<parser::OmpArgumentList>>(x.v.t)};

  auto isVariableListItemOrCommonBlock{[](const Symbol &sym) {
    return IsVariableListItem(sym) ||
        sym.detailsIf<semantics::CommonBlockDetails>();
  }};

  if (flushList) {
    for (const parser::OmpArgument &arg : flushList->v) {
      if (auto *sym{GetArgumentSymbol(arg)};
          sym && !isVariableListItemOrCommonBlock(*sym)) {
        context_.Say(arg.source,
            "FLUSH argument must be a variable list item"_err_en_US);
      }
    }

    if (FindClause(llvm::omp::Clause::OMPC_acquire) ||
        FindClause(llvm::omp::Clause::OMPC_release) ||
        FindClause(llvm::omp::Clause::OMPC_acq_rel)) {
      context_.Say(flushList->source,
          "If memory-order-clause is RELEASE, ACQUIRE, or ACQ_REL, list items must not be specified on the FLUSH directive"_err_en_US);
    }
  }

  unsigned version{context_.langOptions().OpenMPVersion};
  if (version >= 52) {
    auto &flags{std::get<parser::OmpDirectiveSpecification::Flags>(x.v.t)};
    if (flags.test(parser::OmpDirectiveSpecification::Flag::DeprecatedSyntax)) {
      context_.Say(x.source,
          "The syntax \"FLUSH clause (object, ...)\" has been deprecated, use \"FLUSH(object, ...) clause\" instead"_warn_en_US);
    }
  }

  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OpenMPCancelConstruct &x) {
  auto &dirName{std::get<parser::OmpDirectiveName>(x.v.t)};
  auto &maybeClauses{std::get<std::optional<parser::OmpClauseList>>(x.v.t)};
  PushContextAndClauseSets(dirName.source, llvm::omp::Directive::OMPD_cancel);

  if (auto maybeConstruct{GetCancelType(
          llvm::omp::Directive::OMPD_cancel, x.source, maybeClauses)}) {
    CheckCancellationNest(dirName.source, *maybeConstruct);

    if (CurrentDirectiveIsNested()) {
      // nowait can be put on the end directive rather than the start directive
      // so we need to check both
      auto getParentClauses{[&]() {
        const DirectiveContext &parent{GetContextParent()};
        return llvm::concat<const llvm::omp::Clause>(
            parent.actualClauses, parent.endDirectiveClauses);
      }};

      if (llvm::omp::nestedCancelDoAllowedSet.test(*maybeConstruct)) {
        for (llvm::omp::Clause clause : getParentClauses()) {
          if (clause == llvm::omp::Clause::OMPC_nowait) {
            context_.Say(dirName.source,
                "The CANCEL construct cannot be nested inside of a worksharing construct with the NOWAIT clause"_err_en_US);
          }
          if (clause == llvm::omp::Clause::OMPC_ordered) {
            context_.Say(dirName.source,
                "The CANCEL construct cannot be nested inside of a worksharing construct with the ORDERED clause"_err_en_US);
          }
        }
      } else if (llvm::omp::nestedCancelSectionsAllowedSet.test(
                     *maybeConstruct)) {
        for (llvm::omp::Clause clause : getParentClauses()) {
          if (clause == llvm::omp::Clause::OMPC_nowait) {
            context_.Say(dirName.source,
                "The CANCEL construct cannot be nested inside of a worksharing construct with the NOWAIT clause"_err_en_US);
          }
        }
      }
    }
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPCancelConstruct &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OpenMPCriticalConstruct &x) {
  const parser::OmpBeginDirective &beginSpec{x.BeginDir()};
  const std::optional<parser::OmpEndDirective> &endSpec{x.EndDir()};
  PushContextAndClauseSets(beginSpec.DirName().source, beginSpec.DirId());

  const auto &block{std::get<parser::Block>(x.t)};
  CheckNoBranching(
      block, llvm::omp::Directive::OMPD_critical, beginSpec.DirName().source);

  auto getNameFromArg{[](const parser::OmpArgument &arg) {
    if (auto *object{parser::Unwrap<parser::OmpObject>(arg.u)}) {
      if (auto *designator{omp::GetDesignatorFromObj(*object)}) {
        return parser::GetDesignatorNameIfDataRef(*designator);
      }
    }
    return static_cast<const parser::Name *>(nullptr);
  }};

  auto checkArgumentList{[&](const parser::OmpArgumentList &args) {
    if (args.v.size() > 1) {
      context_.Say(args.source,
          "Only a single argument is allowed in CRITICAL directive"_err_en_US);
    } else if (!args.v.empty()) {
      if (!getNameFromArg(args.v.front())) {
        context_.Say(args.v.front().source,
            "CRITICAL argument should be a name"_err_en_US);
      }
    }
  }};

  const parser::Name *beginName{nullptr};
  const parser::Name *endName{nullptr};

  auto &beginArgs{beginSpec.Arguments()};
  checkArgumentList(beginArgs);

  if (!beginArgs.v.empty()) {
    beginName = getNameFromArg(beginArgs.v.front());
  }

  if (endSpec) {
    auto &endArgs{endSpec->Arguments()};
    checkArgumentList(endArgs);

    if (beginArgs.v.empty() != endArgs.v.empty()) {
      parser::CharBlock source{
          beginArgs.v.empty() ? endArgs.source : beginArgs.source};
      context_.Say(source,
          "Either both CRITICAL and END CRITICAL should have an argument, or none of them should"_err_en_US);
    } else if (!beginArgs.v.empty()) {
      endName = getNameFromArg(endArgs.v.front());
      if (beginName && endName) {
        if (beginName->ToString() != endName->ToString()) {
          context_.Say(endName->source,
              "The names on CRITICAL and END CRITICAL must match"_err_en_US);
        }
      }
    }
  }

  for (auto &clause : beginSpec.Clauses().v) {
    auto *hint{std::get_if<parser::OmpClause::Hint>(&clause.u)};
    if (!hint) {
      continue;
    }
    const int64_t OmpSyncHintNone = 0; // omp_sync_hint_none
    std::optional<int64_t> hintValue{GetIntValue(hint->v.v)};
    if (hintValue && *hintValue != OmpSyncHintNone) {
      // Emit a diagnostic if the name is missing, and point to the directive
      // with a missing name.
      parser::CharBlock source;
      if (!beginName) {
        source = beginSpec.DirName().source;
      } else if (endSpec && !endName) {
        source = endSpec->DirName().source;
      }

      if (!source.empty()) {
        context_.Say(source,
            "When HINT other than 'omp_sync_hint_none' is present, CRITICAL directive should have a name"_err_en_US);
      }
    }
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPCriticalConstruct &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(
    const parser::OmpClause::CancellationConstructType &x) {
  llvm::omp::Directive dir{GetContext().directive};
  auto &dirName{std::get<parser::OmpDirectiveName>(x.v.t)};
  unsigned version{context_.langOptions().OpenMPVersion};

  if (dir != llvm::omp::Directive::OMPD_cancel &&
      dir != llvm::omp::Directive::OMPD_cancellation_point) {
    // Do not call CheckAllowed/CheckAllowedClause, because in case of an error
    // it will print "CANCELLATION_CONSTRUCT_TYPE" as the clause name instead
    // of the contained construct name.
    context_.Say(dirName.source, "%s cannot follow %s"_err_en_US,
        parser::omp::GetUpperName(dirName.v, version),
        parser::omp::GetUpperName(dir, version));
  } else {
    switch (dirName.v) {
    case llvm::omp::Directive::OMPD_do:
    case llvm::omp::Directive::OMPD_parallel:
    case llvm::omp::Directive::OMPD_sections:
    case llvm::omp::Directive::OMPD_taskgroup:
      break;
    default:
      context_.Say(dirName.source,
          "%s is not a cancellable construct"_err_en_US,
          parser::omp::GetUpperName(dirName.v, version));
      break;
    }
  }
}

void OmpStructureChecker::Enter(
    const parser::OpenMPCancellationPointConstruct &x) {
  auto &dirName{std::get<parser::OmpDirectiveName>(x.v.t)};
  auto &maybeClauses{std::get<std::optional<parser::OmpClauseList>>(x.v.t)};
  PushContextAndClauseSets(
      dirName.source, llvm::omp::Directive::OMPD_cancellation_point);

  if (auto maybeConstruct{
          GetCancelType(llvm::omp::Directive::OMPD_cancellation_point, x.source,
              maybeClauses)}) {
    CheckCancellationNest(dirName.source, *maybeConstruct);
  }
}

void OmpStructureChecker::Leave(
    const parser::OpenMPCancellationPointConstruct &) {
  dirContext_.pop_back();
}

std::optional<llvm::omp::Directive> OmpStructureChecker::GetCancelType(
    llvm::omp::Directive cancelDir, const parser::CharBlock &cancelSource,
    const std::optional<parser::OmpClauseList> &maybeClauses) {
  if (!maybeClauses) {
    return std::nullopt;
  }
  // Given clauses from CANCEL or CANCELLATION_POINT, identify the construct
  // to which the cancellation applies.
  unsigned version{context_.langOptions().OpenMPVersion};
  std::optional<llvm::omp::Directive> cancelee;
  std::string cancelName{parser::omp::GetUpperName(cancelDir, version)};

  for (const parser::OmpClause &clause : maybeClauses->v) {
    using CancellationConstructType =
        parser::OmpClause::CancellationConstructType;
    if (auto *cctype{std::get_if<CancellationConstructType>(&clause.u)}) {
      if (cancelee) {
        context_.Say(cancelSource,
            "Multiple cancel-directive-name clauses are not allowed on the %s construct"_err_en_US,
            cancelName);
        return std::nullopt;
      }
      cancelee = std::get<parser::OmpDirectiveName>(cctype->v.t).v;
    }
  }

  if (!cancelee) {
    context_.Say(cancelSource,
        "Missing cancel-directive-name clause on the %s construct"_err_en_US,
        cancelName);
    return std::nullopt;
  }

  return cancelee;
}

void OmpStructureChecker::CheckCancellationNest(
    const parser::CharBlock &source, llvm::omp::Directive type) {
  unsigned version{context_.langOptions().OpenMPVersion};
  std::string typeName{parser::omp::GetUpperName(type, version)};

  if (CurrentDirectiveIsNested()) {
    // If construct-type-clause is taskgroup, the cancellation construct must be
    // closely nested inside a task or a taskloop construct and the cancellation
    // region must be closely nested inside a taskgroup region. If
    // construct-type-clause is sections, the cancellation construct must be
    // closely nested inside a sections or section construct. Otherwise, the
    // cancellation construct must be closely nested inside an OpenMP construct
    // that matches the type specified in construct-type-clause of the
    // cancellation construct.
    bool eligibleCancellation{false};

    switch (type) {
    case llvm::omp::Directive::OMPD_taskgroup:
      if (llvm::omp::nestedCancelTaskgroupAllowedSet.test(
              GetContextParent().directive)) {
        eligibleCancellation = true;
        if (dirContext_.size() >= 3) {
          // Check if the cancellation region is closely nested inside a
          // taskgroup region when there are more than two levels of directives
          // in the directive context stack.
          if (GetContextParent().directive == llvm::omp::Directive::OMPD_task ||
              FindClauseParent(llvm::omp::Clause::OMPC_nogroup)) {
            for (int i = dirContext_.size() - 3; i >= 0; i--) {
              if (dirContext_[i].directive ==
                  llvm::omp::Directive::OMPD_taskgroup) {
                break;
              }
              if (llvm::omp::nestedCancelParallelAllowedSet.test(
                      dirContext_[i].directive)) {
                eligibleCancellation = false;
                break;
              }
            }
          }
        }
      }
      if (!eligibleCancellation) {
        context_.Say(source,
            "With %s clause, %s construct must be closely nested inside TASK or TASKLOOP construct and %s region must be closely nested inside TASKGROUP region"_err_en_US,
            typeName, ContextDirectiveAsFortran(), ContextDirectiveAsFortran());
      }
      return;
    case llvm::omp::Directive::OMPD_sections:
      if (llvm::omp::nestedCancelSectionsAllowedSet.test(
              GetContextParent().directive)) {
        eligibleCancellation = true;
      }
      break;
    case llvm::omp::Directive::OMPD_do:
      if (llvm::omp::nestedCancelDoAllowedSet.test(
              GetContextParent().directive)) {
        eligibleCancellation = true;
      }
      break;
    case llvm::omp::Directive::OMPD_parallel:
      if (llvm::omp::nestedCancelParallelAllowedSet.test(
              GetContextParent().directive)) {
        eligibleCancellation = true;
      }
      break;
    default:
      // This is diagnosed later.
      return;
    }
    if (!eligibleCancellation) {
      context_.Say(source,
          "With %s clause, %s construct cannot be closely nested inside %s construct"_err_en_US,
          typeName, ContextDirectiveAsFortran(),
          parser::omp::GetUpperName(GetContextParent().directive, version));
    }
  } else {
    // The cancellation directive cannot be orphaned.
    switch (type) {
    case llvm::omp::Directive::OMPD_taskgroup:
      context_.Say(source,
          "%s %s directive is not closely nested inside TASK or TASKLOOP"_err_en_US,
          ContextDirectiveAsFortran(), typeName);
      break;
    case llvm::omp::Directive::OMPD_sections:
      context_.Say(source,
          "%s %s directive is not closely nested inside SECTION or SECTIONS"_err_en_US,
          ContextDirectiveAsFortran(), typeName);
      break;
    case llvm::omp::Directive::OMPD_do:
      context_.Say(source,
          "%s %s directive is not closely nested inside the construct that matches the DO clause type"_err_en_US,
          ContextDirectiveAsFortran(), typeName);
      break;
    case llvm::omp::Directive::OMPD_parallel:
      context_.Say(source,
          "%s %s directive is not closely nested inside the construct that matches the PARALLEL clause type"_err_en_US,
          ContextDirectiveAsFortran(), typeName);
      break;
    default:
      // This is diagnosed later.
      return;
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpEndDirective &x) {
  parser::CharBlock source{x.DirName().source};
  ResetPartialContext(source);
  switch (x.DirId()) {
  case llvm::omp::Directive::OMPD_scope:
    PushContextAndClauseSets(source, llvm::omp::Directive::OMPD_end_scope);
    break;
  // 2.7.3 end-single-clause -> copyprivate-clause |
  //                            nowait-clause
  case llvm::omp::Directive::OMPD_single:
    PushContextAndClauseSets(source, llvm::omp::Directive::OMPD_end_single);
    break;
  // 2.7.4 end-workshare -> END WORKSHARE [nowait-clause]
  case llvm::omp::Directive::OMPD_workshare:
    PushContextAndClauseSets(source, llvm::omp::Directive::OMPD_end_workshare);
    break;
  default:
    // no clauses are allowed
    break;
  }
}

// TODO: Verify the popping of dirContext requirement after nowait
// implementation, as there is an implicit barrier at the end of the worksharing
// constructs unless a nowait clause is specified. Only OMPD_end_single and
// end_workshareare popped as they are pushed while entering the
// EndBlockDirective.
void OmpStructureChecker::Leave(const parser::OmpEndDirective &x) {
  if ((GetContext().directive == llvm::omp::Directive::OMPD_end_scope) ||
      (GetContext().directive == llvm::omp::Directive::OMPD_end_single) ||
      (GetContext().directive == llvm::omp::Directive::OMPD_end_workshare)) {
    dirContext_.pop_back();
  }
}

// Clauses
// Mainly categorized as
// 1. Checks on 'OmpClauseList' from 'parse-tree.h'.
// 2. Checks on clauses which fall under 'struct OmpClause' from parse-tree.h.
// 3. Checks on clauses which are not in 'struct OmpClause' from parse-tree.h.

void OmpStructureChecker::Leave(const parser::OmpClauseList &) {
  unsigned version{context_.langOptions().OpenMPVersion};

  // 2.7.1 Loop Construct Restriction
  if (llvm::omp::allDoSet.test(GetContext().directive)) {
    if (auto *clause{FindClause(llvm::omp::Clause::OMPC_schedule)}) {
      // only one schedule clause is allowed
      const auto &schedClause{std::get<parser::OmpClause::Schedule>(clause->u)};
      auto &modifiers{OmpGetModifiers(schedClause.v)};
      auto *ordering{
          OmpGetUniqueModifier<parser::OmpOrderingModifier>(modifiers)};
      if (ordering &&
          ordering->v == parser::OmpOrderingModifier::Value::Nonmonotonic) {
        if (FindClause(llvm::omp::Clause::OMPC_ordered)) {
          context_.Say(clause->source,
              "The NONMONOTONIC modifier cannot be specified "
              "if an ORDERED clause is specified"_err_en_US);
        }
      }
    }

    if (auto *clause{FindClause(llvm::omp::Clause::OMPC_ordered)}) {
      // only one ordered clause is allowed
      const auto &orderedClause{
          std::get<parser::OmpClause::Ordered>(clause->u)};

      if (orderedClause.v) {
        CheckNotAllowedIfClause(
            llvm::omp::Clause::OMPC_ordered, {llvm::omp::Clause::OMPC_linear});

        if (auto *clause2{FindClause(llvm::omp::Clause::OMPC_collapse)}) {
          const auto &collapseClause{
              std::get<parser::OmpClause::Collapse>(clause2->u)};
          // ordered and collapse both have parameters
          if (const auto orderedValue{GetIntValue(orderedClause.v)}) {
            if (const auto collapseValue{GetIntValue(collapseClause.v)}) {
              if (*orderedValue > 0 && *orderedValue < *collapseValue) {
                context_.Say(clause->source,
                    "The parameter of the ORDERED clause must be "
                    "greater than or equal to "
                    "the parameter of the COLLAPSE clause"_err_en_US);
              }
            }
          }
        }
      }

      // TODO: ordered region binding check (requires nesting implementation)
    }
  } // doSet

  // 2.8.1 Simd Construct Restriction
  if (llvm::omp::allSimdSet.test(GetContext().directive)) {
    if (auto *clause{FindClause(llvm::omp::Clause::OMPC_simdlen)}) {
      if (auto *clause2{FindClause(llvm::omp::Clause::OMPC_safelen)}) {
        const auto &simdlenClause{
            std::get<parser::OmpClause::Simdlen>(clause->u)};
        const auto &safelenClause{
            std::get<parser::OmpClause::Safelen>(clause2->u)};
        // simdlen and safelen both have parameters
        if (const auto simdlenValue{GetIntValue(simdlenClause.v)}) {
          if (const auto safelenValue{GetIntValue(safelenClause.v)}) {
            if (*safelenValue > 0 && *simdlenValue > *safelenValue) {
              context_.Say(clause->source,
                  "The parameter of the SIMDLEN clause must be less than or "
                  "equal to the parameter of the SAFELEN clause"_err_en_US);
            }
          }
        }
      }
    }

    // 2.11.5 Simd construct restriction (OpenMP 5.1)
    if (auto *sl_clause{FindClause(llvm::omp::Clause::OMPC_safelen)}) {
      if (auto *o_clause{FindClause(llvm::omp::Clause::OMPC_order)}) {
        const auto &orderClause{
            std::get<parser::OmpClause::Order>(o_clause->u)};
        if (std::get<parser::OmpOrderClause::Ordering>(orderClause.v.t) ==
            parser::OmpOrderClause::Ordering::Concurrent) {
          context_.Say(sl_clause->source,
              "The `SAFELEN` clause cannot appear in the `SIMD` directive "
              "with `ORDER(CONCURRENT)` clause"_err_en_US);
        }
      }
    }
  } // SIMD

  // Semantic checks related to presence of multiple list items within the same
  // clause
  CheckMultListItems();

  if (GetContext().directive == llvm::omp::Directive::OMPD_task) {
    if (auto *detachClause{FindClause(llvm::omp::Clause::OMPC_detach)}) {
      if (version == 50 || version == 51) {
        // OpenMP 5.0: 2.10.1 Task construct restrictions
        CheckNotAllowedIfClause(llvm::omp::Clause::OMPC_detach,
            {llvm::omp::Clause::OMPC_mergeable});
      } else if (version >= 52) {
        // OpenMP 5.2: 12.5.2 Detach construct restrictions
        if (FindClause(llvm::omp::Clause::OMPC_final)) {
          context_.Say(GetContext().clauseSource,
              "If a DETACH clause appears on a directive, then the encountering task must not be a FINAL task"_err_en_US);
        }

        const auto &detach{
            std::get<parser::OmpClause::Detach>(detachClause->u)};
        if (const auto *name{parser::Unwrap<parser::Name>(detach.v.v)}) {
          Symbol *eventHandleSym{name->symbol};
          auto checkVarAppearsInDataEnvClause = [&](const parser::OmpObjectList
                                                        &objs,
                                                    std::string clause) {
            for (const auto &obj : objs.v) {
              if (const parser::Name *objName{
                      parser::Unwrap<parser::Name>(obj)}) {
                if (&objName->symbol->GetUltimate() == eventHandleSym) {
                  context_.Say(GetContext().clauseSource,
                      "A variable: `%s` that appears in a DETACH clause cannot appear on %s clause on the same construct"_err_en_US,
                      objName->source, clause);
                }
              }
            }
          };
          if (auto *dataEnvClause{
                  FindClause(llvm::omp::Clause::OMPC_private)}) {
            const auto &pClause{
                std::get<parser::OmpClause::Private>(dataEnvClause->u)};
            checkVarAppearsInDataEnvClause(pClause.v, "PRIVATE");
          } else if (auto *dataEnvClause{
                         FindClause(llvm::omp::Clause::OMPC_shared)}) {
            const auto &sClause{
                std::get<parser::OmpClause::Shared>(dataEnvClause->u)};
            checkVarAppearsInDataEnvClause(sClause.v, "SHARED");
          } else if (auto *dataEnvClause{
                         FindClause(llvm::omp::Clause::OMPC_firstprivate)}) {
            const auto &fpClause{
                std::get<parser::OmpClause::Firstprivate>(dataEnvClause->u)};
            checkVarAppearsInDataEnvClause(fpClause.v, "FIRSTPRIVATE");
          } else if (auto *dataEnvClause{
                         FindClause(llvm::omp::Clause::OMPC_in_reduction)}) {
            const auto &irClause{
                std::get<parser::OmpClause::InReduction>(dataEnvClause->u)};
            checkVarAppearsInDataEnvClause(
                *GetOmpObjectList(irClause), "IN_REDUCTION");
          }
        }
      }
    }
  }

  auto testThreadprivateVarErr = [&](Symbol sym, parser::Name name,
                                     llvmOmpClause clauseTy) {
    if (sym.test(Symbol::Flag::OmpThreadprivate))
      context_.Say(name.source,
          "A THREADPRIVATE variable cannot be in %s clause"_err_en_US,
          parser::omp::GetUpperName(clauseTy, version));
  };

  // [5.1] 2.21.2 Threadprivate Directive Restriction
  OmpClauseSet threadprivateAllowedSet{llvm::omp::Clause::OMPC_copyin,
      llvm::omp::Clause::OMPC_copyprivate, llvm::omp::Clause::OMPC_schedule,
      llvm::omp::Clause::OMPC_num_threads, llvm::omp::Clause::OMPC_thread_limit,
      llvm::omp::Clause::OMPC_if};
  for (auto it : GetContext().clauseInfo) {
    llvmOmpClause type = it.first;
    const auto *clause = it.second;
    if (!threadprivateAllowedSet.test(type)) {
      if (const auto *objList{GetOmpObjectList(*clause)}) {
        for (const auto &ompObject : objList->v) {
          common::visit(
              common::visitors{
                  [&](const parser::Designator &) {
                    if (const auto *name{
                            parser::Unwrap<parser::Name>(ompObject)}) {
                      if (name->symbol) {
                        testThreadprivateVarErr(
                            name->symbol->GetUltimate(), *name, type);
                      }
                    }
                  },
                  [&](const parser::Name &name) {
                    if (name.symbol) {
                      for (const auto &mem :
                          name.symbol->get<CommonBlockDetails>().objects()) {
                        testThreadprivateVarErr(mem->GetUltimate(), name, type);
                        break;
                      }
                    }
                  },
                  [&](const parser::OmpObject::Invalid &invalid) {},
              },
              ompObject.u);
        }
      }
    }
  }

  // Default access-group for DYN_GROUPPRIVATE is "cgroup". On a given
  // construct there can be at most one DYN_GROUPPRIVATE with a given
  // access-group.
  const parser::OmpClause
      *accGrpClause[parser::OmpAccessGroup::Value_enumSize] = {nullptr};
  for (auto [_, clause] :
      FindClauses(llvm::omp::Clause::OMPC_dyn_groupprivate)) {
    auto &wrapper{std::get<parser::OmpClause::DynGroupprivate>(clause->u)};
    auto &modifiers{OmpGetModifiers(wrapper.v)};
    auto accGrp{parser::OmpAccessGroup::Value::Cgroup};
    if (auto *ag{OmpGetUniqueModifier<parser::OmpAccessGroup>(modifiers)}) {
      accGrp = ag->v;
    }
    auto &firstClause{accGrpClause[llvm::to_underlying(accGrp)]};
    if (firstClause) {
      context_
          .Say(clause->source,
              "The access-group modifier can only occur on a single clause in a construct"_err_en_US)
          .Attach(firstClause->source,
              "Previous clause with access-group modifier"_en_US);
      break;
    } else {
      firstClause = clause;
    }
  }

  CheckRequireAtLeastOneOf();
}

void OmpStructureChecker::Enter(const parser::OmpClause &x) {
  SetContextClause(x);

  llvm::omp::Clause id{x.Id()};
  // The visitors for these clauses do their own checks.
  switch (id) {
  case llvm::omp::Clause::OMPC_copyprivate:
  case llvm::omp::Clause::OMPC_enter:
  case llvm::omp::Clause::OMPC_lastprivate:
  case llvm::omp::Clause::OMPC_reduction:
  case llvm::omp::Clause::OMPC_to:
    return;
  default:
    break;
  }

  // Named constants are OK to be used within 'shared' and 'firstprivate'
  // clauses.  The check for this happens a few lines below.
  bool SharedOrFirstprivate = false;
  switch (id) {
  case llvm::omp::Clause::OMPC_shared:
  case llvm::omp::Clause::OMPC_firstprivate:
    SharedOrFirstprivate = true;
    break;
  default:
    break;
  }

  if (const parser::OmpObjectList *objList{GetOmpObjectList(x)}) {
    AnalyzeObjects(*objList);
    SymbolSourceMap symbols;
    GetSymbolsInObjectList(*objList, symbols);
    for (const auto &[symbol, source] : symbols) {
      if (!IsVariableListItem(*symbol) &&
          !(IsNamedConstant(*symbol) && SharedOrFirstprivate)) {
        deferredNonVariables_.insert({symbol, source});
      }
    }
  }
}

// Restrictions specific to each clause are implemented apart from the
// generalized restrictions.

void OmpStructureChecker::Enter(const parser::OmpClause::Destroy &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_destroy);

  llvm::omp::Directive dir{GetContext().directive};
  unsigned version{context_.langOptions().OpenMPVersion};
  if (dir == llvm::omp::Directive::OMPD_depobj) {
    unsigned argSince{52}, noargDeprecatedIn{52};
    if (x.v) {
      if (version < argSince) {
        context_.Say(GetContext().clauseSource,
            "The object parameter in DESTROY clause on DEPOPJ construct is not allowed in %s, %s"_warn_en_US,
            ThisVersion(version), TryVersion(argSince));
      }
    } else {
      if (version >= noargDeprecatedIn) {
        context_.Say(GetContext().clauseSource,
            "The DESTROY clause without argument on DEPOBJ construct is deprecated in %s"_warn_en_US,
            ThisVersion(noargDeprecatedIn));
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Reduction &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_reduction);
  auto &objects{*GetOmpObjectList(x)};

  if (OmpVerifyModifiers(x.v, llvm::omp::OMPC_reduction,
          GetContext().clauseSource, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    const auto *ident{
        OmpGetUniqueModifier<parser::OmpReductionIdentifier>(modifiers)};
    assert(ident && "reduction-identifier is a required modifier");
    if (CheckReductionOperator(*ident, OmpGetModifierSource(modifiers, ident),
            llvm::omp::OMPC_reduction)) {
      CheckReductionObjectTypes(objects, *ident);
    }
    using ReductionModifier = parser::OmpReductionModifier;
    if (auto *modifier{OmpGetUniqueModifier<ReductionModifier>(modifiers)}) {
      CheckReductionModifier(*modifier);
    }
  }
  CheckReductionObjects(objects, llvm::omp::Clause::OMPC_reduction);

  // If this is a worksharing construct then ensure the reduction variable
  // is not private in the parallel region that it binds to.
  if (llvm::omp::nestedReduceWorkshareAllowedSet.test(GetContext().directive)) {
    CheckSharedBindingInOuterContext(objects);
  }

  if (GetContext().directive == llvm::omp::Directive::OMPD_loop) {
    for (auto clause : GetContext().clauseInfo) {
      if (const auto *bindClause{
              std::get_if<parser::OmpClause::Bind>(&clause.second->u)}) {
        if (bindClause->v.v == parser::OmpBindClause::Binding::Teams) {
          context_.Say(GetContext().clauseSource,
              "'REDUCTION' clause not allowed with '!$OMP LOOP BIND(TEAMS)'."_err_en_US);
        }
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::InReduction &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_in_reduction);
  auto &objects{*GetOmpObjectList(x)};

  if (OmpVerifyModifiers(x.v, llvm::omp::OMPC_in_reduction,
          GetContext().clauseSource, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    const auto *ident{
        OmpGetUniqueModifier<parser::OmpReductionIdentifier>(modifiers)};
    assert(ident && "reduction-identifier is a required modifier");
    if (CheckReductionOperator(*ident, OmpGetModifierSource(modifiers, ident),
            llvm::omp::OMPC_in_reduction)) {
      CheckReductionObjectTypes(objects, *ident);
    }
  }
  CheckReductionObjects(objects, llvm::omp::Clause::OMPC_in_reduction);
}

void OmpStructureChecker::Enter(const parser::OmpClause::TaskReduction &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_task_reduction);
  auto &objects{*GetOmpObjectList(x)};

  if (OmpVerifyModifiers(x.v, llvm::omp::OMPC_task_reduction,
          GetContext().clauseSource, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    const auto *ident{
        OmpGetUniqueModifier<parser::OmpReductionIdentifier>(modifiers)};
    assert(ident && "reduction-identifier is a required modifier");
    if (CheckReductionOperator(*ident, OmpGetModifierSource(modifiers, ident),
            llvm::omp::OMPC_task_reduction)) {
      CheckReductionObjectTypes(objects, *ident);
    }
  }
  CheckReductionObjects(objects, llvm::omp::Clause::OMPC_task_reduction);
}

bool OmpStructureChecker::CheckReductionOperator(
    const parser::OmpReductionIdentifier &ident, parser::CharBlock source,
    llvm::omp::Clause clauseId) {
  unsigned version{context_.langOptions().OpenMPVersion};

  auto visitOperator{[&](const parser::DefinedOperator &dOpr) {
    if (const auto *intrinsicOp{
            std::get_if<parser::DefinedOperator::IntrinsicOperator>(&dOpr.u)}) {
      switch (*intrinsicOp) {
      case parser::DefinedOperator::IntrinsicOperator::Add:
      case parser::DefinedOperator::IntrinsicOperator::Multiply:
      case parser::DefinedOperator::IntrinsicOperator::AND:
      case parser::DefinedOperator::IntrinsicOperator::OR:
      case parser::DefinedOperator::IntrinsicOperator::EQV:
      case parser::DefinedOperator::IntrinsicOperator::NEQV:
        return true;
      case parser::DefinedOperator::IntrinsicOperator::Subtract:
        context_.Say(GetContext().clauseSource,
            "The minus reduction operator is deprecated since OpenMP 5.2 and is not supported in the REDUCTION clause."_err_en_US,
            ContextDirectiveAsFortran());
        return false;
      default:
        break;
      }
    }
    // User-defined operators are OK if there has been a declared reduction
    // for that. We mangle those names to store the user details.
    if (const auto *definedOp{std::get_if<parser::DefinedOpName>(&dOpr.u)}) {
      std::string mangled{MangleDefinedOperator(definedOp->v.symbol->name())};
      const Scope &scope{definedOp->v.symbol->owner()};
      if (const Symbol *symbol{scope.FindSymbol(mangled)}) {
        if (symbol->detailsIf<UserReductionDetails>()) {
          return true;
        }
      }
    }
    context_.Say(source, "Invalid reduction operator in %s clause."_err_en_US,
        parser::omp::GetUpperName(clauseId, version));
    return false;
  }};

  auto visitDesignator{[&](const parser::ProcedureDesignator &procD) {
    const parser::Name *name{std::get_if<parser::Name>(&procD.u)};
    bool valid{false};
    if (name && name->symbol) {
      const SourceName &realName{name->symbol->GetUltimate().name()};
      valid =
          llvm::is_contained({"max", "min", "iand", "ior", "ieor"}, realName);
      if (!valid) {
        valid = name->symbol->detailsIf<UserReductionDetails>();
      }
    }
    if (!valid) {
      context_.Say(source,
          "Invalid reduction identifier in %s clause."_err_en_US,
          parser::omp::GetUpperName(clauseId, version));
    }
    return valid;
  }};

  return common::visit(
      common::visitors{visitOperator, visitDesignator}, ident.u);
}

/// Check restrictions on objects that are common to all reduction clauses.
void OmpStructureChecker::CheckReductionObjects(
    const parser::OmpObjectList &objects, llvm::omp::Clause clauseId) {
  unsigned version{context_.langOptions().OpenMPVersion};
  SymbolSourceMap symbols;
  GetSymbolsInObjectList(objects, symbols);

  // Array sections must be a contiguous storage, have non-zero length.
  for (const parser::OmpObject &object : objects.v) {
    CheckIfContiguous(object);
  }
  CheckReductionArraySection(objects, clauseId);
  // An object must be definable.
  CheckDefinableObjects(symbols, clauseId);
  // Procedure pointers are not allowed.
  CheckProcedurePointer(symbols, clauseId);
  // Pointers must not have INTENT(IN).
  CheckIntentInPointer(symbols, clauseId);

  // Disallow common blocks.
  // Iterate on objects because `GetSymbolsInObjectList` expands common block
  // names into the lists of their members.
  for (const parser::OmpObject &object : objects.v) {
    auto *symbol{GetObjectSymbol(object)};
    if (symbol && IsCommonBlock(*symbol)) {
      auto source{GetObjectSource(object)};
      context_.Say(source ? *source : GetContext().clauseSource,
          "Common block names are not allowed in %s clause"_err_en_US,
          parser::omp::GetUpperName(clauseId, version));
    }
  }

  // Denied in all current versions of the standard because structure components
  // are not definable (i.e. they are expressions not variables).
  // Object cannot be a part of another object (except array elements).
  CheckStructureComponent(objects, clauseId);

  if (version >= 50) {
    // If object is an array section or element, the base expression must be
    // a language identifier.
    for (const parser::OmpObject &object : objects.v) {
      if (auto *elem{GetArrayElementFromObj(object)}) {
        const parser::DataRef &base = elem->Base();
        if (!std::holds_alternative<parser::Name>(base.u)) {
          auto source{GetObjectSource(object)};
          context_.Say(source ? *source : GetContext().clauseSource,
              "The base expression of an array element or section in %s clause must be an identifier"_err_en_US,
              parser::omp::GetUpperName(clauseId, version));
        }
      }
    }
    // Type parameter inquiries are not allowed.
    for (const parser::OmpObject &object : objects.v) {
      if (auto *dataRef{GetDataRefFromObj(object)}) {
        if (IsDataRefTypeParamInquiry(dataRef)) {
          auto source{GetObjectSource(object)};
          context_.Say(source ? *source : GetContext().clauseSource,
              "Type parameter inquiry is not permitted in %s clause"_err_en_US,
              parser::omp::GetUpperName(clauseId, version));
        }
      }
    }
  }
}

static bool CheckSymbolSupportsType(const Scope &scope,
    const parser::CharBlock &name, const DeclTypeSpec &type) {
  if (const auto *symbol{scope.FindSymbol(name)}) {
    if (const auto *reductionDetails{
            symbol->detailsIf<UserReductionDetails>()}) {
      return reductionDetails->SupportsType(type);
    }
  }
  // Look through module scopes in the global scope.
  // This covers reductions declared in a module and used via USE association
  const SemanticsContext &semCtx{scope.context()};
  Scope &global = const_cast<SemanticsContext &>(semCtx).globalScope();
  for (const Scope &child : global.children()) {
    if (child.kind() == Scope::Kind::Module) {
      if (const auto *symbol{child.FindSymbol(name)}) {
        if (const auto *reductionDetails{
                symbol->detailsIf<UserReductionDetails>()}) {
          return reductionDetails->SupportsType(type);
        }
      }
    }
  }
  return false;
}

static bool IsReductionAllowedForType(
    const parser::OmpReductionIdentifier &ident, const DeclTypeSpec &type,
    bool cannotBeBuiltinReduction, const Scope &scope,
    SemanticsContext &context) {
  auto isLogical{[](const DeclTypeSpec &type) -> bool {
    return type.category() == DeclTypeSpec::Logical;
  }};
  auto isCharacter{[](const DeclTypeSpec &type) -> bool {
    return type.category() == DeclTypeSpec::Character;
  }};

  auto checkOperator{[&](const parser::DefinedOperator &dOpr) {
    if (const auto *intrinsicOp{
            std::get_if<parser::DefinedOperator::IntrinsicOperator>(&dOpr.u)}) {
      if (cannotBeBuiltinReduction) {
        return false;
      }

      // OMP5.2: The type [...] of a list item that appears in a
      // reduction clause must be valid for the combiner expression
      // See F2023: Table 10.2
      // .LT., .LE., .GT., .GE. are handled as procedure designators
      // below.
      switch (*intrinsicOp) {
      case parser::DefinedOperator::IntrinsicOperator::Multiply:
      case parser::DefinedOperator::IntrinsicOperator::Add:
      case parser::DefinedOperator::IntrinsicOperator::Subtract:
        if (type.IsNumeric(TypeCategory::Integer) ||
            type.IsNumeric(TypeCategory::Real) ||
            type.IsNumeric(TypeCategory::Complex))
          return true;
        break;

      case parser::DefinedOperator::IntrinsicOperator::AND:
      case parser::DefinedOperator::IntrinsicOperator::OR:
      case parser::DefinedOperator::IntrinsicOperator::EQV:
      case parser::DefinedOperator::IntrinsicOperator::NEQV:
        if (isLogical(type)) {
          return true;
        }
        break;

      // Reduction identifier is not in OMP5.2 Table 5.2
      default:
        DIE("This should have been caught in CheckIntrinsicOperator");
        return false;
      }
      parser::CharBlock name{MakeNameFromOperator(*intrinsicOp, context)};
      return CheckSymbolSupportsType(scope, name, type);
    } else if (const auto *definedOp{
                   std::get_if<parser::DefinedOpName>(&dOpr.u)}) {
      return CheckSymbolSupportsType(
          scope, MangleDefinedOperator(definedOp->v.symbol->name()), type);
    }
    llvm_unreachable(
        "A DefinedOperator is either a DefinedOpName or an IntrinsicOperator");
  }};

  auto checkDesignator{[&](const parser::ProcedureDesignator &procD) {
    const parser::Name *name{std::get_if<parser::Name>(&procD.u)};
    CHECK(name && name->symbol);
    if (name && name->symbol) {
      const SourceName &realName{name->symbol->GetUltimate().name()};
      // OMP5.2: The type [...] of a list item that appears in a
      // reduction clause must be valid for the combiner expression
      if (realName == "iand" || realName == "ior" || realName == "ieor") {
        // IAND: arguments must be integers: F2023 16.9.100
        // IEOR: arguments must be integers: F2023 16.9.106
        // IOR: arguments must be integers: F2023 16.9.111
        if (type.IsNumeric(TypeCategory::Integer) &&
            !cannotBeBuiltinReduction) {
          return true;
        }
      } else if (realName == "max" || realName == "min") {
        // MAX: arguments must be integer, real, or character:
        // F2023 16.9.135
        // MIN: arguments must be integer, real, or character:
        // F2023 16.9.141
        if ((type.IsNumeric(TypeCategory::Integer) ||
                type.IsNumeric(TypeCategory::Real) || isCharacter(type)) &&
            !cannotBeBuiltinReduction) {
          return true;
        }
      }

      // If we get here, it may be a user declared reduction, so check
      // if the symbol has UserReductionDetails, and if so, the type is
      // supported.
      if (const auto *reductionDetails{
              name->symbol->detailsIf<UserReductionDetails>()}) {
        return reductionDetails->SupportsType(type);
      }

      // We also need to check for mangled names (max, min, iand, ieor and ior)
      // and then check if the type is there.
      parser::CharBlock mangledName{MangleSpecialFunctions(name->source)};
      return CheckSymbolSupportsType(scope, mangledName, type);
    }
    // Everything else is "not matching type".
    return false;
  }};

  return common::visit(
      common::visitors{checkOperator, checkDesignator}, ident.u);
}

void OmpStructureChecker::CheckReductionObjectTypes(
    const parser::OmpObjectList &objects,
    const parser::OmpReductionIdentifier &ident) {
  SymbolSourceMap symbols;
  GetSymbolsInObjectList(objects, symbols);

  for (auto &[symbol, source] : symbols) {
    // Built in reductions require types which can be used in their initializer
    // and combiner expressions. For example, for +:
    // r = 0; r = r + r2
    // But it might be valid to use these with DECLARE REDUCTION.
    // Assumed size is already caught elsewhere.
    bool cannotBeBuiltinReduction{IsAssumedRank(*symbol)};
    if (auto *type{symbol->GetType()}) {
      const auto &scope{context_.FindScope(symbol->name())};
      if (!IsReductionAllowedForType(
              ident, *type, cannotBeBuiltinReduction, scope, context_)) {
        context_.Say(source,
            "The type of '%s' is incompatible with the reduction operator."_err_en_US,
            symbol->name());
      }
    } else {
      assert(IsProcedurePointer(*symbol) && "Unexpected symbol properties");
    }
  }
}

void OmpStructureChecker::CheckReductionModifier(
    const parser::OmpReductionModifier &modifier) {
  unsigned version{context_.langOptions().OpenMPVersion};

  using ReductionModifier = parser::OmpReductionModifier;
  if (modifier.v == ReductionModifier::Value::Default) {
    // The default one is always ok.
    return;
  }
  const DirectiveContext &dirCtx{GetContext()};
  if (dirCtx.directive == llvm::omp::Directive::OMPD_loop ||
      dirCtx.directive == llvm::omp::Directive::OMPD_taskloop) {
    // [5.2:257:33-34]
    // If a reduction-modifier is specified in a reduction clause that
    // appears on the directive, then the reduction modifier must be
    // default.
    // [5.2:268:16]
    // The reduction-modifier must be default.
    context_.Say(GetContext().clauseSource,
        "REDUCTION modifier on %s directive must be DEFAULT"_err_en_US,
        parser::omp::GetUpperName(dirCtx.directive, version));
    return;
  }
  if (modifier.v == ReductionModifier::Value::Task) {
    // "Task" is only allowed on worksharing or "parallel" directive.
    static llvm::omp::Directive worksharing[]{
        llvm::omp::Directive::OMPD_do, //
        llvm::omp::Directive::OMPD_scope, //
        llvm::omp::Directive::OMPD_sections,
        // There are more worksharing directives, but they do not apply:
        // "for" is C++ only,
        // "single" and "workshare" don't allow reduction clause,
        // "loop" has different restrictions (checked above).
    };
    if (dirCtx.directive != llvm::omp::Directive::OMPD_parallel &&
        !llvm::is_contained(worksharing, dirCtx.directive)) {
      context_.Say(GetContext().clauseSource,
          "Modifier 'TASK' on REDUCTION clause is only allowed with "
          "PARALLEL or worksharing directive"_err_en_US);
    }
  } else if (modifier.v == ReductionModifier::Value::Inscan) {
    // "Inscan" is only allowed on worksharing-loop, worksharing-loop simd,
    // or "simd" directive.
    // The worksharing-loop directives are OMPD_do and OMPD_for. Only the
    // former is allowed in Fortran.
    if (!llvm::omp::scanParentAllowedSet.test(dirCtx.directive)) {
      context_.Say(GetContext().clauseSource,
          "Modifier 'INSCAN' on REDUCTION clause is only allowed with "
          "WORKSHARING LOOP, WORKSHARING LOOP SIMD, "
          "or SIMD directive"_err_en_US);
    }
  } else {
    // Catch-all for potential future modifiers to make sure that this
    // function is up-to-date.
    context_.Say(GetContext().clauseSource,
        "Unexpected modifier on REDUCTION clause"_err_en_US);
  }
}

void OmpStructureChecker::CheckReductionArraySection(
    const parser::OmpObjectList &ompObjectList, llvm::omp::Clause clauseId) {
  for (const auto &ompObject : ompObjectList.v) {
    if (const auto *dataRef{parser::Unwrap<parser::DataRef>(ompObject)}) {
      if (const auto *arrayElement{
              parser::Unwrap<parser::ArrayElement>(ompObject)}) {
        CheckArraySection(*arrayElement, GetLastName(*dataRef), clauseId);
      }
    }
  }
}

void OmpStructureChecker::CheckSharedBindingInOuterContext(
    const parser::OmpObjectList &redObjectList) {
  unsigned version{context_.langOptions().OpenMPVersion};
  //  TODO: Verify the assumption here that the immediately enclosing region is
  //  the parallel region to which the worksharing construct having reduction
  //  binds to.
  if (auto *enclosingContext{GetEnclosingDirContext()}) {
    for (auto it : enclosingContext->clauseInfo) {
      llvmOmpClause type = it.first;
      const auto *clause = it.second;
      if (llvm::omp::privateReductionSet.test(type)) {
        if (const auto *objList{GetOmpObjectList(*clause)}) {
          for (const auto &ompObject : objList->v) {
            if (const auto *name{parser::Unwrap<parser::Name>(ompObject)}) {
              if (const auto *symbol{name->symbol}) {
                for (const auto &redOmpObject : redObjectList.v) {
                  if (const auto *rname{
                          parser::Unwrap<parser::Name>(redOmpObject)}) {
                    if (const auto *rsymbol{rname->symbol}) {
                      if (rsymbol->name() == symbol->name()) {
                        context_.Say(GetContext().clauseSource,
                            "%s variable '%s' is %s in outer context must"
                            " be shared in the parallel regions to which any"
                            " of the worksharing regions arising from the "
                            "worksharing construct bind."_err_en_US,
                            parser::omp::GetUpperName(
                                llvm::omp::Clause::OMPC_reduction, version),
                            symbol->name(),
                            parser::omp::GetUpperName(type, version));
                      }
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Shared &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_shared);
  CheckVarIsNotPartOfAnotherVar(GetContext().clauseSource, x.v, "SHARED");
  CheckCrayPointee(x.v, "SHARED");
}
void OmpStructureChecker::Enter(const parser::OmpClause::Private &x) {
  SymbolSourceMap symbols;
  GetSymbolsInObjectList(x.v, symbols);
  CheckAllowedClause(llvm::omp::Clause::OMPC_private);
  CheckVarIsNotPartOfAnotherVar(GetContext().clauseSource, x.v, "PRIVATE");
  CheckIntentInPointer(symbols, llvm::omp::Clause::OMPC_private);
  CheckCrayPointee(x.v, "PRIVATE");
  CheckAssumedSizeArray(symbols, llvm::omp::Clause::OMPC_private);
}

void OmpStructureChecker::Enter(const parser::OmpClause::Nowait &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_nowait);
}

bool OmpStructureChecker::IsDataRefTypeParamInquiry(
    const parser::DataRef *dataRef) {
  bool dataRefIsTypeParamInquiry{false};
  if (const auto *structComp{
          parser::Unwrap<parser::StructureComponent>(dataRef)}) {
    if (const auto *compSymbol{structComp->Component().symbol}) {
      if (const auto *compSymbolMiscDetails{
              std::get_if<MiscDetails>(&compSymbol->details())}) {
        const auto detailsKind = compSymbolMiscDetails->kind();
        dataRefIsTypeParamInquiry =
            (detailsKind == MiscDetails::Kind::KindParamInquiry ||
                detailsKind == MiscDetails::Kind::LenParamInquiry);
      } else if (compSymbol->has<TypeParamDetails>()) {
        dataRefIsTypeParamInquiry = true;
      }
    }
  }
  return dataRefIsTypeParamInquiry;
}

void OmpStructureChecker::CheckVarIsNotPartOfAnotherVar(
    const parser::CharBlock &source, const parser::OmpObjectList &objList,
    llvm::StringRef clause) {
  for (const auto &ompObject : objList.v) {
    CheckVarIsNotPartOfAnotherVar(source, ompObject, clause);
  }
}

void OmpStructureChecker::CheckVarIsNotPartOfAnotherVar(
    const parser::CharBlock &source, const parser::OmpObject &ompObject,
    llvm::StringRef clause) {
  common::visit(
      common::visitors{
          [&](const parser::Designator &designator) {
            if (const auto *dataRef{
                    std::get_if<parser::DataRef>(&designator.u)}) {
              if (IsDataRefTypeParamInquiry(dataRef)) {
                context_.Say(source,
                    "A type parameter inquiry cannot appear on the %s directive"_err_en_US,
                    ContextDirectiveAsFortran());
              } else if (parser::Unwrap<parser::StructureComponent>(
                             ompObject) ||
                  parser::Unwrap<parser::ArrayElement>(ompObject)) {
                if (llvm::omp::nonPartialVarSet.test(GetContext().directive)) {
                  context_.Say(source,
                      "A variable that is part of another variable (as an array or structure element) cannot appear on the %s directive"_err_en_US,
                      ContextDirectiveAsFortran());
                } else {
                  context_.Say(source,
                      "A variable that is part of another variable (as an array or structure element) cannot appear in a %s clause"_err_en_US,
                      clause.data());
                }
              }
            }
          },
          [&](const parser::Name &name) {},
          [&](const parser::OmpObject::Invalid &invalid) {},
      },
      ompObject.u);
}

void OmpStructureChecker::Enter(const parser::OmpClause::Firstprivate &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_firstprivate);

  CheckVarIsNotPartOfAnotherVar(GetContext().clauseSource, x.v, "FIRSTPRIVATE");
  CheckCrayPointee(x.v, "FIRSTPRIVATE");
  CheckIsLoopIvPartOfClause(llvmOmpClause::OMPC_firstprivate, x.v);

  SymbolSourceMap currSymbols;
  GetSymbolsInObjectList(x.v, currSymbols);
  CheckCopyingPolymorphicAllocatable(
      currSymbols, llvm::omp::Clause::OMPC_firstprivate);
  CheckAssumedSizeArray(currSymbols, llvm::omp::Clause::OMPC_firstprivate);

  DirectivesClauseTriple dirClauseTriple;
  // Check firstprivate variables in worksharing constructs
  dirClauseTriple.emplace(llvm::omp::Directive::OMPD_do,
      std::make_pair(
          llvm::omp::Directive::OMPD_parallel, llvm::omp::privateReductionSet));
  dirClauseTriple.emplace(llvm::omp::Directive::OMPD_sections,
      std::make_pair(
          llvm::omp::Directive::OMPD_parallel, llvm::omp::privateReductionSet));
  dirClauseTriple.emplace(llvm::omp::Directive::OMPD_single,
      std::make_pair(
          llvm::omp::Directive::OMPD_parallel, llvm::omp::privateReductionSet));
  // Check firstprivate variables in distribute construct
  dirClauseTriple.emplace(llvm::omp::Directive::OMPD_distribute,
      std::make_pair(
          llvm::omp::Directive::OMPD_teams, llvm::omp::privateReductionSet));
  dirClauseTriple.emplace(llvm::omp::Directive::OMPD_distribute,
      std::make_pair(llvm::omp::Directive::OMPD_target_teams,
          llvm::omp::privateReductionSet));
  // Check firstprivate variables in task and taskloop constructs
  dirClauseTriple.emplace(llvm::omp::Directive::OMPD_task,
      std::make_pair(llvm::omp::Directive::OMPD_parallel,
          OmpClauseSet{llvm::omp::Clause::OMPC_reduction}));
  dirClauseTriple.emplace(llvm::omp::Directive::OMPD_taskloop,
      std::make_pair(llvm::omp::Directive::OMPD_parallel,
          OmpClauseSet{llvm::omp::Clause::OMPC_reduction}));

  CheckPrivateSymbolsInOuterCxt(
      currSymbols, dirClauseTriple, llvm::omp::Clause::OMPC_firstprivate);
}

void OmpStructureChecker::CheckIsLoopIvPartOfClause(
    llvmOmpClause clause, const parser::OmpObjectList &ompObjectList) {
  unsigned version{context_.langOptions().OpenMPVersion};
  for (const auto &ompObject : ompObjectList.v) {
    if (const parser::Name *name{parser::Unwrap<parser::Name>(ompObject)}) {
      if (name->symbol == GetContext().loopIV) {
        context_.Say(name->source,
            "DO iteration variable %s is not allowed in %s clause."_err_en_US,
            name->ToString(), parser::omp::GetUpperName(clause, version));
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Align &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_align);
  if (const auto &v{GetIntValue(x.v.v)}) {
    if (*v <= 0) {
      context_.Say(GetContext().clauseSource,
          "The alignment should be positive"_err_en_US);
    } else if (!llvm::isPowerOf2_64(*v)) {
      context_.Say(GetContext().clauseSource,
          "The alignment should be a power of 2"_err_en_US);
    }
  }
}

// Restrictions specific to each clause are implemented apart from the
// generalized restrictions.
void OmpStructureChecker::Enter(const parser::OmpClause::Aligned &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_aligned);
  if (OmpVerifyModifiers(
          x.v, llvm::omp::OMPC_aligned, GetContext().clauseSource, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    if (auto *align{OmpGetUniqueModifier<parser::OmpAlignment>(modifiers)}) {
      const auto &v{GetIntValue(align->v)};
      if (!v || *v <= 0) {
        context_.Say(OmpGetModifierSource(modifiers, align),
            "The alignment value should be a constant positive integer"_err_en_US);
      } else if (((*v) & (*v - 1)) != 0) {
        context_.Warn(common::UsageWarning::OpenMPUsage,
            OmpGetModifierSource(modifiers, align),
            "Alignment is not a power of 2, Aligned clause will be ignored"_warn_en_US);
      }
    }
  }
  // 2.8.1 TODO: list-item attribute check
}

void OmpStructureChecker::Enter(const parser::OmpClause::Defaultmap &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_defaultmap);
  unsigned version{context_.langOptions().OpenMPVersion};
  using ImplicitBehavior = parser::OmpDefaultmapClause::ImplicitBehavior;
  auto behavior{std::get<ImplicitBehavior>(x.v.t)};
  if (version <= 45) {
    if (behavior != ImplicitBehavior::Tofrom) {
      context_.Say(GetContext().clauseSource,
          "%s is not allowed in %s, %s"_warn_en_US,
          parser::ToUpperCaseLetters(
              parser::OmpDefaultmapClause::EnumToString(behavior)),
          ThisVersion(version), TryVersion(50));
    }
  }
  if (!OmpVerifyModifiers(x.v, llvm::omp::OMPC_defaultmap,
          GetContext().clauseSource, context_)) {
    // If modifier verification fails, return early.
    return;
  }
  auto &modifiers{OmpGetModifiers(x.v)};
  auto *maybeCategory{
      OmpGetUniqueModifier<parser::OmpVariableCategory>(modifiers)};
  if (maybeCategory) {
    using VariableCategory = parser::OmpVariableCategory;
    VariableCategory::Value category{maybeCategory->v};
    unsigned tryVersion{0};
    if (version <= 45 && category != VariableCategory::Value::Scalar) {
      tryVersion = 50;
    }
    if (version < 52 && category == VariableCategory::Value::All) {
      tryVersion = 52;
    }
    if (tryVersion) {
      context_.Say(GetContext().clauseSource,
          "%s is not allowed in %s, %s"_warn_en_US,
          parser::ToUpperCaseLetters(VariableCategory::EnumToString(category)),
          ThisVersion(version), TryVersion(tryVersion));
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::If &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_if);
  unsigned version{context_.langOptions().OpenMPVersion};
  llvm::omp::Directive dir{GetContext().directive};

  auto isConstituent{[](llvm::omp::Directive dir, llvm::omp::Directive part) {
    using namespace llvm::omp;
    llvm::ArrayRef<Directive> dirLeafs{getLeafConstructsOrSelf(dir)};
    llvm::ArrayRef<Directive> partLeafs{getLeafConstructsOrSelf(part)};
    // Maybe it's sufficient to check if every leaf of `part` is also a leaf
    // of `dir`, but to be safe check if `partLeafs` is a sub-sequence of
    // `dirLeafs`.
    size_t dirSize{dirLeafs.size()}, partSize{partLeafs.size()};
    // Find the first leaf from `part` in `dir`.
    if (auto first = llvm::find(dirLeafs, partLeafs.front());
        first != dirLeafs.end()) {
      // A leaf can only appear once in a compound directive, so if `part`
      // is a subsequence of `dir`, it must start here.
      size_t firstPos{
          static_cast<size_t>(std::distance(dirLeafs.begin(), first))};
      llvm::ArrayRef<Directive> subSeq{
          first, std::min<size_t>(dirSize - firstPos, partSize)};
      return subSeq == partLeafs;
    }
    return false;
  }};

  if (OmpVerifyModifiers(
          x.v, llvm::omp::OMPC_if, GetContext().clauseSource, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    if (auto *dnm{OmpGetUniqueModifier<parser::OmpDirectiveNameModifier>(
            modifiers)}) {
      llvm::omp::Directive sub{dnm->v};
      std::string subName{parser::omp::GetUpperName(sub, version)};
      std::string dirName{parser::omp::GetUpperName(dir, version)};

      parser::CharBlock modifierSource{OmpGetModifierSource(modifiers, dnm)};
      auto desc{OmpGetDescriptor<parser::OmpDirectiveNameModifier>()};
      std::string modName{desc.name.str()};

      if (!isConstituent(dir, sub)) {
        context_
            .Say(modifierSource,
                "%s is not a constituent of the %s directive"_err_en_US,
                subName, dirName)
            .Attach(GetContext().directiveSource,
                "Cannot apply to directive"_en_US);
      } else {
        static llvm::omp::Directive valid45[]{
            llvm::omp::OMPD_cancel, //
            llvm::omp::OMPD_parallel, //
            /* OMP 5.0+ also allows OMPD_simd */
            llvm::omp::OMPD_target, //
            llvm::omp::OMPD_target_data, //
            llvm::omp::OMPD_target_enter_data, //
            llvm::omp::OMPD_target_exit_data, //
            llvm::omp::OMPD_target_update, //
            llvm::omp::OMPD_task, //
            llvm::omp::OMPD_taskloop, //
            /* OMP 5.2+ also allows OMPD_teams */
        };
        if (version < 50 && sub == llvm::omp::OMPD_simd) {
          context_.Say(modifierSource,
              "%s is not allowed as '%s' in %s, %s"_warn_en_US, subName,
              modName, ThisVersion(version), TryVersion(50));
        } else if (version < 52 && sub == llvm::omp::OMPD_teams) {
          context_.Say(modifierSource,
              "%s is not allowed as '%s' in %s, %s"_warn_en_US, subName,
              modName, ThisVersion(version), TryVersion(52));
        } else if (!llvm::is_contained(valid45, sub) &&
            sub != llvm::omp::OMPD_simd && sub != llvm::omp::OMPD_teams) {
          context_.Say(modifierSource,
              "%s is not allowed as '%s' in %s"_err_en_US, subName, modName,
              ThisVersion(version));
        }
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Detach &x) {
  unsigned version{context_.langOptions().OpenMPVersion};
  if (version >= 52) {
    SetContextClauseInfo(llvm::omp::Clause::OMPC_detach);
  } else {
    // OpenMP 5.0: 2.10.1 Task construct restrictions
    CheckAllowedClause(llvm::omp::Clause::OMPC_detach);
  }
  // OpenMP 5.2: 12.5.2 Detach clause restrictions
  if (version >= 52) {
    CheckVarIsNotPartOfAnotherVar(GetContext().clauseSource, x.v.v, "DETACH");
  }

  if (const auto *name{parser::Unwrap<parser::Name>(x.v.v)}) {
    if (version >= 52 && IsPointer(*name->symbol)) {
      context_.Say(GetContext().clauseSource,
          "The event-handle: `%s` must not have the POINTER attribute"_err_en_US,
          name->ToString());
    }
    if (!name->symbol->GetType()->IsNumeric(TypeCategory::Integer)) {
      context_.Say(GetContext().clauseSource,
          "The event-handle: `%s` must be of type integer(kind=omp_event_handle_kind)"_err_en_US,
          name->ToString());
    }
  }
}

void OmpStructureChecker::CheckAllowedMapTypes(parser::OmpMapType::Value type,
    llvm::ArrayRef<parser::OmpMapType::Value> allowed) {
  if (llvm::is_contained(allowed, type)) {
    return;
  }

  llvm::SmallVector<std::string> names;
  llvm::transform(
      allowed, std::back_inserter(names), [](parser::OmpMapType::Value val) {
        return parser::ToUpperCaseLetters(
            parser::OmpMapType::EnumToString(val));
      });
  llvm::sort(names);
  context_.Say(GetContext().clauseSource,
      "Only the %s map types are permitted for MAP clauses on the %s directive"_err_en_US,
      llvm::join(names, ", "), ContextDirectiveAsFortran());
}

void OmpStructureChecker::Enter(const parser::OmpClause::Map &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_map);
  if (!OmpVerifyModifiers(
          x.v, llvm::omp::OMPC_map, GetContext().clauseSource, context_)) {
    return;
  }

  auto &modifiers{OmpGetModifiers(x.v)};
  unsigned version{context_.langOptions().OpenMPVersion};
  if (auto commas{std::get<bool>(x.v.t)}; !commas && version >= 52) {
    context_.Say(GetContext().clauseSource,
        "The specification of modifiers without comma separators for the "
        "'MAP' clause has been deprecated in OpenMP 5.2"_port_en_US);
  }
  if (auto *iter{OmpGetUniqueModifier<parser::OmpIterator>(modifiers)}) {
    CheckIteratorModifier(*iter);
  }

  using Directive = llvm::omp::Directive;
  Directive dir{GetContext().directive};
  llvm::ArrayRef<Directive> leafs{llvm::omp::getLeafConstructsOrSelf(dir)};
  parser::OmpMapType::Value mapType{parser::OmpMapType::Value::Storage};
  const parser::OmpObjectList &objects{DEREF(GetOmpObjectList(x))};

  if (auto *type{OmpGetUniqueModifier<parser::OmpMapType>(modifiers)}) {
    using Value = parser::OmpMapType::Value;
    mapType = type->v;

    static auto isValidForVersion{
        [](parser::OmpMapType::Value t, unsigned version) {
          switch (t) {
          case parser::OmpMapType::Value::Delete:
            return version < 60;
          case parser::OmpMapType::Value::Alloc:
          case parser::OmpMapType::Value::Release:
            return version <= 60;
          case parser::OmpMapType::Value::Storage:
            return version >= 60;
          default:
            return true;
          }
        }};

    llvm::SmallVector<parser::OmpMapType::Value> mapEnteringTypes{[&]() {
      llvm::SmallVector<parser::OmpMapType::Value> result;
      for (size_t i{0}; i != parser::OmpMapType::Value_enumSize; ++i) {
        auto t{static_cast<parser::OmpMapType::Value>(i)};
        if (isValidForVersion(t, version) && IsMapEnteringType(t)) {
          result.push_back(t);
        }
      }
      return result;
    }()};
    llvm::SmallVector<parser::OmpMapType::Value> mapExitingTypes{[&]() {
      llvm::SmallVector<parser::OmpMapType::Value> result;
      for (size_t i{0}; i != parser::OmpMapType::Value_enumSize; ++i) {
        auto t{static_cast<parser::OmpMapType::Value>(i)};
        if (isValidForVersion(t, version) && IsMapExitingType(t)) {
          result.push_back(t);
        }
      }
      return result;
    }()};

    if (llvm::is_contained(leafs, Directive::OMPD_target) ||
        llvm::is_contained(leafs, Directive::OMPD_target_data)) {
      if (version >= 60) {
        // Map types listed in the decay table. [6.0:276]
        CheckAllowedMapTypes(type->v,
            {Value::Alloc, Value::Release, Value::Storage, Value::From,
                Value::To, Value::Tofrom});
      } else {
        CheckAllowedMapTypes(
            type->v, {Value::Alloc, Value::From, Value::To, Value::Tofrom});
      }
    } else if (llvm::is_contained(leafs, Directive::OMPD_target_enter_data)) {
      CheckAllowedMapTypes(type->v, mapEnteringTypes);
    } else if (llvm::is_contained(leafs, Directive::OMPD_target_exit_data)) {
      CheckAllowedMapTypes(type->v, mapExitingTypes);
    }
  }

  if (auto *attach{
          OmpGetUniqueModifier<parser::OmpAttachModifier>(modifiers)}) {
    bool mapEnteringConstructOrMapper{
        llvm::is_contained(leafs, Directive::OMPD_target) ||
        llvm::is_contained(leafs, Directive::OMPD_target_data) ||
        llvm::is_contained(leafs, Directive::OMPD_target_enter_data) ||
        llvm::is_contained(leafs, Directive::OMPD_declare_mapper)};

    if (!mapEnteringConstructOrMapper || !IsMapEnteringType(mapType)) {
      const auto &desc{OmpGetDescriptor<parser::OmpAttachModifier>()};
      context_.Say(OmpGetModifierSource(modifiers, attach),
          "The '%s' modifier can only appear on a map-entering construct or on a DECLARE_MAPPER directive"_err_en_US,
          desc.name.str());
    }

    auto hasBasePointer{[&](const SomeExpr &item) {
      SymbolVector symbols{evaluate::GetSymbolVector(item)};
      return llvm::any_of(
          symbols, [](SymbolRef s) { return IsPointer(s.get()); });
    }};

    evaluate::ExpressionAnalyzer ea{context_};
    auto restore{ea.AllowWholeAssumedSizeArray(true)};
    for (auto &object : objects.v) {
      if (const parser::Designator *d{GetDesignatorFromObj(object)}) {
        if (auto &&expr{ea.Analyze(*d)}) {
          if (hasBasePointer(*expr)) {
            continue;
          }
        }
      }
      auto source{GetObjectSource(object)};
      context_.Say(source ? *source : GetContext().clauseSource,
          "A list-item that appears in a map clause with the ATTACH modifier must have a base-pointer"_err_en_US);
    }
  }

  auto &&typeMods{
      OmpGetRepeatableModifier<parser::OmpMapTypeModifier>(modifiers)};
  struct Less {
    using Iterator = decltype(typeMods.begin());
    bool operator()(Iterator a, Iterator b) const {
      const parser::OmpMapTypeModifier *pa = *a;
      const parser::OmpMapTypeModifier *pb = *b;
      return pa->v < pb->v;
    }
  };
  if (auto maybeIter{FindDuplicate<Less>(typeMods)}) {
    context_.Say(GetContext().clauseSource,
        "Duplicate map-type-modifier entry '%s' will be ignored"_warn_en_US,
        parser::ToUpperCaseLetters(
            parser::OmpMapTypeModifier::EnumToString((**maybeIter)->v)));
  }

  if (version < 60) {
    for (const parser::OmpObject &object : objects.v) {
      if (IsWholeAssumedSizeArray(object)) {
        auto maybeSource{GetObjectSource(object)};
        context_.Say(maybeSource.value_or(GetContext().clauseSource),
            "Whole assumed-size arrays are not allowed on MAP clause"_err_en_US);
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Schedule &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_schedule);
  const parser::OmpScheduleClause &scheduleClause = x.v;
  if (!OmpVerifyModifiers(scheduleClause, llvm::omp::OMPC_schedule,
          GetContext().clauseSource, context_)) {
    return;
  }

  // 2.7 Loop Construct Restriction
  if (llvm::omp::allDoSet.test(GetContext().directive)) {
    auto &modifiers{OmpGetModifiers(scheduleClause)};
    auto kind{std::get<parser::OmpScheduleClause::Kind>(scheduleClause.t)};
    auto &chunk{
        std::get<std::optional<parser::ScalarIntExpr>>(scheduleClause.t)};
    if (chunk) {
      if (kind == parser::OmpScheduleClause::Kind::Runtime ||
          kind == parser::OmpScheduleClause::Kind::Auto) {
        context_.Say(GetContext().clauseSource,
            "When SCHEDULE clause has %s specified, "
            "it must not have chunk size specified"_err_en_US,
            parser::ToUpperCaseLetters(
                parser::OmpScheduleClause::EnumToString(kind)));
      }
      if (const auto &chunkExpr{std::get<std::optional<parser::ScalarIntExpr>>(
              scheduleClause.t)}) {
        RequiresPositiveParameter(
            llvm::omp::Clause::OMPC_schedule, *chunkExpr, "chunk size");
      }
    }

    auto *ordering{
        OmpGetUniqueModifier<parser::OmpOrderingModifier>(modifiers)};
    if (ordering &&
        ordering->v == parser::OmpOrderingModifier::Value::Nonmonotonic) {
      if (kind != parser::OmpScheduleClause::Kind::Dynamic &&
          kind != parser::OmpScheduleClause::Kind::Guided) {
        context_.Say(GetContext().clauseSource,
            "The NONMONOTONIC modifier can only be specified with "
            "SCHEDULE(DYNAMIC) or SCHEDULE(GUIDED)"_err_en_US);
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Device &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_device);
  const parser::OmpDeviceClause &deviceClause{x.v};
  const auto &device{std::get<parser::ScalarIntExpr>(deviceClause.t)};
  unsigned version{context_.langOptions().OpenMPVersion};
  RequiresPositiveParameter(
      llvm::omp::Clause::OMPC_device, device, "device expression");
  llvm::omp::Directive dir{GetContext().directive};

  if (OmpVerifyModifiers(deviceClause, llvm::omp::OMPC_device,
          GetContext().clauseSource, context_)) {
    auto &modifiers{OmpGetModifiers(deviceClause)};

    if (auto *deviceMod{
            OmpGetUniqueModifier<parser::OmpDeviceModifier>(modifiers)}) {
      using Value = parser::OmpDeviceModifier::Value;
      if (dir != llvm::omp::OMPD_target && deviceMod->v == Value::Ancestor) {
        auto name{OmpGetDescriptor<parser::OmpDeviceModifier>().name};
        context_.Say(OmpGetModifierSource(modifiers, deviceMod),
            "The ANCESTOR %s must not appear on the DEVICE clause on any directive other than the TARGET construct. Found on %s construct."_err_en_US,
            name.str(), parser::omp::GetUpperName(dir, version));
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Depend &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_depend);
  llvm::omp::Directive dir{GetContext().directive};
  unsigned version{context_.langOptions().OpenMPVersion};

  auto *doaDep{std::get_if<parser::OmpDoacross>(&x.v.u)};
  auto *taskDep{std::get_if<parser::OmpDependClause::TaskDep>(&x.v.u)};
  assert(((doaDep == nullptr) != (taskDep == nullptr)) &&
      "Unexpected alternative in update clause");

  if (doaDep) {
    CheckDoacross(*doaDep);
    CheckDependenceType(doaDep->GetDepType());
  } else {
    using Modifier = parser::OmpDependClause::TaskDep::Modifier;
    auto &modifiers{std::get<std::optional<std::list<Modifier>>>(taskDep->t)};
    if (!modifiers) {
      context_.Say(GetContext().clauseSource,
          "A DEPEND clause on a TASK construct must have a valid task dependence type"_err_en_US);
      return;
    }
    CheckTaskDependenceType(taskDep->GetTaskDepType());
  }

  if (dir == llvm::omp::OMPD_depobj) {
    // [5.0:255:11], [5.1:288:3]
    // A depend clause on a depobj construct must not have source, sink [or
    // depobj](5.0) as dependence-type.
    if (version >= 50) {
      bool invalidDep{false};
      if (taskDep) {
        if (version == 50) {
          invalidDep = taskDep->GetTaskDepType() ==
              parser::OmpTaskDependenceType::Value::Depobj;
        }
      } else {
        invalidDep = true;
      }
      if (invalidDep) {
        context_.Say(GetContext().clauseSource,
            "A DEPEND clause on a DEPOBJ construct must not have %s as dependence type"_err_en_US,
            version == 50 ? "SINK, SOURCE or DEPOBJ" : "SINK or SOURCE");
      }
    }
  } else if (dir != llvm::omp::OMPD_ordered) {
    if (doaDep) {
      context_.Say(GetContext().clauseSource,
          "The SINK and SOURCE dependence types can only be used with the ORDERED directive, used here in the %s construct"_err_en_US,
          parser::omp::GetUpperName(dir, version));
    }
  }
  if (taskDep) {
    auto &objList{*GetOmpObjectList(*taskDep)};
    if (dir == llvm::omp::OMPD_depobj) {
      // [5.0:255:13], [5.1:288:6], [5.2:322:26]
      // A depend clause on a depobj construct must only specify one locator.
      if (objList.v.size() != 1) {
        context_.Say(GetContext().clauseSource,
            "A DEPEND clause on a DEPOBJ construct must only specify "
            "one locator"_err_en_US);
      }
    }
    for (const auto &object : objList.v) {
      if (const auto *name{std::get_if<parser::Name>(&object.u)}) {
        context_.Say(GetContext().clauseSource,
            "Common block name ('%s') cannot appear in a DEPEND "
            "clause"_err_en_US,
            name->ToString());
      } else if (auto *designator{std::get_if<parser::Designator>(&object.u)}) {
        if (auto *dataRef{std::get_if<parser::DataRef>(&designator->u)}) {
          CheckDependList(*dataRef);
          if (const auto *arr{
                  std::get_if<common::Indirection<parser::ArrayElement>>(
                      &dataRef->u)}) {
            CheckArraySection(arr->value(), GetLastName(*dataRef),
                llvm::omp::Clause::OMPC_depend);
          }
        }
      }
    }
    if (OmpVerifyModifiers(*taskDep, llvm::omp::OMPC_depend,
            GetContext().clauseSource, context_)) {
      auto &modifiers{OmpGetModifiers(*taskDep)};
      if (OmpGetUniqueModifier<parser::OmpIterator>(modifiers)) {
        if (dir == llvm::omp::OMPD_depobj) {
          context_.Say(GetContext().clauseSource,
              "An iterator-modifier may specify multiple locators, a DEPEND clause on a DEPOBJ construct must only specify one locator"_warn_en_US);
        }
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Doacross &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_doacross);
  CheckDoacross(x.v.v);
}

void OmpStructureChecker::CheckDoacross(const parser::OmpDoacross &doa) {
  if (std::holds_alternative<parser::OmpDoacross::Source>(doa.u)) {
    // Nothing to check here.
    return;
  }

  // Process SINK dependence type. SINK may only appear in an ORDER construct,
  // which references a prior ORDERED(n) clause on a DO or SIMD construct
  // that marks the top of the loop nest.

  auto &sink{std::get<parser::OmpDoacross::Sink>(doa.u)};
  const std::list<parser::OmpIteration> &vec{sink.v.v};

  // Check if the variables in the iteration vector are unique.
  struct Less {
    using Iterator = std::list<parser::OmpIteration>::const_iterator;
    bool operator()(Iterator a, Iterator b) const {
      auto namea{std::get<parser::Name>(a->t)};
      auto nameb{std::get<parser::Name>(b->t)};
      assert(namea.symbol && nameb.symbol && "Unresolved symbols");
      // The non-determinism of the "<" doesn't matter, we only care about
      // equality, i.e.  a == b  <=>  !(a < b) && !(b < a)
      return reinterpret_cast<uintptr_t>(namea.symbol) <
          reinterpret_cast<uintptr_t>(nameb.symbol);
    }
  };
  if (auto maybeIter{FindDuplicate<Less>(vec)}) {
    auto name{std::get<parser::Name>((*maybeIter)->t)};
    context_.Say(name.source,
        "Duplicate variable '%s' in the iteration vector"_err_en_US,
        name.ToString());
  }

  // Check if the variables in the iteration vector are induction variables.
  // Ignore any mismatch between the size of the iteration vector and the
  // number of DO constructs on the stack. This is checked elsewhere.

  std::set<const Symbol *> inductionVars;
  for (const LoopConstruct &loop : llvm::reverse(loopStack_)) {
    if (auto *doc{std::get_if<const parser::DoConstruct *>(&loop)}) {
      // Do-construct, collect the induction variable.
      if (auto &control{(*doc)->GetLoopControl()}) {
        if (auto *b{std::get_if<parser::LoopControl::Bounds>(&control->u)}) {
          inductionVars.insert(b->Name().thing.symbol);
        }
      }
    } else {
      // Omp-loop-construct, check if it's do/simd with an ORDERED clause.
      auto *loopc{std::get_if<const parser::OpenMPLoopConstruct *>(&loop)};
      assert(loopc && "Expecting OpenMPLoopConstruct");
      const parser::OmpDirectiveSpecification &beginSpec{(*loopc)->BeginDir()};
      llvm::omp::Directive loopDir{beginSpec.DirId()};
      if (loopDir == llvm::omp::OMPD_do || loopDir == llvm::omp::OMPD_simd) {
        // If it has ORDERED clause, stop the traversal.
        if (parser::omp::FindClause(
                beginSpec, llvm::omp::Clause::OMPC_ordered)) {
          break;
        }
      }
    }
  }
  for (const parser::OmpIteration &iter : vec) {
    auto &name{std::get<parser::Name>(iter.t)};
    if (!inductionVars.count(name.symbol)) {
      context_.Say(name.source,
          "The iteration vector element '%s' is not an induction variable within the ORDERED loop nest"_err_en_US,
          name.ToString());
    }
  }
}

void OmpStructureChecker::CheckCopyingPolymorphicAllocatable(
    SymbolSourceMap &symbols, const llvm::omp::Clause clause) {
  unsigned version{context_.langOptions().OpenMPVersion};
  if (context_.ShouldWarn(common::UsageWarning::Portability)) {
    for (auto &[symbol, source] : symbols) {
      if (IsPolymorphicAllocatable(*symbol)) {
        context_.Warn(common::UsageWarning::Portability, source,
            "If a polymorphic variable with allocatable attribute '%s' is in %s clause, the behavior is unspecified"_port_en_US,
            symbol->name(), parser::omp::GetUpperName(clause, version));
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Copyprivate &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_copyprivate);
  SymbolSourceMap symbols;
  GetSymbolsInObjectList(x.v, symbols);
  CheckVariableListItem(symbols);
  CheckIntentInPointer(symbols, llvm::omp::Clause::OMPC_copyprivate);
  CheckCopyingPolymorphicAllocatable(
      symbols, llvm::omp::Clause::OMPC_copyprivate);
}

void OmpStructureChecker::Enter(const parser::OmpClause::Lastprivate &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_lastprivate);

  const auto &objectList{*GetOmpObjectList(x)};
  CheckVarIsNotPartOfAnotherVar(
      GetContext().clauseSource, objectList, "LASTPRIVATE");
  CheckCrayPointee(objectList, "LASTPRIVATE");

  DirectivesClauseTriple dirClauseTriple;
  SymbolSourceMap currSymbols;
  GetSymbolsInObjectList(objectList, currSymbols);
  CheckDefinableObjects(currSymbols, llvm::omp::Clause::OMPC_lastprivate);
  CheckIntentInPointer(currSymbols, llvm::omp::Clause::OMPC_lastprivate);
  CheckCopyingPolymorphicAllocatable(
      currSymbols, llvm::omp::Clause::OMPC_lastprivate);
  CheckAssumedSizeArray(currSymbols, llvm::omp::Clause::OMPC_lastprivate);

  // Check lastprivate variables in worksharing constructs
  dirClauseTriple.emplace(llvm::omp::Directive::OMPD_do,
      std::make_pair(
          llvm::omp::Directive::OMPD_parallel, llvm::omp::privateReductionSet));
  dirClauseTriple.emplace(llvm::omp::Directive::OMPD_sections,
      std::make_pair(
          llvm::omp::Directive::OMPD_parallel, llvm::omp::privateReductionSet));

  CheckPrivateSymbolsInOuterCxt(
      currSymbols, dirClauseTriple, llvm::omp::Clause::OMPC_lastprivate);

  if (OmpVerifyModifiers(x.v, llvm::omp::OMPC_lastprivate,
          GetContext().clauseSource, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    using LastprivateModifier = parser::OmpLastprivateModifier;
    if (auto *modifier{OmpGetUniqueModifier<LastprivateModifier>(modifiers)}) {
      CheckLastprivateModifier(*modifier);
    }
  }
}

// Add any restrictions related to Modifiers/Directives with
// Lastprivate clause here:
void OmpStructureChecker::CheckLastprivateModifier(
    const parser::OmpLastprivateModifier &modifier) {
  using LastprivateModifier = parser::OmpLastprivateModifier;
  const DirectiveContext &dirCtx{GetContext()};
  if (modifier.v == LastprivateModifier::Value::Conditional &&
      dirCtx.directive == llvm::omp::Directive::OMPD_taskloop) {
    // [5.2:268:17]
    // The conditional lastprivate-modifier must not be specified.
    context_.Say(GetContext().clauseSource,
        "'CONDITIONAL' modifier on lastprivate clause with TASKLOOP "
        "directive is not allowed"_err_en_US);
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Copyin &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_copyin);

  SymbolSourceMap currSymbols;
  GetSymbolsInObjectList(x.v, currSymbols);
  CheckCopyingPolymorphicAllocatable(
      currSymbols, llvm::omp::Clause::OMPC_copyin);
}

void OmpStructureChecker::CheckStructureComponent(
    const parser::OmpObjectList &objects, llvm::omp::Clause clauseId) {
  unsigned version{context_.langOptions().OpenMPVersion};

  auto CheckComponent{[&](const parser::Designator &designator) {
    if (const parser::DataRef *dataRef{
            std::get_if<parser::DataRef>(&designator.u)}) {
      if (!IsDataRefTypeParamInquiry(dataRef)) {
        evaluate::ExpressionAnalyzer ea{context_};
        auto restore{ea.AllowWholeAssumedSizeArray(true)};
        const auto expr{ea.Analyze(designator)};
        if (expr.has_value() && evaluate::HasStructureComponent(expr.value())) {
          context_.Say(designator.source,
              "A variable that is part of another variable cannot appear on the %s clause"_err_en_US,
              parser::omp::GetUpperName(clauseId, version));
        }
      }
    }
  }};

  for (const auto &object : objects.v) {
    common::visit(common::visitors{
                      CheckComponent,
                      [&](const parser::Name &name) {},
                      [&](const parser::OmpObject::Invalid &invalid) {},
                  },
        object.u);
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Update &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_update);
  llvm::omp::Directive dir{GetContext().directive};
  unsigned version{context_.langOptions().OpenMPVersion};

  const parser::OmpDependenceType *depType{nullptr};
  const parser::OmpTaskDependenceType *taskType{nullptr};
  if (auto &maybeUpdate{x.v}) {
    depType = std::get_if<parser::OmpDependenceType>(&maybeUpdate->u);
    taskType = std::get_if<parser::OmpTaskDependenceType>(&maybeUpdate->u);
  }

  if (!depType && !taskType) {
    assert(dir == llvm::omp::Directive::OMPD_atomic &&
        "Unexpected alternative in update clause");
    return;
  }

  if (depType) {
    CheckDependenceType(depType->v);
  } else if (taskType) {
    CheckTaskDependenceType(taskType->v);
  }

  // [5.1:288:4-5]
  // An update clause on a depobj construct must not have source, sink or depobj
  // as dependence-type.
  // [5.2:322:3]
  // task-dependence-type must not be depobj.
  if (dir == llvm::omp::OMPD_depobj) {
    if (version >= 51) {
      bool invalidDep{false};
      if (taskType) {
        invalidDep =
            taskType->v == parser::OmpTaskDependenceType::Value::Depobj;
      } else {
        invalidDep = true;
      }
      if (invalidDep) {
        context_.Say(GetContext().clauseSource,
            "An UPDATE clause on a DEPOBJ construct must not have SINK, SOURCE or DEPOBJ as dependence type"_err_en_US);
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::UseDevicePtr &x) {
  CheckStructureComponent(x.v, llvm::omp::Clause::OMPC_use_device_ptr);
  CheckAllowedClause(llvm::omp::Clause::OMPC_use_device_ptr);
  SymbolSourceMap currSymbols;
  GetSymbolsInObjectList(x.v, currSymbols);
  semantics::UnorderedSymbolSet listVars;
  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_use_device_ptr)) {
    const auto &useDevicePtrClause{
        std::get<parser::OmpClause::UseDevicePtr>(clause->u)};
    const auto &useDevicePtrList{useDevicePtrClause.v};
    std::list<parser::Name> useDevicePtrNameList;
    for (const auto &ompObject : useDevicePtrList.v) {
      if (const auto *name{parser::Unwrap<parser::Name>(ompObject)}) {
        if (name->symbol) {
          if (!(IsBuiltinCPtr(*(name->symbol)))) {
            context_.Warn(common::UsageWarning::OpenMPUsage, clause->source,
                "Use of non-C_PTR type '%s' in USE_DEVICE_PTR is deprecated, use USE_DEVICE_ADDR instead"_warn_en_US,
                name->ToString());
          } else {
            useDevicePtrNameList.push_back(*name);
          }
        }
      }
    }
    CheckMultipleOccurrence(
        listVars, useDevicePtrNameList, clause->source, "USE_DEVICE_PTR");
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::UseDeviceAddr &x) {
  CheckStructureComponent(x.v, llvm::omp::Clause::OMPC_use_device_addr);
  CheckAllowedClause(llvm::omp::Clause::OMPC_use_device_addr);
  SymbolSourceMap currSymbols;
  GetSymbolsInObjectList(x.v, currSymbols);
  semantics::UnorderedSymbolSet listVars;

  for (auto [_, clause] :
      FindClauses(llvm::omp::Clause::OMPC_use_device_addr)) {
    const auto &useDeviceAddrClause{
        std::get<parser::OmpClause::UseDeviceAddr>(clause->u)};
    const auto &useDeviceAddrList{useDeviceAddrClause.v};
    std::list<parser::Name> useDeviceAddrNameList;
    for (const auto &ompObject : useDeviceAddrList.v) {
      if (const auto *name{parser::Unwrap<parser::Name>(ompObject)}) {
        if (name->symbol) {
          useDeviceAddrNameList.push_back(*name);
        }
      }
    }
    CheckMultipleOccurrence(
        listVars, useDeviceAddrNameList, clause->source, "USE_DEVICE_ADDR");
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::IsDevicePtr &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_is_device_ptr);
  SymbolSourceMap currSymbols;
  GetSymbolsInObjectList(x.v, currSymbols);
  semantics::UnorderedSymbolSet listVars;
  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_is_device_ptr)) {
    const auto &isDevicePtrClause{
        std::get<parser::OmpClause::IsDevicePtr>(clause->u)};
    const auto &isDevicePtrList{isDevicePtrClause.v};
    SymbolSourceMap currSymbols;
    GetSymbolsInObjectList(isDevicePtrList, currSymbols);
    for (auto &[symbol, source] : currSymbols) {
      if (!(IsBuiltinCPtr(*symbol))) {
        context_.Say(clause->source,
            "Variable '%s' in IS_DEVICE_PTR clause must be of type C_PTR"_err_en_US,
            source.ToString());
      } else if (!(IsDummy(*symbol))) {
        context_.Warn(common::UsageWarning::OpenMPUsage, clause->source,
            "Variable '%s' in IS_DEVICE_PTR clause must be a dummy argument. "
            "This semantic check is deprecated from OpenMP 5.2 and later."_warn_en_US,
            source.ToString());
      } else if (IsAllocatableOrPointer(*symbol) || IsValue(*symbol)) {
        context_.Warn(common::UsageWarning::OpenMPUsage, clause->source,
            "Variable '%s' in IS_DEVICE_PTR clause must be a dummy argument "
            "that does not have the ALLOCATABLE, POINTER or VALUE attribute. "
            "This semantic check is deprecated from OpenMP 5.2 and later."_warn_en_US,
            source.ToString());
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::HasDeviceAddr &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_has_device_addr);
  SymbolSourceMap currSymbols;
  GetSymbolsInObjectList(x.v, currSymbols);
  semantics::UnorderedSymbolSet listVars;
  for (auto [_, clause] :
      FindClauses(llvm::omp::Clause::OMPC_has_device_addr)) {
    const auto &hasDeviceAddrClause{
        std::get<parser::OmpClause::HasDeviceAddr>(clause->u)};
    const auto &hasDeviceAddrList{hasDeviceAddrClause.v};
    std::list<parser::Name> hasDeviceAddrNameList;
    for (const auto &ompObject : hasDeviceAddrList.v) {
      if (const auto *name{parser::Unwrap<parser::Name>(ompObject)}) {
        if (name->symbol) {
          hasDeviceAddrNameList.push_back(*name);
        }
      }
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::Enter &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_enter);
  if (!OmpVerifyModifiers(
          x.v, llvm::omp::OMPC_enter, GetContext().clauseSource, context_)) {
    return;
  }
  SymbolSourceMap symbols;
  GetSymbolsInObjectList(*GetOmpObjectList(x), symbols);
  for (const auto &[symbol, source] : symbols) {
    if (!IsExtendedListItem(*symbol)) {
      context_.SayWithDecl(*symbol, source,
          "'%s' must be a variable or a procedure"_err_en_US, symbol->name());
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::From &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_from);
  if (!OmpVerifyModifiers(
          x.v, llvm::omp::OMPC_from, GetContext().clauseSource, context_)) {
    return;
  }

  auto &modifiers{OmpGetModifiers(x.v)};
  unsigned version{context_.langOptions().OpenMPVersion};

  if (auto *iter{OmpGetUniqueModifier<parser::OmpIterator>(modifiers)}) {
    CheckIteratorModifier(*iter);
  }

  const auto &objList{*GetOmpObjectList(x)};
  SymbolSourceMap symbols;
  GetSymbolsInObjectList(objList, symbols);
  CheckVariableListItem(symbols);

  // Ref: [4.5:109:19]
  // If a list item is an array section it must specify contiguous storage.
  if (version <= 45) {
    for (const parser::OmpObject &object : objList.v) {
      CheckIfContiguous(object);
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::To &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_to);
  if (!OmpVerifyModifiers(
          x.v, llvm::omp::OMPC_to, GetContext().clauseSource, context_)) {
    return;
  }

  auto &modifiers{OmpGetModifiers(x.v)};
  unsigned version{context_.langOptions().OpenMPVersion};

  // The "to" clause is only allowed on "declare target" (pre-5.1), and
  // "target update". In the former case it can take an extended list item,
  // in the latter a variable (a locator).

  // The "declare target" construct (and the "to" clause on it) are already
  // handled (in the declare-target checkers), so just look at "to" in "target
  // update".
  if (GetContext().directive == llvm::omp::OMPD_declare_target) {
    return;
  }

  assert(GetContext().directive == llvm::omp::OMPD_target_update);
  if (auto *iter{OmpGetUniqueModifier<parser::OmpIterator>(modifiers)}) {
    CheckIteratorModifier(*iter);
  }

  const auto &objList{*GetOmpObjectList(x)};
  SymbolSourceMap symbols;
  GetSymbolsInObjectList(objList, symbols);
  CheckVariableListItem(symbols);

  // Ref: [4.5:109:19]
  // If a list item is an array section it must specify contiguous storage.
  if (version <= 45) {
    for (const parser::OmpObject &object : objList.v) {
      CheckIfContiguous(object);
    }
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::OmpxBare &x) {
  unsigned version{context_.langOptions().OpenMPVersion};
  // Don't call CheckAllowedClause, because it allows "ompx_bare" on
  // a non-combined "target" directive (for reasons of splitting combined
  // directives). In source code it's only allowed on "target teams".
  if (GetContext().directive != llvm::omp::Directive::OMPD_target_teams) {
    context_.Say(GetContext().clauseSource,
        "%s clause is only allowed on combined TARGET TEAMS"_err_en_US,
        parser::omp::GetUpperName(llvm::omp::OMPC_ompx_bare, version));
  }
}

llvm::StringRef OmpStructureChecker::getClauseName(llvm::omp::Clause clause) {
  unsigned version{context_.langOptions().OpenMPVersion};
  return llvm::omp::getOpenMPClauseName(clause, version);
}

llvm::StringRef OmpStructureChecker::getDirectiveName(
    llvm::omp::Directive directive) {
  unsigned version{context_.langOptions().OpenMPVersion};
  return llvm::omp::getOpenMPDirectiveName(directive, version);
}

void OmpStructureChecker::CheckDependList(const parser::DataRef &d) {
  common::visit(
      common::visitors{
          [&](const common::Indirection<parser::ArrayElement> &elem) {
            // Check if the base element is valid on Depend Clause
            CheckDependList(elem.value().Base());
          },
          [&](const common::Indirection<parser::StructureComponent> &comp) {
            CheckDependList(comp.value().Base());
          },
          [&](const common::Indirection<parser::CoindexedNamedObject> &) {
            context_.Say(GetContext().clauseSource,
                "Coarrays are not supported in DEPEND clause"_err_en_US);
          },
          [&](const parser::Name &) {},
      },
      d.u);
}

// Called from both Reduction and Depend clause.
void OmpStructureChecker::CheckArraySection(
    const parser::ArrayElement &arrayElement, const parser::Name &name,
    const llvm::omp::Clause clause) {
  unsigned version{context_.langOptions().OpenMPVersion};
  // Sometimes substring operations are incorrectly parsed as array accesses.
  // Detect this by looking for array accesses on character variables which are
  // not arrays.
  bool isSubstring{false};
  // Cannot analyze a base of an assumed-size array on its own. If we know
  // this is an array (assumed-size or not) we can ignore it, since we're
  // looking for strings.
  if (!IsAssumedSizeArray(*name.symbol)) {
    evaluate::ExpressionAnalyzer ea{context_};
    if (MaybeExpr expr = ea.Analyze(arrayElement.Base())) {
      if (expr->Rank() == 0) {
        // Not an array: rank 0
        if (std::optional<evaluate::DynamicType> type = expr->GetType()) {
          if (type->category() == evaluate::TypeCategory::Character) {
            // Substrings are explicitly denied by the standard [6.0:163:9-11].
            // This is supported as an extension. This restriction was added in
            // OpenMP 5.2.
            isSubstring = true;
            context_.Say(GetContext().clauseSource,
                "The use of substrings in OpenMP argument lists has been disallowed since OpenMP 5.2."_port_en_US);
          } else {
            llvm_unreachable(
                "Array indexing on a variable that isn't an array");
          }
        }
      }
    }
  }
  if (!arrayElement.Subscripts().empty()) {
    for (const auto &subscript : arrayElement.Subscripts()) {
      if (const auto *triplet{
              std::get_if<parser::SubscriptTriplet>(&subscript.u)}) {
        if (std::get<0>(triplet->t) && std::get<1>(triplet->t)) {
          std::optional<int64_t> strideVal{std::nullopt};
          if (const auto &strideExpr = std::get<2>(triplet->t)) {
            // OpenMP 6.0 Section 5.2.5: Array Sections
            // Restrictions: if a stride expression is specified it must be
            // positive. A stride of 0 doesn't make sense.
            strideVal = GetIntValue(strideExpr);
            if (strideVal && *strideVal < 1) {
              context_.Say(GetContext().clauseSource,
                  "'%s' in %s clause must have a positive stride"_err_en_US,
                  name.ToString(), parser::omp::GetUpperName(clause, version));
            }
            if (isSubstring) {
              context_.Say(GetContext().clauseSource,
                  "Cannot specify a step for a substring"_err_en_US);
            }
          }
          const auto &lower{std::get<0>(triplet->t)};
          const auto &upper{std::get<1>(triplet->t)};
          if (lower && upper) {
            const auto lval{GetIntValue(lower)};
            const auto uval{GetIntValue(upper)};
            if (lval && uval) {
              int64_t sectionLen = *uval - *lval;
              if (strideVal) {
                if (*strideVal == 0) {
                  continue;
                }
                sectionLen = sectionLen / *strideVal;
              }

              if (sectionLen < 1) {
                context_.Say(GetContext().clauseSource,
                    "'%s' in %s clause"
                    " is a zero size array section"_err_en_US,
                    name.ToString(),
                    parser::omp::GetUpperName(clause, version));
                break;
              }
            }
          }
        }
      } else if (std::get_if<parser::IntExpr>(&subscript.u)) {
        // base(n) is valid as an array index but not as a substring operation
        if (isSubstring) {
          context_.Say(GetContext().clauseSource,
              "Substrings must be in the form parent-string(lb:ub)"_err_en_US);
        }
      }
    }
  }
}

void OmpStructureChecker::CheckLastPartRefForArraySection(
    const parser::Designator &designator, llvm::omp::Clause clauseId) {
  if (!designator.EndsInBareName()) {
    return;
  }
  if (MaybeExpr expr{AnalyzeExpr(context_, designator)}) {
    if (evaluate::IsArraySection(*expr)) {
      context_.Say(designator.source,
          "If a list item is an array section, the last part-ref of the list item must have a section subscript list in %s clause"_err_en_US,
          parser::ToUpperCaseLetters(getClauseName(clauseId).str()));
    }
  }
}

void OmpStructureChecker::CheckIntentInPointer(
    SymbolSourceMap &symbols, llvm::omp::Clause clauseId) {
  unsigned version{context_.langOptions().OpenMPVersion};
  for (auto &[symbol, source] : symbols) {
    if (IsPointer(*symbol) && IsIntentIn(*symbol)) {
      context_.Say(source,
          "Pointer '%s' with the INTENT(IN) attribute may not appear in a %s clause"_err_en_US,
          symbol->name(), parser::omp::GetUpperName(clauseId, version));
    }
  }
}

void OmpStructureChecker::CheckAssumedSizeArray(
    SymbolSourceMap &symbols, llvm::omp::Clause clauseId) {
  unsigned version{context_.langOptions().OpenMPVersion};
  for (auto &[symbol, source] : symbols) {
    if (IsAssumedSizeArray(*symbol)) {
      context_.Say(source,
          "Assumed-size array '%s' may not appear in a %s clause"_err_en_US,
          symbol->name(), parser::omp::GetUpperName(clauseId, version));
    }
  }
}

void OmpStructureChecker::CheckProcedurePointer(
    SymbolSourceMap &symbols, llvm::omp::Clause clause) {
  unsigned version{context_.langOptions().OpenMPVersion};
  for (const auto &[symbol, source] : symbols) {
    if (IsProcedurePointer(*symbol)) {
      context_.Say(source,
          "Procedure pointer '%s' may not appear in a %s clause"_err_en_US,
          symbol->name(), parser::omp::GetUpperName(clause, version));
    }
  }
}

void OmpStructureChecker::CheckCrayPointee(
    const parser::OmpObjectList &objectList, llvm::StringRef clause,
    bool suggestToUseCrayPointer) {
  SymbolSourceMap symbols;
  GetSymbolsInObjectList(objectList, symbols);
  for (auto it{symbols.begin()}; it != symbols.end(); ++it) {
    const auto *symbol{it->first};
    const auto source{it->second};
    if (symbol->test(Symbol::Flag::CrayPointee)) {
      std::string suggestionMsg = "";
      if (suggestToUseCrayPointer)
        suggestionMsg = ", use Cray Pointer '" +
            semantics::GetCrayPointer(*symbol).name().ToString() + "' instead";
      context_.Say(source,
          "Cray Pointee '%s' may not appear in %s clause%s"_err_en_US,
          symbol->name(), clause.str(), suggestionMsg);
    }
  }
}

void OmpStructureChecker::GetSymbolsInObjectList(
    const parser::OmpObjectList &objectList, SymbolSourceMap &symbols) {
  for (const auto &ompObject : objectList.v) {
    if (const auto *name{parser::Unwrap<parser::Name>(ompObject)}) {
      if (const auto *symbol{name->symbol}) {
        if (const auto *commonBlockDetails{
                symbol->detailsIf<CommonBlockDetails>()}) {
          for (const auto &object : commonBlockDetails->objects()) {
            symbols.emplace(&object->GetUltimate(), name->source);
          }
        } else {
          symbols.emplace(&symbol->GetUltimate(), name->source);
        }
      }
    }
  }
}

void OmpStructureChecker::CheckDefinableObjects(
    SymbolSourceMap &symbols, const llvm::omp::Clause clause) {
  unsigned version{context_.langOptions().OpenMPVersion};
  for (auto &[symbol, source] : symbols) {
    if (auto msg{WhyNotDefinable(source, context_.FindScope(source),
            DefinabilityFlags{}, *symbol)}) {
      context_
          .Say(source,
              "Variable '%s' on the %s clause is not definable"_err_en_US,
              symbol->name(), parser::omp::GetUpperName(clause, version))
          .Attach(std::move(msg->set_severity(parser::Severity::Because)));
    }
  }
}

void OmpStructureChecker::CheckPrivateSymbolsInOuterCxt(
    SymbolSourceMap &currSymbols, DirectivesClauseTriple &dirClauseTriple,
    const llvm::omp::Clause currClause) {
  unsigned version{context_.langOptions().OpenMPVersion};
  SymbolSourceMap enclosingSymbols;
  auto range{dirClauseTriple.equal_range(GetContext().directive)};
  for (auto dirIter{range.first}; dirIter != range.second; ++dirIter) {
    auto enclosingDir{dirIter->second.first};
    auto enclosingClauseSet{dirIter->second.second};
    if (auto *enclosingContext{GetEnclosingContextWithDir(enclosingDir)}) {
      for (auto it{enclosingContext->clauseInfo.begin()};
          it != enclosingContext->clauseInfo.end(); ++it) {
        if (enclosingClauseSet.test(it->first)) {
          if (const auto *ompObjectList{GetOmpObjectList(*it->second)}) {
            GetSymbolsInObjectList(*ompObjectList, enclosingSymbols);
          }
        }
      }

      // Check if the symbols in current context are private in outer context
      for (auto &[symbol, source] : currSymbols) {
        if (enclosingSymbols.find(symbol) != enclosingSymbols.end()) {
          context_.Say(source,
              "%s variable '%s' is PRIVATE in outer context"_err_en_US,
              parser::omp::GetUpperName(currClause, version), symbol->name());
        }
      }
    }
  }
}

bool OmpStructureChecker::CheckTargetBlockOnlyTeams(
    const parser::Block &block) {
  bool nestedTeams{false};

  if (!block.empty()) {
    auto it{block.begin()};
    if (const auto *ompConstruct{
            parser::Unwrap<parser::OpenMPConstruct>(*it)}) {
      if (const auto *ompBlockConstruct{
              std::get_if<parser::OmpBlockConstruct>(&ompConstruct->u)}) {
        llvm::omp::Directive dirId{ompBlockConstruct->BeginDir().DirId()};
        if (dirId == llvm::omp::Directive::OMPD_teams) {
          nestedTeams = true;
        }
      } else if (const auto *ompLoopConstruct{
                     std::get_if<parser::OpenMPLoopConstruct>(
                         &ompConstruct->u)}) {
        llvm::omp::Directive dirId{ompLoopConstruct->BeginDir().DirId()};
        if (llvm::omp::topTeamsSet.test(dirId)) {
          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) ||
        parser::Unwrap<parser::WhereStmt>(*it) ||
        parser::Unwrap<parser::WhereConstruct>(*it)) {
      parser::Walk(*it, ompWorkshareBlockChecker);
    } else if (const auto *ompConstruct{
                   parser::Unwrap<parser::OpenMPConstruct>(*it)}) {
      if (const auto *ompAtomicConstruct{
              std::get_if<parser::OpenMPAtomicConstruct>(&ompConstruct->u)}) {
        // Check if assignment statements in the enclosing OpenMP Atomic
        // construct are allowed in the Workshare construct
        parser::Walk(*ompAtomicConstruct, ompWorkshareBlockChecker);
      } else if (const auto *ompCriticalConstruct{
                     std::get_if<parser::OpenMPCriticalConstruct>(
                         &ompConstruct->u)}) {
        // All the restrictions on the Workshare construct apply to the
        // statements in the enclosing critical constructs
        const auto &criticalBlock{
            std::get<parser::Block>(ompCriticalConstruct->t)};
        CheckWorkshareBlockStmts(criticalBlock, source);
      } else {
        // Check if OpenMP constructs enclosed in the Workshare construct are
        // 'Parallel' constructs
        auto currentDir{llvm::omp::Directive::OMPD_unknown};
        if (const auto *ompBlockConstruct{
                std::get_if<parser::OmpBlockConstruct>(&ompConstruct->u)}) {
          currentDir = ompBlockConstruct->BeginDir().DirId();
        } else if (const auto *ompLoopConstruct{
                       std::get_if<parser::OpenMPLoopConstruct>(
                           &ompConstruct->u)}) {
          currentDir = ompLoopConstruct->BeginDir().DirId();
        } else if (const auto *ompSectionsConstruct{
                       std::get_if<parser::OpenMPSectionsConstruct>(
                           &ompConstruct->u)}) {
          currentDir = ompSectionsConstruct->BeginDir().DirId();
        }

        if (!llvm::omp::topParallelSet.test(currentDir)) {
          context_.Say(source,
              "OpenMP constructs enclosed in WORKSHARE construct may consist "
              "of ATOMIC, CRITICAL or PARALLEL constructs only"_err_en_US);
        }
      }
    } else {
      context_.Say(source,
          "The structured block in a WORKSHARE construct may consist of only "
          "SCALAR or ARRAY assignments, FORALL or WHERE statements, "
          "FORALL, WHERE, ATOMIC, CRITICAL or PARALLEL constructs"_err_en_US);
    }
  }
}

void OmpStructureChecker::CheckWorkdistributeBlockStmts(
    const parser::Block &block, parser::CharBlock source) {
  unsigned version{context_.langOptions().OpenMPVersion};
  unsigned since{60};
  if (version < since)
    context_.Say(source,
        "WORKDISTRIBUTE construct is not allowed in %s, %s"_err_en_US,
        ThisVersion(version), TryVersion(since));

  OmpWorkdistributeBlockChecker ompWorkdistributeBlockChecker{context_, source};

  for (auto it{block.begin()}; it != block.end(); ++it) {
    if (parser::Unwrap<parser::AssignmentStmt>(*it)) {
      parser::Walk(*it, ompWorkdistributeBlockChecker);
    } else {
      context_.Say(source,
          "The structured block in a WORKDISTRIBUTE construct may consist of only SCALAR or ARRAY assignments"_err_en_US);
    }
  }
}

void OmpStructureChecker::CheckIfContiguous(const parser::OmpObject &object) {
  if (!IsContiguous(context_, object).value_or(true)) { // known discontiguous
    const parser::Name *name{GetObjectName(object)};
    assert(name && "Expecting name component");
    context_.Say(name->source,
        "Reference to '%s' must be a contiguous object"_err_en_US,
        name->ToString());
  }
}

namespace {
struct NameHelper {
  template <typename T>
  static const parser::Name *Visit(const common::Indirection<T> &x) {
    return Visit(x.value());
  }
  static const parser::Name *Visit(const parser::Substring &x) {
    return Visit(std::get<parser::DataRef>(x.t));
  }
  static const parser::Name *Visit(const parser::ArrayElement &x) {
    return Visit(x.Base());
  }
  static const parser::Name *Visit(const parser::Designator &x) {
    return common::visit([](auto &&s) { return Visit(s); }, x.u);
  }
  static const parser::Name *Visit(const parser::DataRef &x) {
    return common::visit([](auto &&s) { return Visit(s); }, x.u);
  }
  static const parser::Name *Visit(const parser::OmpObject &x) {
    return common::visit([](auto &&s) { return Visit(s); }, x.u);
  }
  template <typename T> static const parser::Name *Visit(T &&) {
    return nullptr;
  }
  static const parser::Name *Visit(const parser::Name &x) { return &x; }
};
} // namespace

const parser::Name *OmpStructureChecker::GetObjectName(
    const parser::OmpObject &object) {
  return NameHelper::Visit(object);
}

void OmpStructureChecker::Enter(
    const parser::OmpClause::AtomicDefaultMemOrder &x) {
  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_atomic_default_mem_order);
}

void OmpStructureChecker::Enter(const parser::OmpClause::DeviceSafesync &x) {
  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_device_safesync);
}

void OmpStructureChecker::Enter(const parser::OmpClause::DynamicAllocators &x) {
  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_dynamic_allocators);
}

void OmpStructureChecker::Enter(const parser::OmpClause::ReverseOffload &x) {
  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_reverse_offload);
}

void OmpStructureChecker::Enter(const parser::OmpClause::UnifiedAddress &x) {
  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_unified_address);
}

void OmpStructureChecker::Enter(
    const parser::OmpClause::UnifiedSharedMemory &x) {
  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_unified_shared_memory);
}

void OmpStructureChecker::Enter(const parser::OmpClause::SelfMaps &x) {
  CheckAllowedRequiresClause(llvm::omp::Clause::OMPC_self_maps);
}

void OmpStructureChecker::CheckDimsModifier(parser::CharBlock source,
    size_t numValues, const parser::OmpDimsModifier &x) {
  std::string name{OmpGetDescriptor<parser::OmpDimsModifier>().name.str()};

  if (auto dimsVal{GetIntValue(x.v)}) {
    if (*dimsVal > 0) {
      if (static_cast<size_t>(*dimsVal) < numValues) {
        context_.Say(source,
            "The %s specifies %d dimensions but %zu values were provided"_err_en_US,
            name, *dimsVal, numValues);
      }
    } else {
      context_.Say(
          source, "The argument to the %s should be positive"_err_en_US, name);
    }
  }
  // The non-constant expression case is diagnosed elsewhere.
}

void OmpStructureChecker::Enter(const parser::OmpClause::NumTeams &x) {
  constexpr auto clauseId{llvm::omp::Clause::OMPC_num_teams};
  CheckAllowedClause(clauseId);
  parser::CharBlock source{GetContext().clauseSource};
  auto &values{std::get<std::list<parser::ScalarIntExpr>>(x.v.t)};

  if (OmpVerifyModifiers(x.v, clauseId, source, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    if (auto *dims{OmpGetUniqueModifier<parser::OmpDimsModifier>(modifiers)}) {
      CheckDimsModifier(
          OmpGetModifierSource(modifiers, dims), values.size(), *dims);
    }
  }

  for (auto &val : values) {
    RequiresPositiveParameter(clauseId, val);
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::NumThreads &x) {
  constexpr auto clauseId{llvm::omp::Clause::OMPC_num_threads};
  CheckAllowedClause(clauseId);
  parser::CharBlock source{GetContext().clauseSource};
  auto &values{std::get<std::list<parser::ScalarIntExpr>>(x.v.t)};

  if (OmpVerifyModifiers(x.v, clauseId, source, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    if (auto *dims{OmpGetUniqueModifier<parser::OmpDimsModifier>(modifiers)}) {
      CheckDimsModifier(
          OmpGetModifierSource(modifiers, dims), values.size(), *dims);
    }
  }

  for (auto &val : values) {
    RequiresPositiveParameter(clauseId, val);
  }
}

void OmpStructureChecker::Enter(const parser::OmpClause::ThreadLimit &x) {
  constexpr auto clauseId{llvm::omp::Clause::OMPC_thread_limit};
  CheckAllowedClause(clauseId);
  parser::CharBlock source{GetContext().clauseSource};
  auto &values{std::get<std::list<parser::ScalarIntExpr>>(x.v.t)};

  if (OmpVerifyModifiers(x.v, clauseId, source, context_)) {
    auto &modifiers{OmpGetModifiers(x.v)};
    if (auto *dims{OmpGetUniqueModifier<parser::OmpDimsModifier>(modifiers)}) {
      CheckDimsModifier(
          OmpGetModifierSource(modifiers, dims), values.size(), *dims);
    }
  }

  for (auto &val : values) {
    RequiresPositiveParameter(clauseId, val);
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPInteropConstruct &x) {
  bool isDependClauseOccurred{false};
  int targetCount{0}, targetSyncCount{0};
  const auto &dir{std::get<parser::OmpDirectiveName>(x.v.t)};
  std::set<const Symbol *> objectSymbolList;
  PushContextAndClauseSets(dir.source, llvm::omp::Directive::OMPD_interop);
  const auto &clauseList{std::get<std::optional<parser::OmpClauseList>>(x.v.t)};
  for (const auto &clause : clauseList->v) {
    common::visit(
        common::visitors{
            [&](const parser::OmpClause::Init &initClause) {
              if (OmpVerifyModifiers(initClause.v, llvm::omp::OMPC_init,
                      GetContext().directiveSource, context_)) {

                auto &modifiers{OmpGetModifiers(initClause.v)};
                auto &&interopTypeModifier{
                    OmpGetRepeatableModifier<parser::OmpInteropType>(
                        modifiers)};
                for (const auto &it : interopTypeModifier) {
                  if (it->v == parser::OmpInteropType::Value::Targetsync) {
                    ++targetSyncCount;
                  } else {
                    ++targetCount;
                  }
                }
                if (auto *depInfo{
                        OmpGetUniqueModifier<parser::OmpDepinfoModifier>(
                            modifiers)}) {
                  auto &desc{OmpGetDescriptor<parser::OmpDepinfoModifier>()};
                  context_.Say(OmpGetModifierSource(modifiers, depInfo),
                      "The '%s' is not allowed on INTEROP construct"_err_en_US,
                      desc.name.str());
                }
              }
              const auto &interopVar{parser::Unwrap<parser::OmpObject>(
                  std::get<parser::OmpObject>(initClause.v.t))};
              const auto *name{parser::Unwrap<parser::Name>(interopVar)};
              const auto *objectSymbol{name->symbol};
              if (llvm::is_contained(objectSymbolList, objectSymbol)) {
                context_.Say(GetContext().directiveSource,
                    "Each interop-var may be specified for at most one action-clause of each INTEROP construct."_err_en_US);
              } else {
                objectSymbolList.insert(objectSymbol);
              }
            },
            [&](const parser::OmpClause::Depend &dependClause) {
              isDependClauseOccurred = true;
            },
            [&](const parser::OmpClause::Destroy &destroyClause) {
              const auto &interopVar{
                  parser::Unwrap<parser::OmpObject>(destroyClause.v)};
              const auto *name{parser::Unwrap<parser::Name>(interopVar)};
              const auto *objectSymbol{name->symbol};
              if (llvm::is_contained(objectSymbolList, objectSymbol)) {
                context_.Say(GetContext().directiveSource,
                    "Each interop-var may be specified for at most one action-clause of each INTEROP construct."_err_en_US);
              } else {
                objectSymbolList.insert(objectSymbol);
              }
            },
            [&](const parser::OmpClause::Use &useClause) {
              const auto &interopVar{
                  parser::Unwrap<parser::OmpObject>(useClause.v)};
              const auto *name{parser::Unwrap<parser::Name>(interopVar)};
              const auto *objectSymbol{name->symbol};
              if (llvm::is_contained(objectSymbolList, objectSymbol)) {
                context_.Say(GetContext().directiveSource,
                    "Each interop-var may be specified for at most one action-clause of each INTEROP construct."_err_en_US);
              } else {
                objectSymbolList.insert(objectSymbol);
              }
            },
            [&](const auto &) {},
        },
        clause.u);
  }
  if (targetCount > 1 || targetSyncCount > 1) {
    context_.Say(GetContext().directiveSource,
        "Each interop-type may be specified at most once."_err_en_US);
  }
  if (isDependClauseOccurred && !targetSyncCount) {
    context_.Say(GetContext().directiveSource,
        "A DEPEND clause can only appear on the directive if the interop-type includes TARGETSYNC"_err_en_US);
  }
}

void OmpStructureChecker::Leave(const parser::OpenMPInteropConstruct &) {
  dirContext_.pop_back();
}

void OmpStructureChecker::CheckAllowedRequiresClause(llvmOmpClause clause) {
  CheckAllowedClause(clause);
  unsigned version{context_.langOptions().OpenMPVersion};

  if (clause != llvm::omp::Clause::OMPC_atomic_default_mem_order) {
    // Check that it does not appear after a device construct
    if (deviceConstructFound_) {
      context_.Say(GetContext().clauseSource,
          "REQUIRES directive with '%s' clause found lexically after device construct"_err_en_US,
          parser::omp::GetUpperName(clause, version));
    }
  }
}

void OmpStructureChecker::Enter(const parser::OpenMPMisplacedEndDirective &x) {
  context_.Say(x.DirName().source, "Misplaced OpenMP end-directive"_err_en_US);
  PushContextAndClauseSets(
      x.DirName().source, llvm::omp::Directive::OMPD_unknown);
}

void OmpStructureChecker::Leave(const parser::OpenMPMisplacedEndDirective &x) {
  dirContext_.pop_back();
}

void OmpStructureChecker::Enter(const parser::OpenMPInvalidDirective &x) {
  context_.Say(x.source, "Invalid OpenMP directive"_err_en_US);
  PushContextAndClauseSets(x.source, llvm::omp::Directive::OMPD_unknown);
}

void OmpStructureChecker::Leave(const parser::OpenMPInvalidDirective &x) {
  dirContext_.pop_back();
}

// Use when clause falls under 'struct OmpClause' in 'parse-tree.h'.
#define CHECK_SIMPLE_CLAUSE(X, Y) \
  void OmpStructureChecker::Enter(const parser::OmpClause::X &) { \
    CheckAllowedClause(llvm::omp::Clause::Y); \
  }

#define CHECK_REQ_CONSTANT_SCALAR_INT_CLAUSE(X, Y) \
  void OmpStructureChecker::Enter(const parser::OmpClause::X &c) { \
    CheckAllowedClause(llvm::omp::Clause::Y); \
    RequiresConstantPositiveParameter(llvm::omp::Clause::Y, c.v); \
  }

#define CHECK_REQ_SCALAR_INT_CLAUSE(X, Y) \
  void OmpStructureChecker::Enter(const parser::OmpClause::X &c) { \
    CheckAllowedClause(llvm::omp::Clause::Y); \
    RequiresPositiveParameter(llvm::omp::Clause::Y, c.v); \
  }

void OmpStructureChecker::Enter(const parser::OmpClause::Affinity &x) {
  CheckAllowedClause(llvm::omp::Clause::OMPC_affinity);

  auto &modifiers{OmpGetModifiers(x.v)};
  if (auto *iter{OmpGetUniqueModifier<parser::OmpIterator>(modifiers)})
    CheckIteratorModifier(*iter);

  const auto &objects{std::get<parser::OmpObjectList>(x.v.t)};
  for (const parser::OmpObject &object : objects.v) {
    if (const parser::Designator *designator{
            omp::GetDesignatorFromObj(object)}) {
      if (const auto *dataRef{GetDataRefFromObj(object)}) {
        if (const auto *arrayElement{GetArrayElementFromObj(object)}) {
          CheckArraySection(*arrayElement, GetLastName(*dataRef),
              llvm::omp::Clause::OMPC_affinity);
        }
      }

      // CheckArraySection handles ArrayElement cases,
      // but true substrings (e.g. a(2)(2:4)) are parser::Substring and bypass
      // CheckArraySection.
      if (std::holds_alternative<parser::Substring>(designator->u)) {
        context_.Say(designator->source,
            "Substrings are not allowed on AFFINITY clause"_err_en_US);
      }

      // OpenMP 5.2 5.2.5 Array section: if a list item is an array section, the
      // last part-ref of the list item must have a section subscript list.
      CheckLastPartRefForArraySection(
          *designator, llvm::omp::Clause::OMPC_affinity);
    }
  }
}

// Following clauses do not have a separate node in parse-tree.h.
CHECK_SIMPLE_CLAUSE(Absent, OMPC_absent)
CHECK_SIMPLE_CLAUSE(AcqRel, OMPC_acq_rel)
CHECK_SIMPLE_CLAUSE(Acquire, OMPC_acquire)
CHECK_SIMPLE_CLAUSE(AdjustArgs, OMPC_adjust_args)
CHECK_SIMPLE_CLAUSE(AppendArgs, OMPC_append_args)
CHECK_SIMPLE_CLAUSE(Apply, OMPC_apply)
CHECK_SIMPLE_CLAUSE(Bind, OMPC_bind)
CHECK_SIMPLE_CLAUSE(Capture, OMPC_capture)
CHECK_SIMPLE_CLAUSE(Collector, OMPC_collector)
CHECK_SIMPLE_CLAUSE(Combiner, OMPC_combiner)
CHECK_SIMPLE_CLAUSE(Compare, OMPC_compare)
CHECK_SIMPLE_CLAUSE(Contains, OMPC_contains)
CHECK_SIMPLE_CLAUSE(Counts, OMPC_counts)
CHECK_SIMPLE_CLAUSE(Default, OMPC_default)
CHECK_SIMPLE_CLAUSE(Depobj, OMPC_depobj)
CHECK_SIMPLE_CLAUSE(DeviceType, OMPC_device_type)
CHECK_SIMPLE_CLAUSE(DistSchedule, OMPC_dist_schedule)
CHECK_SIMPLE_CLAUSE(Exclusive, OMPC_exclusive)
CHECK_SIMPLE_CLAUSE(Fail, OMPC_fail)
CHECK_SIMPLE_CLAUSE(Filter, OMPC_filter)
CHECK_SIMPLE_CLAUSE(Final, OMPC_final)
CHECK_SIMPLE_CLAUSE(Flush, OMPC_flush)
CHECK_SIMPLE_CLAUSE(Full, OMPC_full)
CHECK_SIMPLE_CLAUSE(Grainsize, OMPC_grainsize)
CHECK_SIMPLE_CLAUSE(GraphId, OMPC_graph_id)
CHECK_SIMPLE_CLAUSE(GraphReset, OMPC_graph_reset)
CHECK_SIMPLE_CLAUSE(Groupprivate, OMPC_groupprivate)
CHECK_SIMPLE_CLAUSE(Holds, OMPC_holds)
CHECK_SIMPLE_CLAUSE(Inbranch, OMPC_inbranch)
CHECK_SIMPLE_CLAUSE(Inclusive, OMPC_inclusive)
CHECK_SIMPLE_CLAUSE(Indirect, OMPC_indirect)
CHECK_SIMPLE_CLAUSE(Induction, OMPC_induction)
CHECK_SIMPLE_CLAUSE(Inductor, OMPC_inductor)
CHECK_SIMPLE_CLAUSE(InitComplete, OMPC_init_complete)
CHECK_SIMPLE_CLAUSE(Initializer, OMPC_initializer)
CHECK_SIMPLE_CLAUSE(Init, OMPC_init)
CHECK_SIMPLE_CLAUSE(Interop, OMPC_interop)
CHECK_SIMPLE_CLAUSE(Link, OMPC_link)
CHECK_SIMPLE_CLAUSE(Local, OMPC_local)
CHECK_SIMPLE_CLAUSE(Match, OMPC_match)
CHECK_SIMPLE_CLAUSE(MemoryOrder, OMPC_memory_order)
CHECK_SIMPLE_CLAUSE(Memscope, OMPC_memscope)
CHECK_SIMPLE_CLAUSE(Mergeable, OMPC_mergeable)
CHECK_SIMPLE_CLAUSE(Message, OMPC_message)
CHECK_SIMPLE_CLAUSE(Nocontext, OMPC_nocontext)
CHECK_SIMPLE_CLAUSE(Nogroup, OMPC_nogroup)
CHECK_SIMPLE_CLAUSE(Nontemporal, OMPC_nontemporal)
CHECK_SIMPLE_CLAUSE(NoOpenmpConstructs, OMPC_no_openmp_constructs)
CHECK_SIMPLE_CLAUSE(NoOpenmp, OMPC_no_openmp)
CHECK_SIMPLE_CLAUSE(NoOpenmpRoutines, OMPC_no_openmp_routines)
CHECK_SIMPLE_CLAUSE(NoParallelism, OMPC_no_parallelism)
CHECK_SIMPLE_CLAUSE(Notinbranch, OMPC_notinbranch)
CHECK_SIMPLE_CLAUSE(Novariants, OMPC_novariants)
CHECK_SIMPLE_CLAUSE(NumTasks, OMPC_num_tasks)
CHECK_SIMPLE_CLAUSE(OmpxAttribute, OMPC_ompx_attribute)
CHECK_SIMPLE_CLAUSE(Order, OMPC_order)
CHECK_SIMPLE_CLAUSE(Otherwise, OMPC_otherwise)
CHECK_SIMPLE_CLAUSE(Partial, OMPC_partial)
CHECK_SIMPLE_CLAUSE(ProcBind, OMPC_proc_bind)
CHECK_SIMPLE_CLAUSE(Read, OMPC_read)
CHECK_SIMPLE_CLAUSE(Relaxed, OMPC_relaxed)
CHECK_SIMPLE_CLAUSE(Release, OMPC_release)
CHECK_SIMPLE_CLAUSE(Replayable, OMPC_replayable)
CHECK_SIMPLE_CLAUSE(Safesync, OMPC_safesync)
CHECK_SIMPLE_CLAUSE(SeqCst, OMPC_seq_cst)
CHECK_SIMPLE_CLAUSE(Severity, OMPC_severity)
CHECK_SIMPLE_CLAUSE(Simd, OMPC_simd)
CHECK_SIMPLE_CLAUSE(Threadprivate, OMPC_threadprivate)
CHECK_SIMPLE_CLAUSE(Threadset, OMPC_threadset)
CHECK_SIMPLE_CLAUSE(Threads, OMPC_threads)
CHECK_SIMPLE_CLAUSE(Transparent, OMPC_transparent)
CHECK_SIMPLE_CLAUSE(Uniform, OMPC_uniform)
CHECK_SIMPLE_CLAUSE(Unknown, OMPC_unknown)
CHECK_SIMPLE_CLAUSE(Untied, OMPC_untied)
CHECK_SIMPLE_CLAUSE(Use, OMPC_use)
CHECK_SIMPLE_CLAUSE(UsesAllocators, OMPC_uses_allocators)
CHECK_SIMPLE_CLAUSE(Weak, OMPC_weak)
CHECK_SIMPLE_CLAUSE(Write, OMPC_write)

CHECK_REQ_SCALAR_INT_CLAUSE(OmpxDynCgroupMem, OMPC_ompx_dyn_cgroup_mem)
CHECK_REQ_SCALAR_INT_CLAUSE(Priority, OMPC_priority)

CHECK_REQ_CONSTANT_SCALAR_INT_CLAUSE(Collapse, OMPC_collapse)
CHECK_REQ_CONSTANT_SCALAR_INT_CLAUSE(Safelen, OMPC_safelen)
CHECK_REQ_CONSTANT_SCALAR_INT_CLAUSE(Simdlen, OMPC_simdlen)

} // namespace Fortran::semantics