[flang] [llvm] [flang][OpenMP] Overhaul implementation of ATOMIC construct (PR #137852)

Tom Eccles via llvm-commits llvm-commits at lists.llvm.org
Wed May 28 10:19:08 PDT 2025


================
@@ -2656,527 +2665,1857 @@ void OmpStructureChecker::Leave(const parser::OmpEndBlockDirective &x) {
   }
 }
 
-inline void OmpStructureChecker::ErrIfAllocatableVariable(
-    const parser::Variable &var) {
-  // Err out if the given symbol has
-  // ALLOCATABLE attribute
-  if (const auto *e{GetExpr(context_, var)})
-    for (const Symbol &symbol : evaluate::CollectSymbols(*e))
-      if (IsAllocatable(symbol)) {
-        const auto &designator =
-            std::get<common::Indirection<parser::Designator>>(var.u);
-        const auto *dataRef =
-            std::get_if<parser::DataRef>(&designator.value().u);
-        const parser::Name *name =
-            dataRef ? std::get_if<parser::Name>(&dataRef->u) : nullptr;
-        if (name)
-          context_.Say(name->source,
-              "%s must not have ALLOCATABLE "
-              "attribute"_err_en_US,
-              name->ToString());
+/// parser::Block is a list of executable constructs, parser::BlockConstruct
+/// is Fortran's BLOCK/ENDBLOCK construct.
+/// Strip the outermost BlockConstructs, return the reference to the Block
+/// in the executable part of the innermost of the stripped constructs.
+/// Specifically, if the given `block` has a single entry (it's a list), and
+/// the entry is a BlockConstruct, get the Block contained within. Repeat
+/// this step as many times as possible.
+static const parser::Block &GetInnermostExecPart(const parser::Block &block) {
+  const parser::Block *iter{&block};
+  while (iter->size() == 1) {
+    const parser::ExecutionPartConstruct &ep{iter->front()};
+    if (auto *exec{std::get_if<parser::ExecutableConstruct>(&ep.u)}) {
+      using BlockConstruct = common::Indirection<parser::BlockConstruct>;
+      if (auto *bc{std::get_if<BlockConstruct>(&exec->u)}) {
+        iter = &std::get<parser::Block>(bc->value().t);
+        continue;
       }
+    }
+    break;
+  }
+  return *iter;
 }
 
-inline void OmpStructureChecker::ErrIfLHSAndRHSSymbolsMatch(
-    const parser::Variable &var, const parser::Expr &expr) {
-  // Err out if the symbol on the LHS is also used on the RHS of the assignment
-  // statement
-  const auto *e{GetExpr(context_, expr)};
-  const auto *v{GetExpr(context_, var)};
-  if (e && v) {
-    auto vSyms{evaluate::GetSymbolVector(*v)};
-    const Symbol &varSymbol = vSyms.front();
-    for (const Symbol &symbol : evaluate::GetSymbolVector(*e)) {
-      if (varSymbol == symbol) {
-        const common::Indirection<parser::Designator> *designator =
-            std::get_if<common::Indirection<parser::Designator>>(&expr.u);
-        if (designator) {
-          auto *z{var.typedExpr.get()};
-          auto *c{expr.typedExpr.get()};
-          if (z->v == c->v) {
-            context_.Say(expr.source,
-                "RHS expression on atomic assignment statement cannot access '%s'"_err_en_US,
-                var.GetSource());
-          }
-        } else {
-          context_.Say(expr.source,
-              "RHS expression on atomic assignment statement cannot access '%s'"_err_en_US,
-              var.GetSource());
-        }
-      }
+// There is no consistent way to get the source of a given ActionStmt, so
+// extract the source information from Statement<ActionStmt> when we can,
+// and keep it around for error reporting in further analyses.
+struct SourcedActionStmt {
+  const parser::ActionStmt *stmt{nullptr};
+  parser::CharBlock source;
+
+  operator bool() const { return stmt != nullptr; }
+};
+
+struct AnalyzedCondStmt {
+  SomeExpr cond{evaluate::NullPointer{}}; // Default ctor is deleted
+  parser::CharBlock source;
+  SourcedActionStmt ift, iff;
+};
+
+static SourcedActionStmt GetActionStmt(
+    const parser::ExecutionPartConstruct *x) {
+  if (x == nullptr) {
+    return SourcedActionStmt{};
+  }
+  if (auto *exec{std::get_if<parser::ExecutableConstruct>(&x->u)}) {
+    using ActionStmt = parser::Statement<parser::ActionStmt>;
+    if (auto *stmt{std::get_if<ActionStmt>(&exec->u)}) {
+      return SourcedActionStmt{&stmt->statement, stmt->source};
     }
   }
+  return SourcedActionStmt{};
 }
 
-inline void OmpStructureChecker::ErrIfNonScalarAssignmentStmt(
-    const parser::Variable &var, const parser::Expr &expr) {
-  // Err out if either the variable on the LHS or the expression on the RHS of
-  // the assignment statement are non-scalar (i.e. have rank > 0 or is of
-  // CHARACTER type)
-  const auto *e{GetExpr(context_, expr)};
-  const auto *v{GetExpr(context_, var)};
-  if (e && v) {
-    if (e->Rank() != 0 ||
-        (e->GetType().has_value() &&
-            e->GetType().value().category() == common::TypeCategory::Character))
-      context_.Say(expr.source,
-          "Expected scalar expression "
-          "on the RHS of atomic assignment "
-          "statement"_err_en_US);
-    if (v->Rank() != 0 ||
-        (v->GetType().has_value() &&
-            v->GetType()->category() == common::TypeCategory::Character))
-      context_.Say(var.GetSource(),
-          "Expected scalar variable "
-          "on the LHS of atomic assignment "
-          "statement"_err_en_US);
-  }
-}
-
-template <typename T, typename D>
-bool OmpStructureChecker::IsOperatorValid(const T &node, const D &variable) {
-  using AllowedBinaryOperators =
-      std::variant<parser::Expr::Add, parser::Expr::Multiply,
-          parser::Expr::Subtract, parser::Expr::Divide, parser::Expr::AND,
-          parser::Expr::OR, parser::Expr::EQV, parser::Expr::NEQV>;
-  using BinaryOperators = std::variant<parser::Expr::Add,
-      parser::Expr::Multiply, parser::Expr::Subtract, parser::Expr::Divide,
-      parser::Expr::AND, parser::Expr::OR, parser::Expr::EQV,
-      parser::Expr::NEQV, parser::Expr::Power, parser::Expr::Concat,
-      parser::Expr::LT, parser::Expr::LE, parser::Expr::EQ, parser::Expr::NE,
-      parser::Expr::GE, parser::Expr::GT>;
-
-  if constexpr (common::HasMember<T, BinaryOperators>) {
-    const auto &variableName{variable.GetSource().ToString()};
-    const auto &exprLeft{std::get<0>(node.t)};
-    const auto &exprRight{std::get<1>(node.t)};
-    if ((exprLeft.value().source.ToString() != variableName) &&
-        (exprRight.value().source.ToString() != variableName)) {
-      context_.Say(variable.GetSource(),
-          "Atomic update statement should be of form "
-          "`%s = %s operator expr` OR `%s = expr operator %s`"_err_en_US,
-          variableName, variableName, variableName, variableName);
-    }
-    return common::HasMember<T, AllowedBinaryOperators>;
+static SourcedActionStmt GetActionStmt(const parser::Block &block) {
+  if (block.size() == 1) {
+    return GetActionStmt(&block.front());
   }
-  return false;
+  return SourcedActionStmt{};
 }
 
-void OmpStructureChecker::CheckAtomicCaptureStmt(
-    const parser::AssignmentStmt &assignmentStmt) {
-  const auto &var{std::get<parser::Variable>(assignmentStmt.t)};
-  const auto &expr{std::get<parser::Expr>(assignmentStmt.t)};
-  common::visit(
-      common::visitors{
-          [&](const common::Indirection<parser::Designator> &designator) {
-            const auto *dataRef =
-                std::get_if<parser::DataRef>(&designator.value().u);
-            const auto *name =
-                dataRef ? std::get_if<parser::Name>(&dataRef->u) : nullptr;
-            if (name && IsAllocatable(*name->symbol))
-              context_.Say(name->source,
-                  "%s must not have ALLOCATABLE "
-                  "attribute"_err_en_US,
-                  name->ToString());
-          },
-          [&](const auto &) {
-            // Anything other than a `parser::Designator` is not allowed
-            context_.Say(expr.source,
-                "Expected scalar variable "
-                "of intrinsic type on RHS of atomic "
-                "assignment statement"_err_en_US);
-          }},
-      expr.u);
-  ErrIfLHSAndRHSSymbolsMatch(var, expr);
-  ErrIfNonScalarAssignmentStmt(var, expr);
-}
-
-void OmpStructureChecker::CheckAtomicWriteStmt(
-    const parser::AssignmentStmt &assignmentStmt) {
-  const auto &var{std::get<parser::Variable>(assignmentStmt.t)};
-  const auto &expr{std::get<parser::Expr>(assignmentStmt.t)};
-  ErrIfAllocatableVariable(var);
-  ErrIfLHSAndRHSSymbolsMatch(var, expr);
-  ErrIfNonScalarAssignmentStmt(var, expr);
-}
-
-void OmpStructureChecker::CheckAtomicUpdateStmt(
-    const parser::AssignmentStmt &assignment) {
-  const auto &expr{std::get<parser::Expr>(assignment.t)};
-  const auto &var{std::get<parser::Variable>(assignment.t)};
-  bool isIntrinsicProcedure{false};
-  bool isValidOperator{false};
-  common::visit(
-      common::visitors{
-          [&](const common::Indirection<parser::FunctionReference> &x) {
-            isIntrinsicProcedure = true;
-            const auto &procedureDesignator{
-                std::get<parser::ProcedureDesignator>(x.value().v.t)};
-            const parser::Name *name{
-                std::get_if<parser::Name>(&procedureDesignator.u)};
-            if (name &&
-                !(name->source == "max" || name->source == "min" ||
-                    name->source == "iand" || name->source == "ior" ||
-                    name->source == "ieor")) {
-              context_.Say(expr.source,
-                  "Invalid intrinsic procedure name in "
-                  "OpenMP ATOMIC (UPDATE) statement"_err_en_US);
-            }
-          },
-          [&](const auto &x) {
-            if (!IsOperatorValid(x, var)) {
-              context_.Say(expr.source,
-                  "Invalid or missing operator in atomic update "
-                  "statement"_err_en_US);
-            } else
-              isValidOperator = true;
-          },
-      },
-      expr.u);
-  if (const auto *e{GetExpr(context_, expr)}) {
-    const auto *v{GetExpr(context_, var)};
-    if (e->Rank() != 0 ||
-        (e->GetType().has_value() &&
-            e->GetType().value().category() == common::TypeCategory::Character))
-      context_.Say(expr.source,
-          "Expected scalar expression "
-          "on the RHS of atomic update assignment "
-          "statement"_err_en_US);
-    if (v->Rank() != 0 ||
-        (v->GetType().has_value() &&
-            v->GetType()->category() == common::TypeCategory::Character))
-      context_.Say(var.GetSource(),
-          "Expected scalar variable "
-          "on the LHS of atomic update assignment "
-          "statement"_err_en_US);
-    auto vSyms{evaluate::GetSymbolVector(*v)};
-    const Symbol &varSymbol = vSyms.front();
-    int numOfSymbolMatches{0};
-    SymbolVector exprSymbols{evaluate::GetSymbolVector(*e)};
-    for (const Symbol &symbol : exprSymbols) {
-      if (varSymbol == symbol) {
-        numOfSymbolMatches++;
-      }
-    }
-    if (isIntrinsicProcedure) {
-      std::string varName = var.GetSource().ToString();
-      if (numOfSymbolMatches != 1)
-        context_.Say(expr.source,
-            "Intrinsic procedure"
-            " arguments in atomic update statement"
-            " must have exactly one occurence of '%s'"_err_en_US,
-            varName);
-      else if (varSymbol != exprSymbols.front() &&
-          varSymbol != exprSymbols.back())
-        context_.Say(expr.source,
-            "Atomic update statement "
-            "should be of the form `%s = intrinsic_procedure(%s, expr_list)` "
-            "OR `%s = intrinsic_procedure(expr_list, %s)`"_err_en_US,
-            varName, varName, varName, varName);
-    } else if (isValidOperator) {
-      if (numOfSymbolMatches != 1)
-        context_.Say(expr.source,
-            "Exactly one occurence of '%s' "
-            "expected on the RHS of atomic update assignment statement"_err_en_US,
-            var.GetSource().ToString());
-    }
+// Compute the `evaluate::Assignment` from parser::ActionStmt. The assumption
+// is that the ActionStmt will be either an assignment or a pointer-assignment,
+// otherwise return std::nullopt.
+static std::optional<evaluate::Assignment> GetEvaluateAssignment(
+    const parser::ActionStmt *x) {
+  if (x == nullptr) {
+    return std::nullopt;
   }
 
-  ErrIfAllocatableVariable(var);
+  using AssignmentStmt = common::Indirection<parser::AssignmentStmt>;
+  using PointerAssignmentStmt =
+      common::Indirection<parser::PointerAssignmentStmt>;
+  using TypedAssignment = parser::AssignmentStmt::TypedAssignment;
+
+  return common::visit(
+      [](auto &&s) -> std::optional<evaluate::Assignment> {
+        using BareS = llvm::remove_cvref_t<decltype(s)>;
+        if constexpr (std::is_same_v<BareS, AssignmentStmt> ||
+            std::is_same_v<BareS, PointerAssignmentStmt>) {
+          const TypedAssignment &typed{s.value().typedAssignment};
+          // ForwardOwningPointer                 typedAssignment
+          // `- GenericAssignmentWrapper          ^.get()
+          //    `- std::optional<Assignment>      ^->v
+          return typed.get()->v;
+        } else {
+          return std::nullopt;
+        }
+      },
+      x->u);
 }
 
-void OmpStructureChecker::CheckAtomicCompareConstruct(
-    const parser::OmpAtomicCompare &atomicCompareConstruct) {
+static std::optional<AnalyzedCondStmt> AnalyzeConditionalStmt(
+    const parser::ExecutionPartConstruct *x) {
+  if (x == nullptr) {
+    return std::nullopt;
+  }
 
-  // TODO: Check that the if-stmt is `if (var == expr) var = new`
-  //       [with or without then/end-do]
+  // Extract the evaluate::Expr from ScalarLogicalExpr.
+  auto getFromLogical{[](const parser::ScalarLogicalExpr &logical) {
+    // ScalarLogicalExpr is Scalar<Logical<common::Indirection<Expr>>>
+    const parser::Expr &expr{logical.thing.thing.value()};
+    return GetEvaluateExpr(expr);
+  }};
 
-  unsigned version{context_.langOptions().OpenMPVersion};
-  if (version < 51) {
-    context_.Say(atomicCompareConstruct.source,
-        "%s construct not allowed in %s, %s"_err_en_US,
-        atomicCompareConstruct.source, ThisVersion(version), TryVersion(51));
-  }
-
-  // TODO: More work needed here. Some of the Update restrictions need to
-  // be added, but Update isn't the same either.
-}
-
-// TODO: Allow cond-update-stmt once compare clause is supported.
-void OmpStructureChecker::CheckAtomicCaptureConstruct(
-    const parser::OmpAtomicCapture &atomicCaptureConstruct) {
-  const parser::AssignmentStmt &stmt1 =
-      std::get<parser::OmpAtomicCapture::Stmt1>(atomicCaptureConstruct.t)
-          .v.statement;
-  const auto &stmt1Var{std::get<parser::Variable>(stmt1.t)};
-  const auto &stmt1Expr{std::get<parser::Expr>(stmt1.t)};
-  const auto *v1 = GetExpr(context_, stmt1Var);
-  const auto *e1 = GetExpr(context_, stmt1Expr);
-
-  const parser::AssignmentStmt &stmt2 =
-      std::get<parser::OmpAtomicCapture::Stmt2>(atomicCaptureConstruct.t)
-          .v.statement;
-  const auto &stmt2Var{std::get<parser::Variable>(stmt2.t)};
-  const auto &stmt2Expr{std::get<parser::Expr>(stmt2.t)};
-  const auto *v2 = GetExpr(context_, stmt2Var);
-  const auto *e2 = GetExpr(context_, stmt2Expr);
-
-  if (e1 && v1 && e2 && v2) {
-    if (semantics::checkForSingleVariableOnRHS(stmt1)) {
-      CheckAtomicCaptureStmt(stmt1);
-      if (semantics::checkForSymbolMatch(v2, e2)) {
-        // ATOMIC CAPTURE construct is of the form [capture-stmt, update-stmt]
-        CheckAtomicUpdateStmt(stmt2);
-      } else {
-        // ATOMIC CAPTURE construct is of the form [capture-stmt, write-stmt]
-        CheckAtomicWriteStmt(stmt2);
+  // Recognize either
+  // ExecutionPartConstruct -> ExecutableConstruct -> ActionStmt -> IfStmt, or
+  // ExecutionPartConstruct -> ExecutableConstruct -> IfConstruct.
+
+  if (auto &&action{GetActionStmt(x)}) {
+    if (auto *ifs{std::get_if<common::Indirection<parser::IfStmt>>(
+            &action.stmt->u)}) {
+      const parser::IfStmt &s{ifs->value()};
+      auto &&maybeCond{
+          getFromLogical(std::get<parser::ScalarLogicalExpr>(s.t))};
+      auto &thenStmt{
+          std::get<parser::UnlabeledStatement<parser::ActionStmt>>(s.t)};
+      if (maybeCond) {
+        return AnalyzedCondStmt{std::move(*maybeCond), action.source,
+            SourcedActionStmt{&thenStmt.statement, thenStmt.source},
+            SourcedActionStmt{}};
       }
-      if (!(*e1 == *v2)) {
-        context_.Say(stmt1Expr.source,
-            "Captured variable/array element/derived-type component %s expected to be assigned in the second statement of ATOMIC CAPTURE construct"_err_en_US,
-            stmt1Expr.source);
-      }
-    } else if (semantics::checkForSymbolMatch(v1, e1) &&
-        semantics::checkForSingleVariableOnRHS(stmt2)) {
-      // ATOMIC CAPTURE construct is of the form [update-stmt, capture-stmt]
-      CheckAtomicUpdateStmt(stmt1);
-      CheckAtomicCaptureStmt(stmt2);
-      // Variable updated in stmt1 should be captured in stmt2
-      if (!(*v1 == *e2)) {
-        context_.Say(stmt1Var.GetSource(),
-            "Updated variable/array element/derived-type component %s expected to be captured in the second statement of ATOMIC CAPTURE construct"_err_en_US,
-            stmt1Var.GetSource());
-      }
-    } else {
-      context_.Say(stmt1Expr.source,
-          "Invalid ATOMIC CAPTURE construct statements. Expected one of [update-stmt, capture-stmt], [capture-stmt, update-stmt], or [capture-stmt, write-stmt]"_err_en_US);
     }
+    return std::nullopt;
   }
-}
 
-void OmpStructureChecker::CheckAtomicMemoryOrderClause(
-    const parser::OmpAtomicClauseList *leftHandClauseList,
-    const parser::OmpAtomicClauseList *rightHandClauseList) {
-  int numMemoryOrderClause{0};
-  int numFailClause{0};
-  auto checkForValidMemoryOrderClause = [&](const parser::OmpAtomicClauseList
-                                                *clauseList) {
-    for (const auto &clause : clauseList->v) {
-      if (std::get_if<parser::OmpFailClause>(&clause.u)) {
-        numFailClause++;
-        if (numFailClause > 1) {
-          context_.Say(clause.source,
-              "More than one FAIL clause not allowed on OpenMP ATOMIC construct"_err_en_US);
-          return;
+  if (auto *exec{std::get_if<parser::ExecutableConstruct>(&x->u)}) {
+    if (auto *ifc{
+            std::get_if<common::Indirection<parser::IfConstruct>>(&exec->u)}) {
+      using ElseBlock = parser::IfConstruct::ElseBlock;
+      using ElseIfBlock = parser::IfConstruct::ElseIfBlock;
+      const parser::IfConstruct &s{ifc->value()};
+
+      if (!std::get<std::list<ElseIfBlock>>(s.t).empty()) {
+        // Not expecting any else-if statements.
+        return std::nullopt;
+      }
+      auto &stmt{std::get<parser::Statement<parser::IfThenStmt>>(s.t)};
+      auto &&maybeCond{getFromLogical(
+          std::get<parser::ScalarLogicalExpr>(stmt.statement.t))};
+      if (!maybeCond) {
+        return std::nullopt;
+      }
+
+      if (auto &maybeElse{std::get<std::optional<ElseBlock>>(s.t)}) {
+        AnalyzedCondStmt result{std::move(*maybeCond), stmt.source,
+            GetActionStmt(std::get<parser::Block>(s.t)),
+            GetActionStmt(std::get<parser::Block>(maybeElse->t))};
+        if (result.ift.stmt && result.iff.stmt) {
+          return result;
         }
       } else {
-        if (std::get_if<parser::OmpMemoryOrderClause>(&clause.u)) {
-          numMemoryOrderClause++;
-          if (numMemoryOrderClause > 1) {
-            context_.Say(clause.source,
-                "More than one memory order clause not allowed on OpenMP ATOMIC construct"_err_en_US);
-            return;
-          }
+        AnalyzedCondStmt result{std::move(*maybeCond), stmt.source,
+            GetActionStmt(std::get<parser::Block>(s.t))};
+        if (result.ift.stmt) {
+          return result;
         }
       }
     }
-  };
-  if (leftHandClauseList) {
-    checkForValidMemoryOrderClause(leftHandClauseList);
-  }
-  if (rightHandClauseList) {
-    checkForValidMemoryOrderClause(rightHandClauseList);
+    return std::nullopt;
   }
-}
 
-void OmpStructureChecker::Enter(const parser::OpenMPAtomicConstruct &x) {
-  common::visit(
-      common::visitors{
-          [&](const parser::OmpAtomic &atomicConstruct) {
-            const auto &dir{std::get<parser::Verbatim>(atomicConstruct.t)};
-            PushContextAndClauseSets(
-                dir.source, llvm::omp::Directive::OMPD_atomic);
-            CheckAtomicUpdateStmt(
-                std::get<parser::Statement<parser::AssignmentStmt>>(
-                    atomicConstruct.t)
-                    .statement);
-            CheckAtomicMemoryOrderClause(
-                &std::get<parser::OmpAtomicClauseList>(atomicConstruct.t),
-                nullptr);
-            CheckHintClause<const parser::OmpAtomicClauseList>(
-                &std::get<parser::OmpAtomicClauseList>(atomicConstruct.t),
-                nullptr, "ATOMIC");
-          },
-          [&](const parser::OmpAtomicUpdate &atomicUpdate) {
-            const auto &dir{std::get<parser::Verbatim>(atomicUpdate.t)};
-            PushContextAndClauseSets(
-                dir.source, llvm::omp::Directive::OMPD_atomic);
-            CheckAtomicUpdateStmt(
-                std::get<parser::Statement<parser::AssignmentStmt>>(
-                    atomicUpdate.t)
-                    .statement);
-            CheckAtomicMemoryOrderClause(
-                &std::get<0>(atomicUpdate.t), &std::get<2>(atomicUpdate.t));
-            CheckHintClause<const parser::OmpAtomicClauseList>(
-                &std::get<0>(atomicUpdate.t), &std::get<2>(atomicUpdate.t),
-                "UPDATE");
-          },
-          [&](const parser::OmpAtomicRead &atomicRead) {
-            const auto &dir{std::get<parser::Verbatim>(atomicRead.t)};
-            PushContextAndClauseSets(
-                dir.source, llvm::omp::Directive::OMPD_atomic);
-            CheckAtomicMemoryOrderClause(
-                &std::get<0>(atomicRead.t), &std::get<2>(atomicRead.t));
-            CheckHintClause<const parser::OmpAtomicClauseList>(
-                &std::get<0>(atomicRead.t), &std::get<2>(atomicRead.t), "READ");
-            CheckAtomicCaptureStmt(
-                std::get<parser::Statement<parser::AssignmentStmt>>(
-                    atomicRead.t)
-                    .statement);
-          },
-          [&](const parser::OmpAtomicWrite &atomicWrite) {
-            const auto &dir{std::get<parser::Verbatim>(atomicWrite.t)};
-            PushContextAndClauseSets(
-                dir.source, llvm::omp::Directive::OMPD_atomic);
-            CheckAtomicMemoryOrderClause(
-                &std::get<0>(atomicWrite.t), &std::get<2>(atomicWrite.t));
-            CheckHintClause<const parser::OmpAtomicClauseList>(
-                &std::get<0>(atomicWrite.t), &std::get<2>(atomicWrite.t),
-                "WRITE");
-            CheckAtomicWriteStmt(
-                std::get<parser::Statement<parser::AssignmentStmt>>(
-                    atomicWrite.t)
-                    .statement);
-          },
-          [&](const parser::OmpAtomicCapture &atomicCapture) {
-            const auto &dir{std::get<parser::Verbatim>(atomicCapture.t)};
-            PushContextAndClauseSets(
-                dir.source, llvm::omp::Directive::OMPD_atomic);
-            CheckAtomicMemoryOrderClause(
-                &std::get<0>(atomicCapture.t), &std::get<2>(atomicCapture.t));
-            CheckHintClause<const parser::OmpAtomicClauseList>(
-                &std::get<0>(atomicCapture.t), &std::get<2>(atomicCapture.t),
-                "CAPTURE");
-            CheckAtomicCaptureConstruct(atomicCapture);
-          },
-          [&](const parser::OmpAtomicCompare &atomicCompare) {
-            const auto &dir{std::get<parser::Verbatim>(atomicCompare.t)};
-            PushContextAndClauseSets(
-                dir.source, llvm::omp::Directive::OMPD_atomic);
-            CheckAtomicMemoryOrderClause(
-                &std::get<0>(atomicCompare.t), &std::get<2>(atomicCompare.t));
-            CheckHintClause<const parser::OmpAtomicClauseList>(
-                &std::get<0>(atomicCompare.t), &std::get<2>(atomicCompare.t),
-                "CAPTURE");
-            CheckAtomicCompareConstruct(atomicCompare);
-          },
-      },
-      x.u);
+  return std::nullopt;
 }
 
-void OmpStructureChecker::Leave(const parser::OpenMPAtomicConstruct &) {
-  dirContext_.pop_back();
+static std::pair<parser::CharBlock, parser::CharBlock> SplitAssignmentSource(
+    parser::CharBlock source) {
+  // Find => in the range, if not found, find = that is not a part of
+  // <=, >=, ==, or /=.
+  auto trim{[](std::string_view v) {
+    const char *begin{v.data()};
+    const char *end{begin + v.size()};
+    while (*begin == ' ' && begin != end) {
+      ++begin;
+    }
+    while (begin != end && end[-1] == ' ') {
+      --end;
+    }
+    assert(begin != end && "Source should not be empty");
+    return parser::CharBlock(begin, end - begin);
+  }};
+
+  std::string_view sv(source.begin(), source.size());
+
+  if (auto where{sv.find("=>")}; where != sv.npos) {
+    std::string_view lhs(sv.data(), where);
+    std::string_view rhs(sv.data() + where + 2, sv.size() - where - 2);
+    return std::make_pair(trim(lhs), trim(rhs));
+  }
+
+  // Go backwards, since all the exclusions above end with a '='.
+  for (size_t next{source.size()}; next > 1; --next) {
+    if (sv[next - 1] == '=' && !llvm::is_contained("<>=/", sv[next - 2])) {
+      std::string_view lhs(sv.data(), next - 1);
+      std::string_view rhs(sv.data() + next, sv.size() - next);
+      return std::make_pair(trim(lhs), trim(rhs));
+    }
+  }
+  llvm_unreachable("Could not find assignment operator");
+}
+
+namespace atomic {
+
+template <typename V> static void MoveAppend(V &accum, V &&other) {
+  for (auto &&s : other) {
+    accum.push_back(std::move(s));
+  }
+}
+
+enum class Operator {
+  Unk,
+  // Operators that are officially allowed in the update operation
+  Add,
+  And,
+  Associated,
+  Div,
+  Eq,
+  Eqv,
+  Ge, // extension
+  Gt,
+  Identity, // extension: x = x is allowed (*), but we should never print
+            // "identity" as the name of the operator
+  Le, // extension
+  Lt,
+  Max,
+  Min,
+  Mul,
+  Ne, // extension
+  Neqv,
+  Or,
+  Sub,
+  // Operators that we recognize for technical reasons
+  True,
+  False,
+  Not,
+  Convert,
+  Resize,
+  Intrinsic,
+  Call,
+  Pow,
+
+  // (*): "x = x + 0" is a valid update statement, but it will be folded
+  //      to "x = x" by the time we look at it. Since the source statements
+  //      "x = x" and "x = x + 0" will end up looking the same, accept the
+  //      former as an extension.
+};
+
+std::string ToString(Operator op) {
+  switch (op) {
+  case Operator::Add:
+    return "+";
+  case Operator::And:
+    return "AND";
+  case Operator::Associated:
+    return "ASSOCIATED";
+  case Operator::Div:
+    return "/";
+  case Operator::Eq:
+    return "==";
+  case Operator::Eqv:
+    return "EQV";
+  case Operator::Ge:
+    return ">=";
+  case Operator::Gt:
+    return ">";
+  case Operator::Identity:
+    return "identity";
----------------
tblah wrote:

>From above:
```
// extension: x = x is allowed (*), but we should never print
// "identity" as the name of the operator
```
maybe this should be an llvm::unreachable, plus some logic at each call?

https://github.com/llvm/llvm-project/pull/137852


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