Check for loosely-strictured block instead of maintaining a flag

flang/include/flang/Parser/dump-parse-tree.h

@@ -713,7 +713,6 @@ public:
   NODE(parser, OmpEndDirective)
   NODE(parser, OpenMPAtomicConstruct)
   NODE(parser, OpenMPBlockConstruct)
-  NODE_ENUM(OpenMPBlockConstruct, Flags)
   NODE(parser, OpenMPCancelConstruct)
   NODE(parser, OpenMPCancellationPointConstruct)
   NODE(parser, OpenMPConstruct)

flang/include/flang/Parser/parse-tree.h

@@ -4783,25 +4783,15 @@ struct OmpEndDirective : public OmpDirectiveSpecification {
 // Common base class for block-associated constructs.
 struct OmpBlockConstruct {
   TUPLE_CLASS_BOILERPLATE(OmpBlockConstruct);
-  ENUM_CLASS(Flags, None, MissingMandatoryEndDirective);
-
-  /// Constructor with defualt value for Flags.
-  OmpBlockConstruct(OmpBeginDirective &&begin, Block &&block,
-      std::optional<OmpEndDirective> &&end)
-      : t(std::move(begin), std::move(block), std::move(end), Flags::None) {}
-
   const OmpBeginDirective &BeginDir() const {
     return std::get<OmpBeginDirective>(t);
   }
   const std::optional<OmpEndDirective> &EndDir() const {
     return std::get<std::optional<OmpEndDirective>>(t);
   }
-  bool isMissingMandatoryEndDirecitive() const {
-    return std::get<Flags>(t) == Flags::MissingMandatoryEndDirective;
-  }
 
   CharBlock source;
-  std::tuple<OmpBeginDirective, Block, std::optional<OmpEndDirective>, Flags> t;
+  std::tuple<OmpBeginDirective, Block, std::optional<OmpEndDirective>> t;
 };
 
 struct OmpMetadirectiveDirective {

flang/lib/Parser/openmp-parsers.cpp

@@ -1474,7 +1474,6 @@ struct OmpBlockConstructParser {
   constexpr OmpBlockConstructParser(llvm::omp::Directive dir) : dir_(dir) {}
 
   std::optional<resultType> Parse(ParseState &state) const {
-    using Flags = OmpBlockConstruct::Flags;
     if (auto &&begin{OmpBeginDirectiveParser(dir_).Parse(state)}) {
       if (auto &&body{attempt(StrictlyStructuredBlockParser{}).Parse(state)}) {
         // Try strictly-structured block with an optional end-directive
@@ -1503,8 +1502,7 @@ struct OmpBlockConstructParser {
         return OmpBlockConstruct{OmpBeginDirective(std::move(*begin)),
             std::move(*body),
             llvm::transformOptional(std::move(*end),
-                [](auto &&s) { return OmpEndDirective(std::move(s)); }),
-            endPresent ? Flags::None : Flags::MissingMandatoryEndDirective};
+                [](auto &&s) { return OmpEndDirective(std::move(s)); })};
       }
     }
     return std::nullopt;

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

@@ -788,7 +788,23 @@ void OmpStructureChecker::Enter(const parser::OpenMPBlockConstruct &x) {
 
   // Missing mandatory end block: this is checked in semantics because that
   // makes it easier to control the error messages.
-  if (x.isMissingMandatoryEndDirecitive()) {
+  // 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). In
+  // other words, the body doesn't contain exactly one parser::BlockConstruct.
+  auto isStrictlyStructuredBlock{[](const parser::Block &block) -> bool {
+    if (block.size() != 1) {
+      return false;
+    }
+    const parser::ExecutionPartConstruct &contents{block.front()};
+    auto *executableConstruct{
+        std::get_if<parser::ExecutableConstruct>(&contents.u)};
+    if (!executableConstruct) {
+      return false;
+    }
+    return std::holds_alternative<common::Indirection<parser::BlockConstruct>>(
+        executableConstruct->u);
+  }};
+  if (!endSpec && !isStrictlyStructuredBlock(block)) {
     context_.Say(
         x.BeginDir().source, "Expected OpenMP end directive"_err_en_US);
   }