[flang][OpenMP] Stop tracking metadirective level in name resolution (#159945)

This was checked in the visitor for OmpDirectiveSpecification, and is
not necessary anymore: the early exit (in case of not being inside of a
METADIRECTIVE) performs the same actions as the code that was skipped,
except it does so through a different sequence of function calls. The
net result ends up being the same in either case.

The processing of the mapper and reduction specifiers inside of
OmpDirectiveSpecification is necesary for the declare directives on
WHEN/OTHERWISE clauses, so it's the early exit that needs to be removed.
In fact, when the DECLARE_MAPPER/REDUCTION use
OmpDirectiveSpecification, this processing will automatically take over
the handling of the contained specifiers.

Author: kparzysz

flang/lib/Semantics/resolve-names.cpp

@@ -1479,14 +1479,6 @@ class OmpVisitor : public virtual DeclarationVisitor {
   static bool NeedsScope(const parser::OmpBlockConstruct &);
   static bool NeedsScope(const parser::OmpClause &);
 
-  bool Pre(const parser::OmpMetadirectiveDirective &x) { //
-    ++metaLevel_;
-    return true;
-  }
-  void Post(const parser::OmpMetadirectiveDirective &) { //
-    --metaLevel_;
-  }
-
   bool Pre(const parser::OpenMPRequiresConstruct &x) {
     AddOmpSourceRange(x.source);
     return true;
@@ -1579,10 +1571,11 @@ class OmpVisitor : public virtual DeclarationVisitor {
 
   bool Pre(const parser::OpenMPDeclareReductionConstruct &x) {
     AddOmpSourceRange(x.source);
+    parser::OmpClauseList empty(std::list<parser::OmpClause>{});
+    auto &maybeClauses{std::get<std::optional<parser::OmpClauseList>>(x.t)};
     ProcessReductionSpecifier(
         std::get<Indirection<parser::OmpReductionSpecifier>>(x.t).value(),
-        std::get<std::optional<parser::OmpClauseList>>(x.t),
-        declaratives_.back());
+        maybeClauses ? *maybeClauses : empty, declaratives_.back());
     return false;
   }
   bool Pre(const parser::OmpMapClause &);
@@ -1738,12 +1731,11 @@ class OmpVisitor : public virtual DeclarationVisitor {
   void ProcessMapperSpecifier(const parser::OmpMapperSpecifier &spec,
       const parser::OmpClauseList &clauses);
   void ProcessReductionSpecifier(const parser::OmpReductionSpecifier &spec,
-      const std::optional<parser::OmpClauseList> &clauses,
+      const parser::OmpClauseList &clauses,
       const parser::OpenMPDeclarativeConstruct *wholeConstruct);
 
   void ResolveCriticalName(const parser::OmpArgument &arg);
 
-  int metaLevel_{0};
   std::vector<const parser::OpenMPDeclarativeConstruct *> declaratives_;
 };
 
@@ -1871,7 +1863,7 @@ std::string MangleDefinedOperator(const parser::CharBlock &name) {
 
 void OmpVisitor::ProcessReductionSpecifier(
     const parser::OmpReductionSpecifier &spec,
-    const std::optional<parser::OmpClauseList> &clauses,
+    const parser::OmpClauseList &clauses,
     const parser::OpenMPDeclarativeConstruct *construct) {
   const parser::Name *name{nullptr};
   parser::CharBlock mangledName;
@@ -1999,39 +1991,31 @@ void OmpVisitor::ResolveCriticalName(const parser::OmpArgument &arg) {
 
 bool OmpVisitor::Pre(const parser::OmpDirectiveSpecification &x) {
   AddOmpSourceRange(x.source);
-  if (metaLevel_ == 0) {
-    // Not in METADIRECTIVE.
-    return true;
-  }
 
-  // If OmpDirectiveSpecification (which contains clauses) is a part of
-  // METADIRECTIVE, some semantic checks may not be applicable.
-  // Disable the semantic analysis for it in such cases to allow the compiler
-  // to parse METADIRECTIVE without flagging errors.
-  auto &maybeArgs{std::get<std::optional<parser::OmpArgumentList>>(x.t)};
-  auto &maybeClauses{std::get<std::optional<parser::OmpClauseList>>(x.t)};
+  const parser::OmpArgumentList &args{x.Arguments()};
+  const parser::OmpClauseList &clauses{x.Clauses()};
 
   switch (x.DirId()) {
   case llvm::omp::Directive::OMPD_declare_mapper:
-    if (maybeArgs && maybeClauses) {
-      const parser::OmpArgument &first{maybeArgs->v.front()};
+    if (!args.v.empty()) {
+      const parser::OmpArgument &first{args.v.front()};
       if (auto *spec{std::get_if<parser::OmpMapperSpecifier>(&first.u)}) {
-        ProcessMapperSpecifier(*spec, *maybeClauses);
+        ProcessMapperSpecifier(*spec, clauses);
       }
     }
     break;
   case llvm::omp::Directive::OMPD_declare_reduction:
-    if (maybeArgs && maybeClauses) {
-      const parser::OmpArgument &first{maybeArgs->v.front()};
+    if (!args.v.empty()) {
+      const parser::OmpArgument &first{args.v.front()};
       if (auto *spec{std::get_if<parser::OmpReductionSpecifier>(&first.u)}) {
-        ProcessReductionSpecifier(*spec, maybeClauses, declaratives_.back());
+        ProcessReductionSpecifier(*spec, clauses, declaratives_.back());
       }
     }
     break;
   default:
     // Default processing.
-    Walk(maybeArgs);
-    Walk(maybeClauses);
+    Walk(args);
+    Walk(clauses);
     break;
   }
   return false;