Add comments

Author: Leporacanthicus

flang/lib/Semantics/resolve-names.cpp

@@ -1758,10 +1758,27 @@ void OmpVisitor::ProcessReductionSpecifier(
           &MakeSymbol(*name, MiscDetails{MiscDetails::Kind::ConstructName});
     }
   }
-  // Creating a new scope in case the combiner expression (or clauses) use
-  // reerved identifiers, like "omp_in". This is a temporary solution until
-  // we deal with these in a more thorough way.
+
   auto &typeList{std::get<parser::OmpTypeNameList>(spec.t)};
+
+  // Create a temporary variable declaration for the three variables
+  // used in the reduction specifier (omp_out, omp_in and omp_priv),
+  // with of the type in the  typeList.
+  //
+  // In theory it would be possible to create only variables that are
+  // actually used, but that requires walking the entire parse-tree of the
+  // expressions, and finding the relevant variables [there may well be other
+  // variables involved too].
+  //
+  // This allows doing semantic analysis where the type is a derived type
+  // e.g omp_out%x = omp_out%x + omp_in%x.
+  //
+  // These need to be temporary (in their own scope). If they are created
+  // as variables in the outer scope, if there's more than one type in the
+  // typelist, duplicate symbols will be reported.
+  const parser::CharBlock ompVarNames[]{
+      {"omp_in", 6}, {"omp_out", 7}, {"omp_priv", 8}};
+
   for (auto &t : typeList.v) {
     PushScope(Scope::Kind::OtherConstruct, nullptr);
     BeginDeclTypeSpec();
@@ -1770,8 +1787,6 @@ void OmpVisitor::ProcessReductionSpecifier(
 
     const DeclTypeSpec *typeSpec{GetDeclTypeSpec()};
     assert(typeSpec && "We should have a type here");
-    const parser::CharBlock ompVarNames[]{
-        {"omp_in", 6}, {"omp_out", 7}, {"omp_priv", 8}};
 
     for (auto &nm : ompVarNames) {
       ObjectEntityDetails details{};