Update as per review comments

Author: Leporacanthicus

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

@@ -4648,7 +4648,7 @@ struct OpenMPDeclareReductionConstruct {
   TUPLE_CLASS_BOILERPLATE(OpenMPDeclareReductionConstruct);
   CharBlock source;
   std::tuple<Verbatim, common::Indirection<OmpReductionSpecifier>,
-      OmpClauseList>
+      std::optional<OmpClauseList>>
       t;
 };
 

flang/lib/Lower/OpenMP/Clauses.h

@@ -231,7 +231,7 @@ using Inbranch = tomp::clause::InbranchT<TypeTy, IdTy, ExprTy>;
 using Inclusive = tomp::clause::InclusiveT<TypeTy, IdTy, ExprTy>;
 using Indirect = tomp::clause::IndirectT<TypeTy, IdTy, ExprTy>;
 using Init = tomp::clause::InitT<TypeTy, IdTy, ExprTy>;
-using Initializer = tomp::clause::InitT<TypeTy, IdTy, ExprTy>;
+using Initializer = tomp::clause::InitializerT<TypeTy, IdTy, ExprTy>;
 using InReduction = tomp::clause::InReductionT<TypeTy, IdTy, ExprTy>;
 using IsDevicePtr = tomp::clause::IsDevicePtrT<TypeTy, IdTy, ExprTy>;
 using Lastprivate = tomp::clause::LastprivateT<TypeTy, IdTy, ExprTy>;

flang/lib/Parser/openmp-parsers.cpp

@@ -1188,7 +1188,7 @@ TYPE_PARSER(construct<OmpInitializerClause>(
 TYPE_PARSER(sourced(construct<OpenMPDeclareReductionConstruct>(
     verbatim("DECLARE REDUCTION"_tok),
     "(" >> indirect(Parser<OmpReductionSpecifier>{}) / ")",
-    Parser<OmpClauseList>{})))
+    maybe(Parser<OmpClauseList>{}))))
 
 // declare-target with list
 TYPE_PARSER(sourced(construct<OmpDeclareTargetWithList>(

flang/lib/Parser/unparse.cpp

@@ -2716,7 +2716,7 @@ class UnparseVisitor {
     Put("(");
     Walk(std::get<common::Indirection<OmpReductionSpecifier>>(x.t));
     Put(")");
-    Walk(std::get<OmpClauseList>(x.t));
+    Walk(std::get<std::optional<OmpClauseList>>(x.t));
     Put("\n");
     EndOpenMP();
   }

flang/lib/Semantics/resolve-names.cpp

@@ -1496,11 +1496,9 @@ class OmpVisitor : public virtual DeclarationVisitor {
 
   bool Pre(const parser::OpenMPDeclareReductionConstruct &x) {
     AddOmpSourceRange(x.source);
-    parser::OmpClauseList emptyList{std::list<parser::OmpClause>{}};
     ProcessReductionSpecifier(
         std::get<Indirection<parser::OmpReductionSpecifier>>(x.t).value(),
-        emptyList);
-    Walk(std::get<parser::OmpClauseList>(x.t));
+        std::get<std::optional<parser::OmpClauseList>>(x.t));
     return false;
   }
   bool Pre(const parser::OmpMapClause &);
@@ -1657,7 +1655,7 @@ class OmpVisitor : public virtual DeclarationVisitor {
   void ProcessMapperSpecifier(const parser::OmpMapperSpecifier &spec,
       const parser::OmpClauseList &clauses);
   void ProcessReductionSpecifier(const parser::OmpReductionSpecifier &spec,
-      const parser::OmpClauseList &clauses);
+      const std::optional<parser::OmpClauseList> &clauses);
 };
 
 bool OmpVisitor::NeedsScope(const parser::OpenMPBlockConstruct &x) {
@@ -1752,7 +1750,7 @@ void OmpVisitor::ProcessMapperSpecifier(const parser::OmpMapperSpecifier &spec,
 
 void OmpVisitor::ProcessReductionSpecifier(
     const parser::OmpReductionSpecifier &spec,
-    const parser::OmpClauseList &clauses) {
+    const std::optional<parser::OmpClauseList> &clauses) {
   const auto &id{std::get<parser::OmpReductionIdentifier>(spec.t)};
   if (auto procDes{std::get_if<parser::ProcedureDesignator>(&id.u)}) {
     if (auto *name{std::get_if<parser::Name>(&procDes->u)}) {
@@ -1794,7 +1792,7 @@ bool OmpVisitor::Pre(const parser::OmpDirectiveSpecification &x) {
     if (maybeArgs && maybeClauses) {
       const parser::OmpArgument &first{maybeArgs->front()};
       if (auto *spec{std::get_if<parser::OmpReductionSpecifier>(&first.u)}) {
-        ProcessReductionSpecifier(*spec, *maybeClauses);
+        ProcessReductionSpecifier(*spec, maybeClauses);
       }
     }
     break;