Argument to GRAPH_RESET is optional

Author: kparzysz

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

@@ -4441,9 +4441,10 @@ struct OmpGraphIdClause {
 // Ref: [6.0:438-439]
 //
 // graph_reset-clause ->
-//    GRAPH_RESET(graph-reset-expression)           // since 6.0
+//    GRAPH_RESET[(graph-reset-expression)]         // since 6.0
 struct OmpGraphResetClause {
-  WRAPPER_CLASS_BOILERPLATE(OmpGraphResetClause, common::Indirection<Expr>);
+  WRAPPER_CLASS_BOILERPLATE(
+      OmpGraphResetClause, std::optional<common::Indirection<Expr>>);
 };
 
 // Ref: [5.0:234-242], [5.1:266-275], [5.2:299], [6.0:472-473]

flang/lib/Parser/openmp-parsers.cpp

@@ -1108,8 +1108,9 @@ TYPE_PARSER( //
                        parenthesized(Parser<OmpGrainsizeClause>{}))) ||
     "GRAPH_ID" >> construct<OmpClause>(construct<OmpClause::GraphId>(
                       parenthesized(Parser<OmpGraphIdClause>{}))) ||
-    "GRAPH_RESET" >> construct<OmpClause>(construct<OmpClause::GraphReset>(
-                         parenthesized(Parser<OmpGraphResetClause>{}))) ||
+    "GRAPH_RESET" >>
+        construct<OmpClause>(construct<OmpClause::GraphReset>(
+            maybe(parenthesized(Parser<OmpGraphResetClause>{})))) ||
     "HAS_DEVICE_ADDR" >>
         construct<OmpClause>(construct<OmpClause::HasDeviceAddr>(
             parenthesized(Parser<OmpObjectList>{}))) ||

flang/test/Parser/OpenMP/taskgraph.f90

@@ -71,3 +71,25 @@ subroutine f01(x, y)
 !PARSE-TREE: | | OmpDirectiveName -> llvm::omp::Directive = taskgraph
 !PARSE-TREE: | | OmpClauseList ->
 !PARSE-TREE: | | Flags = None
+
+
+subroutine f02
+  !$omp taskgraph graph_reset
+  !$omp end taskgraph
+end
+
+!UNPARSE: SUBROUTINE f02
+!UNPARSE: !$OMP TASKGRAPH GRAPH_RESET
+!UNPARSE: !$OMP END TASKGRAPH
+!UNPARSE: END SUBROUTINE
+
+!PARSE-TREE: ExecutionPartConstruct -> ExecutableConstruct -> OpenMPConstruct -> OmpBlockConstruct
+!PARSE-TREE: | OmpBeginDirective
+!PARSE-TREE: | | OmpDirectiveName -> llvm::omp::Directive = taskgraph
+!PARSE-TREE: | | OmpClauseList -> OmpClause -> GraphReset ->
+!PARSE-TREE: | | Flags = None
+!PARSE-TREE: | Block
+!PARSE-TREE: | OmpEndDirective
+!PARSE-TREE: | | OmpDirectiveName -> llvm::omp::Directive = taskgraph
+!PARSE-TREE: | | OmpClauseList ->
+!PARSE-TREE: | | Flags = None

llvm/include/llvm/Frontend/OpenMP/OMP.td

@@ -231,6 +231,7 @@ def OMPC_GraphId : Clause<[Spelling<"graph_id">]> {
 }
 def OMPC_GraphReset : Clause<[Spelling<"graph_reset">]> {
   let flangClass = "OmpGraphResetClause";
+  let isValueOptional = true;
 }
 def OMPC_HasDeviceAddr : Clause<[Spelling<"has_device_addr">]> {
   let clangClass = "OMPHasDeviceAddrClause";