[flang][OpenMP] Add parsing support for Task detach (#112312)

Add parsing support for task detach, along with parse/unparse tests.

Author: NimishMishra

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

@@ -510,6 +510,7 @@ class ParseTreeDumper {
   NODE_ENUM(OmpDefaultmapClause, ImplicitBehavior)
   NODE_ENUM(OmpDefaultmapClause, VariableCategory)
   NODE(parser, OmpDependClause)
+  NODE(parser, OmpDetachClause)
   NODE(OmpDependClause, InOut)
   NODE(OmpDependClause, Sink)
   NODE(OmpDependClause, Source)

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

@@ -3597,6 +3597,11 @@ struct OmpIfClause {
   std::tuple<std::optional<DirectiveNameModifier>, ScalarLogicalExpr> t;
 };
 
+// OpenMPv5.2 12.5.2 detach-clause -> DETACH (event-handle)
+struct OmpDetachClause {
+  WRAPPER_CLASS_BOILERPLATE(OmpDetachClause, OmpObject);
+};
+
 // OMP 5.0 2.19.5.6 in_reduction-clause -> IN_REDUCTION (reduction-identifier:
 //                                         variable-name-list)
 struct OmpInReductionClause {

flang/lib/Lower/OpenMP/Clauses.cpp

@@ -635,8 +635,8 @@ Destroy make(const parser::OmpClause::Destroy &inp,
 
 Detach make(const parser::OmpClause::Detach &inp,
             semantics::SemanticsContext &semaCtx) {
-  // inp -> empty
-  llvm_unreachable("Empty: detach");
+  // inp.v -> parser::OmpDetachClause
+  return Detach{makeObject(inp.v.v, semaCtx)};
 }
 
 Device make(const parser::OmpClause::Device &inp,

flang/lib/Parser/openmp-parsers.cpp

@@ -398,6 +398,9 @@ TYPE_CONTEXT_PARSER("Omp LINEAR clause"_en_US,
         construct<OmpLinearClause>(construct<OmpLinearClause::WithoutModifier>(
             nonemptyList(name), maybe(":" >> scalarIntConstantExpr)))))
 
+// OpenMPv5.2 12.5.2 detach-clause -> DETACH (event-handle)
+TYPE_PARSER(construct<OmpDetachClause>(Parser<OmpObject>{}))
+
 // 2.8.1 ALIGNED (list: alignment)
 TYPE_PARSER(construct<OmpAlignedClause>(
     Parser<OmpObjectList>{}, maybe(":" >> scalarIntConstantExpr)))
@@ -529,6 +532,8 @@ TYPE_PARSER(
                        parenthesized(Parser<OmpReductionClause>{}))) ||
     "IN_REDUCTION" >> construct<OmpClause>(construct<OmpClause::InReduction>(
                           parenthesized(Parser<OmpInReductionClause>{}))) ||
+    "DETACH" >> construct<OmpClause>(construct<OmpClause::Detach>(
+                    parenthesized(Parser<OmpDetachClause>{}))) ||
     "TASK_REDUCTION" >>
         construct<OmpClause>(construct<OmpClause::TaskReduction>(
             parenthesized(Parser<OmpReductionClause>{}))) ||

flang/lib/Parser/unparse.cpp

@@ -2157,6 +2157,7 @@ class UnparseVisitor {
     Put(":");
     Walk(std::get<OmpObjectList>(x.t));
   }
+  void Unparse(const OmpDetachClause &x) { Walk(x.v); }
   void Unparse(const OmpInReductionClause &x) {
     Walk(std::get<OmpReductionOperator>(x.t));
     Put(":");

flang/test/Lower/OpenMP/Todo/task_detach.f90

@@ -0,0 +1,16 @@
+! REQUIRES: openmp_runtime
+! RUN: %not_todo_cmd bbc -emit-fir -fopenmp -fopenmp-version=50 -o - %s 2>&1 | FileCheck %s
+! RUN: %not_todo_cmd %flang_fc1 -emit-fir -fopenmp -fopenmp-version=50 -o - %s 2>&1 | FileCheck %s
+
+!===============================================================================
+! `detach` clause
+!===============================================================================
+
+! CHECK: not yet implemented: OpenMP Block construct clause
+subroutine omp_task_detach()
+  use omp_lib
+  integer (kind=omp_event_handle_kind) :: event
+  !$omp task detach(event)
+  call foo()
+  !$omp end task
+end subroutine omp_task_detach

flang/test/Parser/OpenMP/task.f90

@@ -0,0 +1,17 @@
+! REQUIRES: openmp_runtime
+! RUN: %flang_fc1 -fdebug-dump-parse-tree -fopenmp -fopenmp-version=50  %s | FileCheck --ignore-case %s
+! RUN: %flang_fc1 -fdebug-unparse -fopenmp -fopenmp-version=50  %s | FileCheck --ignore-case --check-prefix="CHECK-UNPARSE" %s
+
+!CHECK: OmpBlockDirective -> llvm::omp::Directive = task
+!CHECK: OmpClauseList -> OmpClause -> Detach -> OmpDetachClause -> OmpObject -> Designator -> DataRef -> Name = 'event'
+
+!CHECK-UNPARSE: INTEGER(KIND=8_4) event
+!CHECK-UNPARSE: !$OMP TASK  DETACH(event)
+!CHECK-UNPARSE: !$OMP END TASK
+subroutine task_detach
+  use omp_lib
+  implicit none
+  integer(kind=omp_event_handle_kind) :: event
+  !$omp task detach(event)
+  !$omp end task
+end subroutine

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

@@ -135,6 +135,7 @@ def OMPC_Destroy : Clause<"destroy"> {
 }
 def OMPC_Detach : Clause<"detach"> {
   let clangClass = "OMPDetachClause";
+  let flangClass = "OmpDetachClause";
 }
 def OMPC_Device : Clause<"device"> {
   let clangClass = "OMPDeviceClause";