[Flang] Add a semantic check and LLVM Lowering support for UNTIED TASK

Implementation details:
The UNTIED clause is recognized by setting the flag=0 for the default
case or performing logical OR to flag if other clauses are specified,
and this flag is passed as an argument to the `__kmpc_omp_task_alloc`
runtime call.

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -2867,6 +2867,7 @@ static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
         !std::holds_alternative<clause::UseDevicePtr>(clause.u) &&
         !std::holds_alternative<clause::InReduction>(clause.u) &&
         !std::holds_alternative<clause::Mergeable>(clause.u) &&
+        !std::holds_alternative<clause::Untied>(clause.u) &&
         !std::holds_alternative<clause::TaskReduction>(clause.u) &&
         !std::holds_alternative<clause::Detach>(clause.u)) {
       std::string name =

flang/lib/Semantics/check-omp-structure.cpp

@@ -213,6 +213,29 @@ class AssociatedLoopChecker {
   std::map<std::string, std::int64_t> constructNamesAndLevels_;
 };
 
+// `OmpDesignatorChecker` is used to check if the designator
+// can appear within the OpenMP construct
+class OmpDesignatorChecker {
+public:
+  OmpDesignatorChecker(SemanticsContext &context) : context_{context} {}
+
+  template <typename T> bool Pre(const T &) { return true; }
+  template <typename T> void Post(const T &) {}
+
+  bool Pre(const parser::Name &name) {
+    if (name.symbol->test(Symbol::Flag::OmpThreadprivate)) {
+      // OpenMP 5.2: 5.2 threadprivate directive restriction
+      context_.Say(name.source,
+          "A THREADPRIVATE variable `%s` cannot appear in a UNTIED TASK region"_err_en_US,
+          name.source);
+    }
+    return true;
+  }
+
+private:
+  SemanticsContext &context_;
+};
+
 bool OmpStructureChecker::CheckAllowedClause(llvmOmpClause clause) {
   unsigned version{context_.langOptions().OpenMPVersion};
   DirectiveContext &dirCtx = GetContext();
@@ -1164,6 +1187,16 @@ void OmpStructureChecker::Enter(const parser::OpenMPBlockConstruct &x) {
     HasInvalidWorksharingNesting(
         beginDir.source, llvm::omp::nestedWorkshareErrSet);
     break;
+  case llvm::omp::Directive::OMPD_task: {
+    const auto &clauses{std::get<parser::OmpClauseList>(beginBlockDir.t)};
+    for (const auto &clause : clauses.v) {
+      if (std::get_if<parser::OmpClause::Untied>(&clause.u)) {
+        OmpDesignatorChecker ompDesignatorChecker{context_};
+        parser::Walk(block, ompDesignatorChecker);
+      }
+    }
+    break;
+  }
   default:
     break;
   }

flang/test/Lower/OpenMP/task.f90

@@ -235,10 +235,27 @@ subroutine task_multiple_clauses()
   !$omp end task
 end subroutine task_multiple_clauses
 
+!===============================================================================
+! `mergeable` clause
+!===============================================================================
+
 subroutine task_mergeable()
 !CHECK: omp.task mergeable {
 !CHECK: omp.terminator
 !CHECK: }
  !$omp task mergeable
  !$omp end task
 end subroutine
+
+!===============================================================================
+! `untied` clause
+!===============================================================================
+
+!CHECK-LABEL: func.func @_QPomp_task_untied() {
+subroutine omp_task_untied()
+  !CHECK: omp.task untied {
+  !$omp task untied
+    call foo()
+  !CHECK: omp.terminator
+  !$omp end task
+end subroutine omp_task_untied

flang/test/Semantics/OpenMP/task-united01.f90

@@ -0,0 +1,28 @@
+! RUN: %python %S/../test_errors.py %s %flang %openmp_flags
+!
+! OpenMP 5.2: 5.2 threadprivate directive restriction
+
+subroutine task_united01()
+    integer, save :: var_01, var_02(2)
+    real          :: var_03
+    common /c/ var_03
+
+    !$omp threadprivate(var_01, var_02)
+    !$omp threadprivate(/c/)
+
+    !$omp task untied
+        !ERROR: A THREADPRIVATE variable `var_01` cannot appear in a UNTIED TASK region
+        var_01    = 10
+        !ERROR: A THREADPRIVATE variable `var_02` cannot appear in a UNTIED TASK region
+        !ERROR: A THREADPRIVATE variable `var_01` cannot appear in a UNTIED TASK region
+        var_02(1) = sum([var_01, 20])
+    !$omp end task
+
+    !$omp task untied
+        !ERROR: A THREADPRIVATE variable `var_02` cannot appear in a UNTIED TASK region
+        !ERROR: A THREADPRIVATE variable `var_02` cannot appear in a UNTIED TASK region
+        var_02(2) = product(var_02)
+        !ERROR: A THREADPRIVATE variable `var_03` cannot appear in a UNTIED TASK region
+        var_03    = 3.14
+    !$omp end task
+end subroutine task_united01

mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp

@@ -258,7 +258,6 @@ static LogicalResult checkImplementationStatus(Operation &op) {
         checkAllocate(op, result);
         checkInReduction(op, result);
         checkPriority(op, result);
-        checkUntied(op, result);
       })
       .Case([&](omp::TaskgroupOp op) {
         checkAllocate(op, result);
@@ -268,6 +267,10 @@ static LogicalResult checkImplementationStatus(Operation &op) {
         checkDepend(op, result);
         checkNowait(op, result);
       })
+      .Case([&](omp::TaskloopOp op) {
+        // TODO: Add other clauses check
+        checkUntied(op, result);
+      })
       .Case([&](omp::WsloopOp op) {
         checkAllocate(op, result);
         checkLinear(op, result);

mlir/test/Target/LLVMIR/openmp-llvm.mlir

@@ -3020,6 +3020,18 @@ module attributes {omp.is_target_device = true} {
 
 // -----
 
+llvm.func @omp_task_untied() {
+  // The third argument is 0: which signifies the united task
+  // CHECK: {{.*}} = call ptr @__kmpc_omp_task_alloc(ptr @1, i32 %{{.*}}, i32 0,
+  // CHECK-SAME:     i64 40, i64 0, ptr @{{.*}})
+  omp.task untied {
+        omp.terminator
+  }
+  llvm.return
+}
+
+// -----
+
 // Third argument is 5: essentially (4 || 1)
 // signifying this task is TIED and MERGEABLE
 

mlir/test/Target/LLVMIR/openmp-todo.mlir

@@ -440,17 +440,6 @@ llvm.func @task_priority(%x : i32) {
 
 // -----
 
-llvm.func @task_untied() {
-  // expected-error@below {{not yet implemented: Unhandled clause untied in omp.task operation}}
-  // expected-error@below {{LLVM Translation failed for operation: omp.task}}
-  omp.task untied {
-    omp.terminator
-  }
-  llvm.return
-}
-
-// -----
-
 llvm.func @taskgroup_allocate(%x : !llvm.ptr) {
   // expected-error@below {{not yet implemented: Unhandled clause allocate in omp.taskgroup operation}}
   // expected-error@below {{LLVM Translation failed for operation: omp.taskgroup}}
@@ -503,6 +492,19 @@ llvm.func @taskloop(%lb : i32, %ub : i32, %step : i32) {
 
 // -----
 
+llvm.func @taskloop_untied(%lb : i32, %ub : i32, %step : i32) {
+  // expected-error@below {{not yet implemented: omp.taskloop}}
+  // expected-error@below {{LLVM Translation failed for operation: omp.taskloop}}
+  omp.taskloop untied {
+    omp.loop_nest (%iv) : i32 = (%lb) to (%ub) step (%step) {
+      omp.yield
+    }
+  }
+  llvm.return
+}
+
+// -----
+
 llvm.func @taskwait_depend(%x: !llvm.ptr) {
   // expected-error@below {{not yet implemented: Unhandled clause depend in omp.taskwait operation}}
   // expected-error@below {{LLVM Translation failed for operation: omp.taskwait}}