[Flang][OpenMP] Add LLVM translation support for UNTIED clause in Task

[Thirumalai-Shaktivel]

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.

[llvmbot]

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Author: Thirumalai Shaktivel (Thirumalai-Shaktivel)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/115283.diff

4 Files Affected:

• (modified) flang/lib/Lower/OpenMP/OpenMP.cpp (+1)
• (removed) flang/test/Lower/OpenMP/Todo/task_untied.f90 (-13)
• (modified) flang/test/Lower/OpenMP/task.f90 (+13)
• (modified) mlir/test/Target/LLVMIR/openmp-llvm.mlir (+11)

diff --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index 4f9e2347308aa1..597871fb41f6aa 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -2844,6 +2844,7 @@ 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)) {
       TODO(clauseLocation, "OpenMP Block construct clause");
     }
diff --git a/flang/test/Lower/OpenMP/Todo/task_untied.f90 b/flang/test/Lower/OpenMP/Todo/task_untied.f90
deleted file mode 100644
index 19621c7aac16d6..00000000000000
--- a/flang/test/Lower/OpenMP/Todo/task_untied.f90
+++ /dev/null
@@ -1,13 +0,0 @@
-! RUN: %not_todo_cmd bbc -emit-fir -fopenmp -o - %s 2>&1 | FileCheck %s
-! RUN: %not_todo_cmd %flang_fc1 -emit-fir -fopenmp -o - %s 2>&1 | FileCheck %s
-
-!===============================================================================
-! `untied` clause
-!===============================================================================
-
-! CHECK: not yet implemented: OpenMP Block construct clause
-subroutine omp_task_untied()
-  !$omp task untied
-  call foo()
-  !$omp end task
-end subroutine omp_task_untied
diff --git a/flang/test/Lower/OpenMP/task.f90 b/flang/test/Lower/OpenMP/task.f90
index 4f00f261fe57df..bf0f3574258076 100644
--- a/flang/test/Lower/OpenMP/task.f90
+++ b/flang/test/Lower/OpenMP/task.f90
@@ -245,3 +245,16 @@ subroutine task_multiple_clauses()
   !CHECK: omp.terminator
   !$omp end task
 end subroutine task_multiple_clauses
+
+!===============================================================================
+! `untied` clause
+!===============================================================================
+
+!CHECK-LABEL: func.func @_QPomp_task_untied() {
+subroutine omp_task_untied()
+  !CHECK: omp.task untied {
+  !$omp task untied
+    call foo()
+  !CHECK: omp.terminator
+  !$omp end task
+end subroutine omp_task_untied
diff --git a/mlir/test/Target/LLVMIR/openmp-llvm.mlir b/mlir/test/Target/LLVMIR/openmp-llvm.mlir
index cdf94b1ceae11b..6eb9fbf0421311 100644
--- a/mlir/test/Target/LLVMIR/openmp-llvm.mlir
+++ b/mlir/test/Target/LLVMIR/openmp-llvm.mlir
@@ -3003,6 +3003,17 @@ 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, i64 40, i64 0, ptr @{{.*}})
+  omp.task untied {
+    omp.terminator
+  }
+  llvm.return
+}
+
+// -----
+
 llvm.func external @foo_before() -> ()
 llvm.func external @foo() -> ()
 llvm.func external @foo_after() -> ()

[tblah]

Please could you add a test showing what happens (TODO or correct behavior) if untied is used with taskloop.

Otherwise the changes look good.

[tblah]

See also the failing mlir test Target/LLVMIR/openmp-llvm.mlir

[Thirumalai-Shaktivel]

Yea, sure. I will check it out and report back.

[Thirumalai-Shaktivel]

Please could you add a test showing what happens (TODO or correct behavior) if untied is used with taskloop.

Taskloop doesn't have the OpenMP lowering support (it throws "not yet implemented: omp.taskloop").
Still, I have added a test and check to catch it.

[tblah]

Thanks for the update. LGTM

[ceseo]

This seems to be breaking one of the test-suite gfortran tests:

FAIL: test-suite::gfortran-regression-compile-regression__gomp__pr44085_f90.test

[omjavaid]

I have temporarily reverted this change as it was breaking various LLVM bots due to failure of following LLVM testsuite GFortran tests: llvm-test-suite/Fortran/gfortran/regression/gomp/pr44085.f90
Please take a look and re-apply after fix. Thanks!