[Flang][OpenMP] : Add a temporary lowering for workshare directive

[kiranchandramohan]

As a temporary solution, lower workshare to the single directive

[tblah]

This patch also needs to remove the TODO here

llvm-project/flang/lib/Lower/OpenMP.cpp

Line 3550 in ef67f63

TODO(currentLocation, "Workshare construct");

[llvmbot]

@llvm/pr-subscribers-flang-fir-hlfir

@llvm/pr-subscribers-flang-openmp

Author: Kiran Chandramohan (kiranchandramohan)

Changes

As a temporary solution, lower workshare to the single directive

---

Full diff: https://github.com/llvm/llvm-project/pull/78268.diff

2 Files Affected:

• (modified) flang/lib/Lower/OpenMP/OpenMP.cpp (+7-2)
• (added) flang/test/Lower/OpenMP/workshare.f90 (+42)

diff --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index 7953bf83cba0fe..d9c3148d0e3d34 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -1740,7 +1740,11 @@ genOMP(Fortran::lower::AbstractConverter &converter,
                /*outerCombined=*/false);
     break;
   case llvm::omp::Directive::OMPD_workshare:
-    TODO(currentLocation, "Workshare construct");
+    // FIXME: Workshare is not a commonly used OpenMP construct, an
+    // implementation for this feature will come later. For the codes
+    // that use this construct, add a single construct for now.
+    genSingleOp(converter, semaCtx, eval, /*genNested=*/true, currentLocation,
+                beginClauseList, endClauseList);
     break;
   default:
     singleDirective = false;
@@ -1775,7 +1779,8 @@ genOMP(Fortran::lower::AbstractConverter &converter,
   }
   if ((llvm::omp::workShareSet & llvm::omp::blockConstructSet)
           .test(directive.v)) {
-    TODO(currentLocation, "Workshare construct");
+    genSingleOp(converter, semaCtx, eval, /*genNested=*/false, currentLocation,
+                beginClauseList, endClauseList);
     combinedDirective = true;
   }
   if (!combinedDirective)
diff --git a/flang/test/Lower/OpenMP/workshare.f90 b/flang/test/Lower/OpenMP/workshare.f90
new file mode 100644
index 00000000000000..1e11677a15e1f0
--- /dev/null
+++ b/flang/test/Lower/OpenMP/workshare.f90
@@ -0,0 +1,42 @@
+
+!RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
+
+!CHECK-LABEL: func @_QPsb1
+subroutine sb1(arr)
+  integer :: arr(:)
+!CHECK: omp.parallel  {
+  !$omp parallel
+!CHECK: omp.single  {
+  !$omp workshare
+    arr = 0
+  !$omp end workshare
+!CHECK: }
+  !$omp end parallel
+!CHECK: }
+end subroutine
+
+!CHECK-LABEL: func @_QPsb2
+subroutine sb2(arr)
+  integer :: arr(:)
+!CHECK: omp.parallel  {
+  !$omp parallel
+!CHECK: omp.single nowait {
+  !$omp workshare
+    arr = 0
+  !$omp end workshare nowait
+!CHECK: }
+  !$omp end parallel
+!CHECK: }
+end subroutine
+
+!CHECK-LABEL: func @_QPsb3
+subroutine sb3(arr)
+  integer :: arr(:)
+!CHECK: omp.parallel  {
+!CHECK: omp.single  {
+  !$omp parallel workshare
+    arr = 0
+  !$omp end parallel workshare
+!CHECK: }
+!CHECK: }
+end subroutine

[kiranchandramohan]

Note: This is only a temporary lowering. There will be further discussions on the best way to implement this. Some of this is covered as part of Ivan's work for the coexecute construct on the target side (https://llvm.org/devmtg/2024-03/#talk8).

[tblah]

LGTM, thanks for this!