[llvm] [OpenMPIRBuilder] Add support for target workshare loops (PR #73360)

[Johannes Doerfert via llvm-commits]

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@@ -2681,11 +2681,255 @@ OpenMPIRBuilder::InsertPointTy OpenMPIRBuilder::applyStaticChunkedWorkshareLoop(
   return {DispatchAfter, DispatchAfter->getFirstInsertionPt()};
 }
 
+// Returns an LLVM function to call for executing an OpenMP static worksharing
+// for loop depending on `type`. Only i32 and i64 are supported by the runtime.
+// Always interpret integers as unsigned similarly to CanonicalLoopInfo.
+static FunctionCallee
+getKmpcForStaticLoopForType(Type *Ty, OpenMPIRBuilder *OMPBuilder,
+                            OpenMPIRBuilder::WorksharingLoopType LoopType) {
+  unsigned Bitwidth = Ty->getIntegerBitWidth();
+  Module &M = OMPBuilder->M;
+  switch (LoopType) {
+  case OpenMPIRBuilder::WorksharingLoopType::ForStaticLoop:
+    if (Bitwidth == 32)
+      return OMPBuilder->getOrCreateRuntimeFunction(
+          M, omp::RuntimeFunction::OMPRTL___kmpc_for_static_loop_4u);
+    if (Bitwidth == 64)
+      return OMPBuilder->getOrCreateRuntimeFunction(
+          M, omp::RuntimeFunction::OMPRTL___kmpc_for_static_loop_8u);
+    break;
+  case OpenMPIRBuilder::WorksharingLoopType::DistributeStaticLoop:
+    if (Bitwidth == 32)
+      return OMPBuilder->getOrCreateRuntimeFunction(
+          M, omp::RuntimeFunction::OMPRTL___kmpc_distribute_static_loop_4u);
+    if (Bitwidth == 64)
+      return OMPBuilder->getOrCreateRuntimeFunction(
+          M, omp::RuntimeFunction::OMPRTL___kmpc_distribute_static_loop_8u);
+    break;
+  case OpenMPIRBuilder::WorksharingLoopType::DistributeForStaticLoop:
+    if (Bitwidth == 32)
+      return OMPBuilder->getOrCreateRuntimeFunction(
+          M, omp::RuntimeFunction::OMPRTL___kmpc_distribute_for_static_loop_4u);
+    if (Bitwidth == 64)
+      return OMPBuilder->getOrCreateRuntimeFunction(
+          M, omp::RuntimeFunction::OMPRTL___kmpc_distribute_for_static_loop_8u);
+    break;
+  }
+  if (Bitwidth != 32 && Bitwidth != 64)
+    llvm_unreachable("unknown OpenMP loop iterator bitwidth");
+  return FunctionCallee();
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jdoerfert wrote:

Doesn't seem sensible to return an empty function callee. Another unreachable?

https://github.com/llvm/llvm-project/pull/73360