[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();
+}
+
+// Inserts a call to proper OpenMP Device RTL function which handles
+// loop worksharing.
+static void createTargetLoopWorkshareCall(
+    OpenMPIRBuilder *OMPBuilder, OpenMPIRBuilder::WorksharingLoopType LoopType,
+    BasicBlock *InsertBlock, Value *Ident, Value *LoopBodyArg,
+    Type *ParallelTaskPtr, Value *TripCount, Function &LoopBodyFn) {
+  Type *TripCountTy = TripCount->getType();
+  Module &M = OMPBuilder->M;
+  IRBuilder<> &Builder = OMPBuilder->Builder;
+  FunctionCallee RTLFn =
+      getKmpcForStaticLoopForType(TripCountTy, OMPBuilder, LoopType);
+  SmallVector<Value *, 8> RealArgs;
+  RealArgs.push_back(Ident);
+  /*loop body func*/
+  RealArgs.push_back(Builder.CreateBitCast(&LoopBodyFn, ParallelTaskPtr));
+  /*loop body args*/
+  RealArgs.push_back(LoopBodyArg);
+  /*num of iters*/
+  RealArgs.push_back(TripCount);
+  if (LoopType == OpenMPIRBuilder::WorksharingLoopType::DistributeStaticLoop) {
+    /*block chunk*/ RealArgs.push_back(TripCountTy->getIntegerBitWidth() == 32
+                                           ? Builder.getInt32(0)
+                                           : Builder.getInt64(0));
+    Builder.CreateCall(RTLFn, RealArgs);
+    return;
+  }
+  FunctionCallee RTLNumThreads = OMPBuilder->getOrCreateRuntimeFunction(
+      M, omp::RuntimeFunction::OMPRTL_omp_get_num_threads);
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jdoerfert wrote:

Hm, if all we do is call this function and pass the result, we can also call it in the runtime... we should keep an eye on this.

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