[Flang][OpenMP][OMPIRBuilder] Add lowering of TargetOp for device codegen

[skatrak]

Summary

This patch adds support in the OpenMPIRBuilder for generating working
device code for OpenMP target regions. It generates and handles the
result of a call to __kmpc_target_init() at the beginning of the
function resulting from outlining each target region, and it also
generates the matching __kmpc_target_deinit() call before returning.

It relies on the implementation of target region outlining for host
codegen to handle the production of the new function and the lowering of
its body based on the contents of the associated target region.

Depends on D147172

[skatrak]

Update after landing parent host codegen for target regions patch. This patch is now ready for review.

[skatrak]

Ping for reviews!

[jsjodin]

LGTM

[skatrak]

Thank you for the review, Jan! I'll wait a day or two before landing the patch in case anybody else has any further comments.

[jsjodin]

Is there a way we can create a MLIR->LLVM IR test with a target region and use the --offload-device-only flag to check that we get the device function generated? It would be nice to have.

[skatrak]

Rebase and add one more unit test.

[skatrak]

In D147940#4350512, @jsjodin wrote:

Is there a way we can create a MLIR->LLVM IR test with a target region and use the --offload-device-only flag to check that we get the device function generated? It would be nice to have.

I just added a unit test to look at the translation from MLIR to LLVM IR of a target region for the device. It doesn't use the --offload-device-only flag, but I think that might be redundant, since that is a driver-only flag. In flang/test/Driver/omp-driver-offload.f90 there is a test that makes sure that, if that option is set, the proper triples for the offloading invocation are added. The new test I just added makes sure that the device function is generated from MLIR if omp.is_device is set and there's an OpenMP target region, and there are other tests making sure that omp.is_device and omp.target are generated in the proper cases. So I think the whole flow involving that command line option and code generation for the device function is tested already.

If this is something that you still think we should have, let me know.

llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

OpenMPIRBuilder::InsertPointTy OpenMPIRBuilder::createTargetData(
   Builder.SetInsertPoint(UI->getParent());
   if (IfCond)
     UI->getParent()->setName("omp_if.end");
   UI->eraseFromParent();
   return Builder.saveIP();
 }
 
 static Function *
-createOutlinedFunction(IRBuilderBase &Builder, StringRef FuncName,
-                       SmallVectorImpl<Value *> &Inputs,
+createOutlinedFunction(OpenMPIRBuilder &OMPBuilder, IRBuilderBase &Builder,
+                       StringRef FuncName, SmallVectorImpl<Value *> &Inputs,
                        OpenMPIRBuilder::TargetBodyGenCallbackTy &CBFunc) {
   SmallVector<Type *> ParameterTypes;
   for (auto &Arg : Inputs)
     ParameterTypes.push_back(Arg->getType());
 
   auto FuncType = FunctionType::get(Builder.getVoidTy(), ParameterTypes,
                                     /*isVarArg*/ false);
   auto Func = Function::Create(FuncType, GlobalValue::InternalLinkage, FuncName,
                                Builder.GetInsertBlock()->getModule());
 
   // Save insert point.
   auto OldInsertPoint = Builder.saveIP();
 
   // Generate the region into the function.
   BasicBlock *EntryBB = BasicBlock::Create(Builder.getContext(), "entry", Func);
   Builder.SetInsertPoint(EntryBB);
+
+  // Insert target init call in the device compilation pass.
+  if (OMPBuilder.Config.isEmbedded())
+    Builder.restoreIP(OMPBuilder.createTargetInit(Builder, /*IsSPMD*/ false));
+
   Builder.restoreIP(CBFunc(Builder.saveIP(), Builder.saveIP()));
 
+  // Insert target deinit call in the device compilation pass.
+  if (OMPBuilder.Config.isEmbedded())
+    OMPBuilder.createTargetDeinit(Builder, /*IsSPMD*/ false);
+
   // Insert return instruction.
   Builder.CreateRetVoid();
 
   // Rewrite uses of input valus to parameters.
   for (auto InArg : zip(Inputs, Func->args())) {
     Value *Input = std::get<0>(InArg);
     Argument &Arg = std::get<1>(InArg);
 

 static void
 emitTargetOutlinedFunction(OpenMPIRBuilder &OMPBuilder, IRBuilderBase &Builder,
                            TargetRegionEntryInfo &EntryInfo,
                            Function *&OutlinedFn, int32_t NumTeams,
                            int32_t NumThreads, SmallVectorImpl<Value *> &Inputs,
                            OpenMPIRBuilder::TargetBodyGenCallbackTy &CBFunc) {
 
   OpenMPIRBuilder::FunctionGenCallback &&GenerateOutlinedFunction =
-      [&Builder, &Inputs, &CBFunc](StringRef EntryFnName) {
-        return createOutlinedFunction(Builder, EntryFnName, Inputs, CBFunc);
+      [&OMPBuilder, &Builder, &Inputs, &CBFunc](StringRef EntryFnName) {
+        return createOutlinedFunction(OMPBuilder, Builder, EntryFnName, Inputs,
+                                      CBFunc);
       };
 
   Constant *OutlinedFnID;
   OMPBuilder.emitTargetRegionFunction(EntryInfo, GenerateOutlinedFunction,
                                       NumTeams, NumThreads, true, OutlinedFn,
                                       OutlinedFnID);
 }
 
 static void emitTargetCall(IRBuilderBase &Builder, Function *OutlinedFn,
                            SmallVectorImpl<Value *> &Args) {
-  // TODO: Add kernel launch call when device codegen is supported.
+  // TODO: Add kernel launch call
   Builder.CreateCall(OutlinedFn, Args);
 }
 
 OpenMPIRBuilder::InsertPointTy OpenMPIRBuilder::createTarget(
     const LocationDescription &Loc, OpenMPIRBuilder::InsertPointTy CodeGenIP,
     TargetRegionEntryInfo &EntryInfo, int32_t NumTeams, int32_t NumThreads,
     SmallVectorImpl<Value *> &Args, TargetBodyGenCallbackTy CBFunc) {
   if (!updateToLocation(Loc))
     return InsertPointTy();
 
   Builder.restoreIP(CodeGenIP);
 
   Function *OutlinedFn;
   emitTargetOutlinedFunction(*this, Builder, EntryInfo, OutlinedFn, NumTeams,
                              NumThreads, Args, CBFunc);
+  if (!Config.isEmbedded())
     emitTargetCall(Builder, OutlinedFn, Args);
   return Builder.saveIP();
 }
 
 std::string OpenMPIRBuilder::getNameWithSeparators(ArrayRef<StringRef> Parts,
                                                    StringRef FirstSeparator,
                                                    StringRef Separator) {
   SmallString<128> Buffer;
   llvm::raw_svector_ostream OS(Buffer);

llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp

 //===- llvm/unittest/IR/OpenMPIRBuilderTest.cpp - OpenMPIRBuilder tests ---===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Frontend/OpenMP/OMPConstants.h"
+#include "llvm/Frontend/OpenMP/OMPDeviceConstants.h"
 #include "llvm/Frontend/OpenMP/OMPIRBuilder.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/DIBuilder.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
TEST_F(OpenMPIRBuilderTest, TargetRegion) {
   // Check that the outlined function exists with the expected prefix
   Function *OutlinedFunc = Call->getCalledFunction();
   EXPECT_NE(OutlinedFunc, nullptr);
   StringRef FunctionName = OutlinedFunc->getName();
   EXPECT_TRUE(FunctionName.startswith("__omp_offloading"));
   EXPECT_FALSE(verifyModule(*M, &errs()));
 }
 
+TEST_F(OpenMPIRBuilderTest, TargetRegionDevice) {
+  OpenMPIRBuilder OMPBuilder(*M);
+  OMPBuilder.setConfig(OpenMPIRBuilderConfig(true, false, false, false));
+  OMPBuilder.initialize();
+
+  F->setName("func");
+  IRBuilder<> Builder(BB);
+  OpenMPIRBuilder::LocationDescription Loc({Builder.saveIP(), DL});
+
+  StoreInst *TargetStore = nullptr;
+  llvm::SmallVector<llvm::Value *, 2> CapturedArgs = {
+      Constant::getIntegerValue(Type::getInt32Ty(Ctx), APInt(32, 0)),
+      Constant::getNullValue(Type::getInt32PtrTy(Ctx))};
+
+  auto BodyGenCB = [&](OpenMPIRBuilder::InsertPointTy AllocaIP,
+                       OpenMPIRBuilder::InsertPointTy CodeGenIP)
+      -> OpenMPIRBuilder::InsertPointTy {
+    Builder.restoreIP(CodeGenIP);
+    TargetStore = Builder.CreateStore(CapturedArgs[0], CapturedArgs[1]);
+    return Builder.saveIP();
+  };
+
+  IRBuilder<>::InsertPoint EntryIP(&F->getEntryBlock(),
+                                   F->getEntryBlock().getFirstInsertionPt());
+  TargetRegionEntryInfo EntryInfo("parent", /*DeviceID=*/1, /*FileID=*/2,
+                                  /*Line=*/3, /*Count=*/0);
+
+  Builder.restoreIP(
+      OMPBuilder.createTarget(Loc, EntryIP, EntryInfo, /*NumTeams=*/-1,
+                              /*NumThreads=*/-1, CapturedArgs, BodyGenCB));
+  Builder.CreateRetVoid();
+  OMPBuilder.finalize();
+
+  // Check outlined function
+  EXPECT_FALSE(verifyModule(*M, &errs()));
+  EXPECT_NE(TargetStore, nullptr);
+  Function *OutlinedFn = TargetStore->getFunction();
+  EXPECT_NE(F, OutlinedFn);
+
+  EXPECT_TRUE(OutlinedFn->hasWeakODRLinkage());
+  EXPECT_EQ(OutlinedFn->arg_size(), 2U);
+  EXPECT_EQ(OutlinedFn->getName(), "__omp_offloading_1_2_parent_l3");
+  EXPECT_TRUE(OutlinedFn->getArg(0)->getType()->isIntegerTy(32));
+  EXPECT_TRUE(OutlinedFn->getArg(1)->getType()->isPointerTy());
+
+  // Check entry block
+  auto &EntryBlock = OutlinedFn->getEntryBlock();
+  Instruction *Init = EntryBlock.getFirstNonPHI();
+  EXPECT_NE(Init, nullptr);
+
+  auto *InitCall = dyn_cast<CallInst>(Init);
+  EXPECT_NE(InitCall, nullptr);
+  EXPECT_EQ(InitCall->getCalledFunction()->getName(), "__kmpc_target_init");
+  EXPECT_EQ(InitCall->arg_size(), 3U);
+  EXPECT_TRUE(isa<GlobalVariable>(InitCall->getArgOperand(0)));
+  EXPECT_EQ(InitCall->getArgOperand(1),
+            ConstantInt::get(Type::getInt8Ty(Ctx), OMP_TGT_EXEC_MODE_GENERIC));
+  EXPECT_EQ(InitCall->getArgOperand(2),
+            ConstantInt::get(Type::getInt1Ty(Ctx), true));
+
+  auto *EntryBlockBranch = EntryBlock.getTerminator();
+  EXPECT_NE(EntryBlockBranch, nullptr);
+  EXPECT_EQ(EntryBlockBranch->getNumSuccessors(), 2U);
+
+  // Check user code block
+  auto *UserCodeBlock = EntryBlockBranch->getSuccessor(0);
+  EXPECT_EQ(UserCodeBlock->getName(), "user_code.entry");
+  EXPECT_EQ(UserCodeBlock->getFirstNonPHI(), TargetStore);
+
+  auto *Deinit = TargetStore->getNextNode();
+  EXPECT_NE(Deinit, nullptr);
+
+  auto *DeinitCall = dyn_cast<CallInst>(Deinit);
+  EXPECT_NE(DeinitCall, nullptr);
+  EXPECT_EQ(DeinitCall->getCalledFunction()->getName(), "__kmpc_target_deinit");
+  EXPECT_EQ(DeinitCall->arg_size(), 2U);
+  EXPECT_TRUE(isa<GlobalVariable>(DeinitCall->getArgOperand(0)));
+  EXPECT_EQ(DeinitCall->getArgOperand(1),
+            ConstantInt::get(Type::getInt8Ty(Ctx), OMP_TGT_EXEC_MODE_GENERIC));
+
+  EXPECT_TRUE(isa<ReturnInst>(DeinitCall->getNextNode()));
+
+  // Check exit block
+  auto *ExitBlock = EntryBlockBranch->getSuccessor(1);
+  EXPECT_EQ(ExitBlock->getName(), "worker.exit");
+  EXPECT_TRUE(isa<ReturnInst>(ExitBlock->getFirstNonPHI()));
+}
+
 TEST_F(OpenMPIRBuilderTest, CreateTask) {
   using InsertPointTy = OpenMPIRBuilder::InsertPointTy;
   OpenMPIRBuilder OMPBuilder(*M);
   OMPBuilder.initialize();
   F->setName("func");
   IRBuilder<> Builder(BB);
 
   AllocaInst *ValPtr32 = Builder.CreateAlloca(Builder.getInt32Ty());

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

 
 static LogicalResult
 convertOmpTarget(Operation &opInst, llvm::IRBuilderBase &builder,
                  LLVM::ModuleTranslation &moduleTranslation) {
 
   if (!targetOpSupported(opInst))
     return failure();
 
-  bool isDevice = false;
-  if (auto offloadMod = dyn_cast<mlir::omp::OffloadModuleInterface>(
-          opInst.getParentOfType<mlir::ModuleOp>().getOperation())) {
-    isDevice = offloadMod.getIsDevice();
-  }
-
-  if (isDevice) // TODO: Implement device codegen.
-    return success();
-
   auto targetOp = cast<omp::TargetOp>(opInst);
   auto &targetRegion = targetOp.getRegion();
 
   llvm::SetVector<Value> operandSet;
   getUsedValuesDefinedAbove(targetRegion, operandSet);
 
   // Collect the input arguments.
   llvm::SmallVector<llvm::Value *> inputs;