Frontend/OpenMP/OMPIRBuilder.cpp

//===- OpenMPIRBuilder.cpp - Builder for LLVM-IR for OpenMP directives ----===//
//
// 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
//
//===----------------------------------------------------------------------===//
/// \file
///
/// This file implements the OpenMPIRBuilder class, which is used as a
/// convenient way to create LLVM instructions for OpenMP directives.
///
//===----------------------------------------------------------------------===//

#include "llvm/Frontend/OpenMP/OMPIRBuilder.h"

#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Error.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/CodeExtractor.h"

#include <sstream>

#define DEBUG_TYPE "openmp-ir-builder"

using namespace llvm;
using namespace omp;
using namespace types;

static cl::opt<bool>
    OptimisticAttributes("openmp-ir-builder-optimistic-attributes", cl::Hidden,
                         cl::desc("Use optimistic attributes describing "
                                  "'as-if' properties of runtime calls."),
                         cl::init(false));

void OpenMPIRBuilder::addAttributes(omp::RuntimeFunction FnID, Function &Fn) {
  LLVMContext &Ctx = Fn.getContext();

#define OMP_ATTRS_SET(VarName, AttrSet) AttributeSet VarName = AttrSet;
#include "llvm/Frontend/OpenMP/OMPKinds.def"

  // Add attributes to the new declaration.
  switch (FnID) {
#define OMP_RTL_ATTRS(Enum, FnAttrSet, RetAttrSet, ArgAttrSets)                \
  case Enum:                                                                   \
    Fn.setAttributes(                                                          \
        AttributeList::get(Ctx, FnAttrSet, RetAttrSet, ArgAttrSets));          \
    break;
#include "llvm/Frontend/OpenMP/OMPKinds.def"
  default:
    // Attributes are optional.
    break;
  }
}

FunctionCallee
OpenMPIRBuilder::getOrCreateRuntimeFunction(Module &M, RuntimeFunction FnID) {
  FunctionType *FnTy = nullptr;
  Function *Fn = nullptr;

  // Try to find the declation in the module first.
  switch (FnID) {
#define OMP_RTL(Enum, Str, IsVarArg, ReturnType, ...)                          \
  case Enum:                                                                   \
    FnTy = FunctionType::get(ReturnType, ArrayRef<Type *>{__VA_ARGS__},        \
                             IsVarArg);                                        \
    Fn = M.getFunction(Str);                                                   \
    break;
#include "llvm/Frontend/OpenMP/OMPKinds.def"
  }

  if (!Fn) {
    // Create a new declaration if we need one.
    switch (FnID) {
#define OMP_RTL(Enum, Str, ...)                                                \
  case Enum:                                                                   \
    Fn = Function::Create(FnTy, GlobalValue::ExternalLinkage, Str, M);         \
    break;
#include "llvm/Frontend/OpenMP/OMPKinds.def"
    }

    // Add information if the runtime function takes a callback function
    if (FnID == OMPRTL___kmpc_fork_call || FnID == OMPRTL___kmpc_fork_teams) {
      if (!Fn->hasMetadata(LLVMContext::MD_callback)) {
        LLVMContext &Ctx = Fn->getContext();
        MDBuilder MDB(Ctx);
        // Annotate the callback behavior of the runtime function:
        //  - The callback callee is argument number 2 (microtask).
        //  - The first two arguments of the callback callee are unknown (-1).
        //  - All variadic arguments to the runtime function are passed to the
        //    callback callee.
        Fn->addMetadata(
            LLVMContext::MD_callback,
            *MDNode::get(Ctx, {MDB.createCallbackEncoding(
                                  2, {-1, -1}, /* VarArgsArePassed */ true)}));
      }
    }

    LLVM_DEBUG(dbgs() << "Created OpenMP runtime function " << Fn->getName()
                      << " with type " << *Fn->getFunctionType() << "\n");
    addAttributes(FnID, *Fn);

  } else {
    LLVM_DEBUG(dbgs() << "Found OpenMP runtime function " << Fn->getName()
                      << " with type " << *Fn->getFunctionType() << "\n");
  }

  assert(Fn && "Failed to create OpenMP runtime function");

  // Cast the function to the expected type if necessary
  Constant *C = ConstantExpr::getBitCast(Fn, FnTy->getPointerTo());
  return {FnTy, C};
}

Function *OpenMPIRBuilder::getOrCreateRuntimeFunctionPtr(RuntimeFunction FnID) {
  FunctionCallee RTLFn = getOrCreateRuntimeFunction(M, FnID);
  auto *Fn = dyn_cast<llvm::Function>(RTLFn.getCallee());
  assert(Fn && "Failed to create OpenMP runtime function pointer");
  return Fn;
}

void OpenMPIRBuilder::initialize() { initializeTypes(M); }

void OpenMPIRBuilder::finalize() {
  for (OutlineInfo &OI : OutlineInfos) {
    assert(!OI.Blocks.empty() &&
           "Outlined regions should have at least a single block!");
    BasicBlock *RegEntryBB = OI.Blocks.front();
    Function *OuterFn = RegEntryBB->getParent();
    CodeExtractorAnalysisCache CEAC(*OuterFn);
    CodeExtractor Extractor(OI.Blocks, /* DominatorTree */ nullptr,
                            /* AggregateArgs */ false,
                            /* BlockFrequencyInfo */ nullptr,
                            /* BranchProbabilityInfo */ nullptr,
                            /* AssumptionCache */ nullptr,
                            /* AllowVarArgs */ true,
                            /* AllowAlloca */ true,
                            /* Suffix */ ".omp_par");

    LLVM_DEBUG(dbgs() << "Before     outlining: " << *OuterFn << "\n");
    assert(Extractor.isEligible() &&
           "Expected OpenMP outlining to be possible!");

    Function *OutlinedFn = Extractor.extractCodeRegion(CEAC);

    LLVM_DEBUG(dbgs() << "After      outlining: " << *OuterFn << "\n");
    LLVM_DEBUG(dbgs() << "   Outlined function: " << *OutlinedFn << "\n");
    assert(OutlinedFn->getReturnType()->isVoidTy() &&
           "OpenMP outlined functions should not return a value!");

    // For compability with the clang CG we move the outlined function after the
    // one with the parallel region.
    OutlinedFn->removeFromParent();
    M.getFunctionList().insertAfter(OuterFn->getIterator(), OutlinedFn);

    // Remove the artificial entry introduced by the extractor right away, we
    // made our own entry block after all.
    {
      BasicBlock &ArtificialEntry = OutlinedFn->getEntryBlock();
      assert(ArtificialEntry.getUniqueSuccessor() == RegEntryBB);
      assert(RegEntryBB->getUniquePredecessor() == &ArtificialEntry);
      RegEntryBB->moveBefore(&ArtificialEntry);
      ArtificialEntry.eraseFromParent();
    }
    assert(&OutlinedFn->getEntryBlock() == RegEntryBB);
    assert(OutlinedFn && OutlinedFn->getNumUses() == 1);

    // Run a user callback, e.g. to add attributes.
    if (OI.PostOutlineCB)
      OI.PostOutlineCB(*OutlinedFn);
  }

  // Allow finalize to be called multiple times.
  OutlineInfos.clear();
}

Value *OpenMPIRBuilder::getOrCreateIdent(Constant *SrcLocStr,
                                         IdentFlag LocFlags) {
  // Enable "C-mode".
  LocFlags |= OMP_IDENT_FLAG_KMPC;

  GlobalVariable *&DefaultIdent = IdentMap[{SrcLocStr, uint64_t(LocFlags)}];
  if (!DefaultIdent) {
    Constant *I32Null = ConstantInt::getNullValue(Int32);
    Constant *IdentData[] = {I32Null,
                             ConstantInt::get(Int32, uint64_t(LocFlags)),
                             I32Null, I32Null, SrcLocStr};
    Constant *Initializer = ConstantStruct::get(
        cast<StructType>(IdentPtr->getPointerElementType()), IdentData);

    // Look for existing encoding of the location + flags, not needed but
    // minimizes the difference to the existing solution while we transition.
    for (GlobalVariable &GV : M.getGlobalList())
      if (GV.getType() == IdentPtr && GV.hasInitializer())
        if (GV.getInitializer() == Initializer)
          return DefaultIdent = &GV;

    DefaultIdent = new GlobalVariable(M, IdentPtr->getPointerElementType(),
                                      /* isConstant = */ false,
                                      GlobalValue::PrivateLinkage, Initializer);
    DefaultIdent->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
    DefaultIdent->setAlignment(Align(8));
  }
  return DefaultIdent;
}

Constant *OpenMPIRBuilder::getOrCreateSrcLocStr(StringRef LocStr) {
  Constant *&SrcLocStr = SrcLocStrMap[LocStr];
  if (!SrcLocStr) {
    Constant *Initializer =
        ConstantDataArray::getString(M.getContext(), LocStr);

    // Look for existing encoding of the location, not needed but minimizes the
    // difference to the existing solution while we transition.
    for (GlobalVariable &GV : M.getGlobalList())
      if (GV.isConstant() && GV.hasInitializer() &&
          GV.getInitializer() == Initializer)
        return SrcLocStr = ConstantExpr::getPointerCast(&GV, Int8Ptr);

    SrcLocStr = Builder.CreateGlobalStringPtr(LocStr);
  }
  return SrcLocStr;
}

Constant *OpenMPIRBuilder::getOrCreateDefaultSrcLocStr() {
  return getOrCreateSrcLocStr(";unknown;unknown;0;0;;");
}

Constant *
OpenMPIRBuilder::getOrCreateSrcLocStr(const LocationDescription &Loc) {
  DILocation *DIL = Loc.DL.get();
  if (!DIL)
    return getOrCreateDefaultSrcLocStr();
  StringRef Filename =
      !DIL->getFilename().empty() ? DIL->getFilename() : M.getName();
  StringRef Function = DIL->getScope()->getSubprogram()->getName();
  Function =
      !Function.empty() ? Function : Loc.IP.getBlock()->getParent()->getName();
  std::string LineStr = std::to_string(DIL->getLine());
  std::string ColumnStr = std::to_string(DIL->getColumn());
  std::stringstream SrcLocStr;
  SrcLocStr << ";" << Filename.data() << ";" << Function.data() << ";"
            << LineStr << ";" << ColumnStr << ";;";
  return getOrCreateSrcLocStr(SrcLocStr.str());
}

Value *OpenMPIRBuilder::getOrCreateThreadID(Value *Ident) {
  return Builder.CreateCall(
      getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_global_thread_num), Ident,
      "omp_global_thread_num");
}

OpenMPIRBuilder::InsertPointTy
OpenMPIRBuilder::CreateBarrier(const LocationDescription &Loc, Directive DK,
                               bool ForceSimpleCall, bool CheckCancelFlag) {
  if (!updateToLocation(Loc))
    return Loc.IP;
  return emitBarrierImpl(Loc, DK, ForceSimpleCall, CheckCancelFlag);
}

OpenMPIRBuilder::InsertPointTy
OpenMPIRBuilder::emitBarrierImpl(const LocationDescription &Loc, Directive Kind,
                                 bool ForceSimpleCall, bool CheckCancelFlag) {
  // Build call __kmpc_cancel_barrier(loc, thread_id) or
  //            __kmpc_barrier(loc, thread_id);

  IdentFlag BarrierLocFlags;
  switch (Kind) {
  case OMPD_for:
    BarrierLocFlags = OMP_IDENT_FLAG_BARRIER_IMPL_FOR;
    break;
  case OMPD_sections:
    BarrierLocFlags = OMP_IDENT_FLAG_BARRIER_IMPL_SECTIONS;
    break;
  case OMPD_single:
    BarrierLocFlags = OMP_IDENT_FLAG_BARRIER_IMPL_SINGLE;
    break;
  case OMPD_barrier:
    BarrierLocFlags = OMP_IDENT_FLAG_BARRIER_EXPL;
    break;
  default:
    BarrierLocFlags = OMP_IDENT_FLAG_BARRIER_IMPL;
    break;
  }

  Constant *SrcLocStr = getOrCreateSrcLocStr(Loc);
  Value *Args[] = {getOrCreateIdent(SrcLocStr, BarrierLocFlags),
                   getOrCreateThreadID(getOrCreateIdent(SrcLocStr))};

  // If we are in a cancellable parallel region, barriers are cancellation
  // points.
  // TODO: Check why we would force simple calls or to ignore the cancel flag.
  bool UseCancelBarrier =
      !ForceSimpleCall && isLastFinalizationInfoCancellable(OMPD_parallel);

  Value *Result =
      Builder.CreateCall(getOrCreateRuntimeFunctionPtr(
                             UseCancelBarrier ? OMPRTL___kmpc_cancel_barrier
                                              : OMPRTL___kmpc_barrier),
                         Args);

  if (UseCancelBarrier && CheckCancelFlag)
    emitCancelationCheckImpl(Result, OMPD_parallel);

  return Builder.saveIP();
}

OpenMPIRBuilder::InsertPointTy
OpenMPIRBuilder::CreateCancel(const LocationDescription &Loc,
                              Value *IfCondition,
                              omp::Directive CanceledDirective) {
  if (!updateToLocation(Loc))
    return Loc.IP;

  // LLVM utilities like blocks with terminators.
  auto *UI = Builder.CreateUnreachable();

  Instruction *ThenTI = UI, *ElseTI = nullptr;
  if (IfCondition)
    SplitBlockAndInsertIfThenElse(IfCondition, UI, &ThenTI, &ElseTI);
  Builder.SetInsertPoint(ThenTI);

  Value *CancelKind = nullptr;
  switch (CanceledDirective) {
#define OMP_CANCEL_KIND(Enum, Str, DirectiveEnum, Value)                       \
  case DirectiveEnum:                                                          \
    CancelKind = Builder.getInt32(Value);                                      \
    break;
#include "llvm/Frontend/OpenMP/OMPKinds.def"
  default:
    llvm_unreachable("Unknown cancel kind!");
  }

  Constant *SrcLocStr = getOrCreateSrcLocStr(Loc);
  Value *Ident = getOrCreateIdent(SrcLocStr);
  Value *Args[] = {Ident, getOrCreateThreadID(Ident), CancelKind};
  Value *Result = Builder.CreateCall(
      getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_cancel), Args);

  // The actual cancel logic is shared with others, e.g., cancel_barriers.
  emitCancelationCheckImpl(Result, CanceledDirective);

  // Update the insertion point and remove the terminator we introduced.
  Builder.SetInsertPoint(UI->getParent());
  UI->eraseFromParent();

  return Builder.saveIP();
}

void OpenMPIRBuilder::emitCancelationCheckImpl(
    Value *CancelFlag, omp::Directive CanceledDirective) {
  assert(isLastFinalizationInfoCancellable(CanceledDirective) &&
         "Unexpected cancellation!");

  // For a cancel barrier we create two new blocks.
  BasicBlock *BB = Builder.GetInsertBlock();
  BasicBlock *NonCancellationBlock;
  if (Builder.GetInsertPoint() == BB->end()) {
    // TODO: This branch will not be needed once we moved to the
    // OpenMPIRBuilder codegen completely.
    NonCancellationBlock = BasicBlock::Create(
        BB->getContext(), BB->getName() + ".cont", BB->getParent());
  } else {
    NonCancellationBlock = SplitBlock(BB, &*Builder.GetInsertPoint());
    BB->getTerminator()->eraseFromParent();
    Builder.SetInsertPoint(BB);
  }
  BasicBlock *CancellationBlock = BasicBlock::Create(
      BB->getContext(), BB->getName() + ".cncl", BB->getParent());

  // Jump to them based on the return value.
  Value *Cmp = Builder.CreateIsNull(CancelFlag);
  Builder.CreateCondBr(Cmp, NonCancellationBlock, CancellationBlock,
                       /* TODO weight */ nullptr, nullptr);

  // From the cancellation block we finalize all variables and go to the
  // post finalization block that is known to the FiniCB callback.
  Builder.SetInsertPoint(CancellationBlock);
  auto &FI = FinalizationStack.back();
  FI.FiniCB(Builder.saveIP());

  // The continuation block is where code generation continues.
  Builder.SetInsertPoint(NonCancellationBlock, NonCancellationBlock->begin());
}

IRBuilder<>::InsertPoint OpenMPIRBuilder::CreateParallel(
    const LocationDescription &Loc, BodyGenCallbackTy BodyGenCB,
    PrivatizeCallbackTy PrivCB, FinalizeCallbackTy FiniCB, Value *IfCondition,
    Value *NumThreads, omp::ProcBindKind ProcBind, bool IsCancellable) {
  if (!updateToLocation(Loc))
    return Loc.IP;

  Constant *SrcLocStr = getOrCreateSrcLocStr(Loc);
  Value *Ident = getOrCreateIdent(SrcLocStr);
  Value *ThreadID = getOrCreateThreadID(Ident);

  if (NumThreads) {
    // Build call __kmpc_push_num_threads(&Ident, global_tid, num_threads)
    Value *Args[] = {
        Ident, ThreadID,
        Builder.CreateIntCast(NumThreads, Int32, /*isSigned*/ false)};
    Builder.CreateCall(
        getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_push_num_threads), Args);
  }

  if (ProcBind != OMP_PROC_BIND_default) {
    // Build call __kmpc_push_proc_bind(&Ident, global_tid, proc_bind)
    Value *Args[] = {
        Ident, ThreadID,
        ConstantInt::get(Int32, unsigned(ProcBind), /*isSigned=*/true)};
    Builder.CreateCall(
        getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_push_proc_bind), Args);
  }

  BasicBlock *InsertBB = Builder.GetInsertBlock();
  Function *OuterFn = InsertBB->getParent();

  // Vector to remember instructions we used only during the modeling but which
  // we want to delete at the end.
  SmallVector<Instruction *, 4> ToBeDeleted;

  Builder.SetInsertPoint(OuterFn->getEntryBlock().getFirstNonPHI());
  AllocaInst *TIDAddr = Builder.CreateAlloca(Int32, nullptr, "tid.addr");
  AllocaInst *ZeroAddr = Builder.CreateAlloca(Int32, nullptr, "zero.addr");

  // If there is an if condition we actually use the TIDAddr and ZeroAddr in the
  // program, otherwise we only need them for modeling purposes to get the
  // associated arguments in the outlined function. In the former case,
  // initialize the allocas properly, in the latter case, delete them later.
  if (IfCondition) {
    Builder.CreateStore(Constant::getNullValue(Int32), TIDAddr);
    Builder.CreateStore(Constant::getNullValue(Int32), ZeroAddr);
  } else {
    ToBeDeleted.push_back(TIDAddr);
    ToBeDeleted.push_back(ZeroAddr);
  }

  // Create an artificial insertion point that will also ensure the blocks we
  // are about to split are not degenerated.
  auto *UI = new UnreachableInst(Builder.getContext(), InsertBB);

  Instruction *ThenTI = UI, *ElseTI = nullptr;
  if (IfCondition)
    SplitBlockAndInsertIfThenElse(IfCondition, UI, &ThenTI, &ElseTI);

  BasicBlock *ThenBB = ThenTI->getParent();
  BasicBlock *PRegEntryBB = ThenBB->splitBasicBlock(ThenTI, "omp.par.entry");
  BasicBlock *PRegBodyBB =
      PRegEntryBB->splitBasicBlock(ThenTI, "omp.par.region");
  BasicBlock *PRegPreFiniBB =
      PRegBodyBB->splitBasicBlock(ThenTI, "omp.par.pre_finalize");
  BasicBlock *PRegExitBB =
      PRegPreFiniBB->splitBasicBlock(ThenTI, "omp.par.exit");

  auto FiniCBWrapper = [&](InsertPointTy IP) {
    // Hide "open-ended" blocks from the given FiniCB by setting the right jump
    // target to the region exit block.
    if (IP.getBlock()->end() == IP.getPoint()) {
      IRBuilder<>::InsertPointGuard IPG(Builder);
      Builder.restoreIP(IP);
      Instruction *I = Builder.CreateBr(PRegExitBB);
      IP = InsertPointTy(I->getParent(), I->getIterator());
    }
    assert(IP.getBlock()->getTerminator()->getNumSuccessors() == 1 &&
           IP.getBlock()->getTerminator()->getSuccessor(0) == PRegExitBB &&
           "Unexpected insertion point for finalization call!");
    return FiniCB(IP);
  };

  FinalizationStack.push_back({FiniCBWrapper, OMPD_parallel, IsCancellable});

  // Generate the privatization allocas in the block that will become the entry
  // of the outlined function.
  InsertPointTy AllocaIP(PRegEntryBB,
                         PRegEntryBB->getTerminator()->getIterator());
  Builder.restoreIP(AllocaIP);
  AllocaInst *PrivTIDAddr =
      Builder.CreateAlloca(Int32, nullptr, "tid.addr.local");
  Instruction *PrivTID = Builder.CreateLoad(PrivTIDAddr, "tid");

  // Add some fake uses for OpenMP provided arguments.
  ToBeDeleted.push_back(Builder.CreateLoad(TIDAddr, "tid.addr.use"));
  ToBeDeleted.push_back(Builder.CreateLoad(ZeroAddr, "zero.addr.use"));

  // ThenBB
  //   |
  //   V
  // PRegionEntryBB         <- Privatization allocas are placed here.
  //   |
  //   V
  // PRegionBodyBB          <- BodeGen is invoked here.
  //   |
  //   V
  // PRegPreFiniBB          <- The block we will start finalization from.
  //   |
  //   V
  // PRegionExitBB          <- A common exit to simplify block collection.
  //

  LLVM_DEBUG(dbgs() << "Before body codegen: " << *OuterFn << "\n");

  // Let the caller create the body.
  assert(BodyGenCB && "Expected body generation callback!");
  InsertPointTy CodeGenIP(PRegBodyBB, PRegBodyBB->begin());
  BodyGenCB(AllocaIP, CodeGenIP, *PRegPreFiniBB);

  LLVM_DEBUG(dbgs() << "After  body codegen: " << *OuterFn << "\n");

  FunctionCallee RTLFn = getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_fork_call);
  if (auto *F = dyn_cast<llvm::Function>(RTLFn.getCallee())) {
    if (!F->hasMetadata(llvm::LLVMContext::MD_callback)) {
      llvm::LLVMContext &Ctx = F->getContext();
      MDBuilder MDB(Ctx);
      // Annotate the callback behavior of the __kmpc_fork_call:
      //  - The callback callee is argument number 2 (microtask).
      //  - The first two arguments of the callback callee are unknown (-1).
      //  - All variadic arguments to the __kmpc_fork_call are passed to the
      //    callback callee.
      F->addMetadata(
          llvm::LLVMContext::MD_callback,
          *llvm::MDNode::get(
              Ctx, {MDB.createCallbackEncoding(2, {-1, -1},
                                               /* VarArgsArePassed */ true)}));
    }
  }

  OutlineInfo OI;
  OI.PostOutlineCB = [=](Function &OutlinedFn) {
    // Add some known attributes.
    OutlinedFn.addParamAttr(0, Attribute::NoAlias);
    OutlinedFn.addParamAttr(1, Attribute::NoAlias);
    OutlinedFn.addFnAttr(Attribute::NoUnwind);
    OutlinedFn.addFnAttr(Attribute::NoRecurse);

    assert(OutlinedFn.arg_size() >= 2 &&
           "Expected at least tid and bounded tid as arguments");
    unsigned NumCapturedVars =
        OutlinedFn.arg_size() - /* tid & bounded tid */ 2;

    CallInst *CI = cast<CallInst>(OutlinedFn.user_back());
    CI->getParent()->setName("omp_parallel");
    Builder.SetInsertPoint(CI);

    // Build call __kmpc_fork_call(Ident, n, microtask, var1, .., varn);
    Value *ForkCallArgs[] = {
        Ident, Builder.getInt32(NumCapturedVars),
        Builder.CreateBitCast(&OutlinedFn, ParallelTaskPtr)};

    SmallVector<Value *, 16> RealArgs;
    RealArgs.append(std::begin(ForkCallArgs), std::end(ForkCallArgs));
    RealArgs.append(CI->arg_begin() + /* tid & bound tid */ 2, CI->arg_end());

    Builder.CreateCall(RTLFn, RealArgs);

    LLVM_DEBUG(dbgs() << "With fork_call placed: "
                      << *Builder.GetInsertBlock()->getParent() << "\n");

    InsertPointTy ExitIP(PRegExitBB, PRegExitBB->end());

    // Initialize the local TID stack location with the argument value.
    Builder.SetInsertPoint(PrivTID);
    Function::arg_iterator OutlinedAI = OutlinedFn.arg_begin();
    Builder.CreateStore(Builder.CreateLoad(OutlinedAI), PrivTIDAddr);

    // If no "if" clause was present we do not need the call created during
    // outlining, otherwise we reuse it in the serialized parallel region.
    if (!ElseTI) {
      CI->eraseFromParent();
    } else {

      // If an "if" clause was present we are now generating the serialized
      // version into the "else" branch.
      Builder.SetInsertPoint(ElseTI);

      // Build calls __kmpc_serialized_parallel(&Ident, GTid);
      Value *SerializedParallelCallArgs[] = {Ident, ThreadID};
      Builder.CreateCall(
          getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_serialized_parallel),
          SerializedParallelCallArgs);

      // OutlinedFn(&GTid, &zero, CapturedStruct);
      CI->removeFromParent();
      Builder.Insert(CI);

      // __kmpc_end_serialized_parallel(&Ident, GTid);
      Value *EndArgs[] = {Ident, ThreadID};
      Builder.CreateCall(
          getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_end_serialized_parallel),
          EndArgs);

      LLVM_DEBUG(dbgs() << "With serialized parallel region: "
                        << *Builder.GetInsertBlock()->getParent() << "\n");
    }

    for (Instruction *I : ToBeDeleted)
      I->eraseFromParent();
  };

  // Adjust the finalization stack, verify the adjustment, and call the
  // finalize function a last time to finalize values between the pre-fini
  // block and the exit block if we left the parallel "the normal way".
  auto FiniInfo = FinalizationStack.pop_back_val();
  (void)FiniInfo;
  assert(FiniInfo.DK == OMPD_parallel &&
         "Unexpected finalization stack state!");

  Instruction *PRegPreFiniTI = PRegPreFiniBB->getTerminator();
  assert(PRegPreFiniTI->getNumSuccessors() == 1 &&
         PRegPreFiniTI->getSuccessor(0) == PRegExitBB &&
         "Unexpected CFG structure!");

  InsertPointTy PreFiniIP(PRegPreFiniBB, PRegPreFiniTI->getIterator());
  FiniCB(PreFiniIP);

  SmallPtrSet<BasicBlock *, 32> ParallelRegionBlockSet;
  SmallVector<BasicBlock *, 32> Worklist;
  ParallelRegionBlockSet.insert(PRegEntryBB);
  ParallelRegionBlockSet.insert(PRegExitBB);

  // Collect all blocks in-between PRegEntryBB and PRegExitBB.
  Worklist.push_back(PRegEntryBB);
  while (!Worklist.empty()) {
    BasicBlock *BB = Worklist.pop_back_val();
    OI.Blocks.push_back(BB);
    for (BasicBlock *SuccBB : successors(BB))
      if (ParallelRegionBlockSet.insert(SuccBB).second)
        Worklist.push_back(SuccBB);
  }

  // Ensure a single exit node for the outlined region by creating one.
  // We might have multiple incoming edges to the exit now due to finalizations,
  // e.g., cancel calls that cause the control flow to leave the region.
  BasicBlock *PRegOutlinedExitBB = PRegExitBB;
  PRegExitBB = SplitBlock(PRegExitBB, &*PRegExitBB->getFirstInsertionPt());
  PRegOutlinedExitBB->setName("omp.par.outlined.exit");
  OI.Blocks.push_back(PRegOutlinedExitBB);

  CodeExtractorAnalysisCache CEAC(*OuterFn);
  CodeExtractor Extractor(OI.Blocks, /* DominatorTree */ nullptr,
                          /* AggregateArgs */ false,
                          /* BlockFrequencyInfo */ nullptr,
                          /* BranchProbabilityInfo */ nullptr,
                          /* AssumptionCache */ nullptr,
                          /* AllowVarArgs */ true,
                          /* AllowAlloca */ true,
                          /* Suffix */ ".omp_par");

  // Find inputs to, outputs from the code region.
  BasicBlock *CommonExit = nullptr;
  SetVector<Value *> Inputs, Outputs, SinkingCands, HoistingCands;
  Extractor.findAllocas(CEAC, SinkingCands, HoistingCands, CommonExit);
  Extractor.findInputsOutputs(Inputs, Outputs, SinkingCands);

  LLVM_DEBUG(dbgs() << "Before privatization: " << *OuterFn << "\n");

  FunctionCallee TIDRTLFn =
      getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_global_thread_num);

  auto PrivHelper = [&](Value &V) {
    if (&V == TIDAddr || &V == ZeroAddr)
      return;

    SmallVector<Use *, 8> Uses;
    for (Use &U : V.uses())
      if (auto *UserI = dyn_cast<Instruction>(U.getUser()))
        if (ParallelRegionBlockSet.count(UserI->getParent()))
          Uses.push_back(&U);

    Value *ReplacementValue = nullptr;
    CallInst *CI = dyn_cast<CallInst>(&V);
    if (CI && CI->getCalledFunction() == TIDRTLFn.getCallee()) {
      ReplacementValue = PrivTID;
    } else {
      Builder.restoreIP(
          PrivCB(AllocaIP, Builder.saveIP(), V, ReplacementValue));
      assert(ReplacementValue &&
             "Expected copy/create callback to set replacement value!");
      if (ReplacementValue == &V)
        return;
    }

    for (Use *UPtr : Uses)
      UPtr->set(ReplacementValue);
  };

  for (Value *Input : Inputs) {
    LLVM_DEBUG(dbgs() << "Captured input: " << *Input << "\n");
    PrivHelper(*Input);
  }
  assert(Outputs.empty() &&
         "OpenMP outlining should not produce live-out values!");

  LLVM_DEBUG(dbgs() << "After  privatization: " << *OuterFn << "\n");
  LLVM_DEBUG({
    for (auto *BB : OI.Blocks)
      dbgs() << " PBR: " << BB->getName() << "\n";
  });

  // Register the outlined info.
  addOutlineInfo(std::move(OI));

  InsertPointTy AfterIP(UI->getParent(), UI->getParent()->end());
  UI->eraseFromParent();

  return AfterIP;
}

void OpenMPIRBuilder::emitFlush(const LocationDescription &Loc) {
  // Build call void __kmpc_flush(ident_t *loc)
  Constant *SrcLocStr = getOrCreateSrcLocStr(Loc);
  Value *Args[] = {getOrCreateIdent(SrcLocStr)};

  Builder.CreateCall(getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_flush), Args);
}

void OpenMPIRBuilder::CreateFlush(const LocationDescription &Loc) {
  if (!updateToLocation(Loc))
    return;
  emitFlush(Loc);
}

void OpenMPIRBuilder::emitTaskwaitImpl(const LocationDescription &Loc) {
  // Build call kmp_int32 __kmpc_omp_taskwait(ident_t *loc, kmp_int32
  // global_tid);
  Constant *SrcLocStr = getOrCreateSrcLocStr(Loc);
  Value *Ident = getOrCreateIdent(SrcLocStr);
  Value *Args[] = {Ident, getOrCreateThreadID(Ident)};

  // Ignore return result until untied tasks are supported.
  Builder.CreateCall(getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_omp_taskwait),
                     Args);
}

void OpenMPIRBuilder::CreateTaskwait(const LocationDescription &Loc) {
  if (!updateToLocation(Loc))
    return;
  emitTaskwaitImpl(Loc);
}

void OpenMPIRBuilder::emitTaskyieldImpl(const LocationDescription &Loc) {
  // Build call __kmpc_omp_taskyield(loc, thread_id, 0);
  Constant *SrcLocStr = getOrCreateSrcLocStr(Loc);
  Value *Ident = getOrCreateIdent(SrcLocStr);
  Constant *I32Null = ConstantInt::getNullValue(Int32);
  Value *Args[] = {Ident, getOrCreateThreadID(Ident), I32Null};

  Builder.CreateCall(getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_omp_taskyield),
                     Args);
}

void OpenMPIRBuilder::CreateTaskyield(const LocationDescription &Loc) {
  if (!updateToLocation(Loc))
    return;
  emitTaskyieldImpl(Loc);
}

OpenMPIRBuilder::InsertPointTy
OpenMPIRBuilder::CreateMaster(const LocationDescription &Loc,
                              BodyGenCallbackTy BodyGenCB,
                              FinalizeCallbackTy FiniCB) {

  if (!updateToLocation(Loc))
    return Loc.IP;

  Directive OMPD = Directive::OMPD_master;
  Constant *SrcLocStr = getOrCreateSrcLocStr(Loc);
  Value *Ident = getOrCreateIdent(SrcLocStr);
  Value *ThreadId = getOrCreateThreadID(Ident);
  Value *Args[] = {Ident, ThreadId};

  Function *EntryRTLFn = getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_master);
  Instruction *EntryCall = Builder.CreateCall(EntryRTLFn, Args);

  Function *ExitRTLFn = getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_end_master);
  Instruction *ExitCall = Builder.CreateCall(ExitRTLFn, Args);

  return EmitOMPInlinedRegion(OMPD, EntryCall, ExitCall, BodyGenCB, FiniCB,
                              /*Conditional*/ true, /*hasFinalize*/ true);
}

OpenMPIRBuilder::InsertPointTy OpenMPIRBuilder::CreateCritical(
    const LocationDescription &Loc, BodyGenCallbackTy BodyGenCB,
    FinalizeCallbackTy FiniCB, StringRef CriticalName, Value *HintInst) {

  if (!updateToLocation(Loc))
    return Loc.IP;

  Directive OMPD = Directive::OMPD_critical;
  Constant *SrcLocStr = getOrCreateSrcLocStr(Loc);
  Value *Ident = getOrCreateIdent(SrcLocStr);
  Value *ThreadId = getOrCreateThreadID(Ident);
  Value *LockVar = getOMPCriticalRegionLock(CriticalName);
  Value *Args[] = {Ident, ThreadId, LockVar};

  SmallVector<llvm::Value *, 4> EnterArgs(std::begin(Args), std::end(Args));
  Function *RTFn = nullptr;
  if (HintInst) {
    // Add Hint to entry Args and create call
    EnterArgs.push_back(HintInst);
    RTFn = getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_critical_with_hint);
  } else {
    RTFn = getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_critical);
  }
  Instruction *EntryCall = Builder.CreateCall(RTFn, EnterArgs);

  Function *ExitRTLFn =
      getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_end_critical);
  Instruction *ExitCall = Builder.CreateCall(ExitRTLFn, Args);

  return EmitOMPInlinedRegion(OMPD, EntryCall, ExitCall, BodyGenCB, FiniCB,
                              /*Conditional*/ false, /*hasFinalize*/ true);
}

OpenMPIRBuilder::InsertPointTy OpenMPIRBuilder::EmitOMPInlinedRegion(
    Directive OMPD, Instruction *EntryCall, Instruction *ExitCall,
    BodyGenCallbackTy BodyGenCB, FinalizeCallbackTy FiniCB, bool Conditional,
    bool HasFinalize) {

  if (HasFinalize)
    FinalizationStack.push_back({FiniCB, OMPD, /*IsCancellable*/ false});

  // Create inlined region's entry and body blocks, in preparation
  // for conditional creation
  BasicBlock *EntryBB = Builder.GetInsertBlock();
  Instruction *SplitPos = EntryBB->getTerminator();
  if (!isa_and_nonnull<BranchInst>(SplitPos))
    SplitPos = new UnreachableInst(Builder.getContext(), EntryBB);
  BasicBlock *ExitBB = EntryBB->splitBasicBlock(SplitPos, "omp_region.end");
  BasicBlock *FiniBB =
      EntryBB->splitBasicBlock(EntryBB->getTerminator(), "omp_region.finalize");

  Builder.SetInsertPoint(EntryBB->getTerminator());
  emitCommonDirectiveEntry(OMPD, EntryCall, ExitBB, Conditional);

  // generate body
  BodyGenCB(/* AllocaIP */ InsertPointTy(),
            /* CodeGenIP */ Builder.saveIP(), *FiniBB);

  // If we didn't emit a branch to FiniBB during body generation, it means
  // FiniBB is unreachable (e.g. while(1);). stop generating all the
  // unreachable blocks, and remove anything we are not going to use.
  auto SkipEmittingRegion = FiniBB->hasNPredecessors(0);
  if (SkipEmittingRegion) {
    FiniBB->eraseFromParent();
    ExitCall->eraseFromParent();
    // Discard finalization if we have it.
    if (HasFinalize) {
      assert(!FinalizationStack.empty() &&
             "Unexpected finalization stack state!");
      FinalizationStack.pop_back();
    }
  } else {
    // emit exit call and do any needed finalization.
    auto FinIP = InsertPointTy(FiniBB, FiniBB->getFirstInsertionPt());
    assert(FiniBB->getTerminator()->getNumSuccessors() == 1 &&
           FiniBB->getTerminator()->getSuccessor(0) == ExitBB &&
           "Unexpected control flow graph state!!");
    emitCommonDirectiveExit(OMPD, FinIP, ExitCall, HasFinalize);
    assert(FiniBB->getUniquePredecessor()->getUniqueSuccessor() == FiniBB &&
           "Unexpected Control Flow State!");
    MergeBlockIntoPredecessor(FiniBB);
  }

  // If we are skipping the region of a non conditional, remove the exit
  // block, and clear the builder's insertion point.
  assert(SplitPos->getParent() == ExitBB &&
         "Unexpected Insertion point location!");
  if (!Conditional && SkipEmittingRegion) {
    ExitBB->eraseFromParent();
    Builder.ClearInsertionPoint();
  } else {
    auto merged = MergeBlockIntoPredecessor(ExitBB);
    BasicBlock *ExitPredBB = SplitPos->getParent();
    auto InsertBB = merged ? ExitPredBB : ExitBB;
    if (!isa_and_nonnull<BranchInst>(SplitPos))
      SplitPos->eraseFromParent();
    Builder.SetInsertPoint(InsertBB);
  }

  return Builder.saveIP();
}

OpenMPIRBuilder::InsertPointTy OpenMPIRBuilder::emitCommonDirectiveEntry(
    Directive OMPD, Value *EntryCall, BasicBlock *ExitBB, bool Conditional) {

  // if nothing to do, Return current insertion point.
  if (!Conditional)
    return Builder.saveIP();

  BasicBlock *EntryBB = Builder.GetInsertBlock();
  Value *CallBool = Builder.CreateIsNotNull(EntryCall);
  auto *ThenBB = BasicBlock::Create(M.getContext(), "omp_region.body");
  auto *UI = new UnreachableInst(Builder.getContext(), ThenBB);

  // Emit thenBB and set the Builder's insertion point there for
  // body generation next. Place the block after the current block.
  Function *CurFn = EntryBB->getParent();
  CurFn->getBasicBlockList().insertAfter(EntryBB->getIterator(), ThenBB);

  // Move Entry branch to end of ThenBB, and replace with conditional
  // branch (If-stmt)
  Instruction *EntryBBTI = EntryBB->getTerminator();
  Builder.CreateCondBr(CallBool, ThenBB, ExitBB);
  EntryBBTI->removeFromParent();
  Builder.SetInsertPoint(UI);
  Builder.Insert(EntryBBTI);
  UI->eraseFromParent();
  Builder.SetInsertPoint(ThenBB->getTerminator());

  // return an insertion point to ExitBB.
  return IRBuilder<>::InsertPoint(ExitBB, ExitBB->getFirstInsertionPt());
}

OpenMPIRBuilder::InsertPointTy OpenMPIRBuilder::emitCommonDirectiveExit(
    omp::Directive OMPD, InsertPointTy FinIP, Instruction *ExitCall,
    bool HasFinalize) {

  Builder.restoreIP(FinIP);

  // If there is finalization to do, emit it before the exit call
  if (HasFinalize) {
    assert(!FinalizationStack.empty() &&
           "Unexpected finalization stack state!");

    FinalizationInfo Fi = FinalizationStack.pop_back_val();
    assert(Fi.DK == OMPD && "Unexpected Directive for Finalization call!");

    Fi.FiniCB(FinIP);

    BasicBlock *FiniBB = FinIP.getBlock();
    Instruction *FiniBBTI = FiniBB->getTerminator();

    // set Builder IP for call creation
    Builder.SetInsertPoint(FiniBBTI);
  }

  // place the Exitcall as last instruction before Finalization block terminator
  ExitCall->removeFromParent();
  Builder.Insert(ExitCall);

  return IRBuilder<>::InsertPoint(ExitCall->getParent(),
                                  ExitCall->getIterator());
}

std::string OpenMPIRBuilder::getNameWithSeparators(ArrayRef<StringRef> Parts,
                                                   StringRef FirstSeparator,
                                                   StringRef Separator) {
  SmallString<128> Buffer;
  llvm::raw_svector_ostream OS(Buffer);
  StringRef Sep = FirstSeparator;
  for (StringRef Part : Parts) {
    OS << Sep << Part;
    Sep = Separator;
  }
  return OS.str().str();
}

Constant *OpenMPIRBuilder::getOrCreateOMPInternalVariable(
    llvm::Type *Ty, const llvm::Twine &Name, unsigned AddressSpace) {
  // TODO: Replace the twine arg with stringref to get rid of the conversion
  // logic. However This is taken from current implementation in clang as is.
  // Since this method is used in many places exclusively for OMP internal use
  // we will keep it as is for temporarily until we move all users to the
  // builder and then, if possible, fix it everywhere in one go.
  SmallString<256> Buffer;
  llvm::raw_svector_ostream Out(Buffer);
  Out << Name;
  StringRef RuntimeName = Out.str();
  auto &Elem = *InternalVars.try_emplace(RuntimeName, nullptr).first;
  if (Elem.second) {
    assert(Elem.second->getType()->getPointerElementType() == Ty &&
           "OMP internal variable has different type than requested");
  } else {
    // TODO: investigate the appropriate linkage type used for the global
    // variable for possibly changing that to internal or private, or maybe
    // create different versions of the function for different OMP internal
    // variables.
    Elem.second = new llvm::GlobalVariable(
        M, Ty, /*IsConstant*/ false, llvm::GlobalValue::CommonLinkage,
        llvm::Constant::getNullValue(Ty), Elem.first(),
        /*InsertBefore=*/nullptr, llvm::GlobalValue::NotThreadLocal,
        AddressSpace);
  }

  return Elem.second;
}

Value *OpenMPIRBuilder::getOMPCriticalRegionLock(StringRef CriticalName) {
  std::string Prefix = Twine("gomp_critical_user_", CriticalName).str();
  std::string Name = getNameWithSeparators({Prefix, "var"}, ".", ".");
  return getOrCreateOMPInternalVariable(KmpCriticalNameTy, Name);
}