llvm-project/clang/lib/CodeGen/CGStmtOpenMP.cpp

//===--- CGStmtOpenMP.cpp - Emit LLVM Code from Statements ----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code to emit OpenMP nodes as LLVM code.
//
//===----------------------------------------------------------------------===//

#include "CGOpenMPRuntime.h"
#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "clang/AST/Stmt.h"
#include "clang/AST/StmtOpenMP.h"
#include "TargetInfo.h"
using namespace clang;
using namespace CodeGen;

namespace {
/// \brief RAII for emitting code of CapturedStmt without function outlining.
class InlinedOpenMPRegion {
  CodeGenFunction &CGF;
  CodeGenFunction::CGCapturedStmtInfo *PrevCapturedStmtInfo;
  const Decl *StoredCurCodeDecl;

  /// \brief A class to emit CapturedStmt construct as inlined statement without
  /// generating a function for outlined code.
  class CGInlinedOpenMPRegionInfo : public CodeGenFunction::CGCapturedStmtInfo {
  public:
    CGInlinedOpenMPRegionInfo() : CGCapturedStmtInfo() {}
  };

public:
  InlinedOpenMPRegion(CodeGenFunction &CGF, const Stmt *S)
      : CGF(CGF), PrevCapturedStmtInfo(CGF.CapturedStmtInfo),
        StoredCurCodeDecl(CGF.CurCodeDecl) {
    CGF.CurCodeDecl = cast<CapturedStmt>(S)->getCapturedDecl();
    CGF.CapturedStmtInfo = new CGInlinedOpenMPRegionInfo();
  }
  ~InlinedOpenMPRegion() {
    delete CGF.CapturedStmtInfo;
    CGF.CapturedStmtInfo = PrevCapturedStmtInfo;
    CGF.CurCodeDecl = StoredCurCodeDecl;
  }
};
} // namespace

//===----------------------------------------------------------------------===//
//                              OpenMP Directive Emission
//===----------------------------------------------------------------------===//

/// \brief Emits code for OpenMP 'if' clause using specified \a CodeGen
/// function. Here is the logic:
/// if (Cond) {
///   CodeGen(true);
/// } else {
///   CodeGen(false);
/// }
static void EmitOMPIfClause(CodeGenFunction &CGF, const Expr *Cond,
                            const std::function<void(bool)> &CodeGen) {
  CodeGenFunction::LexicalScope ConditionScope(CGF, Cond->getSourceRange());

  // If the condition constant folds and can be elided, try to avoid emitting
  // the condition and the dead arm of the if/else.
  bool CondConstant;
  if (CGF.ConstantFoldsToSimpleInteger(Cond, CondConstant)) {
    CodeGen(CondConstant);
    return;
  }

  // Otherwise, the condition did not fold, or we couldn't elide it.  Just
  // emit the conditional branch.
  auto ThenBlock = CGF.createBasicBlock(/*name*/ "omp_if.then");
  auto ElseBlock = CGF.createBasicBlock(/*name*/ "omp_if.else");
  auto ContBlock = CGF.createBasicBlock(/*name*/ "omp_if.end");
  CGF.EmitBranchOnBoolExpr(Cond, ThenBlock, ElseBlock, /*TrueCount*/ 0);

  // Emit the 'then' code.
  CGF.EmitBlock(ThenBlock);
  CodeGen(/*ThenBlock*/ true);
  CGF.EmitBranch(ContBlock);
  // Emit the 'else' code if present.
  {
    // There is no need to emit line number for unconditional branch.
    SuppressDebugLocation SDL(CGF.Builder);
    CGF.EmitBlock(ElseBlock);
  }
  CodeGen(/*ThenBlock*/ false);
  {
    // There is no need to emit line number for unconditional branch.
    SuppressDebugLocation SDL(CGF.Builder);
    CGF.EmitBranch(ContBlock);
  }
  // Emit the continuation block for code after the if.
  CGF.EmitBlock(ContBlock, /*IsFinished*/ true);
}

void CodeGenFunction::EmitOMPAggregateAssign(LValue OriginalAddr,
                                             llvm::Value *PrivateAddr,
                                             const Expr *AssignExpr,
                                             QualType OriginalType,
                                             const VarDecl *VDInit) {
  EmitBlock(createBasicBlock(".omp.assign.begin."));
  if (!isa<CXXConstructExpr>(AssignExpr) || isTrivialInitializer(AssignExpr)) {
    // Perform simple memcpy.
    EmitAggregateAssign(PrivateAddr, OriginalAddr.getAddress(),
                        AssignExpr->getType());
  } else {
    // Perform element-by-element initialization.
    QualType ElementTy;
    auto SrcBegin = OriginalAddr.getAddress();
    auto DestBegin = PrivateAddr;
    auto ArrayTy = OriginalType->getAsArrayTypeUnsafe();
    auto SrcNumElements = emitArrayLength(ArrayTy, ElementTy, SrcBegin);
    auto DestNumElements = emitArrayLength(ArrayTy, ElementTy, DestBegin);
    auto SrcEnd = Builder.CreateGEP(SrcBegin, SrcNumElements);
    auto DestEnd = Builder.CreateGEP(DestBegin, DestNumElements);
    // The basic structure here is a do-while loop, because we don't
    // need to check for the zero-element case.
    auto BodyBB = createBasicBlock("omp.arraycpy.body");
    auto DoneBB = createBasicBlock("omp.arraycpy.done");
    auto IsEmpty =
        Builder.CreateICmpEQ(DestBegin, DestEnd, "omp.arraycpy.isempty");
    Builder.CreateCondBr(IsEmpty, DoneBB, BodyBB);

    // Enter the loop body, making that address the current address.
    auto EntryBB = Builder.GetInsertBlock();
    EmitBlock(BodyBB);
    auto SrcElementPast = Builder.CreatePHI(SrcBegin->getType(), 2,
                                            "omp.arraycpy.srcElementPast");
    SrcElementPast->addIncoming(SrcEnd, EntryBB);
    auto DestElementPast = Builder.CreatePHI(DestBegin->getType(), 2,
                                             "omp.arraycpy.destElementPast");
    DestElementPast->addIncoming(DestEnd, EntryBB);

    // Shift the address back by one element.
    auto NegativeOne = llvm::ConstantInt::get(SizeTy, -1, true);
    auto DestElement = Builder.CreateGEP(DestElementPast, NegativeOne,
                                         "omp.arraycpy.dest.element");
    auto SrcElement = Builder.CreateGEP(SrcElementPast, NegativeOne,
                                        "omp.arraycpy.src.element");
    {
      // Create RunCleanScope to cleanup possible temps.
      CodeGenFunction::RunCleanupsScope Init(*this);
      // Emit initialization for single element.
      LocalDeclMap[VDInit] = SrcElement;
      EmitAnyExprToMem(AssignExpr, DestElement,
                       AssignExpr->getType().getQualifiers(),
                       /*IsInitializer*/ false);
      LocalDeclMap.erase(VDInit);
    }

    // Check whether we've reached the end.
    auto Done =
        Builder.CreateICmpEQ(DestElement, DestBegin, "omp.arraycpy.done");
    Builder.CreateCondBr(Done, DoneBB, BodyBB);
    DestElementPast->addIncoming(DestElement, Builder.GetInsertBlock());
    SrcElementPast->addIncoming(SrcElement, Builder.GetInsertBlock());

    // Done.
    EmitBlock(DoneBB, true);
  }
  EmitBlock(createBasicBlock(".omp.assign.end."));
}

void CodeGenFunction::EmitOMPFirstprivateClause(
    const OMPExecutableDirective &D,
    CodeGenFunction::OMPPrivateScope &PrivateScope) {
  auto PrivateFilter = [](const OMPClause *C) -> bool {
    return C->getClauseKind() == OMPC_firstprivate;
  };
  for (OMPExecutableDirective::filtered_clause_iterator<decltype(PrivateFilter)>
           I(D.clauses(), PrivateFilter); I; ++I) {
    auto *C = cast<OMPFirstprivateClause>(*I);
    auto IRef = C->varlist_begin();
    auto InitsRef = C->inits().begin();
    for (auto IInit : C->private_copies()) {
      auto *OrigVD = cast<VarDecl>(cast<DeclRefExpr>(*IRef)->getDecl());
      auto *VD = cast<VarDecl>(cast<DeclRefExpr>(IInit)->getDecl());
      bool IsRegistered;
      if (*InitsRef != nullptr) {
        // Emit VarDecl with copy init for arrays.
        auto *FD = CapturedStmtInfo->lookup(OrigVD);
        LValue Base = MakeNaturalAlignAddrLValue(
            CapturedStmtInfo->getContextValue(),
            getContext().getTagDeclType(FD->getParent()));
        auto OriginalAddr = EmitLValueForField(Base, FD);
        auto VDInit = cast<VarDecl>(cast<DeclRefExpr>(*InitsRef)->getDecl());
        IsRegistered = PrivateScope.addPrivate(OrigVD, [&]() -> llvm::Value * {
          auto Emission = EmitAutoVarAlloca(*VD);
          // Emit initialization of aggregate firstprivate vars.
          EmitOMPAggregateAssign(OriginalAddr, Emission.getAllocatedAddress(),
                                 VD->getInit(), (*IRef)->getType(), VDInit);
          EmitAutoVarCleanups(Emission);
          return Emission.getAllocatedAddress();
        });
      } else
        IsRegistered = PrivateScope.addPrivate(OrigVD, [&]() -> llvm::Value * {
          // Emit private VarDecl with copy init.
          EmitDecl(*VD);
          return GetAddrOfLocalVar(VD);
        });
      assert(IsRegistered && "counter already registered as private");
      // Silence the warning about unused variable.
      (void)IsRegistered;
      ++IRef, ++InitsRef;
    }
  }
}

void CodeGenFunction::EmitOMPPrivateClause(
    const OMPExecutableDirective &D,
    CodeGenFunction::OMPPrivateScope &PrivateScope) {
  auto PrivateFilter = [](const OMPClause *C) -> bool {
    return C->getClauseKind() == OMPC_private;
  };
  for (OMPExecutableDirective::filtered_clause_iterator<decltype(PrivateFilter)>
           I(D.clauses(), PrivateFilter); I; ++I) {
    auto *C = cast<OMPPrivateClause>(*I);
    auto IRef = C->varlist_begin();
    for (auto IInit : C->private_copies()) {
      auto *OrigVD = cast<VarDecl>(cast<DeclRefExpr>(*IRef)->getDecl());
      auto VD = cast<VarDecl>(cast<DeclRefExpr>(IInit)->getDecl());
      bool IsRegistered =
          PrivateScope.addPrivate(OrigVD, [&]() -> llvm::Value * {
            // Emit private VarDecl with copy init.
            EmitDecl(*VD);
            return GetAddrOfLocalVar(VD);
          });
      assert(IsRegistered && "counter already registered as private");
      // Silence the warning about unused variable.
      (void)IsRegistered;
      ++IRef;
    }
  }
}

/// \brief Emits code for OpenMP parallel directive in the parallel region.
static void EmitOMPParallelCall(CodeGenFunction &CGF,
                                const OMPParallelDirective &S,
                                llvm::Value *OutlinedFn,
                                llvm::Value *CapturedStruct) {
  if (auto C = S.getSingleClause(/*K*/ OMPC_num_threads)) {
    CodeGenFunction::RunCleanupsScope NumThreadsScope(CGF);
    auto NumThreadsClause = cast<OMPNumThreadsClause>(C);
    auto NumThreads = CGF.EmitScalarExpr(NumThreadsClause->getNumThreads(),
                                         /*IgnoreResultAssign*/ true);
    CGF.CGM.getOpenMPRuntime().EmitOMPNumThreadsClause(
        CGF, NumThreads, NumThreadsClause->getLocStart());
  }
  CGF.CGM.getOpenMPRuntime().EmitOMPParallelCall(CGF, S.getLocStart(),
                                                 OutlinedFn, CapturedStruct);
}

void CodeGenFunction::EmitOMPParallelDirective(const OMPParallelDirective &S) {
  auto CS = cast<CapturedStmt>(S.getAssociatedStmt());
  auto CapturedStruct = GenerateCapturedStmtArgument(*CS);
  auto OutlinedFn = CGM.getOpenMPRuntime().EmitOpenMPOutlinedFunction(
      S, *CS->getCapturedDecl()->param_begin());
  if (auto C = S.getSingleClause(/*K*/ OMPC_if)) {
    auto Cond = cast<OMPIfClause>(C)->getCondition();
    EmitOMPIfClause(*this, Cond, [&](bool ThenBlock) {
      if (ThenBlock)
        EmitOMPParallelCall(*this, S, OutlinedFn, CapturedStruct);
      else
        CGM.getOpenMPRuntime().EmitOMPSerialCall(*this, S.getLocStart(),
                                                 OutlinedFn, CapturedStruct);
    });
  } else
    EmitOMPParallelCall(*this, S, OutlinedFn, CapturedStruct);
}

void CodeGenFunction::EmitOMPLoopBody(const OMPLoopDirective &S,
                                      bool SeparateIter) {
  RunCleanupsScope BodyScope(*this);
  // Update counters values on current iteration.
  for (auto I : S.updates()) {
    EmitIgnoredExpr(I);
  }
  // On a continue in the body, jump to the end.
  auto Continue = getJumpDestInCurrentScope("omp.body.continue");
  BreakContinueStack.push_back(BreakContinue(JumpDest(), Continue));
  // Emit loop body.
  EmitStmt(S.getBody());
  // The end (updates/cleanups).
  EmitBlock(Continue.getBlock());
  BreakContinueStack.pop_back();
  if (SeparateIter) {
    // TODO: Update lastprivates if the SeparateIter flag is true.
    // This will be implemented in a follow-up OMPLastprivateClause patch, but
    // result should be still correct without it, as we do not make these
    // variables private yet.
  }
}

void CodeGenFunction::EmitOMPInnerLoop(const OMPLoopDirective &S,
                                       OMPPrivateScope &LoopScope,
                                       bool SeparateIter) {
  auto LoopExit = getJumpDestInCurrentScope("omp.inner.for.end");
  auto Cnt = getPGORegionCounter(&S);

  // Start the loop with a block that tests the condition.
  auto CondBlock = createBasicBlock("omp.inner.for.cond");
  EmitBlock(CondBlock);
  LoopStack.push(CondBlock);

  // If there are any cleanups between here and the loop-exit scope,
  // create a block to stage a loop exit along.
  auto ExitBlock = LoopExit.getBlock();
  if (LoopScope.requiresCleanups())
    ExitBlock = createBasicBlock("omp.inner.for.cond.cleanup");

  auto LoopBody = createBasicBlock("omp.inner.for.body");

  // Emit condition: "IV < LastIteration + 1 [ - 1]"
  // ("- 1" when lastprivate clause is present - separate one iteration).
  llvm::Value *BoolCondVal = EvaluateExprAsBool(S.getCond(SeparateIter));
  Builder.CreateCondBr(BoolCondVal, LoopBody, ExitBlock,
                       PGO.createLoopWeights(S.getCond(SeparateIter), Cnt));

  if (ExitBlock != LoopExit.getBlock()) {
    EmitBlock(ExitBlock);
    EmitBranchThroughCleanup(LoopExit);
  }

  EmitBlock(LoopBody);
  Cnt.beginRegion(Builder);

  // Create a block for the increment.
  auto Continue = getJumpDestInCurrentScope("omp.inner.for.inc");
  BreakContinueStack.push_back(BreakContinue(LoopExit, Continue));

  EmitOMPLoopBody(S);
  EmitStopPoint(&S);

  // Emit "IV = IV + 1" and a back-edge to the condition block.
  EmitBlock(Continue.getBlock());
  EmitIgnoredExpr(S.getInc());
  BreakContinueStack.pop_back();
  EmitBranch(CondBlock);
  LoopStack.pop();
  // Emit the fall-through block.
  EmitBlock(LoopExit.getBlock());
}

void CodeGenFunction::EmitOMPSimdFinal(const OMPLoopDirective &S) {
  auto IC = S.counters().begin();
  for (auto F : S.finals()) {
    if (LocalDeclMap.lookup(cast<DeclRefExpr>((*IC))->getDecl())) {
      EmitIgnoredExpr(F);
    }
    ++IC;
  }
}

static void EmitOMPAlignedClause(CodeGenFunction &CGF, CodeGenModule &CGM,
                                 const OMPAlignedClause &Clause) {
  unsigned ClauseAlignment = 0;
  if (auto AlignmentExpr = Clause.getAlignment()) {
    auto AlignmentCI =
        cast<llvm::ConstantInt>(CGF.EmitScalarExpr(AlignmentExpr));
    ClauseAlignment = static_cast<unsigned>(AlignmentCI->getZExtValue());
  }
  for (auto E : Clause.varlists()) {
    unsigned Alignment = ClauseAlignment;
    if (Alignment == 0) {
      // OpenMP [2.8.1, Description]
      // If no optional parameter is specified, implementation-defined default
      // alignments for SIMD instructions on the target platforms are assumed.
      Alignment = CGM.getTargetCodeGenInfo().getOpenMPSimdDefaultAlignment(
          E->getType());
    }
    assert((Alignment == 0 || llvm::isPowerOf2_32(Alignment)) &&
           "alignment is not power of 2");
    if (Alignment != 0) {
      llvm::Value *PtrValue = CGF.EmitScalarExpr(E);
      CGF.EmitAlignmentAssumption(PtrValue, Alignment);
    }
  }
}

static void EmitPrivateLoopCounters(CodeGenFunction &CGF,
                                    CodeGenFunction::OMPPrivateScope &LoopScope,
                                    ArrayRef<Expr *> Counters) {
  for (auto *E : Counters) {
    auto VD = cast<VarDecl>(cast<DeclRefExpr>(E)->getDecl());
    bool IsRegistered = LoopScope.addPrivate(VD, [&]() -> llvm::Value * {
      // Emit var without initialization.
      auto VarEmission = CGF.EmitAutoVarAlloca(*VD);
      CGF.EmitAutoVarCleanups(VarEmission);
      return VarEmission.getAllocatedAddress();
    });
    assert(IsRegistered && "counter already registered as private");
    // Silence the warning about unused variable.
    (void)IsRegistered;
  }
  (void)LoopScope.Privatize();
}

void CodeGenFunction::EmitOMPSimdDirective(const OMPSimdDirective &S) {
  // Pragma 'simd' code depends on presence of 'lastprivate'.
  // If present, we have to separate last iteration of the loop:
  //
  // if (LastIteration != 0) {
  //   for (IV in 0..LastIteration-1) BODY;
  //   BODY with updates of lastprivate vars;
  //   <Final counter/linear vars updates>;
  // }
  //
  // otherwise (when there's no lastprivate):
  //
  //   for (IV in 0..LastIteration) BODY;
  //   <Final counter/linear vars updates>;
  //

  // Walk clauses and process safelen/lastprivate.
  bool SeparateIter = false;
  LoopStack.setParallel();
  LoopStack.setVectorizerEnable(true);
  for (auto C : S.clauses()) {
    switch (C->getClauseKind()) {
    case OMPC_safelen: {
      RValue Len = EmitAnyExpr(cast<OMPSafelenClause>(C)->getSafelen(),
                               AggValueSlot::ignored(), true);
      llvm::ConstantInt *Val = cast<llvm::ConstantInt>(Len.getScalarVal());
      LoopStack.setVectorizerWidth(Val->getZExtValue());
      // In presence of finite 'safelen', it may be unsafe to mark all
      // the memory instructions parallel, because loop-carried
      // dependences of 'safelen' iterations are possible.
      LoopStack.setParallel(false);
      break;
    }
    case OMPC_aligned:
      EmitOMPAlignedClause(*this, CGM, cast<OMPAlignedClause>(*C));
      break;
    case OMPC_lastprivate:
      SeparateIter = true;
      break;
    default:
      // Not handled yet
      ;
    }
  }

  InlinedOpenMPRegion Region(*this, S.getAssociatedStmt());
  RunCleanupsScope DirectiveScope(*this);

  CGDebugInfo *DI = getDebugInfo();
  if (DI)
    DI->EmitLexicalBlockStart(Builder, S.getSourceRange().getBegin());

  // Emit the loop iteration variable.
  const Expr *IVExpr = S.getIterationVariable();
  const VarDecl *IVDecl = cast<VarDecl>(cast<DeclRefExpr>(IVExpr)->getDecl());
  EmitVarDecl(*IVDecl);
  EmitIgnoredExpr(S.getInit());

  // Emit the iterations count variable.
  // If it is not a variable, Sema decided to calculate iterations count on each
  // iteration (e.g., it is foldable into a constant).
  if (auto LIExpr = dyn_cast<DeclRefExpr>(S.getLastIteration())) {
    EmitVarDecl(*cast<VarDecl>(LIExpr->getDecl()));
    // Emit calculation of the iterations count.
    EmitIgnoredExpr(S.getCalcLastIteration());
  }

  if (SeparateIter) {
    // Emit: if (LastIteration > 0) - begin.
    RegionCounter Cnt = getPGORegionCounter(&S);
    auto ThenBlock = createBasicBlock("simd.if.then");
    auto ContBlock = createBasicBlock("simd.if.end");
    EmitBranchOnBoolExpr(S.getPreCond(), ThenBlock, ContBlock, Cnt.getCount());
    EmitBlock(ThenBlock);
    Cnt.beginRegion(Builder);
    // Emit 'then' code.
    {
      OMPPrivateScope LoopScope(*this);
      EmitPrivateLoopCounters(*this, LoopScope, S.counters());
      EmitOMPInnerLoop(S, LoopScope, /* SeparateIter */ true);
      EmitOMPLoopBody(S, /* SeparateIter */ true);
    }
    EmitOMPSimdFinal(S);
    // Emit: if (LastIteration != 0) - end.
    EmitBranch(ContBlock);
    EmitBlock(ContBlock, true);
  } else {
    {
      OMPPrivateScope LoopScope(*this);
      EmitPrivateLoopCounters(*this, LoopScope, S.counters());
      EmitOMPInnerLoop(S, LoopScope);
    }
    EmitOMPSimdFinal(S);
  }

  if (DI)
    DI->EmitLexicalBlockEnd(Builder, S.getSourceRange().getEnd());
}

/// \brief Emit a helper variable and return corresponding lvalue.
static LValue EmitOMPHelperVar(CodeGenFunction &CGF,
                               const DeclRefExpr *Helper) {
  auto VDecl = cast<VarDecl>(Helper->getDecl());
  CGF.EmitVarDecl(*VDecl);
  return CGF.EmitLValue(Helper);
}

void CodeGenFunction::EmitOMPWorksharingLoop(const OMPLoopDirective &S) {
  // Emit the loop iteration variable.
  auto IVExpr = cast<DeclRefExpr>(S.getIterationVariable());
  auto IVDecl = cast<VarDecl>(IVExpr->getDecl());
  EmitVarDecl(*IVDecl);

  // Emit the iterations count variable.
  // If it is not a variable, Sema decided to calculate iterations count on each
  // iteration (e.g., it is foldable into a constant).
  if (auto LIExpr = dyn_cast<DeclRefExpr>(S.getLastIteration())) {
    EmitVarDecl(*cast<VarDecl>(LIExpr->getDecl()));
    // Emit calculation of the iterations count.
    EmitIgnoredExpr(S.getCalcLastIteration());
  }

  auto &RT = CGM.getOpenMPRuntime();

  // Check pre-condition.
  {
    // Skip the entire loop if we don't meet the precondition.
    RegionCounter Cnt = getPGORegionCounter(&S);
    auto ThenBlock = createBasicBlock("omp.precond.then");
    auto ContBlock = createBasicBlock("omp.precond.end");
    EmitBranchOnBoolExpr(S.getPreCond(), ThenBlock, ContBlock, Cnt.getCount());
    EmitBlock(ThenBlock);
    Cnt.beginRegion(Builder);
    // Emit 'then' code.
    {
      // Emit helper vars inits.
      LValue LB =
          EmitOMPHelperVar(*this, cast<DeclRefExpr>(S.getLowerBoundVariable()));
      LValue UB =
          EmitOMPHelperVar(*this, cast<DeclRefExpr>(S.getUpperBoundVariable()));
      LValue ST =
          EmitOMPHelperVar(*this, cast<DeclRefExpr>(S.getStrideVariable()));
      LValue IL =
          EmitOMPHelperVar(*this, cast<DeclRefExpr>(S.getIsLastIterVariable()));

      OMPPrivateScope LoopScope(*this);
      EmitPrivateLoopCounters(*this, LoopScope, S.counters());

      // Detect the loop schedule kind and chunk.
      auto ScheduleKind = OMPC_SCHEDULE_unknown;
      llvm::Value *Chunk = nullptr;
      if (auto C = cast_or_null<OMPScheduleClause>(
              S.getSingleClause(OMPC_schedule))) {
        ScheduleKind = C->getScheduleKind();
        if (auto Ch = C->getChunkSize()) {
          Chunk = EmitScalarExpr(Ch);
          Chunk = EmitScalarConversion(Chunk, Ch->getType(),
                                       S.getIterationVariable()->getType());
        }
      }
      const unsigned IVSize = getContext().getTypeSize(IVExpr->getType());
      const bool IVSigned = IVExpr->getType()->hasSignedIntegerRepresentation();
      if (RT.isStaticNonchunked(ScheduleKind,
                                /* Chunked */ Chunk != nullptr)) {
        // OpenMP [2.7.1, Loop Construct, Description, table 2-1]
        // When no chunk_size is specified, the iteration space is divided into
        // chunks that are approximately equal in size, and at most one chunk is
        // distributed to each thread. Note that the size of the chunks is
        // unspecified in this case.
        RT.EmitOMPForInit(*this, S.getLocStart(), ScheduleKind, IVSize, IVSigned,
                          IL.getAddress(), LB.getAddress(), UB.getAddress(),
                          ST.getAddress());
        // UB = min(UB, GlobalUB);
        EmitIgnoredExpr(S.getEnsureUpperBound());
        // IV = LB;
        EmitIgnoredExpr(S.getInit());
        // while (idx <= UB) { BODY; ++idx; }
        EmitOMPInnerLoop(S, LoopScope);
        // Tell the runtime we are done.
        RT.EmitOMPForFinish(*this, S.getLocStart(), ScheduleKind);
      } else
        ErrorUnsupported(&S, "OpenMP loop with requested schedule");
    }
    // We're now done with the loop, so jump to the continuation block.
    EmitBranch(ContBlock);
    EmitBlock(ContBlock, true);
  }
}

void CodeGenFunction::EmitOMPForDirective(const OMPForDirective &S) {
  InlinedOpenMPRegion Region(*this, S.getAssociatedStmt());
  RunCleanupsScope DirectiveScope(*this);

  CGDebugInfo *DI = getDebugInfo();
  if (DI)
    DI->EmitLexicalBlockStart(Builder, S.getSourceRange().getBegin());

  EmitOMPWorksharingLoop(S);

  // Emit an implicit barrier at the end.
  CGM.getOpenMPRuntime().EmitOMPBarrierCall(*this, S.getLocStart(),
                                            /*IsExplicit*/ false);
  if (DI)
    DI->EmitLexicalBlockEnd(Builder, S.getSourceRange().getEnd());
}

void CodeGenFunction::EmitOMPForSimdDirective(const OMPForSimdDirective &) {
  llvm_unreachable("CodeGen for 'omp for simd' is not supported yet.");
}

void CodeGenFunction::EmitOMPSectionsDirective(const OMPSectionsDirective &) {
  llvm_unreachable("CodeGen for 'omp sections' is not supported yet.");
}

void CodeGenFunction::EmitOMPSectionDirective(const OMPSectionDirective &) {
  llvm_unreachable("CodeGen for 'omp section' is not supported yet.");
}

void CodeGenFunction::EmitOMPSingleDirective(const OMPSingleDirective &) {
  llvm_unreachable("CodeGen for 'omp single' is not supported yet.");
}

void CodeGenFunction::EmitOMPMasterDirective(const OMPMasterDirective &S) {
  CGM.getOpenMPRuntime().EmitOMPMasterRegion(*this, [&]() -> void {
    InlinedOpenMPRegion Region(*this, S.getAssociatedStmt());
    RunCleanupsScope Scope(*this);
    EmitStmt(cast<CapturedStmt>(S.getAssociatedStmt())->getCapturedStmt());
    EnsureInsertPoint();
  }, S.getLocStart());
}

void CodeGenFunction::EmitOMPCriticalDirective(const OMPCriticalDirective &S) {
  CGM.getOpenMPRuntime().EmitOMPCriticalRegion(
      *this, S.getDirectiveName().getAsString(), [&]() -> void {
    InlinedOpenMPRegion Region(*this, S.getAssociatedStmt());
    RunCleanupsScope Scope(*this);
    EmitStmt(
        cast<CapturedStmt>(S.getAssociatedStmt())->getCapturedStmt());
    EnsureInsertPoint();
  }, S.getLocStart());
}

void
CodeGenFunction::EmitOMPParallelForDirective(const OMPParallelForDirective &) {
  llvm_unreachable("CodeGen for 'omp parallel for' is not supported yet.");
}

void CodeGenFunction::EmitOMPParallelForSimdDirective(
    const OMPParallelForSimdDirective &) {
  llvm_unreachable("CodeGen for 'omp parallel for simd' is not supported yet.");
}

void CodeGenFunction::EmitOMPParallelSectionsDirective(
    const OMPParallelSectionsDirective &) {
  llvm_unreachable("CodeGen for 'omp parallel sections' is not supported yet.");
}

void CodeGenFunction::EmitOMPTaskDirective(const OMPTaskDirective &) {
  llvm_unreachable("CodeGen for 'omp task' is not supported yet.");
}

void CodeGenFunction::EmitOMPTaskyieldDirective(const OMPTaskyieldDirective &) {
  llvm_unreachable("CodeGen for 'omp taskyield' is not supported yet.");
}

void CodeGenFunction::EmitOMPBarrierDirective(const OMPBarrierDirective &S) {
  CGM.getOpenMPRuntime().EmitOMPBarrierCall(*this, S.getLocStart());
}

void CodeGenFunction::EmitOMPTaskwaitDirective(const OMPTaskwaitDirective &) {
  llvm_unreachable("CodeGen for 'omp taskwait' is not supported yet.");
}

void CodeGenFunction::EmitOMPFlushDirective(const OMPFlushDirective &S) {
  CGM.getOpenMPRuntime().EmitOMPFlush(
      *this, [&]() -> ArrayRef<const Expr *> {
               if (auto C = S.getSingleClause(/*K*/ OMPC_flush)) {
                 auto FlushClause = cast<OMPFlushClause>(C);
                 return llvm::makeArrayRef(FlushClause->varlist_begin(),
                                           FlushClause->varlist_end());
               }
               return llvm::None;
             }(),
      S.getLocStart());
}

void CodeGenFunction::EmitOMPOrderedDirective(const OMPOrderedDirective &) {
  llvm_unreachable("CodeGen for 'omp ordered' is not supported yet.");
}

void CodeGenFunction::EmitOMPAtomicDirective(const OMPAtomicDirective &) {
  llvm_unreachable("CodeGen for 'omp atomic' is not supported yet.");
}

void CodeGenFunction::EmitOMPTargetDirective(const OMPTargetDirective &) {
  llvm_unreachable("CodeGen for 'omp target' is not supported yet.");
}

void CodeGenFunction::EmitOMPTeamsDirective(const OMPTeamsDirective &) {
  llvm_unreachable("CodeGen for 'omp teams' is not supported yet.");
}