C++ SILArgument类代码示例

void EpilogueARCContext::initializeDataflow() {
  for (auto &B : *F) {
    // Find the exit blocks.
    if (isInterestedFunctionExitingBlock(&B)) {
      ExitBlocks.insert(&B);
    }
    // Allocate the storage.
    EpilogueARCBlockStates[&B] =
              new (BPA.Allocate()) EpilogueARCBlockState();
  }

  // Split the SILargument into local arguments to each specific basic block.
  llvm::SmallVector<SILValue, 4> ToProcess;
  llvm::DenseSet<SILValue> Processed;
  ToProcess.push_back(Arg);
  while (!ToProcess.empty()) {
    SILValue CArg = ToProcess.pop_back_val();
    if (!CArg)
      continue;
    if (Processed.find(CArg) != Processed.end())
       continue;
    Processed.insert(CArg);
    SILArgument *A = dyn_cast<SILArgument>(CArg);
    if (A && !A->isFunctionArg()) {
      // Find predecessor and break the SILArgument to predecessors.
      for (auto X : A->getParent()->getPreds()) {
        // Try to find the predecessor edge-value.
        SILValue IA = A->getIncomingValue(X);
        EpilogueARCBlockStates[X]->LocalArg = IA;
        // Maybe the edge value is another SILArgument.
        ToProcess.push_back(IA);
      }
    }
  }
}

/// Determine the number of iterations the loop is at most executed. The loop
/// might contain early exits so this is the maximum if no early exits are
/// taken.
static Optional<uint64_t> getMaxLoopTripCount(SILLoop *Loop,
                                              SILBasicBlock *Preheader,
                                              SILBasicBlock *Header,
                                              SILBasicBlock *Latch) {

  // Skip a split backedge.
  SILBasicBlock *OrigLatch = Latch;
  if (!Loop->isLoopExiting(Latch) && !(Latch = Latch->getSinglePredecessor()))
    return None;
  if (!Loop->isLoopExiting(Latch))
    return None;

  // Get the loop exit condition.
  auto *CondBr = dyn_cast<CondBranchInst>(Latch->getTerminator());
  if (!CondBr)
    return None;

  // Match an add 1 recurrence.
  SILArgument *RecArg;
  IntegerLiteralInst *End;
  SILValue RecNext;

  if (!match(CondBr->getCondition(),
             m_BuiltinInst(BuiltinValueKind::ICMP_EQ, m_SILValue(RecNext),
                           m_IntegerLiteralInst(End))))
    return None;
  if (!match(RecNext,
             m_TupleExtractInst(m_ApplyInst(BuiltinValueKind::SAddOver,
                                            m_SILArgument(RecArg), m_One()),
                                0)))
    return None;

  if (RecArg->getParent() != Header)
    return None;

  auto *Start = dyn_cast_or_null<IntegerLiteralInst>(
      RecArg->getIncomingValue(Preheader).getDef());
  if (!Start)
    return None;

  if (RecNext != RecArg->getIncomingValue(OrigLatch))
    return None;

  auto StartVal = Start->getValue();
  auto EndVal = End->getValue();
  if (StartVal.sgt(EndVal))
    return None;

  auto Dist = EndVal - StartVal;
  if (Dist.getBitWidth() > 64)
    return None;

  if (Dist == 0)
    return None;

  return Dist.getZExtValue();
}

void FunctionSignatureTransform::ArgumentExplosionFinalizeOptimizedFunction() {
  SILBasicBlock *BB = &*NewF->begin();
  SILBuilder Builder(BB->begin());
  Builder.setCurrentDebugScope(BB->getParent()->getDebugScope());
  unsigned TotalArgIndex = 0;
  for (ArgumentDescriptor &AD : ArgumentDescList) {
    // Simply continue if do not explode.
    if (!AD.Explode) {
      AIM[TotalArgIndex] = AD.Index;
      TotalArgIndex ++;
      continue;
    }

    // OK, we need to explode this argument.
    unsigned ArgOffset = ++TotalArgIndex;
    unsigned OldArgIndex = ArgOffset - 1; 
    llvm::SmallVector<SILValue, 8> LeafValues;

    // We do this in the same order as leaf types since ProjTree expects that the
    // order of leaf values matches the order of leaf types.
    llvm::SmallVector<const ProjectionTreeNode*, 8> LeafNodes;
    AD.ProjTree.getLeafNodes(LeafNodes);

    for (auto *Node : LeafNodes) {
      auto OwnershipKind = *AD.getTransformedOwnershipKind(Node->getType());
      LeafValues.push_back(BB->insertFunctionArgument(
          ArgOffset++, Node->getType(), OwnershipKind,
          BB->getArgument(OldArgIndex)->getDecl()));
      AIM[TotalArgIndex - 1] = AD.Index;
      TotalArgIndex ++;
    }

    // Then go through the projection tree constructing aggregates and replacing
    // uses.
    AD.ProjTree.replaceValueUsesWithLeafUses(Builder, BB->getParent()->getLocation(),
                                             LeafValues);

    // We ignored debugvalue uses when we constructed the new arguments, in order
    // to preserve as much information as possible, we construct a new value for
    // OrigArg from the leaf values and use that in place of the OrigArg.
    SILValue NewOrigArgValue = AD.ProjTree.computeExplodedArgumentValue(Builder,
                                             BB->getParent()->getLocation(),
                                             LeafValues);

    // Replace all uses of the original arg with the new value.
    SILArgument *OrigArg = BB->getArgument(OldArgIndex);
    OrigArg->replaceAllUsesWith(NewOrigArgValue);

    // Now erase the old argument since it does not have any uses. We also
    // decrement ArgOffset since we have one less argument now.
    BB->eraseArgument(OldArgIndex);
    TotalArgIndex --;
  }
}

void AccessSummaryAnalysis::FunctionSummary::print(raw_ostream &os,
                                                   SILFunction *fn) const {
  unsigned argCount = getArgumentCount();
  os << "(";

  for (unsigned i = 0; i < argCount; i++) {
    if (i > 0) {
      os << ",  ";
    }
    SILArgument *arg = fn->getArgument(i);
    SILModule &m = fn->getModule();
    os << getAccessForArgument(i).getDescription(arg->getType(), m);
  }

  os << ")";
}

void ReleaseCodeMotionContext::computeCodeMotionGenKillSet() {
  for (SILBasicBlock *BB : PO->getPostOrder()) {
    auto *State = BlockStates[BB];
    bool InterestBlock = false;
    for (auto I = BB->rbegin(), E = BB->rend(); I != E; ++I) {
      // Check whether this instruction blocks any RC root code motion.
      for (unsigned i = 0; i < RCRootVault.size(); ++i) {
        if (!State->BBMaxSet.test(i) || !mayBlockCodeMotion(&*I, RCRootVault[i]))
          continue;
        // This instruction blocks this RC root.
        InterestBlock = true;
        State->BBKillSet.set(i);
        State->BBGenSet.reset(i);
      }

      // If this is an epilogue release and we are freezing epilogue release
      // simply continue.
      if (FreezeEpilogueReleases && ERM.isEpilogueRelease(&*I))
        continue;

      // If this is a release instruction, it also generates.
      if (isReleaseInstruction(&*I)) {
        unsigned idx = RCRootIndex[getRCRoot(&*I)];
        State->BBGenSet.set(idx);
        assert(State->BBKillSet.test(idx) && "Killset computed incorrectly");
        State->BBKillSet.reset(idx);
        InterestBlock = true;
      }
    }

    // Handle SILArgument, SILArgument can invalidate.
    for (unsigned i = 0; i < RCRootVault.size(); ++i) {
      SILArgument *A = dyn_cast<SILArgument>(RCRootVault[i]);
      if (!A || A->getParent() != BB)
        continue;
      InterestBlock = true;
      State->BBKillSet.set(i);
      State->BBGenSet.reset(i);
    }

    // Is this interesting to the last iteration of the data flow.
    if (!InterestBlock)
      continue;
    InterestBlocks.insert(BB);
  }
}

  /// Like ValueIsPHI but also check if the PHI has no source
  /// operands, i.e., it was just added.
  static SILArgument *ValueIsNewPHI(SILValue Val, SILSSAUpdater *Updater) {
    SILArgument *PHI = ValueIsPHI(Val, Updater);
    if (PHI) {
      auto *PhiBB = PHI->getParent();
      size_t PhiIdx = PHI->getIndex();

      // If all predecessor edges are 'not set' this is a new phi.
      for (auto *PredBB : PhiBB->getPreds()) {
        OperandValueArrayRef Edges =
            getEdgeValuesForTerminator(PredBB->getTerminator(), PhiBB);

        assert(PhiIdx < Edges.size() && "Not enough edges!");

        SILValue V = Edges[PhiIdx];
        // Check for the 'not set' sentinel.
        if (V.getDef() != Updater->PHISentinel.get())
          return nullptr;
      }
      return PHI;
    }
    return nullptr;
  }

Effects *FunctionEffects::getEffectsOn(SILValue Addr) {
  SILValue BaseAddr = skipValueProjections(skipAddrProjections(Addr));
  switch (BaseAddr->getKind()) {
    case swift::ValueKind::SILArgument: {
      // Can we associate the address to a function parameter?
      SILArgument *Arg = cast<SILArgument>(BaseAddr);
      if (Arg->isFunctionArg()) {
        return &ParamEffects[Arg->getIndex()];
      }
      break;
    }
    case ValueKind::AllocStackInst:
    case ValueKind::AllocRefInst:
    case ValueKind::AllocRefDynamicInst:
    case ValueKind::AllocBoxInst:
      // Effects on locally allocated storage.
      return &LocalEffects;
    default:
      break;
  }
  // Everything else.
  return &GlobalEffects;
}

/// \brief Propagate/remove basic block input values when all predecessors
/// supply the same arguments.
static void propagateBasicBlockArgs(SILBasicBlock &BB) {
  // This functions would simplify the code as following:
  //
  //   bb0:
  //     br bb2(%1 : $Builtin.Int1, %2 : $Builtin.Int1)
  //   bb1:
  //     br bb2(%1 : $Builtin.Int1, %2 : $Builtin.Int1)
  //   bb2(%3 : $Builtin.Int1, %4 : $Builtin.Int1):
  //     use(%3 : $Builtin.Int1)
  //     use(%4 : $Builtin.Int1)
  // =>
  //   bb0:
  //     br bb2
  //   bb1:
  //     br bb2
  //   bb2:
  //     use(%1 : $Builtin.Int1)
  //     use(%2 : $Builtin.Int1)

  // If there are no predecessors or no arguments, there is nothing to do.
  if (BB.pred_empty() || BB.bbarg_empty())
    return;

  // Check if all the predecessors supply the same arguments to the BB.
  SmallVector<SILValue, 4> Args;
  bool checkArgs = false;
  for (SILBasicBlock::pred_iterator PI = BB.pred_begin(), PE = BB.pred_end();
       PI != PE; ++PI) {
    SILBasicBlock *PredB = *PI;

    // We are only simplifying cases where all predecessors are
    // unconditional branch instructions.
    if (!isa<BranchInst>(PredB->getTerminator()))
      return;

    BranchInst *BI = cast<BranchInst>(PredB->getTerminator());
    unsigned Idx = 0;
    assert(!BI->getArgs().empty());
    for (OperandValueArrayRef::iterator AI = BI->getArgs().begin(),
           AE = BI->getArgs().end();
         AI != AE; ++AI, ++Idx) {
      // When processing the first predecessor, record the arguments.
      if (!checkArgs)
        Args.push_back(*AI);
      else
        // On each subsequent predecessor, check the arguments.
        if (Args[Idx] != *AI)
          return;
    }

    // After the first branch is processed, the arguments vector is populated.
    assert(Args.size() > 0);
    checkArgs = true;
  }

  // If we've reached this point, the optimization is valid, so optimize.
  // We know that the incoming arguments from all predecessors are the same,
  // so just use them directly and remove the basic block parameters.

  // Drop the arguments from the branch instructions by creating a new branch
  // instruction and deleting the old one.
  llvm::SmallVector<SILInstruction*, 32> ToBeDeleted;
  for (SILBasicBlock::pred_iterator PI = BB.pred_begin(), PE = BB.pred_end();
       PI != PE; ++PI) {
    SILBasicBlock *PredB = *PI;
    BranchInst *BI = cast<BranchInst>(PredB->getTerminator());
    SILBuilderWithScope Bldr(PredB, BI);
    Bldr.createBranch(BI->getLoc(), BI->getDestBB());
    ToBeDeleted.push_back(BI);
  }

  // Drop the parameters from basic blocks and replace all uses with the passed
  // in arguments.
  unsigned Idx = 0;
  for (SILBasicBlock::bbarg_iterator AI = BB.bbarg_begin(),
                                     AE = BB.bbarg_end();
                                     AI != AE; ++AI, ++Idx) {
    // FIXME: These could be further propagatable now, we might want to move
    // this to CCP and trigger another round of copy propagation.
    SILArgument *Arg = *AI;

    // We were able to fold, so all users should use the new folded value.
    assert(Arg->getTypes().size() == 1 &&
           "Currently, we only support single result instructions.");
    SILValue(Arg).replaceAllUsesWith(Args[Idx]);
    NumBasicBlockArgsPropagated++;
  }

  // Remove args from the block.
  BB.dropAllBBArgs();

  // The old branch instructions are no longer used, erase them.
  recursivelyDeleteTriviallyDeadInstructions(ToBeDeleted, true);
  NumInstructionsRemoved += ToBeDeleted.size();
}

/// \brief Populate the body of the cloned closure, modifying instructions as
/// necessary. This is where we create the actual specialized BB Arguments.
void ClosureSpecCloner::populateCloned() {
  SILFunction *Cloned = getCloned();
  SILFunction *ClosureUser = CallSiteDesc.getApplyCallee();

  // Create arguments for the entry block.
  SILBasicBlock *ClosureUserEntryBB = &*ClosureUser->begin();
  SILBasicBlock *ClonedEntryBB = Cloned->createBasicBlock();

  SmallVector<SILValue, 4> entryArgs;
  entryArgs.reserve(ClosureUserEntryBB->getArguments().size());

  // Remove the closure argument.
  SILArgument *ClosureArg = nullptr;
  for (size_t i = 0, e = ClosureUserEntryBB->args_size(); i != e; ++i) {
    SILArgument *Arg = ClosureUserEntryBB->getArgument(i);
    if (i == CallSiteDesc.getClosureIndex()) {
      ClosureArg = Arg;
      entryArgs.push_back(SILValue());
      continue;
    }

    // Otherwise, create a new argument which copies the original argument
    SILValue MappedValue =
        ClonedEntryBB->createFunctionArgument(Arg->getType(), Arg->getDecl());
    entryArgs.push_back(MappedValue);
  }

  // Next we need to add in any arguments that are not captured as arguments to
  // the cloned function.
  //
  // We do not insert the new mapped arguments into the value map since there by
  // definition is nothing in the partial apply user function that references
  // such arguments. After this pass is done the only thing that will reference
  // the arguments is the partial apply that we will create.
  SILFunction *ClosedOverFun = CallSiteDesc.getClosureCallee();
  auto ClosedOverFunConv = ClosedOverFun->getConventions();
  unsigned NumTotalParams = ClosedOverFunConv.getNumParameters();
  unsigned NumNotCaptured = NumTotalParams - CallSiteDesc.getNumArguments();
  llvm::SmallVector<SILValue, 4> NewPAIArgs;
  for (auto &PInfo : ClosedOverFunConv.getParameters().slice(NumNotCaptured)) {
    auto paramTy = ClosedOverFunConv.getSILType(PInfo);
    SILValue MappedValue = ClonedEntryBB->createFunctionArgument(paramTy);
    NewPAIArgs.push_back(MappedValue);
  }

  SILBuilder &Builder = getBuilder();
  Builder.setInsertionPoint(ClonedEntryBB);

  // Clone FRI and PAI, and replace usage of the removed closure argument
  // with result of cloned PAI.
  SILValue FnVal =
      Builder.createFunctionRef(CallSiteDesc.getLoc(), ClosedOverFun);
  auto *NewClosure = CallSiteDesc.createNewClosure(Builder, FnVal, NewPAIArgs);

  // Clone a chain of ConvertFunctionInsts. This can create further
  // reabstraction partial_apply instructions.
  SmallVector<PartialApplyInst*, 4> NeedsRelease;
  SILValue ConvertedCallee = cloneCalleeConversion(
      CallSiteDesc.getClosureCallerArg(), NewClosure, Builder, NeedsRelease);

  // Make sure that we actually emit the releases for reabstraction thunks. We
  // have guaranteed earlier that we only allow reabstraction thunks if the
  // closure was passed trivial.
  assert(NeedsRelease.empty() || CallSiteDesc.isTrivialNoEscapeParameter());

  entryArgs[CallSiteDesc.getClosureIndex()] = ConvertedCallee;

  // Visit original BBs in depth-first preorder, starting with the
  // entry block, cloning all instructions and terminators.
  cloneFunctionBody(ClosureUser, ClonedEntryBB, entryArgs);

  // Then insert a release in all non failure exit BBs if our partial apply was
  // guaranteed. This is b/c it was passed at +0 originally and we need to
  // balance the initial increment of the newly created closure(s).
  bool ClosureHasRefSemantics = CallSiteDesc.closureHasRefSemanticContext();
  if ((CallSiteDesc.isClosureGuaranteed() ||
       CallSiteDesc.isTrivialNoEscapeParameter()) &&
      (ClosureHasRefSemantics || !NeedsRelease.empty())) {
    for (SILBasicBlock *BB : CallSiteDesc.getNonFailureExitBBs()) {
      SILBasicBlock *OpBB = getOpBasicBlock(BB);

      TermInst *TI = OpBB->getTerminator();
      auto Loc = CleanupLocation::get(NewClosure->getLoc());

      // If we have an exit, we place the release right before it so we know
      // that it will be executed at the end of the epilogue.
      if (TI->isFunctionExiting()) {
        Builder.setInsertionPoint(TI);
        if (ClosureHasRefSemantics)
          Builder.createReleaseValue(Loc, SILValue(NewClosure),
                                     Builder.getDefaultAtomicity());
        for (auto PAI : NeedsRelease)
          Builder.createReleaseValue(Loc, SILValue(PAI),
                                     Builder.getDefaultAtomicity());
        continue;
      }

      // We use casts where findAllNonFailureExitBBs should have made sure that
//.........这里部分代码省略.........

/// \brief Populate the body of the cloned closure, modifying instructions as
/// necessary. This is where we create the actual specialized BB Arguments.
void ClosureSpecCloner::populateCloned() {
  SILFunction *Cloned = getCloned();
  SILFunction *ClosureUser = CallSiteDesc.getApplyCallee();

  // Create arguments for the entry block.
  SILBasicBlock *ClosureUserEntryBB = &*ClosureUser->begin();
  SILBasicBlock *ClonedEntryBB = Cloned->createBasicBlock();

  // Remove the closure argument.
  SILArgument *ClosureArg = nullptr;
  for (size_t i = 0, e = ClosureUserEntryBB->args_size(); i != e; ++i) {
    SILArgument *Arg = ClosureUserEntryBB->getArgument(i);
    if (i == CallSiteDesc.getClosureIndex()) {
      ClosureArg = Arg;
      continue;
    }

    // Otherwise, create a new argument which copies the original argument
    SILValue MappedValue =
        ClonedEntryBB->createFunctionArgument(Arg->getType(), Arg->getDecl());
    ValueMap.insert(std::make_pair(Arg, MappedValue));
  }

  // Next we need to add in any arguments that are not captured as arguments to
  // the cloned function.
  //
  // We do not insert the new mapped arguments into the value map since there by
  // definition is nothing in the partial apply user function that references
  // such arguments. After this pass is done the only thing that will reference
  // the arguments is the partial apply that we will create.
  SILFunction *ClosedOverFun = CallSiteDesc.getClosureCallee();
  CanSILFunctionType ClosedOverFunTy = ClosedOverFun->getLoweredFunctionType();
  unsigned NumTotalParams = ClosedOverFunTy->getParameters().size();
  unsigned NumNotCaptured = NumTotalParams - CallSiteDesc.getNumArguments();
  llvm::SmallVector<SILValue, 4> NewPAIArgs;
  for (auto &PInfo : ClosedOverFunTy->getParameters().slice(NumNotCaptured)) {
    SILValue MappedValue =
        ClonedEntryBB->createFunctionArgument(PInfo.getSILType());
    NewPAIArgs.push_back(MappedValue);
  }

  SILBuilder &Builder = getBuilder();
  Builder.setInsertionPoint(ClonedEntryBB);

  // Clone FRI and PAI, and replace usage of the removed closure argument
  // with result of cloned PAI.
  SILValue FnVal =
      Builder.createFunctionRef(CallSiteDesc.getLoc(), ClosedOverFun);
  auto *NewClosure = CallSiteDesc.createNewClosure(Builder, FnVal, NewPAIArgs);
  ValueMap.insert(std::make_pair(ClosureArg, SILValue(NewClosure)));

  BBMap.insert(std::make_pair(ClosureUserEntryBB, ClonedEntryBB));
  // Recursively visit original BBs in depth-first preorder, starting with the
  // entry block, cloning all instructions other than terminators.
  visitSILBasicBlock(ClosureUserEntryBB);

  // Now iterate over the BBs and fix up the terminators.
  for (auto BI = BBMap.begin(), BE = BBMap.end(); BI != BE; ++BI) {
    Builder.setInsertionPoint(BI->second);
    visit(BI->first->getTerminator());
  }

  // Then insert a release in all non failure exit BBs if our partial apply was
  // guaranteed. This is b/c it was passed at +0 originally and we need to
  // balance the initial increment of the newly created closure.
  if (CallSiteDesc.isClosureGuaranteed() &&
      CallSiteDesc.closureHasRefSemanticContext()) {
    for (SILBasicBlock *BB : CallSiteDesc.getNonFailureExitBBs()) {
      SILBasicBlock *OpBB = BBMap[BB];

      TermInst *TI = OpBB->getTerminator();
      auto Loc = CleanupLocation::get(NewClosure->getLoc());

      // If we have a return, we place the release right before it so we know
      // that it will be executed at the end of the epilogue.
      if (isa<ReturnInst>(TI)) {
        Builder.setInsertionPoint(TI);
        Builder.createReleaseValue(Loc, SILValue(NewClosure),
                                   Atomicity::Atomic);
        continue;
      }

      // We use casts where findAllNonFailureExitBBs should have made sure that
      // this is true. This will ensure that the code is updated when we hit the
      // cast failure in debug builds.
      auto *Unreachable = cast<UnreachableInst>(TI);
      auto PrevIter = std::prev(SILBasicBlock::iterator(Unreachable));
      auto NoReturnApply = FullApplySite::isa(&*PrevIter);

      // We insert the release value right before the no return apply so that if
      // the partial apply is passed into the no-return function as an @owned
      // value, we will retain the partial apply before we release it and
      // potentially eliminate it.
      Builder.setInsertionPoint(NoReturnApply.getInstruction());
      Builder.createReleaseValue(Loc, SILValue(NewClosure), Atomicity::Atomic);
    }
  }
}

unsigned ArgumentDescriptor::updateOptimizedBBArgs(SILBuilder &Builder,
                                                   SILBasicBlock *BB,
                                                   unsigned ArgOffset) {
  // If this argument is completely dead, delete this argument and return
  // ArgOffset.
  if (IsDead) {
    // If we have a callee release and we are dead, set the callee release's
    // operand to undef. We do not need it to have the argument anymore, but we
    // do need the instruction to be non-null.
    //
    // TODO: This should not be necessary.
    for (auto &X : CalleeRelease) {
      SILType CalleeReleaseTy = X->getOperand(0)->getType();
      X->setOperand(
          0, SILUndef::get(CalleeReleaseTy, Builder.getModule()));
    }

    // We should be able to recursively delete all of the remaining
    // instructions.
    SILArgument *Arg = BB->getBBArg(ArgOffset);
    eraseUsesOfValue(Arg);
    BB->eraseBBArg(ArgOffset);
    return ArgOffset;
  }

  // If this argument is not dead and we did not perform SROA, increment the
  // offset and return.
  if (!shouldExplode()) {
    return ArgOffset + 1;
  }

  // Create values for the leaf types.
  llvm::SmallVector<SILValue, 8> LeafValues;

  // Create a reference to the old arg offset and increment arg offset so we can
  // create the new arguments.
  unsigned OldArgOffset = ArgOffset++;

  // We do this in the same order as leaf types since ProjTree expects that the
  // order of leaf values matches the order of leaf types.
  {
    llvm::SmallVector<SILType, 8> LeafTypes;
    ProjTree.getLeafTypes(LeafTypes);
    for (auto Ty : LeafTypes) {
      LeafValues.push_back(BB->insertBBArg(
          ArgOffset++, Ty, BB->getBBArg(OldArgOffset)->getDecl()));
    }
  }

  // Then go through the projection tree constructing aggregates and replacing
  // uses.
  //
  // TODO: What is the right location to use here?
  ProjTree.replaceValueUsesWithLeafUses(Builder, BB->getParent()->getLocation(),
                                        LeafValues);

  // We ignored debugvalue uses when we constructed the new arguments, in order
  // to preserve as much information as possible, we construct a new value for
  // OrigArg from the leaf values and use that in place of the OrigArg.
  SILValue NewOrigArgValue = ProjTree.computeExplodedArgumentValue(Builder,
                                           BB->getParent()->getLocation(),
                                           LeafValues);

  // Replace all uses of the original arg with the new value.
  SILArgument *OrigArg = BB->getBBArg(OldArgOffset);
  OrigArg->replaceAllUsesWith(NewOrigArgValue);

  // Now erase the old argument since it does not have any uses. We also
  // decrement ArgOffset since we have one less argument now.
  BB->eraseBBArg(OldArgOffset);
  --ArgOffset;

  return ArgOffset;
}

void
ConsumedResultToEpilogueRetainMatcher::
findMatchingRetains(SILBasicBlock *BB) {
  // Iterate over the instructions post-order and find retains associated with
  // return value.
  SILValue RV = SILValue();
  for (auto II = BB->rbegin(), IE = BB->rend(); II != IE; ++II) {
    if (ReturnInst *RI = dyn_cast<ReturnInst>(&*II)) {
      RV = RI->getOperand();
      break;
    }
  }

  // Somehow, we managed not to find a return value.
  if (!RV)
    return;

  // OK. we've found the return value, now iterate on the CFG to find all the
  // post-dominating retains.
  //
  // The ConsumedArgToEpilogueReleaseMatcher finds the final releases
  // in the following way. 
  //
  // 1. If an instruction, which is not releaseinst nor releasevalue, that
  // could decrement reference count is found. bail out.
  //
  // 2. If a release is found and the release that can not be mapped to any
  // @owned argument. bail as this release may well be the final release of
  // an @owned argument, but somehow rc-identity fails to prove that.
  //
  // 3. A release that is mapped to an argument which already has a release
  // that overlaps with this release. This release for sure is not the final
  // release.
  constexpr unsigned WorkListMaxSize = 4;

  llvm::DenseSet<SILBasicBlock *> RetainFrees;
  llvm::SmallVector<BasicBlockRetainValue, 4> WorkList;
  llvm::DenseSet<SILBasicBlock *> HandledBBs;
  WorkList.push_back(std::make_pair(BB, RV));
  HandledBBs.insert(BB);
  while (!WorkList.empty()) {
    // Too many blocks ?.
    if (WorkList.size() > WorkListMaxSize) {
      EpilogueRetainInsts.clear();
      return;
    }

    // Try to find a retain %value in this basic block.
    auto R = WorkList.pop_back_val();
    RetainKindValue Kind = findMatchingRetainsInBasicBlock(R.first, R.second);

    // We've found a retain on this path.
    if (Kind.first == FindRetainKind::Found) { 
      EpilogueRetainInsts.push_back(Kind.second);
      continue;
    }

    // There is a MayDecrement instruction.
    if (Kind.first == FindRetainKind::Blocked) {
      EpilogueRetainInsts.clear();
      return;
    }

    // There is a self-recursion. Use the apply instruction as the retain.
    if (Kind.first == FindRetainKind::Recursion) {
      EpilogueRetainInsts.push_back(Kind.second);
      continue;
    }
  
    // Did not find a retain in this block, try to go to its predecessors.
    if (Kind.first == FindRetainKind::None) {
      // We can not find a retain in a block with no predecessors.
      if (R.first->getPreds().begin() == R.first->getPreds().end()) {
        EpilogueRetainInsts.clear();
        return;
      }

      // This block does not have a retain.
      RetainFrees.insert(R.first);

      // If this is a SILArgument of current basic block, we can split it up to
      // values in the predecessors.
      SILArgument *SA = dyn_cast<SILArgument>(R.second);
      if (SA && SA->getParent() != R.first)
        SA = nullptr;

      for (auto X : R.first->getPreds()) {
        if (HandledBBs.find(X) != HandledBBs.end())
          continue;
        // Try to use the predecessor edge-value.
        if (SA && SA->getIncomingValue(X)) {
          WorkList.push_back(std::make_pair(X, SA->getIncomingValue(X)));
        }
        else 
          WorkList.push_back(std::make_pair(X, R.second));
   
        HandledBBs.insert(X);
      }
    }
  }
//.........这里部分代码省略.........

unsigned ArgumentDescriptor::updateOptimizedBBArgs(SILBuilder &Builder,
                                                   SILBasicBlock *BB,
                                                   unsigned ArgOffset) {
  // If this argument is completely dead, delete this argument and return
  // ArgOffset.
  if (IsDead) {
    // If we have a callee release and we are dead, set the callee release's
    // operand to undef. We do not need it to have the argument anymore, but we
    // do need the instruction to be non-null.
    //
    // TODO: This should not be necessary.
    if (CalleeRelease) {
      SILType CalleeReleaseTy = CalleeRelease->getOperand(0)->getType();
      CalleeRelease->setOperand(
          0, SILUndef::get(CalleeReleaseTy, Builder.getModule()));

      // TODO: Currently we cannot mark arguments as dead if they are released
      // in a throw block. But as soon as we can do this, we have to handle
      // CalleeReleaseInThrowBlock as well.
      assert(!CalleeReleaseInThrowBlock &&
             "released arg in throw block cannot be dead");
    }

    // We should be able to recursively delete all of the remaining
    // instructions.
    SILArgument *Arg = BB->getBBArg(ArgOffset);
    eraseUsesOfValue(Arg);
    BB->eraseBBArg(ArgOffset);
    return ArgOffset;
  }

  // If this argument is not dead and we did not perform SROA, increment the
  // offset and return.
  if (!shouldExplode()) {
    return ArgOffset + 1;
  }

  // Create values for the leaf types.
  llvm::SmallVector<SILValue, 8> LeafValues;

  // Create a reference to the old arg offset and increment arg offset so we can
  // create the new arguments.
  unsigned OldArgOffset = ArgOffset++;

  // We do this in the same order as leaf types since ProjTree expects that the
  // order of leaf values matches the order of leaf types.
  {
    llvm::SmallVector<SILType, 8> LeafTypes;
    ProjTree.getLeafTypes(LeafTypes);
    for (auto Ty : LeafTypes) {
      LeafValues.push_back(BB->insertBBArg(
          ArgOffset++, Ty, BB->getBBArg(OldArgOffset)->getDecl()));
    }
  }

  // Then go through the projection tree constructing aggregates and replacing
  // uses.
  //
  // TODO: What is the right location to use here?
  ProjTree.replaceValueUsesWithLeafUses(Builder, BB->getParent()->getLocation(),
                                        LeafValues);

  // Replace all uses of the original arg with undef so it does not have any
  // uses.
  SILArgument *OrigArg = BB->getBBArg(OldArgOffset);
  OrigArg->replaceAllUsesWith(SILUndef::get(OrigArg->getType(), BB->getModule()));

  // Now erase the old argument since it does not have any uses. We also
  // decrement ArgOffset since we have one less argument now.
  BB->eraseBBArg(OldArgOffset);
  --ArgOffset;

  return ArgOffset;
}

void ReleaseCodeMotionContext::computeCodeMotionInsertPoints() {
  // The BBSetIns have converged, run last iteration and figure out insertion
  // point for each RC root.
  for (SILBasicBlock *BB : PO->getPostOrder()) {
    // Intersect in the successor BBSetIns.
    mergeBBDataFlowStates(BB);
    ReleaseBlockState *S = BlockStates[BB];

    // Compute insertion point generated by the edge value transition.
    // If there is a transition from 1 to 0, that means we have a partial
    // merge, which means the release can NOT be hoisted to the current block.
    // place it at the successors.
    for (unsigned i = 0; i < RCRootVault.size(); ++i) {  
      if (S->BBSetOut[i])
        continue;
      for (auto &Succ : BB->getSuccessors()) {
        BlockState *SBB = BlockStates[Succ];
        if (!SBB->BBSetIn[i])
          continue;
        InsertPoints[RCRootVault[i]].push_back(&*(*Succ).begin());
      }
    }

    // Is this block interesting ?
    if (MultiIteration && !InterestBlocks.count(BB))
      continue;

    // Compute insertion point generated by MayUse terminator inst.
    // If terminator instruction can block the RC root. We will have no
    // choice but to anchor the release instructions in the successor blocks.
    for (unsigned i = 0; i < RCRootVault.size(); ++i) {
      SILInstruction *Term = BB->getTerminator();
      if (!S->BBSetOut[i] || !mayBlockCodeMotion(Term, RCRootVault[i]))
        continue;
      for (auto &Succ : BB->getSuccessors()) {
        BlockState *SBB = BlockStates[Succ];
        if (!SBB->BBSetIn[i])
          continue;
        InsertPoints[RCRootVault[i]].push_back(&*(*Succ).begin());
      }
      S->BBSetOut.reset(i);
    }

    // Compute insertion point generated within the basic block. Process
    // instructions in post-order fashion.
    for (auto I = std::next(BB->rbegin()), E = BB->rend(); I != E; ++I) {
      for (unsigned i = 0; i < RCRootVault.size(); ++i) {
        if (!S->BBSetOut[i] || !mayBlockCodeMotion(&*I, RCRootVault[i]))
          continue;
        auto *InsertPt = &*std::next(SILBasicBlock::iterator(&*I));
        InsertPoints[RCRootVault[i]].push_back(InsertPt);
        S->BBSetOut.reset(i);
      }

      // If we are freezing this epilogue release. Simply continue.
      if (FreezeEpilogueReleases && ERM.isEpilogueRelease(&*I))
        continue;

      // This release generates.
      if (isReleaseInstruction(&*I)) {
        S->BBSetOut.set(RCRootIndex[getRCRoot(&*I)]);
      }
    }

    // Compute insertion point generated by SILArgument. SILArgument blocks if
    // it defines the released value.
    for (unsigned i = 0; i < RCRootVault.size(); ++i) {
      if (!S->BBSetOut[i]) 
        continue;
      SILArgument *A = dyn_cast<SILArgument>(RCRootVault[i]);
      if (!A || A->getParent() != BB)
        continue;
      InsertPoints[RCRootVault[i]].push_back(&*BB->begin());
      S->BBSetOut.reset(i);
    }
   
    // Lastly update the BBSetIn, only necessary when we are running a single
    // iteration dataflow.
    if (!MultiIteration) {
      S->updateBBSetIn(S->BBSetOut);
    }
  }
}

void GenericCloner::populateCloned() {
  SILFunction *Cloned = getCloned();

  // Create arguments for the entry block.
  SILBasicBlock *OrigEntryBB = &*Original.begin();
  SILBasicBlock *ClonedEntryBB = Cloned->createBasicBlock();
  getBuilder().setInsertionPoint(ClonedEntryBB);

  llvm::SmallVector<AllocStackInst *, 8> AllocStacks;
  AllocStackInst *ReturnValueAddr = nullptr;

  // Create the entry basic block with the function arguments.
  auto I = OrigEntryBB->args_begin(), E = OrigEntryBB->args_end();
  int ArgIdx = 0;
  while (I != E) {
    SILArgument *OrigArg = *I;
    RegularLocation Loc((Decl *)OrigArg->getDecl());
    AllocStackInst *ASI = nullptr;
    SILType mappedType = remapType(OrigArg->getType());
    if (ReInfo.isArgConverted(ArgIdx)) {
      // We need an alloc_stack as a replacement for the indirect parameter.
      assert(mappedType.isAddress());
      mappedType = mappedType.getObjectType();
      ASI = getBuilder().createAllocStack(Loc, mappedType);
      ValueMap[OrigArg] = ASI;
      AllocStacks.push_back(ASI);
      if (ReInfo.isResultIndex(ArgIdx)) {
        // This result is converted from indirect to direct. The return inst
        // needs to load the value from the alloc_stack. See below.
        assert(!ReturnValueAddr);
        ReturnValueAddr = ASI;
      } else {
        // Store the new direct parameter to the alloc_stack.
        auto *NewArg =
            ClonedEntryBB->createArgument(mappedType, OrigArg->getDecl());
        getBuilder().createStore(Loc, NewArg, ASI,
                                 StoreOwnershipQualifier::Unqualified);

        // Try to create a new debug_value from an existing debug_value_addr.
        for (Operand *ArgUse : OrigArg->getUses()) {
          if (auto *DVAI = dyn_cast<DebugValueAddrInst>(ArgUse->getUser())) {
            getBuilder().createDebugValue(DVAI->getLoc(), NewArg,
                                          DVAI->getVarInfo());
            break;
          }
        }
      }
    } else {
      auto *NewArg =
          ClonedEntryBB->createArgument(mappedType, OrigArg->getDecl());
      ValueMap[OrigArg] = NewArg;
    }
    ++I;
    ++ArgIdx;
  }

  BBMap.insert(std::make_pair(OrigEntryBB, ClonedEntryBB));
  // Recursively visit original BBs in depth-first preorder, starting with the
  // entry block, cloning all instructions other than terminators.
  visitSILBasicBlock(OrigEntryBB);

  // Now iterate over the BBs and fix up the terminators.
  for (auto BI = BBMap.begin(), BE = BBMap.end(); BI != BE; ++BI) {
    getBuilder().setInsertionPoint(BI->second);
    TermInst *OrigTermInst = BI->first->getTerminator();
    if (auto *RI = dyn_cast<ReturnInst>(OrigTermInst)) {
      SILValue ReturnValue;
      if (ReturnValueAddr) {
        // The result is converted from indirect to direct. We have to load the
        // returned value from the alloc_stack.
        ReturnValue =
            getBuilder().createLoad(ReturnValueAddr->getLoc(), ReturnValueAddr,
                                    LoadOwnershipQualifier::Unqualified);
      }
      for (AllocStackInst *ASI : reverse(AllocStacks)) {
        getBuilder().createDeallocStack(ASI->getLoc(), ASI);
      }
      if (ReturnValue) {
        getBuilder().createReturn(RI->getLoc(), ReturnValue);
        continue;
      }
    } else if (isa<ThrowInst>(OrigTermInst)) {
      for (AllocStackInst *ASI : reverse(AllocStacks)) {
        getBuilder().createDeallocStack(ASI->getLoc(), ASI);
      }
    }
    visit(BI->first->getTerminator());
  }
}