C++ ApplySite::getInstruction方法代码示例

/// Generate a new apply of a function_ref to replace an apply of a
/// witness_method when we've determined the actual function we'll end
/// up calling.
static ApplySite
devirtualizeWitnessMethod(ApplySite AI, SILFunction *F,
                          ProtocolConformanceRef C, OptRemark::Emitter *ORE) {
  // We know the witness thunk and the corresponding set of substitutions
  // required to invoke the protocol method at this point.
  auto &Module = AI.getModule();

  // Collect all the required substitutions.
  //
  // The complete set of substitutions may be different, e.g. because the found
  // witness thunk F may have been created by a specialization pass and have
  // additional generic parameters.
  auto SubMap = getWitnessMethodSubstitutions(Module, AI, F, C);

  // Figure out the exact bound type of the function to be called by
  // applying all substitutions.
  auto CalleeCanType = F->getLoweredFunctionType();
  auto SubstCalleeCanType = CalleeCanType->substGenericArgs(Module, SubMap);

  // Collect arguments from the apply instruction.
  auto Arguments = SmallVector<SILValue, 4>();

  // Iterate over the non self arguments and add them to the
  // new argument list, upcasting when required.
  SILBuilderWithScope B(AI.getInstruction());
  SILFunctionConventions substConv(SubstCalleeCanType, Module);
  unsigned substArgIdx = AI.getCalleeArgIndexOfFirstAppliedArg();
  for (auto arg : AI.getArguments()) {
    auto paramType = substConv.getSILArgumentType(substArgIdx++);
    if (arg->getType() != paramType)
      arg = castValueToABICompatibleType(&B, AI.getLoc(), arg,
                                         arg->getType(), paramType);
    Arguments.push_back(arg);
  }
  assert(substArgIdx == substConv.getNumSILArguments());

  // Replace old apply instruction by a new apply instruction that invokes
  // the witness thunk.
  SILBuilderWithScope Builder(AI.getInstruction());
  SILLocation Loc = AI.getLoc();
  FunctionRefInst *FRI = Builder.createFunctionRef(Loc, F);

  ApplySite SAI = replaceApplySite(Builder, Loc, AI, FRI, SubMap, Arguments,
                                   substConv);

  if (ORE)
    ORE->emit([&]() {
        using namespace OptRemark;
        return RemarkPassed("WitnessMethodDevirtualized", *AI.getInstruction())
               << "Devirtualized call to " << NV("Method", F);
      });
  NumWitnessDevirt++;
  return SAI;
}

/// Find the concrete type of the existential argument. Wrapper
/// for findInitExistential in Local.h/cpp. In future, this code
/// can move to Local.h/cpp.
static bool findConcreteType(ApplySite AI, int ArgIdx, CanType &ConcreteType) {
  bool isCopied = false;
  auto Arg = AI.getArgument(ArgIdx);

  /// Ignore any unconditional cast instructions. Is it Safe? Do we need to
  /// also add UnconditionalCheckedCastAddrInst? TODO.
  if (auto *Instance = dyn_cast<UnconditionalCheckedCastInst>(Arg)) {
    Arg = Instance->getOperand();
  }

  /// Return init_existential if the Arg is global_addr.
  if (auto *GAI = dyn_cast<GlobalAddrInst>(Arg)) {
    SILValue InitExistential =
        findInitExistentialFromGlobalAddrAndApply(GAI, AI, ArgIdx);
    /// If the Arg is already init_existential, return the concrete type.
    if (InitExistential &&
        findConcreteTypeFromInitExistential(InitExistential, ConcreteType)) {
      return true;
    }
  }

  /// Handle AllocStack instruction separately.
  if (auto *Instance = dyn_cast<AllocStackInst>(Arg)) {
    if (SILValue Src =
            getAddressOfStackInit(Instance, AI.getInstruction(), isCopied)) {
      Arg = Src;
    }
  }

  /// If the Arg is already init_existential after getAddressofStackInit
  /// call, return the concrete type.
  if (findConcreteTypeFromInitExistential(Arg, ConcreteType)) {
    return true;
  }

  /// Call findInitExistential and determine the init_existential.
  ArchetypeType *OpenedArchetype = nullptr;
  SILValue OpenedArchetypeDef;
  auto FAS = FullApplySite::isa(AI.getInstruction());
  if (!FAS)
    return false;
  SILInstruction *InitExistential =
      findInitExistential(FAS.getArgumentOperands()[ArgIdx], OpenedArchetype,
                          OpenedArchetypeDef, isCopied);
  if (!InitExistential) {
    LLVM_DEBUG(llvm::dbgs() << "ExistentialSpecializer Pass: Bail! Due to "
                               "findInitExistential\n";);

ApplySite SILPerformanceInliner::specializeGeneric(
    ApplySite Apply, llvm::SmallVectorImpl<ApplySite> &NewApplies) {
  assert(NewApplies.empty() && "Expected out parameter for new applies!");

  if (!Apply.hasSubstitutions())
    return ApplySite();

  auto *Callee = Apply.getCalleeFunction();

  if (!Callee || Callee->isExternalDeclaration())
    return ApplySite();

  auto Filter = [](SILInstruction *I) -> bool {
    return ApplySite::isa(I) != ApplySite();
  };

  CloneCollector Collector(Filter);

  SILFunction *SpecializedFunction;
  auto Specialized = trySpecializeApplyOfGeneric(Apply,
                                                 SpecializedFunction,
                                                 Collector);

  if (!Specialized)
    return ApplySite();

  // Track the new applies from the specialization.
  for (auto NewCallSite : Collector.getInstructionPairs())
    NewApplies.push_back(ApplySite(NewCallSite.first));

  auto FullApply = FullApplySite::isa(Apply.getInstruction());

  if (!FullApply) {
    assert(!FullApplySite::isa(Specialized.getInstruction()) &&
           "Unexpected full apply generated!");

    // Replace the old apply with the new and delete the old.
    replaceDeadApply(Apply, Specialized.getInstruction());

    return ApplySite(Specialized);
  }

  // Replace the old apply with the new and delete the old.
  replaceDeadApply(Apply, Specialized.getInstruction());

  return Specialized;
}

/// Generate a new apply of a function_ref to replace an apply of a
/// witness_method when we've determined the actual function we'll end
/// up calling.
static ApplySite devirtualizeWitnessMethod(ApplySite AI, SILFunction *F,
                                           ArrayRef<Substitution> Subs) {
  // We know the witness thunk and the corresponding set of substitutions
  // required to invoke the protocol method at this point.
  auto &Module = AI.getModule();

  // Collect all the required substitutions.
  //
  // The complete set of substitutions may be different, e.g. because the found
  // witness thunk F may have been created by a  specialization pass and have
  // additional generic parameters.
  SmallVector<Substitution, 16> NewSubstList(Subs.begin(), Subs.end());

  // Add the non-self-derived substitutions from the original application.
  ArrayRef<Substitution>  SubstList;
  SubstList = AI.getSubstitutionsWithoutSelfSubstitution();

  for (auto &origSub : SubstList)
    if (!origSub.getArchetype()->isSelfDerived())
      NewSubstList.push_back(origSub);

  // Figure out the exact bound type of the function to be called by
  // applying all substitutions.
  auto CalleeCanType = F->getLoweredFunctionType();
  auto SubstCalleeCanType = CalleeCanType->substGenericArgs(
    Module, Module.getSwiftModule(), NewSubstList);

  // Collect arguments from the apply instruction.
  auto Arguments = SmallVector<SILValue, 4>();

  auto ParamTypes = SubstCalleeCanType->getParameterSILTypes();

  // Iterate over the non self arguments and add them to the
  // new argument list, upcasting when required.
  SILBuilderWithScope B(AI.getInstruction());
  for (unsigned ArgN = 0, ArgE = AI.getNumArguments(); ArgN != ArgE; ++ArgN) {
    SILValue A = AI.getArgument(ArgN);
    auto ParamType = ParamTypes[ParamTypes.size() - AI.getNumArguments() + ArgN];
    if (A.getType() != ParamType)
      A = B.createUpcast(AI.getLoc(), A, ParamType);

    Arguments.push_back(A);
  }

  // Replace old apply instruction by a new apply instruction that invokes
  // the witness thunk.
  SILBuilderWithScope Builder(AI.getInstruction());
  SILLocation Loc = AI.getLoc();
  FunctionRefInst *FRI = Builder.createFunctionRef(Loc, F);

  auto SubstCalleeSILType = SILType::getPrimitiveObjectType(SubstCalleeCanType);
  auto ResultSILType = SubstCalleeCanType->getSILResult();
  ApplySite SAI;

  if (auto *A = dyn_cast<ApplyInst>(AI))
    SAI = Builder.createApply(Loc, FRI, SubstCalleeSILType,
                              ResultSILType, NewSubstList, Arguments,
                              A->isNonThrowing());
  if (auto *TAI = dyn_cast<TryApplyInst>(AI))
    SAI = Builder.createTryApply(Loc, FRI, SubstCalleeSILType,
                                 NewSubstList, Arguments,
                                 TAI->getNormalBB(), TAI->getErrorBB());
  if (auto *PAI = dyn_cast<PartialApplyInst>(AI))
    SAI = Builder.createPartialApply(Loc, FRI, SubstCalleeSILType,
                                     NewSubstList, Arguments, PAI->getType());

  NumWitnessDevirt++;
  return SAI;
}

bool GenericSpecializer::specializeAppliesInFunction(SILFunction &F) {
  bool Changed = false;
  llvm::SmallVector<SILInstruction *, 8> DeadApplies;

  for (auto &BB : F) {
    for (auto It = BB.begin(), End = BB.end(); It != End;) {
      auto &I = *It++;

      // Skip non-apply instructions, apply instructions with no
      // substitutions, apply instructions where we do not statically
      // know the called function, and apply instructions where we do
      // not have the body of the called function.

      ApplySite Apply = ApplySite::isa(&I);
      if (!Apply || !Apply.hasSubstitutions())
        continue;

      auto *Callee = Apply.getCalleeFunction();
      if (!Callee || !Callee->isDefinition())
        continue;

      // We have a call that can potentially be specialized, so
      // attempt to do so.

      // The specializer helper function currently expects a collector
      // argument, but we aren't going to make use of the results so
      // we'll have our filter always return false;
      auto Filter = [](SILInstruction *I) -> bool { return false; };
      CloneCollector Collector(Filter);

      SILFunction *SpecializedFunction;

      auto Specialized =
          trySpecializeApplyOfGeneric(Apply, SpecializedFunction, Collector);

      if (Specialized) {
        Changed = true;

        // If calling the specialization utility resulted in a new
        // function (as opposed to returning a previous
        // specialization), we need to notify the pass manager so that
        // the new function gets optimized.
        if (SpecializedFunction)
          notifyPassManagerOfFunction(SpecializedFunction);

        auto *AI = Apply.getInstruction();

        if (!isa<TryApplyInst>(AI))
          AI->replaceAllUsesWith(Specialized.getInstruction());

        DeadApplies.push_back(AI);
      }
    }
  }

  // Remove all the now-dead applies.
  while (!DeadApplies.empty()) {
    auto *AI = DeadApplies.pop_back_val();
    recursivelyDeleteTriviallyDeadInstructions(AI, true);
  }

  return Changed;
}

bool GenericSpecializer::specializeAppliesInFunction(SILFunction &F) {
  DeadInstructionSet DeadApplies;
  llvm::SmallSetVector<SILInstruction *, 8> Applies;

  bool Changed = false;
  for (auto &BB : F) {
    // Collect the applies for this block in reverse order so that we
    // can pop them off the end of our vector and process them in
    // forward order.
    for (auto It = BB.rbegin(), End = BB.rend(); It != End; ++It) {
      auto *I = &*It;

      // Skip non-apply instructions, apply instructions with no
      // substitutions, apply instructions where we do not statically
      // know the called function, and apply instructions where we do
      // not have the body of the called function.
      ApplySite Apply = ApplySite::isa(I);
      if (!Apply || !Apply.hasSubstitutions())
        continue;

      auto *Callee = Apply.getReferencedFunction();
      if (!Callee || !Callee->isDefinition())
        continue;

      Applies.insert(Apply.getInstruction());
    }

    // Attempt to specialize each apply we collected, deleting any
    // that we do specialize (along with other instructions we clone
    // in the process of doing so). We pop from the end of the list to
    // avoid tricky iterator invalidation issues.
    while (!Applies.empty()) {
      auto *I = Applies.pop_back_val();
      auto Apply = ApplySite::isa(I);
      assert(Apply && "Expected an apply!");
      SILFunction *Callee = Apply.getReferencedFunction();
      assert(Callee && "Expected to have a known callee");

      // We have a call that can potentially be specialized, so
      // attempt to do so.
      llvm::SmallVector<SILFunction *, 2> NewFunctions;
      trySpecializeApplyOfGeneric(Apply, DeadApplies, NewFunctions);

      // Remove all the now-dead applies. We must do this immediately
      // rather than defer it in order to avoid problems with cloning
      // dead instructions when doing recursive specialization.
      while (!DeadApplies.empty()) {
        auto *AI = DeadApplies.pop_back_val();

        // Remove any applies we are deleting so that we don't attempt
        // to specialize them.
        Applies.remove(AI);

        recursivelyDeleteTriviallyDeadInstructions(AI, true);
        Changed = true;
      }

      // If calling the specialization utility resulted in new functions
      // (as opposed to returning a previous specialization), we need to notify
      // the pass manager so that the new functions get optimized.
      for (SILFunction *NewF : reverse(NewFunctions)) {
        notifyPassManagerOfFunction(NewF, Callee);
      }
    }
  }

  return Changed;
}

/// Generate a new apply of a function_ref to replace an apply of a
/// witness_method when we've determined the actual function we'll end
/// up calling.
static ApplySite devirtualizeWitnessMethod(ApplySite AI, SILFunction *F,
                                           ArrayRef<Substitution> Subs) {
  // We know the witness thunk and the corresponding set of substitutions
  // required to invoke the protocol method at this point.
  auto &Module = AI.getModule();

  // Collect all the required substitutions.
  //
  // The complete set of substitutions may be different, e.g. because the found
  // witness thunk F may have been created by a specialization pass and have
  // additional generic parameters.
  SmallVector<Substitution, 16> NewSubstList(Subs.begin(), Subs.end());
  if (auto generics = AI.getOrigCalleeType()->getGenericSignature()) {
    ArrayRef<Substitution> origSubs = AI.getSubstitutions();
    for (auto genericParam : generics->getAllDependentTypes()) {
      auto origSub = origSubs.front();
      origSubs = origSubs.slice(1);

      // Ignore generic parameters derived from 'self', the generic
      // parameter at depth 0, index 0.
      auto type = genericParam->getCanonicalType();
      while (auto memberType = dyn_cast<DependentMemberType>(type)) {
        type = memberType.getBase();
      }
      auto paramType = cast<GenericTypeParamType>(type);
      if (paramType->getDepth() == 0) {
        // There shouldn't be any other parameters at this depth.
        assert(paramType->getIndex() == 0);
        continue;
      }

      // Okay, remember this substitution.
      NewSubstList.push_back(origSub);
    }

    assert(origSubs.empty() && "subs not parallel to dependent types");
  }

  // Figure out the exact bound type of the function to be called by
  // applying all substitutions.
  auto CalleeCanType = F->getLoweredFunctionType();
  auto SubstCalleeCanType = CalleeCanType->substGenericArgs(
    Module, Module.getSwiftModule(), NewSubstList);

  // Collect arguments from the apply instruction.
  auto Arguments = SmallVector<SILValue, 4>();

  // Iterate over the non self arguments and add them to the
  // new argument list, upcasting when required.
  SILBuilderWithScope B(AI.getInstruction());
  for (unsigned ArgN = 0, ArgE = AI.getNumArguments(); ArgN != ArgE; ++ArgN) {
    SILValue A = AI.getArgument(ArgN);
    auto ParamType = SubstCalleeCanType->getSILArgumentType(
      SubstCalleeCanType->getNumSILArguments() - AI.getNumArguments() + ArgN);
    if (A->getType() != ParamType)
      A = B.createUpcast(AI.getLoc(), A, ParamType);

    Arguments.push_back(A);
  }

  // Replace old apply instruction by a new apply instruction that invokes
  // the witness thunk.
  SILBuilderWithScope Builder(AI.getInstruction());
  SILLocation Loc = AI.getLoc();
  FunctionRefInst *FRI = Builder.createFunctionRef(Loc, F);

  auto SubstCalleeSILType = SILType::getPrimitiveObjectType(SubstCalleeCanType);
  auto ResultSILType = SubstCalleeCanType->getSILResult();
  ApplySite SAI;

  if (auto *A = dyn_cast<ApplyInst>(AI))
    SAI = Builder.createApply(Loc, FRI, SubstCalleeSILType,
                              ResultSILType, NewSubstList, Arguments,
                              A->isNonThrowing());
  if (auto *TAI = dyn_cast<TryApplyInst>(AI))
    SAI = Builder.createTryApply(Loc, FRI, SubstCalleeSILType,
                                 NewSubstList, Arguments,
                                 TAI->getNormalBB(), TAI->getErrorBB());
  if (auto *PAI = dyn_cast<PartialApplyInst>(AI))
    SAI = Builder.createPartialApply(Loc, FRI, SubstCalleeSILType,
                                     NewSubstList, Arguments, PAI->getType());

  NumWitnessDevirt++;
  return SAI;
}

/// \brief Devirtualize an apply of a class method.
///
/// \p AI is the apply to devirtualize.
/// \p ClassOrMetatype is a class value or metatype value that is the
///    self argument of the apply we will devirtualize.
/// return the result value of the new ApplyInst if created one or null.
FullApplySite swift::devirtualizeClassMethod(FullApplySite AI,
                                             SILValue ClassOrMetatype,
                                             OptRemark::Emitter *ORE) {
  LLVM_DEBUG(llvm::dbgs() << "    Trying to devirtualize : "
                          << *AI.getInstruction());

  SILModule &Mod = AI.getModule();
  auto *MI = cast<MethodInst>(AI.getCallee());
  auto ClassOrMetatypeType = ClassOrMetatype->getType();
  auto *F = getTargetClassMethod(Mod, ClassOrMetatypeType, MI);

  CanSILFunctionType GenCalleeType = F->getLoweredFunctionType();

  SubstitutionMap Subs =
    getSubstitutionsForCallee(Mod, GenCalleeType,
                              ClassOrMetatypeType.getASTType(),
                              AI);
  CanSILFunctionType SubstCalleeType = GenCalleeType;
  if (GenCalleeType->isPolymorphic())
    SubstCalleeType = GenCalleeType->substGenericArgs(Mod, Subs);
  SILFunctionConventions substConv(SubstCalleeType, Mod);

  SILBuilderWithScope B(AI.getInstruction());
  SILLocation Loc = AI.getLoc();
  FunctionRefInst *FRI = B.createFunctionRef(Loc, F);

  // Create the argument list for the new apply, casting when needed
  // in order to handle covariant indirect return types and
  // contravariant argument types.
  llvm::SmallVector<SILValue, 8> NewArgs;

  auto IndirectResultArgIter = AI.getIndirectSILResults().begin();
  for (auto ResultTy : substConv.getIndirectSILResultTypes()) {
    NewArgs.push_back(
        castValueToABICompatibleType(&B, Loc, *IndirectResultArgIter,
                                     IndirectResultArgIter->getType(), ResultTy));
    ++IndirectResultArgIter;
  }

  auto ParamArgIter = AI.getArgumentsWithoutIndirectResults().begin();
  // Skip the last parameter, which is `self`. Add it below.
  for (auto param : substConv.getParameters().drop_back()) {
    auto paramType = substConv.getSILType(param);
    NewArgs.push_back(
        castValueToABICompatibleType(&B, Loc, *ParamArgIter,
                                     ParamArgIter->getType(), paramType));
    ++ParamArgIter;
  }

  // Add the self argument, upcasting if required because we're
  // calling a base class's method.
  auto SelfParamTy = substConv.getSILType(SubstCalleeType->getSelfParameter());
  NewArgs.push_back(castValueToABICompatibleType(&B, Loc,
                                                 ClassOrMetatype,
                                                 ClassOrMetatypeType,
                                                 SelfParamTy));

  ApplySite NewAS = replaceApplySite(B, Loc, AI, FRI, Subs, NewArgs, substConv);
  FullApplySite NewAI = FullApplySite::isa(NewAS.getInstruction());
  assert(NewAI);

  LLVM_DEBUG(llvm::dbgs() << "        SUCCESS: " << F->getName() << "\n");
  if (ORE)
    ORE->emit([&]() {
        using namespace OptRemark;
        return RemarkPassed("ClassMethodDevirtualized", *AI.getInstruction())
               << "Devirtualized call to class method " << NV("Method", F);
      });
  NumClassDevirt++;

  return NewAI;
}

/// Delete an apply site that's been successfully devirtualized.
void swift::deleteDevirtualizedApply(ApplySite Old) {
  auto *OldApply = Old.getInstruction();
  recursivelyDeleteTriviallyDeadInstructions(OldApply, true);
}

/// Attempt to devirtualize the given apply if possible, and return a
/// new instruction in that case, or nullptr otherwise.
ApplySite swift::tryDevirtualizeApply(ApplySite AI,
                                      ClassHierarchyAnalysis *CHA,
                                      OptRemark::Emitter *ORE) {
  LLVM_DEBUG(llvm::dbgs() << "    Trying to devirtualize: "
                          << *AI.getInstruction());

  // Devirtualize apply instructions that call witness_method instructions:
  //
  //   %8 = witness_method $Optional<UInt16>, #LogicValue.boolValue!getter.1
  //   %9 = apply %8<Self = CodeUnit?>(%6#1) : ...
  //
  if (isa<WitnessMethodInst>(AI.getCallee()))
    return tryDevirtualizeWitnessMethod(AI, ORE);

  // TODO: check if we can also de-virtualize partial applies of class methods.
  FullApplySite FAS = FullApplySite::isa(AI.getInstruction());
  if (!FAS)
    return ApplySite();

  /// Optimize a class_method and alloc_ref pair into a direct function
  /// reference:
  ///
  /// \code
  /// %XX = alloc_ref $Foo
  /// %YY = class_method %XX : $Foo, #Foo.get!1 : [email protected](method)...
  /// \endcode
  ///
  ///  or
  ///
  /// %XX = metatype $...
  /// %YY = class_method %XX : ...
  ///
  ///  into
  ///
  /// %YY = function_ref @...
  if (auto *CMI = dyn_cast<ClassMethodInst>(FAS.getCallee())) {
    auto &M = FAS.getModule();
    auto Instance = stripUpCasts(CMI->getOperand());
    auto ClassType = Instance->getType();
    if (ClassType.is<MetatypeType>())
      ClassType = ClassType.getMetatypeInstanceType(M);

    auto *CD = ClassType.getClassOrBoundGenericClass();

    if (isEffectivelyFinalMethod(FAS, ClassType, CD, CHA))
      return tryDevirtualizeClassMethod(FAS, Instance, ORE,
                                        true /*isEffectivelyFinalMethod*/);

    // Try to check if the exact dynamic type of the instance is statically
    // known.
    if (auto Instance = getInstanceWithExactDynamicType(CMI->getOperand(),
                                                        CMI->getModule(),
                                                        CHA))
      return tryDevirtualizeClassMethod(FAS, Instance, ORE);

    if (auto ExactTy = getExactDynamicType(CMI->getOperand(), CMI->getModule(),
                                           CHA)) {
      if (ExactTy == CMI->getOperand()->getType())
        return tryDevirtualizeClassMethod(FAS, CMI->getOperand(), ORE);
    }
  }

  if (isa<SuperMethodInst>(FAS.getCallee())) {
    if (FAS.hasSelfArgument()) {
      return tryDevirtualizeClassMethod(FAS, FAS.getSelfArgument(), ORE);
    }

    // It is an invocation of a class method.
    // Last operand is the metatype that should be used for dispatching.
    return tryDevirtualizeClassMethod(FAS, FAS.getArguments().back(), ORE);
  }

  return ApplySite();
}

/// Generate a new apply of a function_ref to replace an apply of a
/// witness_method when we've determined the actual function we'll end
/// up calling.
static ApplySite devirtualizeWitnessMethod(ApplySite AI, SILFunction *F,
                                           ProtocolConformanceRef C) {
  // We know the witness thunk and the corresponding set of substitutions
  // required to invoke the protocol method at this point.
  auto &Module = AI.getModule();

  // Collect all the required substitutions.
  //
  // The complete set of substitutions may be different, e.g. because the found
  // witness thunk F may have been created by a specialization pass and have
  // additional generic parameters.
  SmallVector<Substitution, 4> NewSubs;

  getWitnessMethodSubstitutions(AI, F, C, NewSubs);

  // Figure out the exact bound type of the function to be called by
  // applying all substitutions.
  auto CalleeCanType = F->getLoweredFunctionType();
  auto SubstCalleeCanType = CalleeCanType->substGenericArgs(Module, NewSubs);

  // Collect arguments from the apply instruction.
  auto Arguments = SmallVector<SILValue, 4>();

  // Iterate over the non self arguments and add them to the
  // new argument list, upcasting when required.
  SILBuilderWithScope B(AI.getInstruction());
  SILFunctionConventions substConv(SubstCalleeCanType, Module);
  unsigned substArgIdx = AI.getCalleeArgIndexOfFirstAppliedArg();
  for (auto arg : AI.getArguments()) {
    auto paramType = substConv.getSILArgumentType(substArgIdx++);
    if (arg->getType() != paramType)
      arg = castValueToABICompatibleType(&B, AI.getLoc(), arg,
                                         arg->getType(), paramType);
    Arguments.push_back(arg);
  }
  assert(substArgIdx == substConv.getNumSILArguments());

  // Replace old apply instruction by a new apply instruction that invokes
  // the witness thunk.
  SILBuilderWithScope Builder(AI.getInstruction());
  SILLocation Loc = AI.getLoc();
  FunctionRefInst *FRI = Builder.createFunctionRef(Loc, F);

  auto SubstCalleeSILType = SILType::getPrimitiveObjectType(SubstCalleeCanType);
  auto ResultSILType = substConv.getSILResultType();
  ApplySite SAI;

  if (auto *A = dyn_cast<ApplyInst>(AI))
    SAI = Builder.createApply(Loc, FRI, SubstCalleeSILType,
                              ResultSILType, NewSubs, Arguments,
                              A->isNonThrowing());
  if (auto *TAI = dyn_cast<TryApplyInst>(AI))
    SAI = Builder.createTryApply(Loc, FRI, SubstCalleeSILType,
                                 NewSubs, Arguments,
                                 TAI->getNormalBB(), TAI->getErrorBB());
  if (auto *PAI = dyn_cast<PartialApplyInst>(AI))
    SAI = Builder.createPartialApply(Loc, FRI, SubstCalleeSILType,
                                     NewSubs, Arguments, PAI->getType());

  NumWitnessDevirt++;
  return SAI;
}

/// Generate a new apply of a function_ref to replace an apply of a
/// witness_method when we've determined the actual function we'll end
/// up calling.
static ApplySite devirtualizeWitnessMethod(ApplySite AI, SILFunction *F,
                                           ProtocolConformanceRef C) {
  // We know the witness thunk and the corresponding set of substitutions
  // required to invoke the protocol method at this point.
  auto &Module = AI.getModule();

  // Collect all the required substitutions.
  //
  // The complete set of substitutions may be different, e.g. because the found
  // witness thunk F may have been created by a specialization pass and have
  // additional generic parameters.
  SmallVector<Substitution, 4> NewSubs;

  getWitnessMethodSubstitutions(AI, F, C, NewSubs);

  // Figure out the exact bound type of the function to be called by
  // applying all substitutions.
  auto CalleeCanType = F->getLoweredFunctionType();
  auto SubstCalleeCanType = CalleeCanType->substGenericArgs(Module, NewSubs);

  // Bail if some of the arguments cannot be converted into
  // types required by the found devirtualized method.
  if (!canPassOrConvertAllArguments(AI, SubstCalleeCanType))
    return ApplySite();

  // Collect arguments from the apply instruction.
  auto Arguments = SmallVector<SILValue, 4>();

  // Iterate over the non self arguments and add them to the
  // new argument list, upcasting when required.
  SILBuilderWithScope B(AI.getInstruction());
  for (unsigned ArgN = 0, ArgE = AI.getNumArguments(); ArgN != ArgE; ++ArgN) {
    SILValue A = AI.getArgument(ArgN);
    auto ParamType = SubstCalleeCanType->getSILArgumentType(
      SubstCalleeCanType->getNumSILArguments() - AI.getNumArguments() + ArgN);
    if (A->getType() != ParamType)
      A = B.createUpcast(AI.getLoc(), A, ParamType);

    Arguments.push_back(A);
  }

  // Replace old apply instruction by a new apply instruction that invokes
  // the witness thunk.
  SILBuilderWithScope Builder(AI.getInstruction());
  SILLocation Loc = AI.getLoc();
  FunctionRefInst *FRI = Builder.createFunctionRef(Loc, F);

  auto SubstCalleeSILType = SILType::getPrimitiveObjectType(SubstCalleeCanType);
  auto ResultSILType = SubstCalleeCanType->getSILResult();
  ApplySite SAI;

  if (auto *A = dyn_cast<ApplyInst>(AI))
    SAI = Builder.createApply(Loc, FRI, SubstCalleeSILType,
                              ResultSILType, NewSubs, Arguments,
                              A->isNonThrowing());
  if (auto *TAI = dyn_cast<TryApplyInst>(AI))
    SAI = Builder.createTryApply(Loc, FRI, SubstCalleeSILType,
                                 NewSubs, Arguments,
                                 TAI->getNormalBB(), TAI->getErrorBB());
  if (auto *PAI = dyn_cast<PartialApplyInst>(AI))
    SAI = Builder.createPartialApply(Loc, FRI, SubstCalleeSILType,
                                     NewSubs, Arguments, PAI->getType());

  NumWitnessDevirt++;
  return SAI;
}