swift-mirror/lib/SILPasses/Devirtualizer.cpp

//===-- Devirtualizer.cpp ------ Devirtualize virtual calls ---------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// Devirtualizes virtual function calls into direct function calls.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "sil-devirtualizer"
#include "swift/Basic/DemangleWrappers.h"
#include "swift/Basic/Fallthrough.h"
#include "swift/SIL/SILArgument.h"
#include "swift/SIL/SILBuilder.h"
#include "swift/SIL/SILFunction.h"
#include "swift/SIL/SILInstruction.h"
#include "swift/SIL/SILModule.h"
#include "swift/SILAnalysis/ClassHierarchyAnalysis.h"
#include "swift/SILPasses/Passes.h"
#include "swift/SILPasses/Utils/Local.h"
#include "swift/SILPasses/PassManager.h"
#include "swift/SILPasses/Transforms.h"
#include "swift/SILPasses/Utils/SILInliner.h"
#include "swift/AST/ASTContext.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/CommandLine.h"
using namespace swift;

STATISTIC(NumInlineCaches, "Number of monomorphic inline caches inserted");
STATISTIC(NumDevirtualized, "Number of calls devirtualzied");
STATISTIC(NumDynApply, "Number of dynamic apply devirtualzied");
STATISTIC(NumAMI, "Number of witness_method devirtualzied");

// The number of subclasses to allow when placing polymorphic inline caches.
static const int MaxNumPolymorphicInlineCaches = 6;

//===----------------------------------------------------------------------===//
//                         Class Method Optimization
//===----------------------------------------------------------------------===//

/// Is this an instruction kind which allows us to conclude definitively what
/// the class decls of its results are.
///
/// FIXME: We can expand this to use typed GEPs.
static bool isClassDeclOracle(ValueKind Kind) {
  switch (Kind) {
  case ValueKind::AllocRefInst:
  case ValueKind::AllocRefDynamicInst:
  case ValueKind::MetatypeInst:
    return true;
  default:
    return false;
  }
}

/// \brief Recursively searches the ClassDecl for a class_method operand.
/// Return the ClassDecl from the point of construction of \p S or null.
static ClassDecl *getClassFromConstructor(SILValue S) {
  // First strip off casts.
  S = S.stripCasts();

  // Then if S is not a class decl oracle, we can not ascertain what its results
  // "true" type is.
  if (!isClassDeclOracle(S->getKind()))
    return nullptr;

  // Look for a a static ClassTypes in AllocRefInst or MetatypeInst.
  if (AllocRefInst *ARI = dyn_cast<AllocRefInst>(S))
    return ARI->getType().getClassOrBoundGenericClass();

  auto *MTI = dyn_cast<MetatypeInst>(S);
  if (!MTI)
    return nullptr;

  CanType instTy = MTI->getType().castTo<MetatypeType>().getInstanceType();
  return instTy.getClassOrBoundGenericClass();
}

/// \brief Devirtualize an Apply instruction and a class member obtained
/// using the class_method instruction into a direct call to a specific
/// member of a specific class.
///
/// \p AI is the apply to devirtualize.
/// \p Member is the class member to devirtualize.
/// \p ClassInstance is the operand for the ClassMethodInst or an alternative
///    reference (duch as downcasted class reference).
/// \p KnownClass (can be null) is a specific class type to devirtualize to.
static bool devirtMethod(ApplyInst *AI, SILDeclRef Member,
                         SILValue ClassInstance, ClassDecl *Class) {
  DEBUG(llvm::dbgs() << "    Trying to devirtualize : " << *AI);

  // First attempt to lookup the origin for our class method. The origin should
  // either be a metatype or an alloc_ref.
  DEBUG(llvm::dbgs() << "        Origin: " << ClassInstance);

  assert(Class && "Invalid class type");

  // Otherwise lookup from the module the least derived implementing method from
  // the module vtables.
  SILModule &Mod = AI->getModule();
  SILFunction *F = Mod.lookUpSILFunctionFromVTable(Class, Member);

  // If we do not find any such function, we have no function to devirtualize
  // to... so bail.
  if (!F) {
    DEBUG(llvm::dbgs() << "        FAIL: Could not find matching VTable or "
                          "vtable method for this class.\n");
    return false;
  }

  // Ok, we found a function F that we can devirtualization our class method
  // to. We want to do everything on the substituted type in the case of
  // generics. Thus construct our subst callee type for F.
  SILModule &M = F->getModule();
  CanSILFunctionType GenCalleeType = F->getLoweredFunctionType();
  CanSILFunctionType SubstCalleeType =
    GenCalleeType->substGenericArgs(M, M.getSwiftModule(),
                                             AI->getSubstitutions());


  // If F's this pointer has a different type from CMI's operand and the
  // "this" pointer type is a super class of the CMI's operand, insert an
  // upcast.
  auto paramTypes =
    SubstCalleeType->getParameterSILTypesWithoutIndirectResult();

  // We should always have a this pointer. Assert on debug builds, return
  // nullptr on release builds.
  assert(!paramTypes.empty() &&
         "Must have a this pointer when calling a class method inst.");
  if (paramTypes.empty())
    return false;

  // Grab the self type from the function ref and the self type from the class
  // method inst.
  SILType FuncSelfTy = paramTypes[paramTypes.size() - 1];
  SILType OriginTy = ClassInstance.getType();
  SILBuilder B(AI);

  // Then compare the two types and if they are unequal...
  if (FuncSelfTy != OriginTy) {
    assert(FuncSelfTy.isSuperclassOf(OriginTy) && "Can not call a class method"
           " on a non-subclass of the class_methods class.");

    // Otherwise, upcast origin to the appropriate type.
    ClassInstance = B.createUpcast(AI->getLoc(), ClassInstance, FuncSelfTy);
  }

  // Success! Perform the devirtualization.
  FunctionRefInst *FRI = B.createFunctionRef(AI->getLoc(), F);

  // Construct a new arg list. First process all non-self operands, ref, addr
  // casting them to the appropriate types for F so that we allow for covariant
  // indirect return types and contravariant arguments.
  llvm::SmallVector<SILValue, 8> NewArgs;
  auto Args = AI->getArguments();
  auto allParamTypes = SubstCalleeType->getParameterSILTypes();

  // For each old argument Op...
  for (unsigned i = 0, e = Args.size() - 1; i != e; ++i) {
    SILValue Op = Args[i];
    SILType OpTy = Op.getType();
    SILType FOpTy = allParamTypes[i];

    // If the type matches the type for the given parameter in F, just add it to
    // our arg list and continue.
    if (OpTy == FOpTy) {
      NewArgs.push_back(Op);
      continue;
    }

    // Otherwise we have either a covariant return type or a contravariant
    // argument type. Cast it appropriately.
    assert((OpTy.isAddress() || OpTy.isHeapObjectReferenceType()) &&
           "Only addresses and refs can have their types changed due to "
           "covariant return types or contravariant argument types.");

    // If OpTy is an address, perform an unchecked_addr_cast.
    if (OpTy.isAddress()) {
      NewArgs.push_back(B.createUncheckedAddrCast(AI->getLoc(), Op, FOpTy));
    } else {
      // Otherwise perform a ref cast.
      NewArgs.push_back(B.createUncheckedRefCast(AI->getLoc(), Op, FOpTy));
    }
  }

  // Add in self to the end.
  NewArgs.push_back(ClassInstance);

  // If we have a direct return type, make sure we use the subst callee return
  // type. If we have an indirect return type, AI's return type of the empty
  // tuple should be ok.
  SILType ReturnType = AI->getType();
  if (!SubstCalleeType->hasIndirectResult()) {
    ReturnType = SubstCalleeType->getSILResult();
  }

  SILType SubstCalleeSILType = SILType::getPrimitiveObjectType(SubstCalleeType);
  ApplyInst *NewAI =
      B.createApply(AI->getLoc(), FRI, SubstCalleeSILType, ReturnType,
                    AI->getSubstitutions(), NewArgs);

  // If our return type differs from AI's return type, then we know that we have
  // a covariant return type. Cast it before we RAUW. This can not happen 
  if (ReturnType != AI->getType()) {
    assert((ReturnType.isAddress() || ReturnType.isHeapObjectReferenceType()) &&
           "Only addresses and refs can have their types changed due to "
           "covariant return types or contravariant argument types.");

    SILValue CastedAI = NewAI;
    if (ReturnType.isAddress()) {
      CastedAI = B.createUncheckedAddrCast(AI->getLoc(), NewAI, AI->getType());
    } else {
      CastedAI = B.createUncheckedRefCast(AI->getLoc(), NewAI, AI->getType());
    }
    SILValue(AI).replaceAllUsesWith(CastedAI);
  } else {
    AI->replaceAllUsesWith(NewAI);
  }

  AI->eraseFromParent();

  DEBUG(llvm::dbgs() << "        SUCCESS: " << F->getName() << "\n");
  NumDevirtualized++;
  return true;
}

//===----------------------------------------------------------------------===//
//                        Witness Method Optimization
//===----------------------------------------------------------------------===//

namespace {

class WitnessMethodDevirtualizer {

  //==-----------
  // Input fields

  /// The apply that we are attempting to optimize.
  ApplyInst *AI;

  /// The witness method that is the callee of the apply.
  WitnessMethodInst *WMI;

  /// The conformance that the witness method is using.
  ProtocolConformance *C;

  /// The SILFunction devirtualization target.
  SILFunction *F;

  /// If we have a specialized protocol conformance, the substitutions for the
  /// conformance.
  ArrayRef<Substitution> Subs;

  /// The witness table which we got F, Subs from.
  SILWitnessTable *WT;


  //==---------------
  // Workspace fields

  /// If we needed to change Self, this field contains the modified self.
  Optional<SILValue> Self;

  /// If we had other substitutions that
  SmallVector<Substitution, 16> SubstList;

  /// Field which distinguishes the SubstList being empty from it not having a
  /// value. This could be as apart of an optional but I don't think that
  bool HasSubstList;

  /// If we needed to modify the subst callee type of the function, this is the
  /// new subst callee type.
  Optional<SILType> SubstCalleeSILType;

  /// If we needed to modify the result type of the function, this is the new
  /// result type.
  Optional<SILType> ResultSILType;

public:
  WitnessMethodDevirtualizer(ApplyInst *AI, WitnessMethodInst *WMI,
                             ProtocolConformance *C, SILFunction *F,
                             ArrayRef<Substitution> Subs, SILWitnessTable *WT)
      : AI(AI), WMI(WMI), C(C), F(F), Subs(Subs), WT(WT), Self(), SubstList(),
        HasSubstList(false), SubstCalleeSILType(), ResultSILType() {}

  /// Main entry point.
  bool devirtualize();
private:

  bool processNormalProtocolConformance();
  bool processInheritedProtocolConformance();
  bool
  processSpecializedProtocolConformance(SpecializedProtocolConformance *SPC,
                                        ProtocolConformance *GenericConf);
};

} // end anonymous namespace

bool WitnessMethodDevirtualizer::devirtualize() {
  /// Use to quite the unused-private-field warning.
  (void)WMI;

  /// First check if we have a simple normal protocol conformance.
  if (isa<NormalProtocolConformance>(C))
    return processNormalProtocolConformance();

  /// If we dont and do not have any substitutions, we must then have a pure
  /// inherited protocol conformance.
  if (Subs.empty()) {
#if 1
    // Disable inherited protocol conformance for seed 5.
    return false;
#else
    assert(isa<InheritedProtocolConformance>(C) &&
           "At this point C must be an inherited protocol conformance.");
    return processInheritedProtocolConformance();
#endif
  }

  /// If we have substitutions, we must have some sort of specialized protocol
  /// conformance. If it is just a simple specialized + normal protocol
  /// conformance, handle it early.
  if (auto *SPC = dyn_cast<SpecializedProtocolConformance>(C)) {
    if (auto *GNC =
          dyn_cast<NormalProtocolConformance>(SPC->getGenericConformance())) {
      return processSpecializedProtocolConformance(SPC, GNC);
    }
  }

  // Otherwise, we have a complicated specialized, inherited protocol
  // conformance that we need to devirtualize.
  return false;
}

bool WitnessMethodDevirtualizer::processNormalProtocolConformance() {
  // Ok, we found the member we are looking for. Devirtualize away!
  SILBuilder Builder(AI);
  SILLocation Loc = AI->getLoc();
  FunctionRefInst *FRI = Builder.createFunctionRef(Loc, F);

  // Collect args from the apply inst.
  SmallVector<SILValue, 4> Args;

  // First add the non self arguments to the new argument list.
  for (SILValue A : AI->getArgumentsWithoutSelf())
    Args.push_back(A);

  // Then add the self argument since the self argument is always last.
  if (!Self)
    Self = AI->getSelfArgument();
  Args.push_back(*Self);

  SmallVector<Substitution, 16> NewSubstList(Subs.begin(),
                                             Subs.end());

  // Add the non-self-derived substitutions from the original application.
  for (auto &origSub : AI->getSubstitutionsWithoutSelfSubstitution()) {
    if (!origSub.getArchetype()->isSelfDerived())
      NewSubstList.push_back(origSub);
  }

  if (!SubstCalleeSILType)
    SubstCalleeSILType = AI->getSubstCalleeSILType();
  if (!ResultSILType)
    ResultSILType = AI->getType();

  ApplyInst *SAI = Builder.createApply(Loc, FRI, *SubstCalleeSILType,
                                       *ResultSILType, NewSubstList, Args);
  AI->replaceAllUsesWith(SAI);
  AI->eraseFromParent();
  NumAMI++;
  return true;
}

bool WitnessMethodDevirtualizer::processInheritedProtocolConformance() {
  // Since we do not need to worry about substitutions, we can just insert an
  // upcast of self to the appropriate type.
  Self = AI->getSelfArgument();
  CanType Ty = WT->getConformance()->getType()->getCanonicalType();
  SILType SILTy = SILType::getPrimitiveType(Ty, Self->getType().getCategory());
  SILType SelfTy = Self->getType();
  (void)SelfTy;

  assert(SILTy.isSuperclassOf(SelfTy) &&
         "Should only create upcasts for sub class devirtualization.");
  Self = SILBuilder(AI).createUpcast(AI->getLoc(), *Self, SILTy);

  SmallVector<Substitution, 16> SelfDerivedSubstitutions;
  for (auto &origSub : AI->getSubstitutions())
    if (origSub.getArchetype()->isSelfDerived())
      SelfDerivedSubstitutions.push_back(origSub);

  // If we have more than 1 substitution on AI that is self derived, that means
  // we either have a property or a typealias. We currently do not specialize
  // those correctly implying that we will have an archetype instead of a
  // concrete type here that we can not work with. Thus bail and don't do
  // anything.
  if (SelfDerivedSubstitutions.size() > 1)
    return false;

  // Grab self and substitute into the old generic callee type to get the new
  // non-generic callee type.
  assert(SelfDerivedSubstitutions.size() == 1 &&
         "Must have a substitution for self.");
  Substitution NewSelfSub{
    AI->getSelfSubstitution().getArchetype(),
    Ty,
    AI->getSelfSubstitution().getConformances(),
  };

  CanSILFunctionType OrigType = AI->getOrigCalleeType();
  CanSILFunctionType SubstCalleeType = OrigType->substGenericArgs(
      AI->getModule(), AI->getModule().getSwiftModule(),
      ArrayRef<Substitution>(NewSelfSub));

  SubstCalleeSILType = SILType::getPrimitiveObjectType(SubstCalleeType);

  // Then pass of our new self to the normal protocol conformance witness method
  // handling code.
  return processNormalProtocolConformance();
}

/// The substitution is going to fail if there are more dependent types than
/// substitutions.
static bool isSubstitutionGoingToFailHack(ArrayRef<Substitution> Subs,
                                          CanSILFunctionType GenCalleeType) {
  auto *GenSig = GenCalleeType->getGenericSignature();
  unsigned NumSubsNeccessary = 0;
  for (auto depTy : GenSig->getAllDependentTypes()) {
    if (depTy->getAs<SubstitutableType>() ||
        depTy->getAs<DependentMemberType>()) {
      ++NumSubsNeccessary;
    }
  }
  if (NumSubsNeccessary > Subs.size())
    return true;
  return false;
}

bool
WitnessMethodDevirtualizer::
processSpecializedProtocolConformance(SpecializedProtocolConformance *SPC,
                                      ProtocolConformance *GenericConf) {
  // We do not need to worry about covariant/contravariant return types here
  // since we don't support that for 1.0. But when we do this needs to be
  // updated.
  SILModule &M = F->getModule();
  CanSILFunctionType GenCalleeType = F->getLoweredFunctionType();

  // HACK: work around the fact that the substitution below might fail (there
  // are more dependent types than substitutions).
  //
  // Note: This is probably problem in the AST generics code. It is not an issue
  // of the devirtualizer.
  if (isSubstitutionGoingToFailHack(Subs, GenCalleeType))
    return false;

  CanSILFunctionType SubstCalleeType =
    GenCalleeType->substGenericArgs(M, M.getSwiftModule(),
                                             Subs);

  std::copy(Subs.begin(), Subs.end(), SubstList.begin());
  HasSubstList = true;
  SubstCalleeSILType = SILType::getPrimitiveObjectType(SubstCalleeType);
  ResultSILType = SubstCalleeType->getSILResult();

  return processNormalProtocolConformance();
}

/// Devirtualize apply instructions that call witness_method instructions:
///
///   %8 = witness_method $Optional<UInt16>, #LogicValue.boolValue!getter.1
///   %9 = apply %8<Self = CodeUnit?>(%6#1) : ...
///
static bool optimizeWitnessMethod(ApplyInst *AI, WitnessMethodInst *WMI) {
  ProtocolConformance *C = WMI->getConformance();
  if (!C) {
    DEBUG(llvm::dbgs() << "        FAIL: Null conformance.\n");
    return false;
  }

  // Lookup the function reference in the witness tables.
  SILFunction *F;
  ArrayRef<Substitution> Subs;
  SILWitnessTable *WT;
  std::tie(F, WT, Subs) =
      AI->getModule().findFuncInWitnessTable(C, WMI->getMember());

  if (!F) {
    assert(!WT && "WitnessTable should always be null if F is.");
    DEBUG(llvm::dbgs() << "        FAIL: Did not find a matching witness "
                          "table or witness method.\n");
    return false;
  }
  assert(WT && "WitnessTable should never be null if F is not.");

  WitnessMethodDevirtualizer WMD{AI, WMI, C, F, Subs, WT};

  return WMD.devirtualize();
}

//===----------------------------------------------------------------------===//
//                        Protocol Method Optimization
//===----------------------------------------------------------------------===//


/// \brief Scan the uses of the protocol object and return the initialization
/// instruction, which can be copy_addr or init_existential.
/// There needs to be only one initialization instruction and the
/// object must not be captured by any instruction that may re-initialize it.
static SILInstruction *
findSingleInitNoCaptureProtocol(SILValue ProtocolObject) {
  DEBUG(llvm::dbgs() << "        Checking if protocol object is captured: "
        << ProtocolObject);
  SILInstruction *Init = 0;
  for (auto UI = ProtocolObject->use_begin(), E = ProtocolObject->use_end();
       UI != E; UI++) {
    switch (UI.getUser()->getKind()) {
    case ValueKind::CopyAddrInst: {
      // If we are reading the content of the protocol (to initialize
      // something else) then its okay.
      if (cast<CopyAddrInst>(UI.getUser())->getSrc() == ProtocolObject)
        continue;

      // Fall through.
      SWIFT_FALLTHROUGH;
    }

    case ValueKind::InitExistentialInst: {
      // Make sure there is a single initialization:
      if (Init) {
        DEBUG(llvm::dbgs() << "            FAIL: Multiple Protocol "
              "initializers: " << *UI.getUser() << " and " << *Init);
        return nullptr;
      }
      // This is the first initialization.
      Init = UI.getUser();
      continue;
    }
    case ValueKind::OpenExistentialInst:
    case ValueKind::ProjectExistentialInst:
    case ValueKind::ProtocolMethodInst:
    case ValueKind::DeallocBoxInst:
    case ValueKind::DeallocRefInst:
    case ValueKind::DeallocStackInst:
    case ValueKind::StrongReleaseInst:
    case ValueKind::DestroyAddrInst:
    case ValueKind::ReleaseValueInst:
      continue;

    // A thin apply inst that uses this object as a callee does not capture it.
    case ValueKind::ApplyInst: {
      auto *AI = cast<ApplyInst>(UI.getUser());
      if (AI->isCalleeThin() && AI->getCallee() == ProtocolObject)
        continue;

      // Fallthrough
      SWIFT_FALLTHROUGH;
    }

    default: {
      DEBUG(llvm::dbgs() << "            FAIL: Protocol captured by: "
                         << *UI.getUser());
      return nullptr;
    }
    }
  }
  DEBUG(llvm::dbgs() << "            Protocol not captured.\n");
  return Init;
}

/// \brief Replaces a virtual ApplyInst instruction with a new ApplyInst
/// instruction that does not use a project_existential \p PEI and calls \p F
/// directly. See visitApplyInst.
static ApplyInst *replaceDynApplyWithStaticApply(ApplyInst *AI, SILFunction *F,
                                                 ArrayRef<Substitution> Subs,
                                                 InitExistentialInst *In,
                                                 ProjectExistentialInst *PEI) {
  // Creates a new FunctionRef Inst and inserts it to the basic block.
  FunctionRefInst *FRI = new (AI->getModule()) FunctionRefInst(AI->getLoc(), F);
  AI->getParent()->getInstList().insert(AI, FRI);
  SmallVector<SILValue, 4> Args;

  // Push all of the args and replace uses of PEI with the InitExistentional.
  MutableArrayRef<Operand> OrigArgs = AI->getArgumentOperands();
  for (unsigned i = 0; i < OrigArgs.size(); i++) {
    SILValue A = OrigArgs[i].get();
    Args.push_back(A.getDef() == PEI ? In : A);
  }

  // Create a new non-virtual ApplyInst.
  SILType SubstFnTy = FRI->getType().substGenericArgs(F->getModule(),
                                                               Subs);
  ApplyInst *SAI = ApplyInst::create(
      AI->getLoc(), FRI, SubstFnTy,
      SubstFnTy.castTo<SILFunctionType>()->getResult().getSILType(),
      Subs, Args, false, *F);
  AI->getParent()->getInstList().insert(AI, SAI);
  AI->replaceAllUsesWith(SAI);
  AI->eraseFromParent();
  return SAI;
}

static bool substitutionListHasUnboundGenerics(ArrayRef<Substitution> Subs) {
  for (auto &Sub : Subs)
    if (Sub.getReplacement()->getCanonicalType()->hasArchetype())
      return true;
  return false;
}

/// Temperary helper method that should be removed when inherited protocol
/// conformances are implemented for protocol methods.
static bool
inheritenceProtocolConformanceFreeConformance(ProtocolConformance *C) {
  if (isa<NormalProtocolConformance>(C))
    return true;

  if (auto *SPC = dyn_cast<SpecializedProtocolConformance>(C))
    if (isa<NormalProtocolConformance>(SPC->getGenericConformance()))
      return true;

  return false;
}

/// Devirtualize protocol_method + project_existential + init_existential
/// instructions.  For example:
///
/// %0 = alloc_box $Pingable
/// %1 = init_existential %0#1 : $*Pingable, $*Foo  <-- Foo is the static type!
/// %4 = project_existential %0#1 : $*Pingable to $*@sil_self Pingable
/// %5 = protocol_method %0#1 : $*Pingable, #Pingable.ping!1 :
/// %8 = apply %5(ARGUMENTS ... , %4) :
static bool optimizeProtocolMethod(ApplyInst *AI, ProtocolMethodInst *PMI) {
  if (!PMI)
    return false;

  DEBUG(llvm::dbgs() << "        Found ProtocolMethodInst: " << *PMI);

  // Find the last argument, which is the Self argument, which may be a
  // project_existential instruction.
  if (!AI->getNumArguments())
    return false;

  SILValue Self = AI->getSelfArgument();
  ProjectExistentialInst *PEI = dyn_cast<ProjectExistentialInst>(Self);
  if (!PEI)
    return false;

  DEBUG(llvm::dbgs() << "        Found ProjectExistentialInst: " << *PEI);

  // Make sure that the project_existential and protocol_method instructions
  // use the same protocol.
  SILValue ProtocolObject = PMI->getOperand();
  if (PEI->getOperand().getDef() != ProtocolObject.getDef())
    return false;

  DEBUG(llvm::dbgs() << "        Protocol to devirtualize : "
                     << *ProtocolObject.getDef());

  // Find a single initialization point, and make sure the protocol is not
  // captured. We also handle the case where the initializer is the copy_addr
  // instruction by looking at the source object.
  SILInstruction *InitInst = findSingleInitNoCaptureProtocol(ProtocolObject);
  if (CopyAddrInst *CAI = dyn_cast_or_null<CopyAddrInst>(InitInst)) {
    if (!CAI->isInitializationOfDest() || !CAI->isTakeOfSrc())
      return false;

    InitInst = findSingleInitNoCaptureProtocol(CAI->getSrc());
  }

  InitExistentialInst *Init = dyn_cast_or_null<InitExistentialInst>(InitInst);
  if (!Init)
    return false;
  DEBUG(llvm::dbgs() << "        InitExistentialInst : " << *Init);

  SILModule &Mod = Init->getModule();
  // For each protocol that our type conforms to:
  for (ProtocolConformance *Conf : Init->getConformances()) {

    SILFunction *StaticRef;
    ArrayRef<Substitution> Subs;
    SILWitnessTable *WT;
    std::tie(StaticRef, WT, Subs) =
      Mod.findFuncInWitnessTable(Conf, PMI->getMember());

    if (!StaticRef) {
      assert(!WT && "WT must always be null if static ref is.");
      continue;
    }
    assert(WT && "WT must never be null if static ref is also not.");

    // If any of our subs is generic, bail...
    if (substitutionListHasUnboundGenerics(Subs))
      continue;

    // If we have any form of inherited protocol conformance, bail.
    //
    // FIXME: Handle this along the lines of what was done with the witness
    // method devirtualization.
    if (!inheritenceProtocolConformanceFreeConformance(Conf))
      return false;

    DEBUG(llvm::dbgs() << "        SUCCESS! Devirtualized : " << *AI);
    ApplyInst *NewApply =
        replaceDynApplyWithStaticApply(AI, StaticRef, Subs, Init, PEI);
    (void)NewApply;

    DEBUG(llvm::dbgs() << "                To : " << *NewApply);
    NumDynApply++;
    return true;
  }

  DEBUG(llvm::dbgs() << "        FAIL: Could not find a witness table "
                        "for: " << *PMI);
  return false;
}

//===----------------------------------------------------------------------===//
//                              Top Level Driver
//===----------------------------------------------------------------------===//

/// Return the final class decl using metadata.
static ClassDecl *getClassFromClassMetadata(ClassMethodInst *CMI) {
  const DeclContext *associatedDC = CMI->getModule().getAssociatedContext();
  if (!associatedDC) {
    // Without an associated context, we can't perform any access-based
    // optimizations.
    return nullptr;
  }

  SILDeclRef Member = CMI->getMember();
  FuncDecl *FD = Member.getFuncDecl();
  SILType ClassType = CMI->getOperand().stripCasts().getType();
  ClassDecl *CD = ClassType.getClassOrBoundGenericClass();

  // Only handle valid non-dynamic non-overridden members.
  if (!CD || !FD || FD->isInvalid() || FD->isDynamic() || FD->isOverridden())
    return nullptr;

  // Only handle members defined within the SILModule's associated context.
  if (!FD->isChildContextOf(associatedDC))
    return nullptr;

  if (!FD->hasAccessibility())
    return nullptr;

  // Only consider 'private' members, unless associatedDC is the entire module.
  switch (FD->getAccessibility()) {
  case Accessibility::Public:
    return nullptr;
  case Accessibility::Internal:
    if (associatedDC != CMI->getModule().getSwiftModule())
      return nullptr;
    break;
  case Accessibility::Private:
    break;
  }

  Type selfTypeInMember = FD->getDeclContext()->getDeclaredTypeInContext();
  return selfTypeInMember->getClassOrBoundGenericClass();
}

static bool optimizeApplyInst(ApplyInst *AI) {
  DEBUG(llvm::dbgs() << "    Trying to optimize ApplyInst : " << *AI);

  // 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 (auto *AMI = dyn_cast<WitnessMethodInst>(AI->getCallee()))
    return optimizeWitnessMethod(AI, AMI);

  /// 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 : $@cc(method) @thin ...
  /// \endcode
  ///
  ///  or
  ///
  /// %XX = metatype $...
  /// %YY = class_method %XX : ...
  ///
  ///  into
  ///
  /// %YY = function_ref @...
  if (auto *CMI = dyn_cast<ClassMethodInst>(AI->getCallee())) {
    // Check if the class member is known to be final.
    if (ClassDecl *C = getClassFromClassMetadata(CMI))
      return devirtMethod(AI, CMI->getMember(), CMI->getOperand(), C);

    // Try to search for the point of construction.
    if (ClassDecl *C = getClassFromConstructor(CMI->getOperand()))
      return devirtMethod(AI, CMI->getMember(),
                          CMI->getOperand().stripCasts(), C);
  }

  // Devirtualize protocol_method + project_existential + init_existential
  // instructions.  For example:
  //
  // %0 = alloc_box $Pingable
  // %1 = init_existential %0#1 : $*Pingable, $*Foo  <-- Foo is the static type!
  // %4 = project_existential %0#1 : $*Pingable to $*@sil_self Pingable
  // %5 = protocol_method %0#1 : $*Pingable, #Pingable.ping!1 :
  // %8 = apply %5(ARGUMENTS ... , %4) :
  ProtocolMethodInst *PMI = dyn_cast<ProtocolMethodInst>(AI->getCallee());
  if (!PMI)
    return false;
  return optimizeProtocolMethod(AI, PMI);
}

namespace {

class SILDevirtualizationPass : public SILModuleTransform {
public:
  virtual ~SILDevirtualizationPass() {}

  /// The entry point to the transformation.
  virtual void run() {

    bool Changed = false;

    // Perform devirtualization locally and compute potential polymorphic
    // arguments for all existing functions.
    for (auto &F : *getModule()) {
      DEBUG(llvm::dbgs() << "*** Devirtualizing Function: "
              << demangle_wrappers::demangleSymbolAsString(F.getName())
              << "\n");
      for (auto &BB : F) {
        for (auto II = BB.begin(), IE = BB.end(); II != IE;) {
          ApplyInst *AI = dyn_cast<ApplyInst>(&*II);
          ++II;

          if (!AI)
            continue;

          Changed |= optimizeApplyInst(AI);
        }
      }
      DEBUG(llvm::dbgs() << "\n");
    }

    if (Changed) {
      PM->scheduleAnotherIteration();
      invalidateAnalysis(SILAnalysis::InvalidationKind::CallGraph);
    }
  }

  StringRef getName() override { return "Devirtualization"; }
};

} // end anonymous namespace

SILTransform *swift::createDevirtualization() {
  return new SILDevirtualizationPass();
}

// A utility function for cloning the apply instruction.
static ApplyInst *CloneApply(ApplyInst *AI, SILBuilder &Builder) {
  // Clone the Apply.
  auto Args = AI->getArguments();
  SmallVector<SILValue, 8> Ret(Args.size());
  for (unsigned i = 0, e = Args.size(); i != e; ++i)
    Ret[i] = Args[i];

  return Builder.createApply(AI->getLoc(), AI->getCallee(),
                             AI->getSubstCalleeSILType(),
                             AI->getType(),
                             AI->getSubstitutions(),
                             Ret, AI->isTransparent());
}

/// Insert monomorphic inline caches for a specific class type \p SubClassTy.
static ApplyInst* insertMonomorphicInlineCaches(ApplyInst *AI,
                                                SILType SubClassTy) {
  ClassMethodInst *CMI = cast<ClassMethodInst>(AI->getCallee());
  SILValue ClassInstance = CMI->getOperand();
  ClassDecl *CD = SubClassTy.getClassOrBoundGenericClass();

  // Create a diamond shaped control flow and a checked_cast_branch
  // instruction that checks the exact type of the object.
  // This cast selects between two paths: one that calls the slow dynamic
  // dispatch and one that calls the specific method.
  SILBasicBlock::iterator It = AI;
  SILFunction *F = AI->getFunction();
  SILBasicBlock *Entry = AI->getParent();

  // Iden is the basic block containing the direct call.
  SILBasicBlock *Iden = F->createBasicBlock();
  // Virt is the block containing the slow virtual call.
  SILBasicBlock *Virt = F->createBasicBlock();
  Iden->createArgument(SubClassTy);

  SILBasicBlock *Continue = Entry->splitBasicBlock(It);

  SILBuilder Builder(Entry);
  // Create the checked_cast_branch instruction that checks at runtime if the
  // class instance is identical to the SILType.
  assert(SubClassTy.getClassOrBoundGenericClass() &&
         "Dest type must be a class type");
  It = Builder.createCheckedCastBranch(AI->getLoc(), /*exact*/ true,
                                       ClassInstance, SubClassTy, Iden, Virt);

  SILBuilder VirtBuilder(Virt);
  SILBuilder IdenBuilder(Iden);
  // This is the class reference downcasted into subclass SubClassTy.
  SILValue DownCastedClassInstance = Iden->getBBArg(0);

  // Try sinking the retain of the class instance into the diamond. This may
  // allow additional ARC optimizations on the fast path.
  if (It != Entry->begin()) {
    StrongRetainInst *SRI = dyn_cast<StrongRetainInst>(--It);
    // Try to skip another instruction, in case the class_method came first.
    if (!SRI && It != Entry->begin())
      SRI = dyn_cast<StrongRetainInst>(--It);
    if (SRI && SRI->getOperand() == ClassInstance) {
      VirtBuilder.createStrongRetain(SRI->getLoc(), ClassInstance);
      IdenBuilder.createStrongRetain(SRI->getLoc(), DownCastedClassInstance);
      SRI->eraseFromParent();
    }
  }

  // Copy the two apply instructions into the two blocks.
  ApplyInst *IdenAI = CloneApply(AI, IdenBuilder);
  ApplyInst *VirtAI = CloneApply(AI, VirtBuilder);

  // Create a PHInode for returning the return value from both apply
  // instructions.
  SILArgument *Arg = Continue->createArgument(AI->getType());
  IdenBuilder.createBranch(AI->getLoc(), Continue, ArrayRef<SILValue>(IdenAI));
  VirtBuilder.createBranch(AI->getLoc(), Continue, ArrayRef<SILValue>(VirtAI));

  // Remove the old Apply instruction.
  AI->replaceAllUsesWith(Arg);
  AI->eraseFromParent();

  // Update the stats.
  NumInlineCaches++;

  // Devirtualize the apply instruction on the identical path.
  devirtMethod(IdenAI, CMI->getMember(), DownCastedClassInstance, CD);

  // Sink class_method instructions down to their single user.
  if (CMI->hasOneUse())
    CMI->moveBefore(CMI->use_begin()->getUser());

  return VirtAI;
}

/// \brief Try to insert inline cahces for the call \p AI. This function
/// returns true if a change was made.
static bool insertInlineCaches(ApplyInst *AI, ClassHierarchyAnalysis *CHA) {
  ClassMethodInst *CMI = cast<ClassMethodInst>(AI->getCallee());
  assert(CMI && "Invalid class method instruction");

  SILValue ClassInstance = CMI->getOperand();
  SILType InstanceType = ClassInstance.stripCasts().getType();
  ClassDecl *CD = InstanceType.getClassOrBoundGenericClass();

  // Check if it is legal to insert inline caches.
  if (!CD || CMI->isVolatile() || ClassInstance.getType() != InstanceType)
    return false;

  if (!CHA->hasKnownSubclasses(CD)) {
    DEBUG(llvm::dbgs() << "Inserting monomorphic inline caches for class " <<
          CD->getName() << "\n");
    return insertMonomorphicInlineCaches(AI, InstanceType);
  }

  // Collect the subclasses for the class.
  ClassHierarchyAnalysis::ClassList &Subs = CHA->getSubClasses(CD);

  if (Subs.size() > MaxNumPolymorphicInlineCaches) {
    DEBUG(llvm::dbgs() << "Class " << CD->getName() << " has too many (" <<
          Subs.size() << ") subclasses. Not inserting inline caches.\n");
    return false;
  }

  DEBUG(llvm::dbgs() << "Class " << CD->getName() << " is a superclass. "
        "Inserting polymorphic inline caches.\n");

  // Generate the polymorphic inline cache using multiple monomorphic caches.
  for (auto S : Subs) {
    DEBUG(llvm::dbgs() << "Inserting a cache for class " << CD->getName() <<
          " and subclass " << S->getName() << "\n");

    CanType CanClassType = S->getDeclaredType()->getCanonicalType();
    SILType InstanceType = SILType::getPrimitiveObjectType(CanClassType);
    if (!InstanceType.getClassOrBoundGenericClass())
      continue;

    AI = insertMonomorphicInlineCaches(AI, InstanceType);
    assert(AI && "Unable to insert inline caches!");
  }

  return true;
}

namespace {
  /// Generate inline caches of virtual calls by speculating that the requested
  /// class is at the bottom of the class hierarchy.
  class SILInlineCaches : public SILFunctionTransform {
  public:
    virtual ~SILInlineCaches() {}

    virtual void run() {
      ClassHierarchyAnalysis *CHA = PM->getAnalysis<ClassHierarchyAnalysis>();

      bool Changed = false;

      // Collect virtual calls that may be specialized.
      SmallVector<ApplyInst *, 16> ToSpecialize;
      for (auto &BB : *getFunction()) {
        for (auto II = BB.begin(), IE = BB.end(); II != IE; ++II) {
          ApplyInst *AI = dyn_cast<ApplyInst>(&*II);
          if (AI && isa<ClassMethodInst>(AI->getCallee()))
            ToSpecialize.push_back(AI);
        }
      }

      // Create the inline caches.
      for (auto AI : ToSpecialize)
        Changed |= insertInlineCaches(AI, CHA);

      if (Changed) {
        invalidateAnalysis(SILAnalysis::InvalidationKind::CallGraph);
      }
    }

    StringRef getName() override { return "Inline Caches"; }
  };

} // end anonymous namespace

SILTransform *swift::createInlineCaches() {
  return new SILInlineCaches();
}