swift-mirror/lib/SIL/SILModule.cpp

//===--- SILModule.cpp - SILModule implementation -------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "sil-module"
#include "swift/Serialization/SerializedSILLoader.h"
#include "swift/AST/GenericEnvironment.h"
#include "swift/AST/ProtocolConformance.h"
#include "swift/SIL/FormalLinkage.h"
#include "swift/SIL/SILDebugScope.h"
#include "swift/SIL/SILModule.h"
#include "swift/Strings.h"
#include "Linker.h"
#include "swift/SIL/SILVisitor.h"
#include "swift/SIL/SILValue.h"
#include "swift/ClangImporter/ClangModule.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/YAMLTraits.h"
#include <functional>
using namespace swift;
using namespace Lowering;

class SILModule::SerializationCallback : public SerializedSILLoader::Callback {
  void didDeserialize(ModuleDecl *M, SILFunction *fn) override {
    updateLinkage(fn);
  }

  void didDeserialize(ModuleDecl *M, SILGlobalVariable *var) override {
    updateLinkage(var);
    
    // For globals we currently do not support available_externally.
    // In the interpreter it would result in two instances for a single global:
    // one in the imported module and one in the main module.
    var->setDeclaration(true);
  }

  void didDeserialize(ModuleDecl *M, SILVTable *vtable) override {
    // TODO: should vtables get linkage?
    //updateLinkage(vtable);
  }

  void didDeserialize(ModuleDecl *M, SILWitnessTable *wt) override {
    updateLinkage(wt);
  }

  template <class T> void updateLinkage(T *decl) {
    switch (decl->getLinkage()) {
    case SILLinkage::Public:
      decl->setLinkage(SILLinkage::PublicExternal);
      return;
    case SILLinkage::PublicNonABI:
      // PublicNonABI functions receive SharedExternal linkage, so that
      // they have "link once" semantics when deserialized by multiple
      // translation units in the same Swift module.
      decl->setLinkage(SILLinkage::SharedExternal);
      return;
    case SILLinkage::Hidden:
      decl->setLinkage(SILLinkage::HiddenExternal);
      return;
    case SILLinkage::Shared:
      decl->setLinkage(SILLinkage::SharedExternal);
      return;
    case SILLinkage::Private:
      decl->setLinkage(SILLinkage::PrivateExternal);
      return;
    case SILLinkage::PublicExternal:
    case SILLinkage::HiddenExternal:
    case SILLinkage::SharedExternal:
    case SILLinkage::PrivateExternal:
      return;
    }
  }

  void didDeserializeFunctionBody(ModuleDecl *M, SILFunction *fn) override {
    // Callbacks are currently applied in the order they are registered.
    for (auto callBack : fn->getModule().getDeserializationCallbacks())
      callBack(M, fn);
  }
};

SILModule::SILModule(ModuleDecl *SwiftModule, SILOptions &Options,
                     const DeclContext *associatedDC, bool wholeModule)
    : TheSwiftModule(SwiftModule), AssociatedDeclContext(associatedDC),
      Stage(SILStage::Raw), Callback(new SILModule::SerializationCallback()),
      wholeModule(wholeModule), Options(Options), serialized(false),
      SerializeSILAction(), Types(*this) {}

SILModule::~SILModule() {
  // Decrement ref count for each SILGlobalVariable with static initializers.
  for (SILGlobalVariable &v : silGlobals)
    v.dropAllReferences();

  // Drop everything functions in this module reference.
  //
  // This is necessary since the functions may reference each other.  We don't
  // need to worry about sil_witness_tables since witness tables reference each
  // other via protocol conformances and sil_vtables don't reference each other
  // at all.
  for (SILFunction &F : *this)
    F.dropAllReferences();
}

std::unique_ptr<SILModule>
SILModule::createEmptyModule(ModuleDecl *M, SILOptions &Options,
                             bool WholeModule) {
  return std::unique_ptr<SILModule>(
      new SILModule(M, Options, M, WholeModule));
}

ASTContext &SILModule::getASTContext() const {
  return TheSwiftModule->getASTContext();
}

void *SILModule::allocate(unsigned Size, unsigned Align) const {
  if (getASTContext().LangOpts.UseMalloc)
    return AlignedAlloc(Size, Align);

  return BPA.Allocate(Size, Align);
}

void *SILModule::allocateInst(unsigned Size, unsigned Align) const {
  return AlignedAlloc(Size, Align);
}

void SILModule::deallocateInst(SILInstruction *I) {
  AlignedFree(I);
}

SILWitnessTable *
SILModule::createWitnessTableDeclaration(ProtocolConformance *C,
                                         SILLinkage linkage) {
  // If we are passed in a null conformance (a valid value), just return nullptr
  // since we cannot map a witness table to it.
  if (!C)
    return nullptr;

  // Extract the base NormalProtocolConformance.
  NormalProtocolConformance *NormalC = C->getRootNormalConformance();

  return SILWitnessTable::create(*this, linkage, NormalC);
}

SILWitnessTable *
SILModule::lookUpWitnessTable(ProtocolConformanceRef C,
                              bool deserializeLazily) {
  // If we have an abstract conformance passed in (a legal value), just return
  // nullptr.
  if (!C.isConcrete())
    return nullptr;

  return lookUpWitnessTable(C.getConcrete());
}

SILWitnessTable *
SILModule::lookUpWitnessTable(const ProtocolConformance *C,
                              bool deserializeLazily) {
  assert(C && "null conformance passed to lookUpWitnessTable");

  const NormalProtocolConformance *NormalC = C->getRootNormalConformance();
  // Attempt to lookup the witness table from the table.
  auto found = WitnessTableMap.find(NormalC);
  if (found == WitnessTableMap.end()) {
#ifndef NDEBUG
    // Make sure that all witness tables are in the witness table lookup
    // cache.
    //
    // This code should not be hit normally since we add witness tables to the
    // lookup cache when we create them. We don't just assert here since there
    // is the potential for a conformance without a witness table to be passed
    // to this function.
    for (SILWitnessTable &WT : witnessTables)
      assert(WT.getConformance() != NormalC &&
             "Found witness table that is not"
             " in the witness table lookup cache.");
#endif
    return nullptr;
  }

  SILWitnessTable *wtable = found->second;
  assert(wtable != nullptr && "Should never map a conformance to a null witness"
                          " table.");

  // If we have a definition, return it.
  if (wtable->isDefinition())
    return wtable;

  // If the module is at or past the Lowered stage, then we can't do any
  // further deserialization, since pre-IRGen SIL lowering changes the types
  // of definitions to make them incompatible with canonical serialized SIL.
  switch (getStage()) {
  case SILStage::Canonical:
  case SILStage::Raw:
    break;
    
  case SILStage::Lowered:
    return wtable;
  }

  // Otherwise try to deserialize it. If we succeed return the deserialized
  // function.
  //
  // *NOTE* In practice, wtable will be deserializedTable, but I do not want to rely
  // on that behavior for now.
  if (deserializeLazily)
    if (auto deserialized = getSILLoader()->lookupWitnessTable(wtable))
      return deserialized;

  // If we fail, just return the declaration.
  return wtable;
}

SILDefaultWitnessTable *
SILModule::lookUpDefaultWitnessTable(const ProtocolDecl *Protocol,
                                     bool deserializeLazily) {
  // Note: we only ever look up default witness tables in the translation unit
  // that is currently being compiled, since they SILGen generates them when it
  // visits the protocol declaration, and IRGen emits them when emitting the
  // protocol descriptor metadata for the protocol.

  auto found = DefaultWitnessTableMap.find(Protocol);
  if (found == DefaultWitnessTableMap.end()) {
    if (deserializeLazily) {
      SILLinkage linkage =
        getSILLinkage(getDeclLinkage(Protocol), ForDefinition);
      SILDefaultWitnessTable *wtable =
        SILDefaultWitnessTable::create(*this, linkage, Protocol);
      wtable = getSILLoader()->lookupDefaultWitnessTable(wtable);
      if (wtable)
        DefaultWitnessTableMap[Protocol] = wtable;
      return wtable;
    }

    return nullptr;
  }

  return found->second;
}

SILDefaultWitnessTable *
SILModule::createDefaultWitnessTableDeclaration(const ProtocolDecl *Protocol,
                                                SILLinkage Linkage) {
  return SILDefaultWitnessTable::create(*this, Linkage, Protocol);
}

void SILModule::deleteWitnessTable(SILWitnessTable *Wt) {
  NormalProtocolConformance *Conf = Wt->getConformance();
  assert(lookUpWitnessTable(Conf, false) == Wt);
  WitnessTableMap.erase(Conf);
  witnessTables.erase(Wt);
}

SILFunction *SILModule::getOrCreateFunction(
    SILLocation loc, StringRef name, SILLinkage linkage,
    CanSILFunctionType type, IsBare_t isBareSILFunction,
    IsTransparent_t isTransparent, IsSerialized_t isSerialized,
    ProfileCounter entryCount, IsThunk_t isThunk, SubclassScope subclassScope) {
  assert(!type->isNoEscape() && "Function decls always have escaping types.");
  if (auto fn = lookUpFunction(name)) {
    assert(fn->getLoweredFunctionType() == type);
    assert(stripExternalFromLinkage(fn->getLinkage()) ==
           stripExternalFromLinkage(linkage));
    return fn;
  }

  auto fn = SILFunction::create(*this, linkage, name, type, nullptr, loc,
                                isBareSILFunction, isTransparent, isSerialized,
                                entryCount, isThunk, subclassScope);
  fn->setDebugScope(new (*this) SILDebugScope(loc, fn));
  return fn;
}

static bool verifySILSelfParameterType(SILDeclRef DeclRef,
                                       SILFunction *F, CanSILFunctionType FTy) {
  SILModule &M = F->getModule();
  SILParameterInfo PInfo = FTy->getSelfParameter();
  CanType CTy = PInfo.getType();
  SILType Ty = SILType::getPrimitiveObjectType(CTy);

  // We do not care about trivial parameters (for now). There seem to be
  // cases where we lower them as unowned.
  //
  // *NOTE* We do not run this check when we have a generic type since
  // *generic types do not have type lowering and are always treated as
  // *non-trivial since we do not know the type.
  if (CTy->hasArchetype() || CTy->hasTypeParameter() ||
      M.getTypeLowering(Ty).isTrivial())
    return true;

  // If this function is a constructor or destructor, bail. These have @owned
  // parameters.
  if (DeclRef.isConstructor() || DeclRef.isDestructor())
    return true;

  // Otherwise, if this function type has a guaranteed self parameter type,
  // make sure that we have a +0 self param.
  return !FTy->getExtInfo().hasGuaranteedSelfParam() ||
          PInfo.isGuaranteed() || PInfo.isIndirectMutating();
}

static void addFunctionAttributes(SILFunction *F, DeclAttributes &Attrs,
                                  SILModule &M) {
  for (auto *A : Attrs.getAttributes<SemanticsAttr>())
    F->addSemanticsAttr(cast<SemanticsAttr>(A)->Value);

  // Propagate @_specialize.
  for (auto *A : Attrs.getAttributes<SpecializeAttr>()) {
    auto *SA = cast<SpecializeAttr>(A);
    auto kind = SA->getSpecializationKind() ==
                        SpecializeAttr::SpecializationKind::Full
                    ? SILSpecializeAttr::SpecializationKind::Full
                    : SILSpecializeAttr::SpecializationKind::Partial;
    F->addSpecializeAttr(SILSpecializeAttr::create(
        M, SA->getRequirements(), SA->isExported(), kind));
  }

  if (auto *OA = Attrs.getAttribute<OptimizeAttr>()) {
    F->setOptimizationMode(OA->getMode());
  }

  // @_silgen_name and @_cdecl functions may be called from C code somewhere.
  if (Attrs.hasAttribute<SILGenNameAttr>() ||
      Attrs.hasAttribute<CDeclAttr>())
    F->setHasCReferences(true);

  if (Attrs.hasAttribute<WeakLinkedAttr>())
    F->setWeakLinked();
}

SILFunction *SILModule::getOrCreateFunction(SILLocation loc,
                                            SILDeclRef constant,
                                            ForDefinition_t forDefinition,
                                            ProfileCounter entryCount) {

  auto name = constant.mangle();
  auto constantType = Types.getConstantFunctionType(constant);
  SILLinkage linkage = constant.getLinkage(forDefinition);

  if (auto fn = lookUpFunction(name)) {
    assert(fn->getLoweredFunctionType() == constantType);
    assert(fn->getLinkage() == linkage ||
           (forDefinition == ForDefinition_t::NotForDefinition &&
            fn->getLinkage() ==
                constant.getLinkage(ForDefinition_t::ForDefinition)));
    if (forDefinition) {
      // In all the cases where getConstantLinkage returns something
      // different for ForDefinition, it returns an available-externally
      // linkage.
      if (isAvailableExternally(fn->getLinkage())) {
        fn->setLinkage(constant.getLinkage(ForDefinition));
      }
    }
    return fn;
  }

  IsTransparent_t IsTrans = constant.isTransparent()
                            ? IsTransparent
                            : IsNotTransparent;
  IsSerialized_t IsSer = constant.isSerialized();

  EffectsKind EK = constant.hasEffectsAttribute()
                   ? constant.getEffectsAttribute()
                   : EffectsKind::Unspecified;

  Inline_t inlineStrategy = InlineDefault;
  if (constant.isNoinline())
    inlineStrategy = NoInline;
  else if (constant.isAlwaysInline())
    inlineStrategy = AlwaysInline;

  auto *F =
      SILFunction::create(*this, linkage, name, constantType, nullptr, None,
                          IsNotBare, IsTrans, IsSer, entryCount, IsNotThunk,
                          constant.getSubclassScope(), inlineStrategy, EK);
  F->setDebugScope(new (*this) SILDebugScope(loc, F));

  F->setGlobalInit(constant.isGlobal());
  if (constant.hasDecl()) {
    auto decl = constant.getDecl();

    if (constant.isForeign && decl->hasClangNode())
      F->setClangNodeOwner(decl);

    if (auto *accessor = dyn_cast<AccessorDecl>(decl)) {
      auto *storage = accessor->getStorage();
      // Add attributes for e.g. computed properties.
      addFunctionAttributes(F, storage->getAttrs(), *this);
    }
    addFunctionAttributes(F, decl->getAttrs(), *this);
  }

  // If this function has a self parameter, make sure that it has a +0 calling
  // convention. This cannot be done for general function types, since
  // function_ref's SILFunctionTypes do not have archetypes associated with
  // it.
  CanSILFunctionType FTy = F->getLoweredFunctionType();
  if (FTy->hasSelfParam()) {
    (void)&verifySILSelfParameterType;
    assert(verifySILSelfParameterType(constant, F, FTy) &&
           "Invalid signature for SIL Self parameter type");
  }
                                      

  return F;
}

SILFunction *SILModule::getOrCreateSharedFunction(
    SILLocation loc, StringRef name, CanSILFunctionType type,
    IsBare_t isBareSILFunction, IsTransparent_t isTransparent,
    IsSerialized_t isSerialized, ProfileCounter entryCount, IsThunk_t isThunk) {
  return getOrCreateFunction(loc, name, SILLinkage::Shared, type,
                             isBareSILFunction, isTransparent, isSerialized,
                             entryCount, isThunk, SubclassScope::NotApplicable);
}

SILFunction *SILModule::createFunction(
    SILLinkage linkage, StringRef name, CanSILFunctionType loweredType,
    GenericEnvironment *genericEnv, Optional<SILLocation> loc,
    IsBare_t isBareSILFunction, IsTransparent_t isTrans,
    IsSerialized_t isSerialized, ProfileCounter entryCount, IsThunk_t isThunk,
    SubclassScope subclassScope, Inline_t inlineStrategy, EffectsKind EK,
    SILFunction *InsertBefore, const SILDebugScope *DebugScope) {
  return SILFunction::create(*this, linkage, name, loweredType, genericEnv, loc,
                             isBareSILFunction, isTrans, isSerialized,
                             entryCount, isThunk, subclassScope, inlineStrategy,
                             EK, InsertBefore, DebugScope);
}

const IntrinsicInfo &SILModule::getIntrinsicInfo(Identifier ID) {
  unsigned OldSize = IntrinsicIDCache.size();
  IntrinsicInfo &Info = IntrinsicIDCache[ID];

  // If the element was is in the cache, return it.
  if (OldSize == IntrinsicIDCache.size())
    return Info;

  // Otherwise, lookup the ID and Type and store them in the map.
  StringRef NameRef = getBuiltinBaseName(getASTContext(), ID.str(), Info.Types);
  Info.ID = (llvm::Intrinsic::ID)getLLVMIntrinsicID(NameRef);

  return Info;
}

const BuiltinInfo &SILModule::getBuiltinInfo(Identifier ID) {
  unsigned OldSize = BuiltinIDCache.size();
  BuiltinInfo &Info = BuiltinIDCache[ID];

  // If the element was is in the cache, return it.
  if (OldSize == BuiltinIDCache.size())
    return Info;

  // Otherwise, lookup the ID and Type and store them in the map.
  // Find the matching ID.
  StringRef OperationName =
    getBuiltinBaseName(getASTContext(), ID.str(), Info.Types);

  // Several operation names have suffixes and don't match the name from
  // Builtins.def, so handle those first.
  if (OperationName.startswith("fence_"))
    Info.ID = BuiltinValueKind::Fence;
  else if (OperationName.startswith("cmpxchg_"))
    Info.ID = BuiltinValueKind::CmpXChg;
  else if (OperationName.startswith("atomicrmw_"))
    Info.ID = BuiltinValueKind::AtomicRMW;
  else if (OperationName.startswith("atomicload_"))
    Info.ID = BuiltinValueKind::AtomicLoad;
  else if (OperationName.startswith("atomicstore_"))
    Info.ID = BuiltinValueKind::AtomicStore;
  else if (OperationName.startswith("allocWithTailElems_"))
    Info.ID = BuiltinValueKind::AllocWithTailElems;
  else {
    // Switch through the rest of builtins.
#define BUILTIN(Id, Name, Attrs) \
    if (OperationName == Name) { Info.ID = BuiltinValueKind::Id; } else
#include "swift/AST/Builtins.def"
    /* final "else" */ { Info.ID = BuiltinValueKind::None; }
  }

  return Info;
}

SILFunction *SILModule::lookUpFunction(SILDeclRef fnRef) {
  auto name = fnRef.mangle();
  return lookUpFunction(name);
}

bool SILModule::loadFunction(SILFunction *F) {
  SILFunction *NewF = getSILLoader()->lookupSILFunction(F);
  if (!NewF)
    return false;

  assert(F == NewF);
  return true;
}

bool SILModule::linkFunction(SILFunction *F, SILModule::LinkingMode Mode) {
  return SILLinkerVisitor(*this, Mode).processFunction(F);
}

SILFunction *SILModule::findFunction(StringRef Name, SILLinkage Linkage) {
  assert((Linkage == SILLinkage::Public ||
          Linkage == SILLinkage::PublicExternal) &&
         "Only a lookup of public functions is supported currently");

  SILFunction *F = nullptr;

  // First, check if there is a function with a required name in the
  // current module.
  SILFunction *CurF = lookUpFunction(Name);

  // Nothing to do if the current module has a required function
  // with a proper linkage already.
  if (CurF && CurF->getLinkage() == Linkage) {
    F = CurF;
  } else {
    assert((!CurF || CurF->getLinkage() != Linkage) &&
           "hasFunction should be only called for functions that are not "
           "contained in the SILModule yet or do not have a required linkage");
  }

  if (!F) {
    if (CurF) {
      // Perform this lookup only if a function with a given
      // name is present in the current module.
      // This is done to reduce the amount of IO from the
      // swift module file.
      if (!getSILLoader()->hasSILFunction(Name, Linkage))
        return nullptr;
      // The function in the current module will be changed.
      F = CurF;
    }

    // If function with a given name wasn't seen anywhere yet
    // or if it is known to exist, perform a lookup.
    if (!F) {
      // Try to load the function from other modules.
      F = getSILLoader()->lookupSILFunction(Name, /*declarationOnly*/ true,
                                            Linkage);
      // Bail if nothing was found and we are not sure if
      // this function exists elsewhere.
      if (!F)
        return nullptr;
      assert(F && "SILFunction should be present in one of the modules");
      assert(F->getLinkage() == Linkage && "SILFunction has a wrong linkage");
    }
  }

  // If a function exists already and it is a non-optimizing
  // compilation, simply convert it into an external declaration,
  // so that a compiled version from the shared library is used.
  if (F->isDefinition() &&
      !F->getModule().getOptions().shouldOptimize()) {
    F->convertToDeclaration();
  }
  if (F->isExternalDeclaration())
    F->setSerialized(IsSerialized_t::IsNotSerialized);
  F->setLinkage(Linkage);
  return F;
}

bool SILModule::hasFunction(StringRef Name) {
  if (lookUpFunction(Name))
    return true;
  return getSILLoader()->hasSILFunction(Name);
}

void SILModule::linkAllFromCurrentModule() {
  getSILLoader()->getAllForModule(getSwiftModule()->getName(),
                                  /*PrimaryFile=*/nullptr);
}

void SILModule::invalidateSILLoaderCaches() {
  getSILLoader()->invalidateCaches();
}

void SILModule::removeFromZombieList(StringRef Name) {
  if (auto *Zombie = ZombieFunctionTable.lookup(Name)) {
    ZombieFunctionTable.erase(Name);
    zombieFunctions.remove(Zombie);
  }
}

/// Erase a function from the module.
void SILModule::eraseFunction(SILFunction *F) {
  assert(! F->isZombie() && "zombie function is in list of alive functions");
  // The owner of the function's Name is the FunctionTable key. As we remove
  // the function from the table we have to store the name string elsewhere:
  // in zombieFunctionNames.
  StringRef copiedName = F->getName().copy(zombieFunctionNames);
  FunctionTable.erase(F->getName());
  F->Name = copiedName;

  // The function is dead, but we need it later (at IRGen) for debug info
  // or vtable stub generation. So we move it into the zombie list.
  getFunctionList().remove(F);
  zombieFunctions.push_back(F);
  ZombieFunctionTable[copiedName] = F;
  F->setZombie();

  // This opens dead-function-removal opportunities for called functions.
  // (References are not needed anymore.)
  F->dropAllReferences();
}

void SILModule::invalidateFunctionInSILCache(SILFunction *F) {
  getSILLoader()->invalidateFunction(F);
}

/// Erase a global SIL variable from the module.
void SILModule::eraseGlobalVariable(SILGlobalVariable *G) {
  GlobalVariableMap.erase(G->getName());
  getSILGlobalList().erase(G);
}

SILVTable *SILModule::lookUpVTable(const ClassDecl *C) {
  if (!C)
    return nullptr;

  // First try to look up R from the lookup table.
  auto R = VTableMap.find(C);
  if (R != VTableMap.end())
    return R->second;

  // If that fails, try to deserialize it. If that fails, return nullptr.
  SILVTable *Vtbl = getSILLoader()->lookupVTable(C);
  if (!Vtbl)
    return nullptr;

  // If we succeeded, map C -> VTbl in the table and return VTbl.
  VTableMap[C] = Vtbl;
  return Vtbl;
}

SerializedSILLoader *SILModule::getSILLoader() {
  // If the SILLoader is null, create it.
  if (!SILLoader)
    SILLoader = SerializedSILLoader::create(getASTContext(), this,
                                            Callback.get());
  // Return the SerializedSILLoader.
  return SILLoader.get();
}

/// \brief Given a conformance \p C and a protocol requirement \p Requirement,
/// search the witness table for the conformance and return the witness thunk
/// for the requirement.
std::pair<SILFunction *, SILWitnessTable *>
SILModule::lookUpFunctionInWitnessTable(ProtocolConformanceRef C,
                                        SILDeclRef Requirement) {
  // Look up the witness table associated with our protocol conformance from the
  // SILModule.
  auto Ret = lookUpWitnessTable(C);

  // If no witness table was found, bail.
  if (!Ret) {
    DEBUG(llvm::dbgs() << "        Failed speculative lookup of witness for: ";
          C.dump(); Requirement.dump());
    return std::make_pair(nullptr, nullptr);
  }

  // Okay, we found the correct witness table. Now look for the method.
  for (auto &Entry : Ret->getEntries()) {
    // Look at method entries only.
    if (Entry.getKind() != SILWitnessTable::WitnessKind::Method)
      continue;

    SILWitnessTable::MethodWitness MethodEntry = Entry.getMethodWitness();
    // Check if this is the member we were looking for.
    if (MethodEntry.Requirement != Requirement)
      continue;

    return std::make_pair(MethodEntry.Witness, Ret);
  }

  return std::make_pair(nullptr, nullptr);
}

/// \brief Given a protocol \p Protocol and a requirement \p Requirement,
/// search the protocol's default witness table and return the default
/// witness thunk for the requirement.
std::pair<SILFunction *, SILDefaultWitnessTable *>
SILModule::lookUpFunctionInDefaultWitnessTable(const ProtocolDecl *Protocol,
                                               SILDeclRef Requirement,
                                               bool deserializeLazily) {
  // Look up the default witness table associated with our protocol from the
  // SILModule.
  auto Ret = lookUpDefaultWitnessTable(Protocol, deserializeLazily);

  // If no default witness table was found, bail.
  //
  // FIXME: Could be an assert if we fix non-single-frontend mode to link
  // together serialized SIL emitted by each translation unit.
  if (!Ret) {
    DEBUG(llvm::dbgs() << "        Failed speculative lookup of default "
          "witness for " << Protocol->getName() << " ";
          Requirement.dump());
    return std::make_pair(nullptr, nullptr);
  }

  // Okay, we found the correct default witness table. Now look for the method.
  for (auto &Entry : Ret->getEntries()) {
    // Ignore dummy entries semitted for non-method requirements, as well as
    // requirements without default implementations.
    if (!Entry.isValid())
      continue;

    // Check if this is the member we were looking for.
    if (Entry.getRequirement() != Requirement)
      continue;

    return std::make_pair(Entry.getWitness(), Ret);
  }

  // This requirement doesn't have a default implementation.
  return std::make_pair(nullptr, nullptr);
}

SILFunction *
SILModule::
lookUpFunctionInVTable(ClassDecl *Class, SILDeclRef Member) {
  // Try to lookup a VTable for Class from the module...
  auto *Vtbl = lookUpVTable(Class);

  // Bail, if the lookup of VTable fails.
  if (!Vtbl) {
    return nullptr;
  }

  // Ok, we have a VTable. Try to lookup the SILFunction implementation from
  // the VTable.
  if (auto E = Vtbl->getEntry(*this, Member))
    return E->Implementation;

  return nullptr;
}

void SILModule::registerDeserializationCallback(
    SILFunctionBodyCallback callBack) {
  if (std::find(DeserializationCallbacks.begin(),
                DeserializationCallbacks.end(), callBack)
      == DeserializationCallbacks.end())
    DeserializationCallbacks.push_back(callBack);
}

ArrayRef<SILModule::SILFunctionBodyCallback>
SILModule::getDeserializationCallbacks() {
  return DeserializationCallbacks;
}

void SILModule::
registerDeleteNotificationHandler(DeleteNotificationHandler* Handler) {
  // Ask the handler (that can be an analysis, a pass, or some other data
  // structure) if it wants to receive delete notifications.
  if (Handler->needsNotifications()) {
    NotificationHandlers.insert(Handler);
  }
}

void SILModule::
removeDeleteNotificationHandler(DeleteNotificationHandler* Handler) {
  NotificationHandlers.remove(Handler);
}

void SILModule::notifyDeleteHandlers(SILNode *node) {
  for (auto *Handler : NotificationHandlers) {
    Handler->handleDeleteNotification(node);
  }
}

// TODO: We should have an "isNoReturn" bit on Swift's BuiltinInfo, but for
// now, let's recognize noreturn intrinsics and builtins specially here.
bool SILModule::isNoReturnBuiltinOrIntrinsic(Identifier Name) {
  const auto &IntrinsicInfo = getIntrinsicInfo(Name);
  if (IntrinsicInfo.ID != llvm::Intrinsic::not_intrinsic) {
    return IntrinsicInfo.hasAttribute(llvm::Attribute::NoReturn);
  }
  const auto &BuiltinInfo = getBuiltinInfo(Name);
  switch (BuiltinInfo.ID) {
  default:
    return false;
  case BuiltinValueKind::Unreachable:
  case BuiltinValueKind::CondUnreachable:
  case BuiltinValueKind::UnexpectedError:
  case BuiltinValueKind::ErrorInMain:
    return true;
  }
}

bool SILModule::
shouldSerializeEntitiesAssociatedWithDeclContext(const DeclContext *DC) const {
  // Serialize entities associated with this module's associated context.
  if (DC->isChildContextOf(getAssociatedContext())) {
    return true;
  }
  
  // Serialize entities associated with clang modules, since other entities
  // may depend on them, and someone who deserializes those entities may not
  // have their own copy.
  if (isa<ClangModuleUnit>(DC->getModuleScopeContext())) {
    return true;
  }
  
  return false;
}

/// Returns true if it is the OnoneSupport module.
bool SILModule::isOnoneSupportModule() const {
  return getSwiftModule()->getName().str() == SWIFT_ONONE_SUPPORT;
}

/// Returns true if it is the optimized OnoneSupport module.
bool SILModule::isOptimizedOnoneSupportModule() const {
  return getOptions().shouldOptimize() && isOnoneSupportModule();
}

void SILModule::setSerializeSILAction(SILModule::ActionCallback Action) {
  assert(!SerializeSILAction && "Serialization action can be set only once");
  SerializeSILAction = Action;
}

SILModule::ActionCallback SILModule::getSerializeSILAction() const {
  return SerializeSILAction;
}

void SILModule::serialize() {
  assert(SerializeSILAction && "Serialization action should be set");
  assert(!isSerialized() && "The module was serialized already");
  SerializeSILAction();
  setSerialized();
}

void SILModule::setOptRecordStream(
    std::unique_ptr<llvm::yaml::Output> &&Stream,
    std::unique_ptr<llvm::raw_ostream> &&RawStream) {
  OptRecordStream = std::move(Stream);
  OptRecordRawStream = std::move(RawStream);
}

SILProperty *SILProperty::create(SILModule &M,
                                 bool Serialized,
                                 AbstractStorageDecl *Decl,
                                 Optional<KeyPathPatternComponent> Component) {
  auto prop = new (M) SILProperty(Serialized, Decl, Component);
  M.properties.push_back(prop);
  return prop;
}

// Definition from SILLinkage.h.
SILLinkage swift::getDeclSILLinkage(const ValueDecl *decl) {
  AccessLevel access = decl->getEffectiveAccess();
  SILLinkage linkage;
  switch (access) {
  case AccessLevel::Private:
  case AccessLevel::FilePrivate:
    linkage = SILLinkage::Private;
    break;
  case AccessLevel::Internal:
    linkage = SILLinkage::Hidden;
    break;
  case AccessLevel::Public:
  case AccessLevel::Open:
    linkage = SILLinkage::Public;
    break;
  }
  return linkage;
}