text: //===--- SILGen.cpp - Implements Lowering of ASTs -> SIL ------------------===//
  //
  // 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 "silgen"
  #include "ManagedValue.h"
  #include "RValue.h"
  #include "SILGenFunction.h"
  #include "SILGenFunctionBuilder.h"
  #include "Scope.h"
  #include "swift/AST/DiagnosticsSIL.h"
  #include "swift/AST/GenericEnvironment.h"
  #include "swift/AST/Initializer.h"
  #include "swift/AST/NameLookup.h"
  #include "swift/AST/ParameterList.h"
  #include "swift/AST/PrettyStackTrace.h"
  #include "swift/AST/ProtocolConformance.h"
  #include "swift/AST/ResilienceExpansion.h"
  #include "swift/Basic/Statistic.h"
  #include "swift/Basic/Timer.h"
  #include "swift/ClangImporter/ClangModule.h"
  #include "swift/SIL/PrettyStackTrace.h"
  #include "swift/SIL/SILArgument.h"
  #include "swift/SIL/SILDebugScope.h"
  #include "swift/SIL/SILProfiler.h"
  #include "swift/Serialization/SerializedModuleLoader.h"
  #include "swift/Serialization/SerializedSILLoader.h"
  #include "swift/Strings.h"
  #include "swift/Subsystems.h"
  #include "llvm/ProfileData/InstrProfReader.h"
  #include "llvm/Support/Debug.h"
  using namespace swift;
  using namespace Lowering;
  
  //===----------------------------------------------------------------------===//
  // SILGenModule Class implementation
  //===----------------------------------------------------------------------===//
  
  SILGenModule::SILGenModule(SILModule &M, ModuleDecl *SM)
      : M(M), Types(M.Types), SwiftModule(SM), TopLevelSGF(nullptr) {
    SILOptions &Opts = M.getOptions();
    if (!Opts.UseProfile.empty()) {
      auto ReaderOrErr = llvm::IndexedInstrProfReader::create(Opts.UseProfile);
      if (auto E = ReaderOrErr.takeError()) {
        diagnose(SourceLoc(), diag::profile_read_error, Opts.UseProfile,
                 llvm::toString(std::move(E)));
        Opts.UseProfile.erase();
      }
      M.setPGOReader(std::move(ReaderOrErr.get()));
    }
  }
  
  SILGenModule::~SILGenModule() {
    assert(!TopLevelSGF && "active source file lowering!?");
    M.verify();
  }
  
  static SILDeclRef
  getBridgingFn(Optional<SILDeclRef> &cacheSlot,
                SILGenModule &SGM,
                Identifier moduleName,
                StringRef functionName,
                Optional<std::initializer_list<Type>> inputTypes,
                Optional<Type> outputType) {
    // FIXME: the optionality of outputType and the presence of trustInputTypes
    // are hacks for cases where coming up with those types is complicated, i.e.,
    // when dealing with generic bridging functions.
  
    if (!cacheSlot) {
      ASTContext &ctx = SGM.M.getASTContext();
      ModuleDecl *mod = ctx.getLoadedModule(moduleName);
      if (!mod) {
        SGM.diagnose(SourceLoc(), diag::bridging_module_missing,
                     moduleName.str(), functionName);
        llvm::report_fatal_error("unable to set up the ObjC bridge!");
      }
  
      SmallVector<ValueDecl *, 2> decls;
      mod->lookupValue(/*AccessPath=*/{}, ctx.getIdentifier(functionName),
                       NLKind::QualifiedLookup, decls);
      if (decls.empty()) {
        SGM.diagnose(SourceLoc(), diag::bridging_function_missing,
                     moduleName.str(), functionName);
        llvm::report_fatal_error("unable to set up the ObjC bridge!");
      }
      if (decls.size() != 1) {
        SGM.diagnose(SourceLoc(), diag::bridging_function_overloaded,
                     moduleName.str(), functionName);
        llvm::report_fatal_error("unable to set up the ObjC bridge!");
      }
  
      auto *fd = dyn_cast<FuncDecl>(decls.front());
      if (!fd) {
        SGM.diagnose(SourceLoc(), diag::bridging_function_not_function,
                     moduleName.str(), functionName);
        llvm::report_fatal_error("unable to set up the ObjC bridge!");
      }
  
      assert(fd->hasInterfaceType() && "bridging functions must be type-checked");
  
      // Check that the function takes the expected arguments and returns the
      // expected result type.
      SILDeclRef c(fd);
      auto funcTy = SGM.Types.getConstantFunctionType(c);
      SILFunctionConventions fnConv(funcTy, SGM.M);
  
      if (inputTypes) {
        auto toSILType = [&SGM](Type ty) { return SGM.getLoweredType(ty); };
        if (fnConv.hasIndirectSILResults()
            || funcTy->getNumParameters() != inputTypes->size()
            || !std::equal(
                   fnConv.getParameterSILTypes().begin(),
                   fnConv.getParameterSILTypes().end(),
                   makeTransformIterator(inputTypes->begin(), toSILType))) {
          SGM.diagnose(fd->getLoc(), diag::bridging_function_not_correct_type,
                       moduleName.str(), functionName);
          llvm::report_fatal_error("unable to set up the ObjC bridge!");
        }
      }
  
      if (outputType
          && fnConv.getSingleSILResultType() != SGM.getLoweredType(*outputType)) {
        SGM.diagnose(fd->getLoc(), diag::bridging_function_not_correct_type,
                     moduleName.str(), functionName);
        llvm::report_fatal_error("unable to set up the ObjC bridge!");
      }
  
      cacheSlot = c;
    }
  
    LLVM_DEBUG(llvm::dbgs() << "bridging function "
                            << moduleName << '.' << functionName
                            << " mapped to ";
               cacheSlot->print(llvm::dbgs()));
  
    return *cacheSlot;
  }
  
  #define REQUIRED(X) { Types.get##X##Type() }
  #define OPTIONAL(X) { OptionalType::get(Types.get##X##Type()) }
  #define GENERIC(X) None
  
  #define GET_BRIDGING_FN(Module, FromKind, FromTy, ToKind, ToTy) \
    SILDeclRef SILGenModule::get##FromTy##To##ToTy##Fn() { \
      return getBridgingFn(FromTy##To##ToTy##Fn, *this, \
                           getASTContext().Id_##Module, \
                           "_convert" #FromTy "To" #ToTy, \
                           FromKind(FromTy), \
                           ToKind(ToTy)); \
    }
  
  GET_BRIDGING_FN(Darwin, REQUIRED, Bool, REQUIRED, DarwinBoolean)
  GET_BRIDGING_FN(Darwin, REQUIRED, DarwinBoolean, REQUIRED, Bool)
  GET_BRIDGING_FN(ObjectiveC, REQUIRED, Bool, REQUIRED, ObjCBool)
  GET_BRIDGING_FN(ObjectiveC, REQUIRED, ObjCBool, REQUIRED, Bool)
  GET_BRIDGING_FN(Foundation, OPTIONAL, NSError, REQUIRED, Error)
  GET_BRIDGING_FN(Foundation, REQUIRED, Error, REQUIRED, NSError)
  
  #undef GET_BRIDGING_FN
  #undef REQUIRED
  #undef OPTIONAL
  #undef GENERIC
  
  static FuncDecl *diagnoseMissingIntrinsic(SILGenModule &sgm,
                                            SILLocation loc,
                                            const char *name) {
    sgm.diagnose(loc, diag::bridging_function_missing,
                 sgm.getASTContext().StdlibModuleName.str(), name);
    return nullptr;
  }
  
  #define FUNC_DECL(NAME, ID)                             \
    FuncDecl *SILGenModule::get##NAME(SILLocation loc) {  \
      if (auto fn = getASTContext().get##NAME())   \
        return fn;                                        \
      return diagnoseMissingIntrinsic(*this, loc, ID);    \
    }
  #include "swift/AST/KnownDecls.def"
  
  ProtocolDecl *SILGenModule::getObjectiveCBridgeable(SILLocation loc) {
    if (ObjectiveCBridgeable)
      return *ObjectiveCBridgeable;
  
    // Find the _ObjectiveCBridgeable protocol.
    auto &ctx = getASTContext();
    auto proto = ctx.getProtocol(KnownProtocolKind::ObjectiveCBridgeable);
    if (!proto)
      diagnose(loc, diag::bridging_objcbridgeable_missing);
  
    ObjectiveCBridgeable = proto;
    return proto;
  }
  
  FuncDecl *SILGenModule::getBridgeToObjectiveCRequirement(SILLocation loc) {
    if (BridgeToObjectiveCRequirement)
      return *BridgeToObjectiveCRequirement;
  
    // Find the _ObjectiveCBridgeable protocol.
    auto proto = getObjectiveCBridgeable(loc);
    if (!proto) {
      BridgeToObjectiveCRequirement = nullptr;
      return nullptr;
    }
  
    // Look for _bridgeToObjectiveC().
    auto &ctx = getASTContext();
    FuncDecl *found = nullptr;
    DeclName name(ctx, ctx.Id_bridgeToObjectiveC, llvm::ArrayRef<Identifier>());
    auto flags = OptionSet<NominalTypeDecl::LookupDirectFlags>();
    flags |= NominalTypeDecl::LookupDirectFlags::IgnoreNewExtensions;
    for (auto member : proto->lookupDirect(name, flags)) {
      if (auto func = dyn_cast<FuncDecl>(member)) {
        found = func;
        break;
      }
    }
  
    if (!found)
      diagnose(loc, diag::bridging_objcbridgeable_broken, name);
  
    BridgeToObjectiveCRequirement = found;
    return found;
  }
  
  FuncDecl *SILGenModule::getUnconditionallyBridgeFromObjectiveCRequirement(
      SILLocation loc) {
    if (UnconditionallyBridgeFromObjectiveCRequirement)
      return *UnconditionallyBridgeFromObjectiveCRequirement;
  
    // Find the _ObjectiveCBridgeable protocol.
    auto proto = getObjectiveCBridgeable(loc);
    if (!proto) {
      UnconditionallyBridgeFromObjectiveCRequirement = nullptr;
      return nullptr;
    }
  
    // Look for _bridgeToObjectiveC().
    auto &ctx = getASTContext();
    FuncDecl *found = nullptr;
    DeclName name(ctx, ctx.getIdentifier("_unconditionallyBridgeFromObjectiveC"),
                  llvm::makeArrayRef(Identifier()));
    auto flags = OptionSet<NominalTypeDecl::LookupDirectFlags>();
    flags |= NominalTypeDecl::LookupDirectFlags::IgnoreNewExtensions;
    for (auto member : proto->lookupDirect(name, flags)) {
      if (auto func = dyn_cast<FuncDecl>(member)) {
        found = func;
        break;
      }
    }
  
    if (!found)
      diagnose(loc, diag::bridging_objcbridgeable_broken, name);
  
    UnconditionallyBridgeFromObjectiveCRequirement = found;
    return found;
  }
  
  AssociatedTypeDecl *
  SILGenModule::getBridgedObjectiveCTypeRequirement(SILLocation loc) {
    if (BridgedObjectiveCType)
      return *BridgedObjectiveCType;
  
    // Find the _ObjectiveCBridgeable protocol.
    auto proto = getObjectiveCBridgeable(loc);
    if (!proto) {
      BridgeToObjectiveCRequirement = nullptr;
      return nullptr;
    }
  
    // Look for _bridgeToObjectiveC().
    auto &ctx = getASTContext();
    AssociatedTypeDecl *found = nullptr;
    DeclName name(ctx.Id_ObjectiveCType);
    auto flags = OptionSet<NominalTypeDecl::LookupDirectFlags>();
    flags |= NominalTypeDecl::LookupDirectFlags::IgnoreNewExtensions;
    for (auto member : proto->lookupDirect(name, flags)) {
      if (auto assocType = dyn_cast<AssociatedTypeDecl>(member)) {
        found = assocType;
        break;
      }
    }
  
    if (!found)
      diagnose(loc, diag::bridging_objcbridgeable_broken, name);
  
    BridgedObjectiveCType = found;
    return found;
  }
  
  ProtocolConformance *
  SILGenModule::getConformanceToObjectiveCBridgeable(SILLocation loc, Type type) {
    auto proto = getObjectiveCBridgeable(loc);
    if (!proto) return nullptr;
  
    // Find the conformance to _ObjectiveCBridgeable.
    auto result = SwiftModule->lookupConformance(type, proto);
    if (result) return result->getConcrete();
    return nullptr;
  }
  
  ProtocolDecl *SILGenModule::getBridgedStoredNSError(SILLocation loc) {
    if (BridgedStoredNSError)
      return *BridgedStoredNSError;
  
    // Find the _BridgedStoredNSError protocol.
    auto &ctx = getASTContext();
    auto proto = ctx.getProtocol(KnownProtocolKind::BridgedStoredNSError);
    BridgedStoredNSError = proto;
    return proto;
  }
  
  VarDecl *SILGenModule::getNSErrorRequirement(SILLocation loc) {
    if (NSErrorRequirement)
      return *NSErrorRequirement;
  
    // Find the _BridgedStoredNSError protocol.
    auto proto = getBridgedStoredNSError(loc);
    if (!proto) {
      NSErrorRequirement = nullptr;
      return nullptr;
    }
  
    // Look for _nsError.
    auto &ctx = getASTContext();
    VarDecl *found = nullptr;
    auto flags = OptionSet<NominalTypeDecl::LookupDirectFlags>();
    flags |= NominalTypeDecl::LookupDirectFlags::IgnoreNewExtensions;
    for (auto member : proto->lookupDirect(ctx.Id_nsError, flags)) {
      if (auto var = dyn_cast<VarDecl>(member)) {
        found = var;
        break;
      }
    }
  
    NSErrorRequirement = found;
    return found;
  }
  
  Optional<ProtocolConformanceRef>
  SILGenModule::getConformanceToBridgedStoredNSError(SILLocation loc, Type type) {
    auto proto = getBridgedStoredNSError(loc);
    if (!proto) return None;
  
    // Find the conformance to _BridgedStoredNSError.
    return SwiftModule->lookupConformance(type, proto);
  }
  
  ProtocolConformance *SILGenModule::getNSErrorConformanceToError() {
    if (NSErrorConformanceToError)
      return *NSErrorConformanceToError;
  
    auto &ctx = getASTContext();
    auto nsError = ctx.getNSErrorDecl();
    if (!nsError) {
      NSErrorConformanceToError = nullptr;
      return nullptr;
    }
  
    auto error = ctx.getErrorDecl();
    if (!error) {
      NSErrorConformanceToError = nullptr;
      return nullptr;
    }
  
    auto conformance =
      SwiftModule->lookupConformance(nsError->getDeclaredInterfaceType(),
                                     cast<ProtocolDecl>(error));
  
    if (conformance && conformance->isConcrete())
      NSErrorConformanceToError = conformance->getConcrete();
    else
      NSErrorConformanceToError = nullptr;
    return *NSErrorConformanceToError;
  }
  
  SILFunction *
  SILGenModule::getKeyPathProjectionCoroutine(bool isReadAccess,
                                              KeyPathTypeKind typeKind) {
    bool isBaseInout;
    bool isResultInout;
    StringRef functionName;
    NominalTypeDecl *keyPathDecl;
    if (isReadAccess) {
      assert(typeKind == KPTK_KeyPath ||
             typeKind == KPTK_WritableKeyPath ||
             typeKind == KPTK_ReferenceWritableKeyPath);
      functionName = "swift_readAtKeyPath";
      isBaseInout = false;
      isResultInout = false;
      keyPathDecl = getASTContext().getKeyPathDecl();
    } else if (typeKind == KPTK_WritableKeyPath) {
      functionName = "swift_modifyAtWritableKeyPath";
      isBaseInout = true;
      isResultInout = true;
      keyPathDecl = getASTContext().getWritableKeyPathDecl();
    } else if (typeKind == KPTK_ReferenceWritableKeyPath) {
      functionName = "swift_modifyAtReferenceWritableKeyPath";
      isBaseInout = false;
      isResultInout = true;
      keyPathDecl = getASTContext().getReferenceWritableKeyPathDecl();
    } else {
      llvm_unreachable("bad combination");
    }
  
    auto fn = M.lookUpFunction(functionName);
    if (fn) return fn;
  
    auto rootType = CanGenericTypeParamType::get(0, 0, getASTContext());
    auto valueType = CanGenericTypeParamType::get(0, 1, getASTContext());
  
    // Build the generic signature <A, B>.
    auto sig = GenericSignature::get({rootType, valueType}, {});
  
    auto keyPathTy = BoundGenericType::get(keyPathDecl, Type(),
                                           { rootType, valueType })
      ->getCanonicalType();
  
    // (@in_guaranteed/@inout Root, @guaranteed KeyPath<Root, Value>)
    SILParameterInfo params[] = {
      { rootType,
        isBaseInout ? ParameterConvention::Indirect_Inout
                    : ParameterConvention::Indirect_In_Guaranteed },
      { keyPathTy, ParameterConvention::Direct_Guaranteed },
    };
  
    // -> @yields @in_guaranteed/@inout Value
    SILYieldInfo yields[] = {
      { valueType,
        isResultInout ? ParameterConvention::Indirect_Inout
                      : ParameterConvention::Indirect_In_Guaranteed },
    };
  
    auto extInfo =
      SILFunctionType::ExtInfo(SILFunctionTypeRepresentation::Thin,
                               /*pseudogeneric*/false,
                               /*non-escaping*/false);
  
    auto functionTy = SILFunctionType::get(sig, extInfo,
                                           SILCoroutineKind::YieldOnce,
                                           ParameterConvention::Direct_Unowned,
                                           params,
                                           yields,
                                           /*results*/ {},
                                           /*error result*/ {},
                                           getASTContext());
  
    auto env = sig->createGenericEnvironment();
  
    SILGenFunctionBuilder builder(*this);
    fn = builder.createFunction(SILLinkage::PublicExternal,
                                functionName,
                                functionTy,
                                env,
                                /*location*/ None,
                                IsNotBare,
                                IsNotTransparent,
                                IsNotSerialized,
                                IsNotDynamic);
  
    return fn;
  }
  
  
  SILFunction *SILGenModule::emitTopLevelFunction(SILLocation Loc) {
    ASTContext &C = getASTContext();
    auto extInfo = SILFunctionType::ExtInfo()
      .withRepresentation(SILFunctionType::Representation::CFunctionPointer);
  
    // Use standard library types if we have them; otherwise, fall back to
    // builtins.
    CanType Int32Ty;
    if (auto Int32Decl = C.getInt32Decl()) {
      Int32Ty = Int32Decl->getDeclaredInterfaceType()->getCanonicalType();
    } else {
      Int32Ty = CanType(BuiltinIntegerType::get(32, C));
    }
  
    CanType PtrPtrInt8Ty = C.TheRawPointerType;
    if (auto PointerDecl = C.getUnsafeMutablePointerDecl()) {
      if (auto Int8Decl = C.getInt8Decl()) {
        Type Int8Ty = Int8Decl->getDeclaredInterfaceType();
        Type PointerInt8Ty = BoundGenericType::get(PointerDecl,
                                                   nullptr,
                                                   Int8Ty);
        Type OptPointerInt8Ty = OptionalType::get(PointerInt8Ty);
        PtrPtrInt8Ty = BoundGenericType::get(PointerDecl,
                                             nullptr,
                                             OptPointerInt8Ty)
          ->getCanonicalType();
      }
    }
  
    SILParameterInfo params[] = {
      SILParameterInfo(Int32Ty, ParameterConvention::Direct_Unowned),
      SILParameterInfo(PtrPtrInt8Ty, ParameterConvention::Direct_Unowned),
    };
  
    CanSILFunctionType topLevelType = SILFunctionType::get(nullptr, extInfo,
                                     SILCoroutineKind::None,
                                     ParameterConvention::Direct_Unowned,
                                     params, /*yields*/ {},
                                     SILResultInfo(Int32Ty,
                                                   ResultConvention::Unowned),
                                     None,
                                     C);
  
    SILGenFunctionBuilder builder(*this);
    return builder.createFunction(
        SILLinkage::Public, SWIFT_ENTRY_POINT_FUNCTION, topLevelType, nullptr,
        Loc, IsBare, IsNotTransparent, IsNotSerialized, IsNotDynamic,
        ProfileCounter(), IsNotThunk, SubclassScope::NotApplicable);
  }
  
  SILFunction *SILGenModule::getEmittedFunction(SILDeclRef constant,
                                                ForDefinition_t forDefinition) {
    auto found = emittedFunctions.find(constant);
    if (found != emittedFunctions.end()) {
      SILFunction *F = found->second;
      if (forDefinition) {
        // In all the cases where getConstantLinkage returns something
        // different for ForDefinition, it returns an available-externally
        // linkage.
        if (isAvailableExternally(F->getLinkage())) {
          F->setLinkage(constant.getLinkage(ForDefinition));
        }
      }
      return F;
    }
  
    return nullptr;
  }
  
  static SILFunction *getFunctionToInsertAfter(SILGenModule &SGM,
                                               SILDeclRef insertAfter) {
    // If the decl ref was emitted, emit after its function.
    while (insertAfter) {
      auto found = SGM.emittedFunctions.find(insertAfter);
      if (found != SGM.emittedFunctions.end()) {
        return found->second;
      }
  
      // Otherwise, try to insert after the function we would be transitively
      // be inserted after.
      auto foundDelayed = SGM.delayedFunctions.find(insertAfter);
      if (foundDelayed != SGM.delayedFunctions.end()) {
        insertAfter = foundDelayed->second.insertAfter;
      } else {
        break;
      }
    }
  
    // If the decl ref is nil, just insert at the beginning.
    return nullptr;
  }
  
  static bool hasSILBody(FuncDecl *fd) {
    return fd->getBody(/*canSynthesize=*/false);
  }
  
  static bool haveProfiledAssociatedFunction(SILDeclRef constant) {
    return constant.isDefaultArgGenerator() || constant.isForeign ||
           constant.isCurried;
  }
  
  SILProfiler *
  SILGenModule::getOrCreateProfilerForConstructors(DeclContext *ctx,
                                                   ConstructorDecl *cd) {
    const auto &Opts = M.getOptions();
    if (!Opts.GenerateProfile && Opts.UseProfile.empty())
      return nullptr;
  
    // Profile nominal types and extensions separately, as they may live in
    // distinct files. For extensions, just pass in the constructor, because
    // there are no stored property initializers to visit.
    Decl *decl = nullptr;
    if (isa<ExtensionDecl>(ctx))
      decl = cd;
    else
      decl = ctx->getSelfNominalTypeDecl();
    assert(decl && "No decl available for profiling in this context");
  
    SILProfiler *&profiler = constructorProfilers[decl];
    if (!profiler)
      profiler = SILProfiler::create(M, ForDefinition, decl);
    return profiler;
  }
  
  /// Set up the function for profiling instrumentation.
  static void setUpForProfiling(SILDeclRef constant, SILFunction *F,
                                ForDefinition_t forDefinition) {
    if (!forDefinition)
      return;
  
    ASTNode profiledNode;
    if (!haveProfiledAssociatedFunction(constant)) {
      if (constant.hasDecl()) {
        if (auto *fd = constant.getFuncDecl()) {
          if (hasSILBody(fd)) {
            F->createProfiler(fd, forDefinition);
            profiledNode = fd->getBody(/*canSynthesize=*/false);
          }
        }
      } else if (auto *ace = constant.getAbstractClosureExpr()) {
        F->createProfiler(ace, forDefinition);
        profiledNode = ace;
      }
      // Set the function entry count for PGO.
      if (SILProfiler *SP = F->getProfiler())
        F->setEntryCount(SP->getExecutionCount(profiledNode));
    }
  }
  
  SILFunction *SILGenModule::getFunction(SILDeclRef constant,
                                         ForDefinition_t forDefinition) {
    // If we already emitted the function, return it (potentially preparing it
    // for definition).
    if (auto emitted = getEmittedFunction(constant, forDefinition)) {
      setUpForProfiling(constant, emitted, forDefinition);
      return emitted;
    }
  
    // Note: Do not provide any SILLocation. You can set it afterwards.
    SILGenFunctionBuilder builder(*this);
    auto *F = builder.getOrCreateFunction(constant.hasDecl() ? constant.getDecl()
                                                             : (Decl *)nullptr,
                                          constant, forDefinition);
    setUpForProfiling(constant, F, forDefinition);
  
    assert(F && "SILFunction should have been defined");
  
    emittedFunctions[constant] = F;
  
    // If we delayed emitting this function previously, we need it now.
    auto foundDelayed = delayedFunctions.find(constant);
    if (foundDelayed != delayedFunctions.end()) {
      // Move the function to its proper place within the module.
      M.functions.remove(F);
      SILFunction *insertAfter = getFunctionToInsertAfter(*this,
                                                foundDelayed->second.insertAfter);
      if (!insertAfter) {
        M.functions.push_front(F);
      } else {
        M.functions.insertAfter(insertAfter->getIterator(), F);
      }
  
      forcedFunctions.push_back(*foundDelayed);
      delayedFunctions.erase(foundDelayed);
    } else {
      // We would have registered a delayed function as "last emitted" when we
      // enqueued. If the function wasn't delayed, then we're emitting it now.
      lastEmittedFunction = constant;
    }
  
    return F;
  }
  
  bool SILGenModule::hasFunction(SILDeclRef constant) {
    return emittedFunctions.count(constant);
  }
  
  void SILGenModule::visitFuncDecl(FuncDecl *fd) { emitFunction(fd); }
  
  /// Emit a function now, if it's externally usable or has been referenced in
  /// the current TU, or remember how to emit it later if not.
  template<typename /*void (SILFunction*)*/ Fn>
  static void emitOrDelayFunction(SILGenModule &SGM,
                                  SILDeclRef constant,
                                  Fn &&emitter,
                                  bool forceEmission = false) {
    auto emitAfter = SGM.lastEmittedFunction;
  
    SILFunction *f = nullptr;
  
    // If the function is explicit or may be externally referenced, or if we're
    // forcing emission, we must emit it.
    bool mayDelay;
    // Shared thunks and Clang-imported definitions can always be delayed.
    if (constant.isThunk() || constant.isClangImported()) {
      mayDelay = !forceEmission;
    // Implicit decls may be delayed if they can't be used externally.
    } else {
      auto linkage = constant.getLinkage(ForDefinition);
      mayDelay = !forceEmission &&
                 (constant.isImplicit() &&
                  !isPossiblyUsedExternally(linkage, SGM.M.isWholeModule()));
    }
  
    // Avoid emitting a delayable definition if it hasn't already been referenced.
    if (mayDelay)
      f = SGM.getEmittedFunction(constant, ForDefinition);
    else
      f = SGM.getFunction(constant, ForDefinition);
  
    // If we don't want to emit now, remember how for later.
    if (!f) {
      SGM.delayedFunctions.insert({constant, {emitAfter,
                                              std::forward<Fn>(emitter)}});
      // Even though we didn't emit the function now, update the
      // lastEmittedFunction so that we preserve the original ordering that
      // the symbols would have been emitted in.
      SGM.lastEmittedFunction = constant;
      return;
    }
  
    emitter(f);
  }
  
  void SILGenModule::preEmitFunction(SILDeclRef constant,
                                llvm::PointerUnion<ValueDecl *,
                                                   Expr *> astNode,
                                     SILFunction *F,
                                     SILLocation Loc) {
    // By default, use the astNode to create the location.
    if (Loc.isNull()) {
      if (auto *decl = astNode.get<ValueDecl *>())
        Loc = RegularLocation(decl);
      else
        Loc = RegularLocation(astNode.get<Expr *>());
    }
  
    assert(F->empty() && "already emitted function?!");
  
    if (F->getLoweredFunctionType()->isPolymorphic())
      F->setGenericEnvironment(Types.getConstantGenericEnvironment(constant));
  
    // Create a debug scope for the function using astNode as source location.
    F->setDebugScope(new (M) SILDebugScope(Loc, F));
  
    LLVM_DEBUG(llvm::dbgs() << "lowering ";
               F->printName(llvm::dbgs());
               llvm::dbgs() << " : ";
               F->getLoweredType().print(llvm::dbgs());
               llvm::dbgs() << '\n';
               if (astNode) {
                 if (auto *decl = astNode.dyn_cast<ValueDecl *>()) {
                   decl->dump(llvm::dbgs());
                 } else {
                   astNode.get<Expr *>()->dump(llvm::dbgs());
                   llvm::dbgs() << "\n";
                 }
                 llvm::dbgs() << '\n';
               });
  }
  
  void SILGenModule::postEmitFunction(SILDeclRef constant,
                                      SILFunction *F) {
    assert(!F->isExternalDeclaration() && "did not emit any function body?!");
    LLVM_DEBUG(llvm::dbgs() << "lowered sil:\n";
               F->print(llvm::dbgs()));
    F->verify();
  }
  
  void SILGenModule::
  emitMarkFunctionEscapeForTopLevelCodeGlobals(SILLocation loc,
                                               const CaptureInfo &captureInfo) {
    assert(TopLevelSGF && TopLevelSGF->B.hasValidInsertionPoint()
           && "no valid code generator for top-level function?!");
  
    SmallVector<SILValue, 4> Captures;
    
    for (auto capture : captureInfo.getCaptures()) {
      // Decls captured by value don't escape.
      auto It = TopLevelSGF->VarLocs.find(capture.getDecl());
      if (It == TopLevelSGF->VarLocs.end() ||
          !It->getSecond().value->getType().isAddress())
        continue;
      
      Captures.push_back(It->second.value);
    }
    
    if (!Captures.empty())
      TopLevelSGF->B.createMarkFunctionEscape(loc, Captures);
  }
  
  void SILGenModule::emitAbstractFuncDecl(AbstractFunctionDecl *AFD) {
    // Emit any default argument generators.
    emitDefaultArgGenerators(AFD, AFD->getParameters());
  
    // If this is a function at global scope, it may close over a global variable.
    // If we're emitting top-level code, then emit a "mark_function_escape" that
    // lists the captured global variables so that definite initialization can
    // reason about this escape point.
    if (!AFD->getDeclContext()->isLocalContext() &&
        TopLevelSGF && TopLevelSGF->B.hasValidInsertionPoint()) {
      emitMarkFunctionEscapeForTopLevelCodeGlobals(AFD, AFD->getCaptureInfo());
    }
    
    // If the declaration is exported as a C function, emit its native-to-foreign
    // thunk too, if it wasn't already forced.
    if (AFD->getAttrs().hasAttribute<CDeclAttr>()) {
      auto thunk = SILDeclRef(AFD).asForeign();
      if (!hasFunction(thunk))
        emitNativeToForeignThunk(thunk);
    }
  }
  
  void SILGenModule::emitFunction(FuncDecl *fd) {
    SILDeclRef::Loc decl = fd;
  
    emitAbstractFuncDecl(fd);
  
    if (hasSILBody(fd)) {
      FrontendStatsTracer Tracer(getASTContext().Stats, "SILGen-funcdecl", fd);
      PrettyStackTraceDecl stackTrace("emitting SIL for", fd);
  
      SILDeclRef constant(decl);
  
      bool ForCoverageMapping = doesASTRequireProfiling(M, fd);
  
      emitOrDelayFunction(*this, constant, [this,constant,fd](SILFunction *f){
        preEmitFunction(constant, fd, f, fd);
        PrettyStackTraceSILFunction X("silgen emitFunction", f);
        SILGenFunction(*this, *f, fd).emitFunction(fd);
        postEmitFunction(constant, f);
      }, /*forceEmission=*/ForCoverageMapping);
    }
  }
  
  void SILGenModule::addGlobalVariable(VarDecl *global) {
    // We create SILGlobalVariable here.
    getSILGlobalVariable(global, ForDefinition);
  }
  
  void SILGenModule::emitConstructor(ConstructorDecl *decl) {
    // FIXME: Handle 'self' like any other argument here.
    // Emit any default argument getter functions.
    emitAbstractFuncDecl(decl);
  
    // We never emit constructors in protocols.
    if (isa<ProtocolDecl>(decl->getDeclContext()))
      return;
  
    // Always-unavailable imported constructors are factory methods
    // that have been imported as constructors and then hidden by an
    // imported init method.
    if (decl->hasClangNode() &&
        decl->getAttrs().isUnavailable(decl->getASTContext()))
      return;
  
    SILDeclRef constant(decl);
    DeclContext *declCtx = decl->getDeclContext();
  
    bool ForCoverageMapping = doesASTRequireProfiling(M, decl);
  
    if (declCtx->getSelfClassDecl()) {
      // Designated initializers for classes, as well as @objc convenience
      // initializers, have have separate entry points for allocation and
      // initialization.
      if (decl->isDesignatedInit() || decl->isObjC()) {
        emitOrDelayFunction(
            *this, constant, [this, constant, decl](SILFunction *f) {
              preEmitFunction(constant, decl, f, decl);
              PrettyStackTraceSILFunction X("silgen emitConstructor", f);
              SILGenFunction(*this, *f, decl).emitClassConstructorAllocator(decl);
              postEmitFunction(constant, f);
            });
  
        // Constructors may not have bodies if they've been imported, or if they've
        // been parsed from a parseable interface.
        if (decl->hasBody()) {
          SILDeclRef initConstant(decl, SILDeclRef::Kind::Initializer);
          emitOrDelayFunction(
              *this, initConstant,
              [this, initConstant, decl, declCtx](SILFunction *initF) {
                preEmitFunction(initConstant, decl, initF, decl);
                PrettyStackTraceSILFunction X("silgen constructor initializer",
                                              initF);
                initF->setProfiler(
                    getOrCreateProfilerForConstructors(declCtx, decl));
                SILGenFunction(*this, *initF, decl)
                  .emitClassConstructorInitializer(decl);
                postEmitFunction(initConstant, initF);
              },
              /*forceEmission=*/ForCoverageMapping);
        }
        return;
      }
    }
  
    // Struct and enum constructors do everything in a single function, as do
    // non-@objc convenience initializers for classes.
    if (decl->hasBody()) {
      emitOrDelayFunction(
          *this, constant, [this, constant, decl, declCtx](SILFunction *f) {
            preEmitFunction(constant, decl, f, decl);
            PrettyStackTraceSILFunction X("silgen emitConstructor", f);
            f->setProfiler(getOrCreateProfilerForConstructors(declCtx, decl));
            SILGenFunction(*this, *f, decl).emitValueConstructor(decl);
            postEmitFunction(constant, f);
          });
    }
  }
  
  void SILGenModule::emitEnumConstructor(EnumElementDecl *decl) {
    // Enum element constructors are always emitted by need, so don't need
    // delayed emission.
    SILDeclRef constant(decl);
    SILFunction *f = getFunction(constant, ForDefinition);
    preEmitFunction(constant, decl, f, decl);
    PrettyStackTraceSILFunction X("silgen enum constructor", f);
    SILGenFunction(*this, *f, decl->getDeclContext()).emitEnumConstructor(decl);
    postEmitFunction(constant, f);
  }
  
  SILFunction *SILGenModule::emitClosure(AbstractClosureExpr *ce) {
    SILDeclRef constant(ce);
    SILFunction *f = getFunction(constant, ForDefinition);
  
    // Generate the closure function, if we haven't already.
    //
    // We may visit the same closure expr multiple times in some cases,
    // for instance, when closures appear as in-line initializers of stored
    // properties. In these cases the closure will be emitted into every
    // initializer of the containing type.
    if (!f->isExternalDeclaration())
      return f;
  
    preEmitFunction(constant, ce, f, ce);
    PrettyStackTraceSILFunction X("silgen closureexpr", f);
    SILGenFunction(*this, *f, ce).emitClosure(ce);
    postEmitFunction(constant, f);
    return f;
  }
  
  /// Determine whether the given class requires a separate instance
  /// variable initialization method.
  static bool requiresIVarInitialization(SILGenModule &SGM, ClassDecl *cd) {
    if (!cd->requiresStoredPropertyInits())
      return false;
  
    for (Decl *member : cd->getMembers()) {
      auto pbd = dyn_cast<PatternBindingDecl>(member);
      if (!pbd) continue;
  
      for (auto entry : pbd->getPatternList())
        if (entry.getNonLazyInit())
          return true;
    }
  
    return false;
  }
  
  bool SILGenModule::hasNonTrivialIVars(ClassDecl *cd) {
    for (Decl *member : cd->getMembers()) {
      auto *vd = dyn_cast<VarDecl>(member);
      if (!vd || !vd->hasStorage()) continue;
  
      const TypeLowering &ti = Types.getTypeLowering(vd->getType());
      if (!ti.isTrivial())
        return true;
    }
  
    return false;
  }
  
  bool SILGenModule::requiresIVarDestroyer(ClassDecl *cd) {
    // Only needed if we have non-trivial ivars, we're not a root class, and
    // the superclass is not @objc.
    return (hasNonTrivialIVars(cd) &&
            cd->getSuperclass() &&
            !cd->getSuperclass()->getClassOrBoundGenericClass()->hasClangNode());
  }
  
  /// TODO: This needs a better name.
  void SILGenModule::emitObjCAllocatorDestructor(ClassDecl *cd,
                                                 DestructorDecl *dd) {
    // Emit the native deallocating destructor for -dealloc.
    // Destructors are a necessary part of class metadata, so can't be delayed.
    if (dd->hasBody()) {
      SILDeclRef dealloc(dd, SILDeclRef::Kind::Deallocator);
      SILFunction *f = getFunction(dealloc, ForDefinition);
      preEmitFunction(dealloc, dd, f, dd);
      PrettyStackTraceSILFunction X("silgen emitDestructor -dealloc", f);
      f->createProfiler(dd, ForDefinition);
      SILGenFunction(*this, *f, dd).emitObjCDestructor(dealloc);
      postEmitFunction(dealloc, f);
    }
  
    // Emit the Objective-C -dealloc entry point if it has
    // something to do beyond messaging the superclass's -dealloc.
    if (dd->hasBody() && dd->getBody()->getNumElements() != 0)
      emitObjCDestructorThunk(dd);
  
    // Emit the ivar initializer, if needed.
    if (requiresIVarInitialization(*this, cd)) {
      auto ivarInitializer = SILDeclRef(cd, SILDeclRef::Kind::IVarInitializer)
        .asForeign();
      SILFunction *f = getFunction(ivarInitializer, ForDefinition);
      preEmitFunction(ivarInitializer, dd, f, dd);
      PrettyStackTraceSILFunction X("silgen emitDestructor ivar initializer", f);
      SILGenFunction(*this, *f, cd).emitIVarInitializer(ivarInitializer);
      postEmitFunction(ivarInitializer, f);
    }
  
    // Emit the ivar destroyer, if needed.
    if (hasNonTrivialIVars(cd)) {
      auto ivarDestroyer = SILDeclRef(cd, SILDeclRef::Kind::IVarDestroyer)
        .asForeign();
      SILFunction *f = getFunction(ivarDestroyer, ForDefinition);
      preEmitFunction(ivarDestroyer, dd, f, dd);
      PrettyStackTraceSILFunction X("silgen emitDestructor ivar destroyer", f);
      SILGenFunction(*this, *f, cd).emitIVarDestroyer(ivarDestroyer);
      postEmitFunction(ivarDestroyer, f);
    }
  }
  
  void SILGenModule::emitDestructor(ClassDecl *cd, DestructorDecl *dd) {
    emitAbstractFuncDecl(dd);
    
    // Emit the ivar destroyer, if needed.
    if (requiresIVarDestroyer(cd)) {
      SILDeclRef ivarDestroyer(cd, SILDeclRef::Kind::IVarDestroyer);
      SILFunction *f = getFunction(ivarDestroyer, ForDefinition);
      preEmitFunction(ivarDestroyer, dd, f, dd);
      PrettyStackTraceSILFunction X("silgen emitDestructor ivar destroyer", f);
      SILGenFunction(*this, *f, dd).emitIVarDestroyer(ivarDestroyer);
      postEmitFunction(ivarDestroyer, f);
    }
  
    // If the class would use the Objective-C allocator, only emit -dealloc.
    if (usesObjCAllocator(cd)) {
      emitObjCAllocatorDestructor(cd, dd);
      return;
    }
  
    // Emit the destroying destructor.
    // Destructors are a necessary part of class metadata, so can't be delayed.
    if (dd->hasBody()) {
      SILDeclRef destroyer(dd, SILDeclRef::Kind::Destroyer);
      SILFunction *f = getFunction(destroyer, ForDefinition);
      preEmitFunction(destroyer, dd, f, dd);
      PrettyStackTraceSILFunction X("silgen emitDestroyingDestructor", f);
      SILGenFunction(*this, *f, dd).emitDestroyingDestructor(dd);
      f->setDebugScope(new (M) SILDebugScope(dd, f));
      postEmitFunction(destroyer, f);
    }
  
    // Emit the deallocating destructor.
    {
      SILDeclRef deallocator(dd, SILDeclRef::Kind::Deallocator);
      SILFunction *f = getFunction(deallocator, ForDefinition);
      preEmitFunction(deallocator, dd, f, dd);
      PrettyStackTraceSILFunction X("silgen emitDeallocatingDestructor", f);
      f->createProfiler(dd, ForDefinition);
      SILGenFunction(*this, *f, dd).emitDeallocatingDestructor(dd);
      f->setDebugScope(new (M) SILDebugScope(dd, f));
      postEmitFunction(deallocator, f);
    }
  }
  
  void SILGenModule::emitDefaultArgGenerator(SILDeclRef constant, Expr *arg,
                                             DefaultArgumentKind kind,
                                             DeclContext *initDC) {
    switch (kind) {
    case DefaultArgumentKind::None:
      llvm_unreachable("No default argument here?");
  
    case DefaultArgumentKind::Normal:
      break;
  
    case DefaultArgumentKind::Inherited:
      return;
  
    case DefaultArgumentKind::Column:
    case DefaultArgumentKind::File:
    case DefaultArgumentKind::Line:
    case DefaultArgumentKind::Function:
    case DefaultArgumentKind::DSOHandle:
    case DefaultArgumentKind::NilLiteral:
    case DefaultArgumentKind::EmptyArray:
    case DefaultArgumentKind::EmptyDictionary:
      return;
    }
  
    emitOrDelayFunction(*this, constant,
        [this,constant,arg,initDC](SILFunction *f) {
      preEmitFunction(constant, arg, f, arg);
      PrettyStackTraceSILFunction X("silgen emitDefaultArgGenerator ", f);
      SILGenFunction SGF(*this, *f, initDC);
      SGF.emitGeneratorFunction(constant, arg);
      postEmitFunction(constant, f);
    });
  }
  
  void SILGenModule::
  emitStoredPropertyInitialization(PatternBindingDecl *pbd, unsigned i) {
    const PatternBindingEntry &pbdEntry = pbd->getPatternList()[i];
    auto *var = pbdEntry.getAnchoringVarDecl();
    auto *init = pbdEntry.getInit();
    auto *initDC = pbdEntry.getInitContext();
    assert(!pbdEntry.isInitializerLazy());
  
    SILDeclRef constant(var, SILDeclRef::Kind::StoredPropertyInitializer);
    emitOrDelayFunction(*this, constant,
                        [this,constant,init,initDC,var](SILFunction *f) {
      preEmitFunction(constant, init, f, init);
      PrettyStackTraceSILFunction X("silgen emitStoredPropertyInitialization", f);
  
      // Inherit a profiler instance from the constructor.
      f->setProfiler(
          getOrCreateProfilerForConstructors(var->getDeclContext(), nullptr));
  
      SILGenFunction(*this, *f, initDC).emitGeneratorFunction(constant, init);
      postEmitFunction(constant, f);
    });
  }
  
  SILFunction *SILGenModule::emitLazyGlobalInitializer(StringRef funcName,
                                                   PatternBindingDecl *binding,
                                                       unsigned pbdEntry) {
    ASTContext &C = M.getASTContext();
    auto *onceBuiltin =
        cast<FuncDecl>(getBuiltinValueDecl(C, C.getIdentifier("once")));
    auto blockParam = onceBuiltin->getParameters()->get(1);
    auto *type = blockParam->getType()->castTo<FunctionType>();
    Type initType = FunctionType::get({}, TupleType::getEmpty(C),
                                      type->getExtInfo());
    auto initSILType = getLoweredType(initType).castTo<SILFunctionType>();
  
    SILGenFunctionBuilder builder(*this);
    auto *f = builder.createFunction(
        SILLinkage::Private, funcName, initSILType, nullptr, SILLocation(binding),
        IsNotBare, IsNotTransparent, IsNotSerialized, IsNotDynamic);
    f->setDebugScope(new (M) SILDebugScope(RegularLocation(binding), f));
    auto dc = binding->getDeclContext();
    SILGenFunction(*this, *f, dc).emitLazyGlobalInitializer(binding, pbdEntry);
    f->verify();
  
    return f;
  }
  
  void SILGenModule::emitGlobalAccessor(VarDecl *global,
                                        SILGlobalVariable *onceToken,
                                        SILFunction *onceFunc) {
    SILDeclRef accessor(global, SILDeclRef::Kind::GlobalAccessor);
    emitOrDelayFunction(*this, accessor,
                        [this,accessor,global,onceToken,onceFunc](SILFunction *f){
      preEmitFunction(accessor, global, f, global);
      PrettyStackTraceSILFunction X("silgen emitGlobalAccessor", f);
      SILGenFunction(*this, *f, global->getDeclContext())
        .emitGlobalAccessor(global, onceToken, onceFunc);
      postEmitFunction(accessor, f);
    });
  }
  
  void SILGenModule::emitDefaultArgGenerators(SILDeclRef::Loc decl,
                                              ParameterList *paramList) {
    unsigned index = 0;
    for (auto param : *paramList) {
      if (auto defaultArg = param->getDefaultValue())
        emitDefaultArgGenerator(SILDeclRef::getDefaultArgGenerator(decl, index),
                                defaultArg, param->getDefaultArgumentKind(),
                                param->getDefaultArgumentInitContext());
      ++index;
    }
  }
  
  void SILGenModule::emitObjCMethodThunk(FuncDecl *method) {
    auto thunk = SILDeclRef(method).asForeign();
  
    // Don't emit the thunk if it already exists.
    if (hasFunction(thunk))
      return;
  
    // ObjC entry points are always externally usable, so can't be delay-emitted.
  
    SILFunction *f = getFunction(thunk, ForDefinition);
    preEmitFunction(thunk, method, f, method);
    PrettyStackTraceSILFunction X("silgen emitObjCMethodThunk", f);
    f->setBare(IsBare);
    f->setThunk(IsThunk);
    SILGenFunction(*this, *f, method).emitNativeToForeignThunk(thunk);
    postEmitFunction(thunk, f);
  }
  
  void SILGenModule::emitObjCPropertyMethodThunks(AbstractStorageDecl *prop) {
    // If we don't actually need an entry point for the getter, do nothing.
    if (!prop->getGetter() || !requiresObjCMethodEntryPoint(prop->getGetter()))
      return;
  
    auto getter = SILDeclRef(prop->getGetter(), SILDeclRef::Kind::Func)
      .asForeign();
  
    // Don't emit the thunks if they already exist.
    if (hasFunction(getter))
      return;
  
    RegularLocation ThunkBodyLoc(prop);
    ThunkBodyLoc.markAutoGenerated();
    // ObjC entry points are always externally usable, so emitting can't be
    // delayed.
    {
      SILFunction *f = getFunction(getter, ForDefinition);
      preEmitFunction(getter, prop, f, ThunkBodyLoc);
      PrettyStackTraceSILFunction X("silgen objc property getter thunk", f);
      f->setBare(IsBare);
      f->setThunk(IsThunk);
      SILGenFunction(*this, *f, prop->getGetter())
        .emitNativeToForeignThunk(getter);
      postEmitFunction(getter, f);
    }
  
    if (!prop->isSettable(prop->getDeclContext()))
      return;
  
    // FIXME: Add proper location.
    auto setter = SILDeclRef(prop->getSetter(), SILDeclRef::Kind::Func)
      .asForeign();
  
    SILFunction *f = getFunction(setter, ForDefinition);
    preEmitFunction(setter, prop, f, ThunkBodyLoc);
    PrettyStackTraceSILFunction X("silgen objc property setter thunk", f);
    f->setBare(IsBare);
    f->setThunk(IsThunk);
    SILGenFunction(*this, *f, prop->getSetter()).emitNativeToForeignThunk(setter);
    postEmitFunction(setter, f);
  }
  
  void SILGenModule::emitObjCConstructorThunk(ConstructorDecl *constructor) {
    auto thunk = SILDeclRef(constructor, SILDeclRef::Kind::Initializer)
      .asForeign();
  
    // Don't emit the thunk if it already exists.
    if (hasFunction(thunk))
      return;
    // ObjC entry points are always externally usable, so emitting can't be
    // delayed.
  
    SILFunction *f = getFunction(thunk, ForDefinition);
    preEmitFunction(thunk, constructor, f, constructor);
    PrettyStackTraceSILFunction X("silgen objc constructor thunk", f);
    f->setBare(IsBare);
    f->setThunk(IsThunk);
    SILGenFunction(*this, *f, constructor).emitNativeToForeignThunk(thunk);
    postEmitFunction(thunk, f);
  }
  
  void SILGenModule::emitObjCDestructorThunk(DestructorDecl *destructor) {
    auto thunk = SILDeclRef(destructor, SILDeclRef::Kind::Deallocator)
      .asForeign();
  
    // Don't emit the thunk if it already exists.
    if (hasFunction(thunk))
      return;
    SILFunction *f = getFunction(thunk, ForDefinition);
    preEmitFunction(thunk, destructor, f, destructor);
    PrettyStackTraceSILFunction X("silgen objc destructor thunk", f);
    f->setBare(IsBare);
    f->setThunk(IsThunk);
    SILGenFunction(*this, *f, destructor).emitNativeToForeignThunk(thunk);
    postEmitFunction(thunk, f);
  }
  
  void SILGenModule::visitPatternBindingDecl(PatternBindingDecl *pd) {
    assert(!TopLevelSGF && "script mode PBDs should be in TopLevelCodeDecls");
    for (unsigned i = 0, e = pd->getNumPatternEntries(); i != e; ++i)
      if (pd->getNonLazyInit(i))
        emitGlobalInitialization(pd, i);
  }
  
  void SILGenModule::visitVarDecl(VarDecl *vd) {
    if (vd->hasStorage())
      addGlobalVariable(vd);
  
    // Emit the variable's opaque accessors.
    vd->visitExpectedOpaqueAccessors([&](AccessorKind kind) {
      auto accessor = vd->getAccessor(kind);
      if (!accessor) return;
  
      // Only emit the accessor if it wasn't added to the surrounding decl
      // list by the parser.  We can test that easily by looking at the impl
      // info, since all of these accessors have a corresponding access kind
      // whose impl should definitely point at the accessor if it was parsed.
      //
      // This is an unfortunate formation rule, but it's easier than messing
      // with the invariants for now.
      bool shouldEmit = [&] {
        auto impl = vd->getImplInfo();
        switch (kind) {
        case AccessorKind::Get:
          return impl.getReadImpl() != ReadImplKind::Get;
        case AccessorKind::Read:
          return impl.getReadImpl() != ReadImplKind::Read;
        case AccessorKind::Set:
          return impl.getWriteImpl() != WriteImplKind::Set &&
                 impl.getWriteImpl() != WriteImplKind::StoredWithObservers;
        case AccessorKind::Modify:
          return impl.getReadWriteImpl() != ReadWriteImplKind::Modify;
  #define ACCESSOR(ID) \
        case AccessorKind::ID:
  #define OPAQUE_ACCESSOR(ID, KEYWORD)
  #include "swift/AST/AccessorKinds.def"
          llvm_unreachable("not an opaque accessor");
        }
      }();
      if (!shouldEmit) return;
  
      emitFunction(accessor);
    });
  
    tryEmitPropertyDescriptor(vd);
  }
  
  bool
  SILGenModule::canStorageUseStoredKeyPathComponent(AbstractStorageDecl *decl,
                                                    ResilienceExpansion expansion) {
    // If the declaration is resilient, we have to treat the component as
    // computed.
    if (decl->isResilient(M.getSwiftModule(), expansion))
      return false;
  
    auto strategy = decl->getAccessStrategy(AccessSemantics::Ordinary,
                                            decl->supportsMutation()
                                              ? AccessKind::ReadWrite
                                              : AccessKind::Read,
                                            M.getSwiftModule(),
                                            expansion);
    switch (strategy.getKind()) {
    case AccessStrategy::Storage: {
      // Keypaths rely on accessors to handle the special behavior of weak or
      // unowned properties.
      if (decl->getInterfaceType()->is<ReferenceStorageType>())
        return false;
      // If the stored value would need to be reabstracted in fully opaque
      // context, then we have to treat the component as computed.
      auto componentObjTy = decl->getValueInterfaceType();
      if (auto genericEnv =
                decl->getInnermostDeclContext()->getGenericEnvironmentOfContext())
        componentObjTy = genericEnv->mapTypeIntoContext(componentObjTy);
      auto storageTy = M.Types.getSubstitutedStorageType(decl, componentObjTy);
      auto opaqueTy =
        M.Types.getLoweredType(AbstractionPattern::getOpaque(), componentObjTy);
      
      return storageTy.getAddressType() == opaqueTy.getAddressType();
    }
    case AccessStrategy::DirectToAccessor:
    case AccessStrategy::DispatchToAccessor:
    case AccessStrategy::MaterializeToTemporary:
      return false;
    }
    llvm_unreachable("unhandled strategy");
  }
  
  static bool canStorageUseTrivialDescriptor(SILGenModule &SGM,
                                             AbstractStorageDecl *decl) {
    // A property can use a trivial property descriptor if the key path component
    // that an external module would form given publicly-exported information
    // about the property is never equivalent to the canonical component for the
    // key path.
    // This means that the property isn't stored (without promising to be always
    // stored) and doesn't have a setter with less-than-public visibility.
    auto expansion = ResilienceExpansion::Maximal;
  
    switch (SGM.M.getSwiftModule()->getResilienceStrategy()) {
    case ResilienceStrategy::Default: {
      if (SGM.canStorageUseStoredKeyPathComponent(decl, expansion)) {
        // External modules can't directly access storage, unless this is a
        // property in a fixed-layout type.
        return !decl->isFormallyResilient();
      }
      // If the type is computed and doesn't have a setter that's hidden from
      // the public, then external components can form the canonical key path
      // without our help.
      auto setter = decl->getSetter();
      if (setter == nullptr)
        return true;
      
      auto setterLinkage = SILDeclRef(setter, SILDeclRef::Kind::Func)
        .getLinkage(NotForDefinition);
      
      if (setterLinkage == SILLinkage::PublicExternal
          || setterLinkage == SILLinkage::Public)
        return true;
      
      return false;
    }
    case ResilienceStrategy::Resilient: {
      // A resilient module needs to handle binaries compiled against its older
      // versions. This means we have to be a bit more conservative, since in
      // earlier versions, a settable property may have withheld the setter,
      // or a fixed-layout type may not have been.
      // Without availability information, only get-only computed properties
      // can resiliently use trivial descriptors.
      return !SGM.canStorageUseStoredKeyPathComponent(decl, expansion)
        && decl->getSetter() == nullptr;
    }
    }
    llvm_unreachable("unhandled strategy");
  }
  
  void SILGenModule::tryEmitPropertyDescriptor(AbstractStorageDecl *decl) {
    // TODO: Key path code emission doesn't handle opaque values properly yet.
    if (!SILModuleConventions(M).useLoweredAddresses())
      return;
    
    if (!decl->exportsPropertyDescriptor())
      return;
  
    PrettyStackTraceDecl stackTrace("emitting property descriptor for", decl);
  
    Type baseTy;
    if (decl->getDeclContext()->isTypeContext()) {
      // TODO: Static properties should eventually be referenceable as
      // keypaths from T.Type -> Element, viz `baseTy = MetatypeType::get(baseTy)`
      assert(!decl->isStatic());
      
      baseTy = decl->getDeclContext()->getSelfInterfaceType()
                   ->getCanonicalType(decl->getInnermostDeclContext()
                                          ->getGenericSignatureOfContext());
    } else {
      // TODO: Global variables should eventually be referenceable as
      // key paths from (), viz. baseTy = TupleType::getEmpty(getASTContext());
      llvm_unreachable("should not export a property descriptor yet");
    }
  
    auto genericEnv = decl->getInnermostDeclContext()
                          ->getGenericEnvironmentOfContext();
    unsigned baseOperand = 0;
    bool needsGenericContext = true;
    
    if (canStorageUseTrivialDescriptor(*this, decl)) {
      (void)SILProperty::create(M, /*serialized*/ false, decl, None);
      return;
    }
    
    SubstitutionMap subs;
    if (genericEnv)
      subs = genericEnv->getForwardingSubstitutionMap();
    
    auto component = emitKeyPathComponentForDecl(SILLocation(decl),
                                                 genericEnv,
                                                 ResilienceExpansion::Maximal,
                                                 baseOperand, needsGenericContext,
                                                 subs, decl, {},
                                                 baseTy->getCanonicalType(),
                                                 /*property descriptor*/ true);
    
    (void)SILProperty::create(M, /*serialized*/ false, decl, component);
  }
  
  void SILGenModule::visitIfConfigDecl(IfConfigDecl *ICD) {
    // Nothing to do for these kinds of decls - anything active has been added
    // to the enclosing declaration.
  }
  
  void SILGenModule::visitPoundDiagnosticDecl(PoundDiagnosticDecl *PDD) {
    // Nothing to do for #error/#warning; they've already been emitted.
  }
  
  void SILGenModule::visitTopLevelCodeDecl(TopLevelCodeDecl *td) {
    assert(TopLevelSGF && "top-level code in a non-main source file!");
  
    if (!TopLevelSGF->B.hasValidInsertionPoint())
      return;
  
    // A single SILFunction may be used to lower multiple top-level decls. When
    // this happens, fresh profile counters must be assigned to the new decl.
    TopLevelSGF->F.discardProfiler();
    TopLevelSGF->F.createProfiler(td, ForDefinition);
  
    TopLevelSGF->emitProfilerIncrement(td->getBody());
   
    DebugScope DS(*TopLevelSGF, CleanupLocation(td));
  
    for (auto &ESD : td->getBody()->getElements()) {
      if (!TopLevelSGF->B.hasValidInsertionPoint()) {
        if (auto *S = ESD.dyn_cast<Stmt*>()) {
          if (S->isImplicit())
            continue;
        } else if (auto *E = ESD.dyn_cast<Expr*>()) {
          if (E->isImplicit())
            continue;
        }
  
        diagnose(ESD.getStartLoc(), diag::unreachable_code);
        // There's no point in trying to emit anything else.
        return;
      }
  
      if (auto *S = ESD.dyn_cast<Stmt*>()) {
        TopLevelSGF->emitStmt(S);
      } else if (auto *E = ESD.dyn_cast<Expr*>()) {
        TopLevelSGF->emitIgnoredExpr(E);
      } else {
        TopLevelSGF->visit(ESD.get<Decl*>());
      }
    }
  }
  
  void SILGenModule::useConformance(ProtocolConformanceRef conformanceRef) {
    // We don't need to emit dependent conformances.
    if (conformanceRef.isAbstract()) 
      return;
  
    auto conformance = conformanceRef.getConcrete();
    auto root = conformance->getRootNormalConformance();
  
    // If we already emitted this witness table, we don't need to track the fact
    // we need it.
    if (emittedWitnessTables.count(root))
      return;
  
    // If we delayed emitting this witness table, force it.
    auto foundDelayed = delayedConformances.find(root);
    if (foundDelayed != delayedConformances.end()) {
      forcedConformances.push_back(*foundDelayed);
      delayedConformances.erase(foundDelayed);
      return;
    }
  
    // Otherwise, just remember the fact we used this conformance.
    usedConformances.insert(root);
  }
  
  void SILGenModule::useConformancesFromSubstitutions(
                                                  const SubstitutionMap subs) {
    for (auto conf : subs.getConformances())
      useConformance(conf);
  }
  
  namespace {
  
  /// An RAII class to scope source file codegen.
  class SourceFileScope {
    SILGenModule &sgm;
    SourceFile *sf;
    Optional<Scope> scope;
  public:
    SourceFileScope(SILGenModule &sgm, SourceFile *sf) : sgm(sgm), sf(sf) {
      // If this is the script-mode file for the module, create a toplevel.
      if (sf->isScriptMode()) {
        assert(!sgm.TopLevelSGF && "already emitted toplevel?!");
        assert(!sgm.M.lookUpFunction(SWIFT_ENTRY_POINT_FUNCTION)
               && "already emitted toplevel?!");
  
        RegularLocation TopLevelLoc = RegularLocation::getModuleLocation();
        SILFunction *toplevel = sgm.emitTopLevelFunction(TopLevelLoc);
  
        // Assign a debug scope pointing into the void to the top level function.
        toplevel->setDebugScope(new (sgm.M) SILDebugScope(TopLevelLoc, toplevel));
  
        sgm.TopLevelSGF = new SILGenFunction(sgm, *toplevel, sf);
        sgm.TopLevelSGF->MagicFunctionName = sgm.SwiftModule->getName();
        auto moduleCleanupLoc = CleanupLocation::getModuleCleanupLocation();
        sgm.TopLevelSGF->prepareEpilog(Type(), true, moduleCleanupLoc);
  
        // Create the argc and argv arguments.
        auto prologueLoc = RegularLocation::getModuleLocation();
        prologueLoc.markAsPrologue();
        auto entry = sgm.TopLevelSGF->B.getInsertionBB();
        auto paramTypeIter =
            sgm.TopLevelSGF->F.getConventions().getParameterSILTypes().begin();
        entry->createFunctionArgument(*paramTypeIter);
        entry->createFunctionArgument(*std::next(paramTypeIter));
  
        scope.emplace(sgm.TopLevelSGF->Cleanups, moduleCleanupLoc);
      }
    }
  
    ~SourceFileScope() {
      if (sgm.TopLevelSGF) {
        scope.reset();
  
        // Unregister the top-level function emitter.
        auto &SGF = *sgm.TopLevelSGF;
        sgm.TopLevelSGF = nullptr;
  
        // Write out the epilog.
        auto moduleLoc = RegularLocation::getModuleLocation();
        moduleLoc.markAutoGenerated();
        auto returnInfo = SGF.emitEpilogBB(moduleLoc);
        auto returnLoc = returnInfo.second;
        returnLoc.markAutoGenerated();
  
        SILType returnType = SGF.F.getConventions().getSingleSILResultType();
        auto emitTopLevelReturnValue = [&](unsigned value) -> SILValue {
          // Create an integer literal for the value.
          auto litType = SILType::getBuiltinIntegerType(32, sgm.getASTContext());
          SILValue retValue =
            SGF.B.createIntegerLiteral(moduleLoc, litType, value);
  
          // Wrap that in a struct if necessary.
          if (litType != returnType) {
            retValue = SGF.B.createStruct(moduleLoc, returnType, retValue);
          }
          return retValue;
        };
  
        // Fallthrough should signal a normal exit by returning 0.
        SILValue returnValue;
        if (SGF.B.hasValidInsertionPoint())
          returnValue = emitTopLevelReturnValue(0);
  
        // Handle the implicit rethrow block.
        auto rethrowBB = SGF.ThrowDest.getBlock();
        SGF.ThrowDest = JumpDest::invalid();
  
        // If the rethrow block wasn't actually used, just remove it.
        if (rethrowBB->pred_empty()) {
          SGF.eraseBasicBlock(rethrowBB);
  
        // Otherwise, we need to produce a unified return block.
        } else {
          auto returnBB = SGF.createBasicBlock();
          if (SGF.B.hasValidInsertionPoint())
            SGF.B.createBranch(returnLoc, returnBB, returnValue);
          returnValue =
              returnBB->createPhiArgument(returnType, ValueOwnershipKind::Owned);
          SGF.B.emitBlock(returnBB);
  
          // Emit the rethrow block.
          SILGenSavedInsertionPoint savedIP(SGF, rethrowBB,
                                            FunctionSection::Postmatter);
  
          // Log the error.
          SILValue error = rethrowBB->getArgument(0);
          SGF.B.createBuiltin(moduleLoc,
                              sgm.getASTContext().getIdentifier("errorInMain"),
                              sgm.Types.getEmptyTupleType(), {}, {error});
  
          // Then end the lifetime of the error.
          //
          // We do this to appease the ownership verifier. We do not care about
          // actually destroying the value since we are going to immediately exit,
          // so this saves us a slight bit of code-size since end_lifetime is
          // stripped out after ownership is removed.
          SGF.B.createEndLifetime(moduleLoc, error);
  
          // Signal an abnormal exit by returning 1.
          SGF.Cleanups.emitCleanupsForReturn(CleanupLocation::get(moduleLoc),
                                             IsForUnwind);
          SGF.B.createBranch(returnLoc, returnBB, emitTopLevelReturnValue(1));
        }
  
        // Return.
        if (SGF.B.hasValidInsertionPoint())
          SGF.B.createReturn(returnLoc, returnValue);
  
        // Okay, we're done emitting the top-level function; destroy the
        // emitter and verify the result.
        SILFunction *toplevel = &SGF.getFunction();
        delete &SGF;
  
        LLVM_DEBUG(llvm::dbgs() << "lowered toplevel sil:\n";
                   toplevel->print(llvm::dbgs()));
        toplevel->verify();
      }
  
      // If the source file contains an artificial main, emit the implicit
      // toplevel code.
      if (auto mainClass = sf->getMainClass()) {
        assert(!sgm.M.lookUpFunction(SWIFT_ENTRY_POINT_FUNCTION)
               && "already emitted toplevel before main class?!");
  
        RegularLocation TopLevelLoc = RegularLocation::getModuleLocation();
        SILFunction *toplevel = sgm.emitTopLevelFunction(TopLevelLoc);
  
        // Assign a debug scope pointing into the void to the top level function.
        toplevel->setDebugScope(new (sgm.M) SILDebugScope(TopLevelLoc, toplevel));
  
        // Create the argc and argv arguments.
        SILGenFunction SGF(sgm, *toplevel, sf);
        auto entry = SGF.B.getInsertionBB();
        auto paramTypeIter =
            SGF.F.getConventions().getParameterSILTypes().begin();
        entry->createFunctionArgument(*paramTypeIter);
        entry->createFunctionArgument(*std::next(paramTypeIter));
        SGF.emitArtificialTopLevel(mainClass);
      }
    }
  };
  
  } // end anonymous namespace
  
  void SILGenModule::emitSourceFile(SourceFile *sf) {
    SourceFileScope scope(*this, sf);
    FrontendStatsTracer StatsTracer(getASTContext().Stats, "SILgen-file", sf);
    for (Decl *D : sf->Decls) {
      FrontendStatsTracer StatsTracer(getASTContext().Stats, "SILgen-decl", D);
      visit(D);
    }
  
    for (Decl *D : sf->LocalTypeDecls) {
      FrontendStatsTracer StatsTracer(getASTContext().Stats, "SILgen-tydecl", D);
      visit(D);
    }
  
    // Mark any conformances as "used".
    for (auto conformance : sf->getUsedConformances())
      useConformance(ProtocolConformanceRef(conformance));
  }
  
  //===----------------------------------------------------------------------===//
  // SILModule::constructSIL method implementation
  //===----------------------------------------------------------------------===//
  
  std::unique_ptr<SILModule>
  SILModule::constructSIL(ModuleDecl *mod, SILOptions &options, FileUnit *SF) {
    SharedTimer timer("SILGen");
    const DeclContext *DC;
    if (SF) {
      DC = SF;
    } else {
      DC = mod;
    }
  
    std::unique_ptr<SILModule> M(
        new SILModule(mod, options, DC, /*wholeModule*/ SF == nullptr));
    SILGenModule SGM(*M, mod);
  
    if (SF) {
      if (auto *file = dyn_cast<SourceFile>(SF)) {
        SGM.emitSourceFile(file);
      } else if (auto *file = dyn_cast<SerializedASTFile>(SF)) {
        if (file->isSIB())
          M->getSILLoader()->getAllForModule(mod->getName(), file);
      }
    } else {
      for (auto file : mod->getFiles()) {
        auto nextSF = dyn_cast<SourceFile>(file);
        if (!nextSF || nextSF->ASTStage != SourceFile::TypeChecked)
          continue;
        SGM.emitSourceFile(nextSF);
      }
  
      // Also make sure to process any intermediate files that may contain SIL
      bool hasSIB = std::any_of(mod->getFiles().begin(),
                                mod->getFiles().end(),
                                [](const FileUnit *File) -> bool {
        auto *SASTF = dyn_cast<SerializedASTFile>(File);
        return SASTF && SASTF->isSIB();
      });
      if (hasSIB)
        M->getSILLoader()->getAllForModule(mod->getName(), nullptr);
    }
  
    // Emit external definitions used by this module.
    for (size_t i = 0, e = mod->getASTContext().LastCheckedExternalDefinition;
         i != e; ++i) {
      auto def = mod->getASTContext().ExternalDefinitions[i];
      SGM.emitExternalDefinition(def);
    }
  
    // Emit any delayed definitions that were forced.
    // Emitting these may in turn force more definitions, so we have to take care
    // to keep pumping the queues.
    while (!SGM.forcedFunctions.empty()
           || !SGM.forcedConformances.empty()) {
      while (!SGM.forcedFunctions.empty()) {
        auto &front = SGM.forcedFunctions.front();
        front.second.emitter(SGM.getFunction(front.first, ForDefinition));
        SGM.forcedFunctions.pop_front();
      }
      while (!SGM.forcedConformances.empty()) {
        auto &front = SGM.forcedConformances.front();
        SGM.getWitnessTable(front.first);
        SGM.forcedConformances.pop_front();
      }
    }
  
    return M;
  }
  
  std::unique_ptr<SILModule>
  swift::performSILGeneration(ModuleDecl *mod, SILOptions &options) {
    return SILModule::constructSIL(mod, options, nullptr);
  }
  
  std::unique_ptr<SILModule>
  swift::performSILGeneration(FileUnit &sf, SILOptions &options) {
    return SILModule::constructSIL(sf.getParentModule(), options, &sf);
  }
  