//===--- CGException.cpp - Emit LLVM Code for C++ exceptions ----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This contains code dealing with C++ exception related code generation.
//
//===----------------------------------------------------------------------===//

#include "CGCXXABI.h"
#include "CGCleanup.h"
#include "CGObjCRuntime.h"
#include "CodeGenFunction.h"
#include "ConstantEmitter.h"
#include "TargetInfo.h"
#include "clang/AST/Mangle.h"
#include "clang/AST/StmtCXX.h"
#include "clang/AST/StmtObjC.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/Basic/DiagnosticSema.h"
#include "clang/Basic/TargetBuiltins.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/IntrinsicsWebAssembly.h"
#include "llvm/Support/SaveAndRestore.h"

using namespace clang;
using namespace CodeGen;

static llvm::FunctionCallee getFreeExceptionFn(CodeGenModule &CGM) {
  // void __cxa_free_exception(void *thrown_exception);

  llvm::FunctionType *FTy =
    llvm::FunctionType::get(CGM.VoidTy, CGM.Int8PtrTy, /*isVarArg=*/false);

  return CGM.CreateRuntimeFunction(FTy, "__cxa_free_exception");
}

static llvm::FunctionCallee getSehTryBeginFn(CodeGenModule &CGM) {
  llvm::FunctionType *FTy =
      llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
  return CGM.CreateRuntimeFunction(FTy, "llvm.seh.try.begin");
}

static llvm::FunctionCallee getSehTryEndFn(CodeGenModule &CGM) {
  llvm::FunctionType *FTy =
      llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
  return CGM.CreateRuntimeFunction(FTy, "llvm.seh.try.end");
}

static llvm::FunctionCallee getUnexpectedFn(CodeGenModule &CGM) {
  // void __cxa_call_unexpected(void *thrown_exception);

  llvm::FunctionType *FTy =
    llvm::FunctionType::get(CGM.VoidTy, CGM.Int8PtrTy, /*isVarArg=*/false);

  return CGM.CreateRuntimeFunction(FTy, "__cxa_call_unexpected");
}

llvm::FunctionCallee CodeGenModule::getTerminateFn() {
  // void __terminate();

  llvm::FunctionType *FTy =
    llvm::FunctionType::get(VoidTy, /*isVarArg=*/false);

  StringRef name;

  // In C++, use std::terminate().
  if (getLangOpts().CPlusPlus &&
      getTarget().getCXXABI().isItaniumFamily()) {
    name = "_ZSt9terminatev";
  } else if (getLangOpts().CPlusPlus &&
             getTarget().getCXXABI().isMicrosoft()) {
    if (getLangOpts().isCompatibleWithMSVC(LangOptions::MSVC2015))
      name = "__std_terminate";
    else
      name = "?terminate@@YAXXZ";
  } else if (getLangOpts().ObjC &&
             getLangOpts().ObjCRuntime.hasTerminate())
    name = "objc_terminate";
  else
    name = "abort";
  return CreateRuntimeFunction(FTy, name);
}

static llvm::FunctionCallee getCatchallRethrowFn(CodeGenModule &CGM,
                                                 StringRef Name) {
  llvm::FunctionType *FTy =
    llvm::FunctionType::get(CGM.VoidTy, CGM.Int8PtrTy, /*isVarArg=*/false);

  return CGM.CreateRuntimeFunction(FTy, Name);
}

const EHPersonality EHPersonality::GNU_C = { "__gcc_personality_v0", nullptr };
const EHPersonality
EHPersonality::GNU_C_SJLJ = { "__gcc_personality_sj0", nullptr };
const EHPersonality
EHPersonality::GNU_C_SEH = { "__gcc_personality_seh0", nullptr };
const EHPersonality
EHPersonality::NeXT_ObjC = { "__objc_personality_v0", nullptr };
const EHPersonality
EHPersonality::GNU_CPlusPlus = { "__gxx_personality_v0", nullptr };
const EHPersonality
EHPersonality::GNU_CPlusPlus_SJLJ = { "__gxx_personality_sj0", nullptr };
const EHPersonality
EHPersonality::GNU_CPlusPlus_SEH = { "__gxx_personality_seh0", nullptr };
const EHPersonality
EHPersonality::GNU_ObjC = {"__gnu_objc_personality_v0", "objc_exception_throw"};
const EHPersonality
EHPersonality::GNU_ObjC_SJLJ = {"__gnu_objc_personality_sj0", "objc_exception_throw"};
const EHPersonality
EHPersonality::GNU_ObjC_SEH = {"__gnu_objc_personality_seh0", "objc_exception_throw"};
const EHPersonality
EHPersonality::GNU_ObjCXX = { "__gnustep_objcxx_personality_v0", nullptr };
const EHPersonality
EHPersonality::GNUstep_ObjC = { "__gnustep_objc_personality_v0", nullptr };
const EHPersonality
EHPersonality::MSVC_except_handler = { "_except_handler3", nullptr };
const EHPersonality
EHPersonality::MSVC_C_specific_handler = { "__C_specific_handler", nullptr };
const EHPersonality
EHPersonality::MSVC_CxxFrameHandler3 = { "__CxxFrameHandler3", nullptr };
const EHPersonality
EHPersonality::GNU_Wasm_CPlusPlus = { "__gxx_wasm_personality_v0", nullptr };
const EHPersonality EHPersonality::XL_CPlusPlus = {"__xlcxx_personality_v1",
                                                   nullptr};

static const EHPersonality &getCPersonality(const TargetInfo &Target,
                                            const LangOptions &L) {
  const llvm::Triple &T = Target.getTriple();
  if (T.isWindowsMSVCEnvironment())
    return EHPersonality::MSVC_CxxFrameHandler3;
  if (L.hasSjLjExceptions())
    return EHPersonality::GNU_C_SJLJ;
  if (L.hasDWARFExceptions())
    return EHPersonality::GNU_C;
  if (L.hasSEHExceptions())
    return EHPersonality::GNU_C_SEH;
  return EHPersonality::GNU_C;
}

static const EHPersonality &getObjCPersonality(const TargetInfo &Target,
                                               const LangOptions &L) {
  const llvm::Triple &T = Target.getTriple();
  if (T.isWindowsMSVCEnvironment())
    return EHPersonality::MSVC_CxxFrameHandler3;

  switch (L.ObjCRuntime.getKind()) {
  case ObjCRuntime::FragileMacOSX:
    return getCPersonality(Target, L);
  case ObjCRuntime::MacOSX:
  case ObjCRuntime::iOS:
  case ObjCRuntime::WatchOS:
    return EHPersonality::NeXT_ObjC;
  case ObjCRuntime::GNUstep:
    if (L.ObjCRuntime.getVersion() >= VersionTuple(1, 7))
      return EHPersonality::GNUstep_ObjC;
    LLVM_FALLTHROUGH;
  case ObjCRuntime::GCC:
  case ObjCRuntime::ObjFW:
    if (L.hasSjLjExceptions())
      return EHPersonality::GNU_ObjC_SJLJ;
    if (L.hasSEHExceptions())
      return EHPersonality::GNU_ObjC_SEH;
    return EHPersonality::GNU_ObjC;
  }
  llvm_unreachable("bad runtime kind");
}

static const EHPersonality &getCXXPersonality(const TargetInfo &Target,
                                              const LangOptions &L) {
  const llvm::Triple &T = Target.getTriple();
  if (T.isWindowsMSVCEnvironment())
    return EHPersonality::MSVC_CxxFrameHandler3;
  if (T.isOSAIX())
    return EHPersonality::XL_CPlusPlus;
  if (L.hasSjLjExceptions())
    return EHPersonality::GNU_CPlusPlus_SJLJ;
  if (L.hasDWARFExceptions())
    return EHPersonality::GNU_CPlusPlus;
  if (L.hasSEHExceptions())
    return EHPersonality::GNU_CPlusPlus_SEH;
  if (L.hasWasmExceptions())
    return EHPersonality::GNU_Wasm_CPlusPlus;
  return EHPersonality::GNU_CPlusPlus;
}

/// Determines the personality function to use when both C++
/// and Objective-C exceptions are being caught.
static const EHPersonality &getObjCXXPersonality(const TargetInfo &Target,
                                                 const LangOptions &L) {
  if (Target.getTriple().isWindowsMSVCEnvironment())
    return EHPersonality::MSVC_CxxFrameHandler3;

  switch (L.ObjCRuntime.getKind()) {
  // In the fragile ABI, just use C++ exception handling and hope
  // they're not doing crazy exception mixing.
  case ObjCRuntime::FragileMacOSX:
    return getCXXPersonality(Target, L);

  // The ObjC personality defers to the C++ personality for non-ObjC
  // handlers.  Unlike the C++ case, we use the same personality
  // function on targets using (backend-driven) SJLJ EH.
  case ObjCRuntime::MacOSX:
  case ObjCRuntime::iOS:
  case ObjCRuntime::WatchOS:
    return getObjCPersonality(Target, L);

  case ObjCRuntime::GNUstep:
    return EHPersonality::GNU_ObjCXX;

  // The GCC runtime's personality function inherently doesn't support
  // mixed EH.  Use the ObjC personality just to avoid returning null.
  case ObjCRuntime::GCC:
  case ObjCRuntime::ObjFW:
    return getObjCPersonality(Target, L);
  }
  llvm_unreachable("bad runtime kind");
}

static const EHPersonality &getSEHPersonalityMSVC(const llvm::Triple &T) {
  if (T.getArch() == llvm::Triple::x86)
    return EHPersonality::MSVC_except_handler;
  return EHPersonality::MSVC_C_specific_handler;
}

const EHPersonality &EHPersonality::get(CodeGenModule &CGM,
                                        const FunctionDecl *FD) {
  const llvm::Triple &T = CGM.getTarget().getTriple();
  const LangOptions &L = CGM.getLangOpts();
  const TargetInfo &Target = CGM.getTarget();

  // Functions using SEH get an SEH personality.
  if (FD && FD->usesSEHTry())
    return getSEHPersonalityMSVC(T);

  if (L.ObjC)
    return L.CPlusPlus ? getObjCXXPersonality(Target, L)
                       : getObjCPersonality(Target, L);
  return L.CPlusPlus ? getCXXPersonality(Target, L)
                     : getCPersonality(Target, L);
}

const EHPersonality &EHPersonality::get(CodeGenFunction &CGF) {
  const auto *FD = CGF.CurCodeDecl;
  // For outlined finallys and filters, use the SEH personality in case they
  // contain more SEH. This mostly only affects finallys. Filters could
  // hypothetically use gnu statement expressions to sneak in nested SEH.
  FD = FD ? FD : CGF.CurSEHParent;
  return get(CGF.CGM, dyn_cast_or_null<FunctionDecl>(FD));
}

static llvm::FunctionCallee getPersonalityFn(CodeGenModule &CGM,
                                             const EHPersonality &Personality) {
  return CGM.CreateRuntimeFunction(llvm::FunctionType::get(CGM.Int32Ty, true),
                                   Personality.PersonalityFn,
                                   llvm::AttributeList(), /*Local=*/true);
}

static llvm::Constant *getOpaquePersonalityFn(CodeGenModule &CGM,
                                        const EHPersonality &Personality) {
  llvm::FunctionCallee Fn = getPersonalityFn(CGM, Personality);
  llvm::PointerType* Int8PtrTy = llvm::PointerType::get(
      llvm::Type::getInt8Ty(CGM.getLLVMContext()),
      CGM.getDataLayout().getProgramAddressSpace());

  return llvm::ConstantExpr::getBitCast(cast<llvm::Constant>(Fn.getCallee()),
                                        Int8PtrTy);
}

/// Check whether a landingpad instruction only uses C++ features.
static bool LandingPadHasOnlyCXXUses(llvm::LandingPadInst *LPI) {
  for (unsigned I = 0, E = LPI->getNumClauses(); I != E; ++I) {
    // Look for something that would've been returned by the ObjC
    // runtime's GetEHType() method.
    llvm::Value *Val = LPI->getClause(I)->stripPointerCasts();
    if (LPI->isCatch(I)) {
      // Check if the catch value has the ObjC prefix.
      if (llvm::GlobalVariable *GV = dyn_cast<llvm::GlobalVariable>(Val))
        // ObjC EH selector entries are always global variables with
        // names starting like this.
        if (GV->getName().startswith("OBJC_EHTYPE"))
          return false;
    } else {
      // Check if any of the filter values have the ObjC prefix.
      llvm::Constant *CVal = cast<llvm::Constant>(Val);
      for (llvm::User::op_iterator
              II = CVal->op_begin(), IE = CVal->op_end(); II != IE; ++II) {
        if (llvm::GlobalVariable *GV =
            cast<llvm::GlobalVariable>((*II)->stripPointerCasts()))
          // ObjC EH selector entries are always global variables with
          // names starting like this.
          if (GV->getName().startswith("OBJC_EHTYPE"))
            return false;
      }
    }
  }
  return true;
}

/// Check whether a personality function could reasonably be swapped
/// for a C++ personality function.
static bool PersonalityHasOnlyCXXUses(llvm::Constant *Fn) {
  for (llvm::User *U : Fn->users()) {
    // Conditionally white-list bitcasts.
    if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(U)) {
      if (CE->getOpcode() != llvm::Instruction::BitCast) return false;
      if (!PersonalityHasOnlyCXXUses(CE))
        return false;
      continue;
    }

    // Otherwise it must be a function.
    llvm::Function *F = dyn_cast<llvm::Function>(U);
    if (!F) return false;

    for (auto BB = F->begin(), E = F->end(); BB != E; ++BB) {
      if (BB->isLandingPad())
        if (!LandingPadHasOnlyCXXUses(BB->getLandingPadInst()))
          return false;
    }
  }

  return true;
}

/// Try to use the C++ personality function in ObjC++.  Not doing this
/// can cause some incompatibilities with gcc, which is more
/// aggressive about only using the ObjC++ personality in a function
/// when it really needs it.
void CodeGenModule::SimplifyPersonality() {
  // If we're not in ObjC++ -fexceptions, there's nothing to do.
  if (!LangOpts.CPlusPlus || !LangOpts.ObjC || !LangOpts.Exceptions)
    return;

  // Both the problem this endeavors to fix and the way the logic
  // above works is specific to the NeXT runtime.
  if (!LangOpts.ObjCRuntime.isNeXTFamily())
    return;

  const EHPersonality &ObjCXX = EHPersonality::get(*this, /*FD=*/nullptr);
  const EHPersonality &CXX = getCXXPersonality(getTarget(), LangOpts);
  if (&ObjCXX == &CXX)
    return;

  assert(std::strcmp(ObjCXX.PersonalityFn, CXX.PersonalityFn) != 0 &&
         "Different EHPersonalities using the same personality function.");

  llvm::Function *Fn = getModule().getFunction(ObjCXX.PersonalityFn);

  // Nothing to do if it's unused.
  if (!Fn || Fn->use_empty()) return;

  // Can't do the optimization if it has non-C++ uses.
  if (!PersonalityHasOnlyCXXUses(Fn)) return;

  // Create the C++ personality function and kill off the old
  // function.
  llvm::FunctionCallee CXXFn = getPersonalityFn(*this, CXX);

  // This can happen if the user is screwing with us.
  if (Fn->getType() != CXXFn.getCallee()->getType())
    return;

  Fn->replaceAllUsesWith(CXXFn.getCallee());
  Fn->eraseFromParent();
}

/// Returns the value to inject into a selector to indicate the
/// presence of a catch-all.
static llvm::Constant *getCatchAllValue(CodeGenFunction &CGF) {
  // Possibly we should use @llvm.eh.catch.all.value here.
  return llvm::ConstantPointerNull::get(CGF.Int8PtrTy);
}

namespace {
  /// A cleanup to free the exception object if its initialization
  /// throws.
  struct FreeException final : EHScopeStack::Cleanup {
    llvm::Value *exn;
    FreeException(llvm::Value *exn) : exn(exn) {}
    void Emit(CodeGenFunction &CGF, Flags flags) override {
      CGF.EmitNounwindRuntimeCall(getFreeExceptionFn(CGF.CGM), exn);
    }
  };
} // end anonymous namespace

// Emits an exception expression into the given location.  This
// differs from EmitAnyExprToMem only in that, if a final copy-ctor
// call is required, an exception within that copy ctor causes
// std::terminate to be invoked.
void CodeGenFunction::EmitAnyExprToExn(const Expr *e, Address addr) {
  // Make sure the exception object is cleaned up if there's an
  // exception during initialization.
  pushFullExprCleanup<FreeException>(EHCleanup, addr.getPointer());
  EHScopeStack::stable_iterator cleanup = EHStack.stable_begin();

  // __cxa_allocate_exception returns a void*;  we need to cast this
  // to the appropriate type for the object.
  llvm::Type *ty = ConvertTypeForMem(e->getType())->getPointerTo();
  Address typedAddr = Builder.CreateBitCast(addr, ty);

  // FIXME: this isn't quite right!  If there's a final unelided call
  // to a copy constructor, then according to [except.terminate]p1 we
  // must call std::terminate() if that constructor throws, because
  // technically that copy occurs after the exception expression is
  // evaluated but before the exception is caught.  But the best way
  // to handle that is to teach EmitAggExpr to do the final copy
  // differently if it can't be elided.
  EmitAnyExprToMem(e, typedAddr, e->getType().getQualifiers(),
                   /*IsInit*/ true);

  // Deactivate the cleanup block.
  DeactivateCleanupBlock(cleanup,
                         cast<llvm::Instruction>(typedAddr.getPointer()));
}

Address CodeGenFunction::getExceptionSlot() {
  if (!ExceptionSlot)
    ExceptionSlot = CreateTempAlloca(Int8PtrTy, "exn.slot");
  return Address(ExceptionSlot, getPointerAlign());
}

Address CodeGenFunction::getEHSelectorSlot() {
  if (!EHSelectorSlot)
    EHSelectorSlot = CreateTempAlloca(Int32Ty, "ehselector.slot");
  return Address(EHSelectorSlot, CharUnits::fromQuantity(4));
}

llvm::Value *CodeGenFunction::getExceptionFromSlot() {
  return Builder.CreateLoad(getExceptionSlot(), "exn");
}

llvm::Value *CodeGenFunction::getSelectorFromSlot() {
  return Builder.CreateLoad(getEHSelectorSlot(), "sel");
}

void CodeGenFunction::EmitCXXThrowExpr(const CXXThrowExpr *E,
                                       bool KeepInsertionPoint) {
  if (const Expr *SubExpr = E->getSubExpr()) {
    QualType ThrowType = SubExpr->getType();
    if (ThrowType->isObjCObjectPointerType()) {
      const Stmt *ThrowStmt = E->getSubExpr();
      const ObjCAtThrowStmt S(E->getExprLoc(), const_cast<Stmt *>(ThrowStmt));
      CGM.getObjCRuntime().EmitThrowStmt(*this, S, false);
    } else {
      CGM.getCXXABI().emitThrow(*this, E);
    }
  } else {
    CGM.getCXXABI().emitRethrow(*this, /*isNoReturn=*/true);
  }

  // throw is an expression, and the expression emitters expect us
  // to leave ourselves at a valid insertion point.
  if (KeepInsertionPoint)
    EmitBlock(createBasicBlock("throw.cont"));
}

void CodeGenFunction::EmitStartEHSpec(const Decl *D) {
  if (!CGM.getLangOpts().CXXExceptions)
    return;

  const FunctionDecl* FD = dyn_cast_or_null<FunctionDecl>(D);
  if (!FD) {
    // Check if CapturedDecl is nothrow and create terminate scope for it.
    if (const CapturedDecl* CD = dyn_cast_or_null<CapturedDecl>(D)) {
      if (CD->isNothrow())
        EHStack.pushTerminate();
    }
    return;
  }
  const FunctionProtoType *Proto = FD->getType()->getAs<FunctionProtoType>();
  if (!Proto)
    return;

  ExceptionSpecificationType EST = Proto->getExceptionSpecType();
  // In C++17 and later, 'throw()' aka EST_DynamicNone is treated the same way
  // as noexcept. In earlier standards, it is handled in this block, along with
  // 'throw(X...)'.
  if (EST == EST_Dynamic ||
      (EST == EST_DynamicNone && !getLangOpts().CPlusPlus17)) {
    // TODO: Revisit exception specifications for the MS ABI.  There is a way to
    // encode these in an object file but MSVC doesn't do anything with it.
    if (getTarget().getCXXABI().isMicrosoft())
      return;
    // In Wasm EH we currently treat 'throw()' in the same way as 'noexcept'. In
    // case of throw with types, we ignore it and print a warning for now.
    // TODO Correctly handle exception specification in Wasm EH
    if (CGM.getLangOpts().hasWasmExceptions()) {
      if (EST == EST_DynamicNone)
        EHStack.pushTerminate();
      else
        CGM.getDiags().Report(D->getLocation(),
                              diag::warn_wasm_dynamic_exception_spec_ignored)
            << FD->getExceptionSpecSourceRange();
      return;
    }
    // Currently Emscripten EH only handles 'throw()' but not 'throw' with
    // types. 'throw()' handling will be done in JS glue code so we don't need
    // to do anything in that case. Just print a warning message in case of
    // throw with types.
    // TODO Correctly handle exception specification in Emscripten EH
    if (getTarget().getCXXABI() == TargetCXXABI::WebAssembly &&
        CGM.getLangOpts().getExceptionHandling() ==
            LangOptions::ExceptionHandlingKind::None &&
        EST == EST_Dynamic)
      CGM.getDiags().Report(D->getLocation(),
                            diag::warn_wasm_dynamic_exception_spec_ignored)
          << FD->getExceptionSpecSourceRange();

    unsigned NumExceptions = Proto->getNumExceptions();
    EHFilterScope *Filter = EHStack.pushFilter(NumExceptions);

    for (unsigned I = 0; I != NumExceptions; ++I) {
      QualType Ty = Proto->getExceptionType(I);
      QualType ExceptType = Ty.getNonReferenceType().getUnqualifiedType();
      llvm::Value *EHType = CGM.GetAddrOfRTTIDescriptor(ExceptType,
                                                        /*ForEH=*/true);
      Filter->setFilter(I, EHType);
    }
  } else if (Proto->canThrow() == CT_Cannot) {
    // noexcept functions are simple terminate scopes.
    if (!getLangOpts().EHAsynch) // -EHa: HW exception still can occur
      EHStack.pushTerminate();
  }
}

/// Emit the dispatch block for a filter scope if necessary.
static void emitFilterDispatchBlock(CodeGenFunction &CGF,
                                    EHFilterScope &filterScope) {
  llvm::BasicBlock *dispatchBlock = filterScope.getCachedEHDispatchBlock();
  if (!dispatchBlock) return;
  if (dispatchBlock->use_empty()) {
    delete dispatchBlock;
    return;
  }

  CGF.EmitBlockAfterUses(dispatchBlock);

  // If this isn't a catch-all filter, we need to check whether we got
  // here because the filter triggered.
  if (filterScope.getNumFilters()) {
    // Load the selector value.
    llvm::Value *selector = CGF.getSelectorFromSlot();
    llvm::BasicBlock *unexpectedBB = CGF.createBasicBlock("ehspec.unexpected");

    llvm::Value *zero = CGF.Builder.getInt32(0);
    llvm::Value *failsFilter =
        CGF.Builder.CreateICmpSLT(selector, zero, "ehspec.fails");
    CGF.Builder.CreateCondBr(failsFilter, unexpectedBB,
                             CGF.getEHResumeBlock(false));

    CGF.EmitBlock(unexpectedBB);
  }

  // Call __cxa_call_unexpected.  This doesn't need to be an invoke
  // because __cxa_call_unexpected magically filters exceptions
  // according to the last landing pad the exception was thrown
  // into.  Seriously.
  llvm::Value *exn = CGF.getExceptionFromSlot();
  CGF.EmitRuntimeCall(getUnexpectedFn(CGF.CGM), exn)
    ->setDoesNotReturn();
  CGF.Builder.CreateUnreachable();
}

void CodeGenFunction::EmitEndEHSpec(const Decl *D) {
  if (!CGM.getLangOpts().CXXExceptions)
    return;

  const FunctionDecl* FD = dyn_cast_or_null<FunctionDecl>(D);
  if (!FD) {
    // Check if CapturedDecl is nothrow and pop terminate scope for it.
    if (const CapturedDecl* CD = dyn_cast_or_null<CapturedDecl>(D)) {
      if (CD->isNothrow() && !EHStack.empty())
        EHStack.popTerminate();
    }
    return;
  }
  const FunctionProtoType *Proto = FD->getType()->getAs<FunctionProtoType>();
  if (!Proto)
    return;

  ExceptionSpecificationType EST = Proto->getExceptionSpecType();
  if (EST == EST_Dynamic ||
      (EST == EST_DynamicNone && !getLangOpts().CPlusPlus17)) {
    // TODO: Revisit exception specifications for the MS ABI.  There is a way to
    // encode these in an object file but MSVC doesn't do anything with it.
    if (getTarget().getCXXABI().isMicrosoft())
      return;
    // In wasm we currently treat 'throw()' in the same way as 'noexcept'. In
    // case of throw with types, we ignore it and print a warning for now.
    // TODO Correctly handle exception specification in wasm
    if (CGM.getLangOpts().hasWasmExceptions()) {
      if (EST == EST_DynamicNone)
        EHStack.popTerminate();
      return;
    }
    EHFilterScope &filterScope = cast<EHFilterScope>(*EHStack.begin());
    emitFilterDispatchBlock(*this, filterScope);
    EHStack.popFilter();
  } else if (Proto->canThrow() == CT_Cannot &&
              /* possible empty when under async exceptions */
             !EHStack.empty()) {
    EHStack.popTerminate();
  }
}

void CodeGenFunction::EmitCXXTryStmt(const CXXTryStmt &S) {
  EnterCXXTryStmt(S);
  EmitStmt(S.getTryBlock());
  ExitCXXTryStmt(S);
}

void CodeGenFunction::EnterCXXTryStmt(const CXXTryStmt &S, bool IsFnTryBlock) {
  unsigned NumHandlers = S.getNumHandlers();
  EHCatchScope *CatchScope = EHStack.pushCatch(NumHandlers);

  for (unsigned I = 0; I != NumHandlers; ++I) {
    const CXXCatchStmt *C = S.getHandler(I);

    llvm::BasicBlock *Handler = createBasicBlock("catch");
    if (C->getExceptionDecl()) {
      // FIXME: Dropping the reference type on the type into makes it
      // impossible to correctly implement catch-by-reference
      // semantics for pointers.  Unfortunately, this is what all
      // existing compilers do, and it's not clear that the standard
      // personality routine is capable of doing this right.  See C++ DR 388:
      //   http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#388
      Qualifiers CaughtTypeQuals;
      QualType CaughtType = CGM.getContext().getUnqualifiedArrayType(
          C->getCaughtType().getNonReferenceType(), CaughtTypeQuals);

      CatchTypeInfo TypeInfo{nullptr, 0};
      if (CaughtType->isObjCObjectPointerType())
        TypeInfo.RTTI = CGM.getObjCRuntime().GetEHType(CaughtType);
      else
        TypeInfo = CGM.getCXXABI().getAddrOfCXXCatchHandlerType(
            CaughtType, C->getCaughtType());
      CatchScope->setHandler(I, TypeInfo, Handler);
    } else {
      // No exception decl indicates '...', a catch-all.
      CatchScope->setHandler(I, CGM.getCXXABI().getCatchAllTypeInfo(), Handler);
      // Under async exceptions, catch(...) need to catch HW exception too
      // Mark scope with SehTryBegin as a SEH __try scope
      if (getLangOpts().EHAsynch)
        EmitRuntimeCallOrInvoke(getSehTryBeginFn(CGM));
    }
  }
}

llvm::BasicBlock *
CodeGenFunction::getEHDispatchBlock(EHScopeStack::stable_iterator si) {
  if (EHPersonality::get(*this).usesFuncletPads())
    return getFuncletEHDispatchBlock(si);

  // The dispatch block for the end of the scope chain is a block that
  // just resumes unwinding.
  if (si == EHStack.stable_end())
    return getEHResumeBlock(true);

  // Otherwise, we should look at the actual scope.
  EHScope &scope = *EHStack.find(si);

  llvm::BasicBlock *dispatchBlock = scope.getCachedEHDispatchBlock();
  if (!dispatchBlock) {
    switch (scope.getKind()) {
    case EHScope::Catch: {
      // Apply a special case to a single catch-all.
      EHCatchScope &catchScope = cast<EHCatchScope>(scope);
      if (catchScope.getNumHandlers() == 1 &&
          catchScope.getHandler(0).isCatchAll()) {
        dispatchBlock = catchScope.getHandler(0).Block;

      // Otherwise, make a dispatch block.
      } else {
        dispatchBlock = createBasicBlock("catch.dispatch");
      }
      break;
    }

    case EHScope::Cleanup:
      dispatchBlock = createBasicBlock("ehcleanup");
      break;

    case EHScope::Filter:
      dispatchBlock = createBasicBlock("filter.dispatch");
      break;

    case EHScope::Terminate:
      dispatchBlock = getTerminateHandler();
      break;
    }
    scope.setCachedEHDispatchBlock(dispatchBlock);
  }
  return dispatchBlock;
}

llvm::BasicBlock *
CodeGenFunction::getFuncletEHDispatchBlock(EHScopeStack::stable_iterator SI) {
  // Returning nullptr indicates that the previous dispatch block should unwind
  // to caller.
  if (SI == EHStack.stable_end())
    return nullptr;

  // Otherwise, we should look at the actual scope.
  EHScope &EHS = *EHStack.find(SI);

  llvm::BasicBlock *DispatchBlock = EHS.getCachedEHDispatchBlock();
  if (DispatchBlock)
    return DispatchBlock;

  if (EHS.getKind() == EHScope::Terminate)
    DispatchBlock = getTerminateFunclet();
  else
    DispatchBlock = createBasicBlock();
  CGBuilderTy Builder(*this, DispatchBlock);

  switch (EHS.getKind()) {
  case EHScope::Catch:
    DispatchBlock->setName("catch.dispatch");
    break;

  case EHScope::Cleanup:
    DispatchBlock->setName("ehcleanup");
    break;

  case EHScope::Filter:
    llvm_unreachable("exception specifications not handled yet!");

  case EHScope::Terminate:
    DispatchBlock->setName("terminate");
    break;
  }
  EHS.setCachedEHDispatchBlock(DispatchBlock);
  return DispatchBlock;
}

/// Check whether this is a non-EH scope, i.e. a scope which doesn't
/// affect exception handling.  Currently, the only non-EH scopes are
/// normal-only cleanup scopes.
static bool isNonEHScope(const EHScope &S) {
  switch (S.getKind()) {
  case EHScope::Cleanup:
    return !cast<EHCleanupScope>(S).isEHCleanup();
  case EHScope::Filter:
  case EHScope::Catch:
  case EHScope::Terminate:
    return false;
  }

  llvm_unreachable("Invalid EHScope Kind!");
}

llvm::BasicBlock *CodeGenFunction::getInvokeDestImpl() {
  assert(EHStack.requiresLandingPad());
  assert(!EHStack.empty());

  // If exceptions are disabled/ignored and SEH is not in use, then there is no
  // invoke destination. SEH "works" even if exceptions are off. In practice,
  // this means that C++ destructors and other EH cleanups don't run, which is
  // consistent with MSVC's behavior, except in the presence of -EHa
  const LangOptions &LO = CGM.getLangOpts();
  if (!LO.Exceptions || LO.IgnoreExceptions) {
    if (!LO.Borland && !LO.MicrosoftExt)
      return nullptr;
    if (!currentFunctionUsesSEHTry())
      return nullptr;
  }

  // CUDA device code doesn't have exceptions.
  if (LO.CUDA && LO.CUDAIsDevice)
    return nullptr;

  // Check the innermost scope for a cached landing pad.  If this is
  // a non-EH cleanup, we'll check enclosing scopes in EmitLandingPad.
  llvm::BasicBlock *LP = EHStack.begin()->getCachedLandingPad();
  if (LP) return LP;

  const EHPersonality &Personality = EHPersonality::get(*this);

  if (!CurFn->hasPersonalityFn())
    CurFn->setPersonalityFn(getOpaquePersonalityFn(CGM, Personality));

  if (Personality.usesFuncletPads()) {
    // We don't need separate landing pads in the funclet model.
    LP = getEHDispatchBlock(EHStack.getInnermostEHScope());
  } else {
    // Build the landing pad for this scope.
    LP = EmitLandingPad();
  }

  assert(LP);

  // Cache the landing pad on the innermost scope.  If this is a
  // non-EH scope, cache the landing pad on the enclosing scope, too.
  for (EHScopeStack::iterator ir = EHStack.begin(); true; ++ir) {
    ir->setCachedLandingPad(LP);
    if (!isNonEHScope(*ir)) break;
  }

  return LP;
}

llvm::BasicBlock *CodeGenFunction::EmitLandingPad() {
  assert(EHStack.requiresLandingPad());
  assert(!CGM.getLangOpts().IgnoreExceptions &&
         "LandingPad should not be emitted when -fignore-exceptions are in "
         "effect.");
  EHScope &innermostEHScope = *EHStack.find(EHStack.getInnermostEHScope());
  switch (innermostEHScope.getKind()) {
  case EHScope::Terminate:
    return getTerminateLandingPad();

  case EHScope::Catch:
  case EHScope::Cleanup:
  case EHScope::Filter:
    if (llvm::BasicBlock *lpad = innermostEHScope.getCachedLandingPad())
      return lpad;
  }

  // Save the current IR generation state.
  CGBuilderTy::InsertPoint savedIP = Builder.saveAndClearIP();
  auto DL = ApplyDebugLocation::CreateDefaultArtificial(*this, CurEHLocation);

  // Create and configure the landing pad.
  llvm::BasicBlock *lpad = createBasicBlock("lpad");
  EmitBlock(lpad);

  llvm::LandingPadInst *LPadInst =
      Builder.CreateLandingPad(llvm::StructType::get(Int8PtrTy, Int32Ty), 0);

  llvm::Value *LPadExn = Builder.CreateExtractValue(LPadInst, 0);
  Builder.CreateStore(LPadExn, getExceptionSlot());
  llvm::Value *LPadSel = Builder.CreateExtractValue(LPadInst, 1);
  Builder.CreateStore(LPadSel, getEHSelectorSlot());

  // Save the exception pointer.  It's safe to use a single exception
  // pointer per function because EH cleanups can never have nested
  // try/catches.
  // Build the landingpad instruction.

  // Accumulate all the handlers in scope.
  bool hasCatchAll = false;
  bool hasCleanup = false;
  bool hasFilter = false;
  SmallVector<llvm::Value*, 4> filterTypes;
  llvm::SmallPtrSet<llvm::Value*, 4> catchTypes;
  for (EHScopeStack::iterator I = EHStack.begin(), E = EHStack.end(); I != E;
       ++I) {

    switch (I->getKind()) {
    case EHScope::Cleanup:
      // If we have a cleanup, remember that.
      hasCleanup = (hasCleanup || cast<EHCleanupScope>(*I).isEHCleanup());
      continue;

    case EHScope::Filter: {
      assert(I.next() == EHStack.end() && "EH filter is not end of EH stack");
      assert(!hasCatchAll && "EH filter reached after catch-all");

      // Filter scopes get added to the landingpad in weird ways.
      EHFilterScope &filter = cast<EHFilterScope>(*I);
      hasFilter = true;

      // Add all the filter values.
      for (unsigned i = 0, e = filter.getNumFilters(); i != e; ++i)
        filterTypes.push_back(filter.getFilter(i));
      goto done;
    }

    case EHScope::Terminate:
      // Terminate scopes are basically catch-alls.
      assert(!hasCatchAll);
      hasCatchAll = true;
      goto done;

    case EHScope::Catch:
      break;
    }

    EHCatchScope &catchScope = cast<EHCatchScope>(*I);
    for (unsigned hi = 0, he = catchScope.getNumHandlers(); hi != he; ++hi) {
      EHCatchScope::Handler handler = catchScope.getHandler(hi);
      assert(handler.Type.Flags == 0 &&
             "landingpads do not support catch handler flags");

      // If this is a catch-all, register that and abort.
      if (!handler.Type.RTTI) {
        assert(!hasCatchAll);
        hasCatchAll = true;
        goto done;
      }

      // Check whether we already have a handler for this type.
      if (catchTypes.insert(handler.Type.RTTI).second)
        // If not, add it directly to the landingpad.
        LPadInst->addClause(handler.Type.RTTI);
    }
  }

 done:
  // If we have a catch-all, add null to the landingpad.
  assert(!(hasCatchAll && hasFilter));
  if (hasCatchAll) {
    LPadInst->addClause(getCatchAllValue(*this));

  // If we have an EH filter, we need to add those handlers in the
  // right place in the landingpad, which is to say, at the end.
  } else if (hasFilter) {
    // Create a filter expression: a constant array indicating which filter
    // types there are. The personality routine only lands here if the filter
    // doesn't match.
    SmallVector<llvm::Constant*, 8> Filters;
    llvm::ArrayType *AType =
      llvm::ArrayType::get(!filterTypes.empty() ?
                             filterTypes[0]->getType() : Int8PtrTy,
                           filterTypes.size());

    for (unsigned i = 0, e = filterTypes.size(); i != e; ++i)
      Filters.push_back(cast<llvm::Constant>(filterTypes[i]));
    llvm::Constant *FilterArray = llvm::ConstantArray::get(AType, Filters);
    LPadInst->addClause(FilterArray);

    // Also check whether we need a cleanup.
    if (hasCleanup)
      LPadInst->setCleanup(true);

  // Otherwise, signal that we at least have cleanups.
  } else if (hasCleanup) {
    LPadInst->setCleanup(true);
  }

  assert((LPadInst->getNumClauses() > 0 || LPadInst->isCleanup()) &&
         "landingpad instruction has no clauses!");

  // Tell the backend how to generate the landing pad.
  Builder.CreateBr(getEHDispatchBlock(EHStack.getInnermostEHScope()));

  // Restore the old IR generation state.
  Builder.restoreIP(savedIP);

  return lpad;
}

static void emitCatchPadBlock(CodeGenFunction &CGF, EHCatchScope &CatchScope) {
  llvm::BasicBlock *DispatchBlock = CatchScope.getCachedEHDispatchBlock();
  assert(DispatchBlock);

  CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveIP();
  CGF.EmitBlockAfterUses(DispatchBlock);

  llvm::Value *ParentPad = CGF.CurrentFuncletPad;
  if (!ParentPad)
    ParentPad = llvm::ConstantTokenNone::get(CGF.getLLVMContext());
  llvm::BasicBlock *UnwindBB =
      CGF.getEHDispatchBlock(CatchScope.getEnclosingEHScope());

  unsigned NumHandlers = CatchScope.getNumHandlers();
  llvm::CatchSwitchInst *CatchSwitch =
      CGF.Builder.CreateCatchSwitch(ParentPad, UnwindBB, NumHandlers);

  // Test against each of the exception types we claim to catch.
  for (unsigned I = 0; I < NumHandlers; ++I) {
    const EHCatchScope::Handler &Handler = CatchScope.getHandler(I);

    CatchTypeInfo TypeInfo = Handler.Type;
    if (!TypeInfo.RTTI)
      TypeInfo.RTTI = llvm::Constant::getNullValue(CGF.VoidPtrTy);

    CGF.Builder.SetInsertPoint(Handler.Block);

    if (EHPersonality::get(CGF).isMSVCXXPersonality()) {
      CGF.Builder.CreateCatchPad(
          CatchSwitch, {TypeInfo.RTTI, CGF.Builder.getInt32(TypeInfo.Flags),
                        llvm::Constant::getNullValue(CGF.VoidPtrTy)});
    } else {
      CGF.Builder.CreateCatchPad(CatchSwitch, {TypeInfo.RTTI});
    }

    CatchSwitch->addHandler(Handler.Block);
  }
  CGF.Builder.restoreIP(SavedIP);
}

// Wasm uses Windows-style EH instructions, but it merges all catch clauses into
// one big catchpad, within which we use Itanium's landingpad-style selector
// comparison instructions.
static void emitWasmCatchPadBlock(CodeGenFunction &CGF,
                                  EHCatchScope &CatchScope) {
  llvm::BasicBlock *DispatchBlock = CatchScope.getCachedEHDispatchBlock();
  assert(DispatchBlock);

  CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveIP();
  CGF.EmitBlockAfterUses(DispatchBlock);

  llvm::Value *ParentPad = CGF.CurrentFuncletPad;
  if (!ParentPad)
    ParentPad = llvm::ConstantTokenNone::get(CGF.getLLVMContext());
  llvm::BasicBlock *UnwindBB =
      CGF.getEHDispatchBlock(CatchScope.getEnclosingEHScope());

  unsigned NumHandlers = CatchScope.getNumHandlers();
  llvm::CatchSwitchInst *CatchSwitch =
      CGF.Builder.CreateCatchSwitch(ParentPad, UnwindBB, NumHandlers);

  // We don't use a landingpad instruction, so generate intrinsic calls to
  // provide exception and selector values.
  llvm::BasicBlock *WasmCatchStartBlock = CGF.createBasicBlock("catch.start");
  CatchSwitch->addHandler(WasmCatchStartBlock);
  CGF.EmitBlockAfterUses(WasmCatchStartBlock);

  // Create a catchpad instruction.
  SmallVector<llvm::Value *, 4> CatchTypes;
  for (unsigned I = 0, E = NumHandlers; I < E; ++I) {
    const EHCatchScope::Handler &Handler = CatchScope.getHandler(I);
    CatchTypeInfo TypeInfo = Handler.Type;
    if (!TypeInfo.RTTI)
      TypeInfo.RTTI = llvm::Constant::getNullValue(CGF.VoidPtrTy);
    CatchTypes.push_back(TypeInfo.RTTI);
  }
  auto *CPI = CGF.Builder.CreateCatchPad(CatchSwitch, CatchTypes);

  // Create calls to wasm.get.exception and wasm.get.ehselector intrinsics.
  // Before they are lowered appropriately later, they provide values for the
  // exception and selector.
  llvm::Function *GetExnFn =
      CGF.CGM.getIntrinsic(llvm::Intrinsic::wasm_get_exception);
  llvm::Function *GetSelectorFn =
      CGF.CGM.getIntrinsic(llvm::Intrinsic::wasm_get_ehselector);
  llvm::CallInst *Exn = CGF.Builder.CreateCall(GetExnFn, CPI);
  CGF.Builder.CreateStore(Exn, CGF.getExceptionSlot());
  llvm::CallInst *Selector = CGF.Builder.CreateCall(GetSelectorFn, CPI);

  llvm::Function *TypeIDFn = CGF.CGM.getIntrinsic(llvm::Intrinsic::eh_typeid_for);

  // If there's only a single catch-all, branch directly to its handler.
  if (CatchScope.getNumHandlers() == 1 &&
      CatchScope.getHandler(0).isCatchAll()) {
    CGF.Builder.CreateBr(CatchScope.getHandler(0).Block);
    CGF.Builder.restoreIP(SavedIP);
    return;
  }

  // Test against each of the exception types we claim to catch.
  for (unsigned I = 0, E = NumHandlers;; ++I) {
    assert(I < E && "ran off end of handlers!");
    const EHCatchScope::Handler &Handler = CatchScope.getHandler(I);
    CatchTypeInfo TypeInfo = Handler.Type;
    if (!TypeInfo.RTTI)
      TypeInfo.RTTI = llvm::Constant::getNullValue(CGF.VoidPtrTy);

    // Figure out the next block.
    llvm::BasicBlock *NextBlock;

    bool EmitNextBlock = false, NextIsEnd = false;

    // If this is the last handler, we're at the end, and the next block is a
    // block that contains a call to the rethrow function, so we can unwind to
    // the enclosing EH scope. The call itself will be generated later.
    if (I + 1 == E) {
      NextBlock = CGF.createBasicBlock("rethrow");
      EmitNextBlock = true;
      NextIsEnd = true;

      // If the next handler is a catch-all, we're at the end, and the
      // next block is that handler.
    } else if (CatchScope.getHandler(I + 1).isCatchAll()) {
      NextBlock = CatchScope.getHandler(I + 1).Block;
      NextIsEnd = true;

      // Otherwise, we're not at the end and we need a new block.
    } else {
      NextBlock = CGF.createBasicBlock("catch.fallthrough");
      EmitNextBlock = true;
    }

    // Figure out the catch type's index in the LSDA's type table.
    llvm::CallInst *TypeIndex = CGF.Builder.CreateCall(TypeIDFn, TypeInfo.RTTI);
    TypeIndex->setDoesNotThrow();

    llvm::Value *MatchesTypeIndex =
        CGF.Builder.CreateICmpEQ(Selector, TypeIndex, "matches");
    CGF.Builder.CreateCondBr(MatchesTypeIndex, Handler.Block, NextBlock);

    if (EmitNextBlock)
      CGF.EmitBlock(NextBlock);
    if (NextIsEnd)
      break;
  }

  CGF.Builder.restoreIP(SavedIP);
}

/// Emit the structure of the dispatch block for the given catch scope.
/// It is an invariant that the dispatch block already exists.
static void emitCatchDispatchBlock(CodeGenFunction &CGF,
                                   EHCatchScope &catchScope) {
  if (EHPersonality::get(CGF).isWasmPersonality())
    return emitWasmCatchPadBlock(CGF, catchScope);
  if (EHPersonality::get(CGF).usesFuncletPads())
    return emitCatchPadBlock(CGF, catchScope);

  llvm::BasicBlock *dispatchBlock = catchScope.getCachedEHDispatchBlock();
  assert(dispatchBlock);

  // If there's only a single catch-all, getEHDispatchBlock returned
  // that catch-all as the dispatch block.
  if (catchScope.getNumHandlers() == 1 &&
      catchScope.getHandler(0).isCatchAll()) {
    assert(dispatchBlock == catchScope.getHandler(0).Block);
    return;
  }

  CGBuilderTy::InsertPoint savedIP = CGF.Builder.saveIP();
  CGF.EmitBlockAfterUses(dispatchBlock);

  // Select the right handler.
  llvm::Function *llvm_eh_typeid_for =
    CGF.CGM.getIntrinsic(llvm::Intrinsic::eh_typeid_for);

  // Load the selector value.
  llvm::Value *selector = CGF.getSelectorFromSlot();

  // Test against each of the exception types we claim to catch.
  for (unsigned i = 0, e = catchScope.getNumHandlers(); ; ++i) {
    assert(i < e && "ran off end of handlers!");
    const EHCatchScope::Handler &handler = catchScope.getHandler(i);

    llvm::Value *typeValue = handler.Type.RTTI;
    assert(handler.Type.Flags == 0 &&
           "landingpads do not support catch handler flags");
    assert(typeValue && "fell into catch-all case!");
    typeValue = CGF.Builder.CreateBitCast(typeValue, CGF.Int8PtrTy);

    // Figure out the next block.
    bool nextIsEnd;
    llvm::BasicBlock *nextBlock;

    // If this is the last handler, we're at the end, and the next
    // block is the block for the enclosing EH scope.
    if (i + 1 == e) {
      nextBlock = CGF.getEHDispatchBlock(catchScope.getEnclosingEHScope());
      nextIsEnd = true;

    // If the next handler is a catch-all, we're at the end, and the
    // next block is that handler.
    } else if (catchScope.getHandler(i+1).isCatchAll()) {
      nextBlock = catchScope.getHandler(i+1).Block;
      nextIsEnd = true;

    // Otherwise, we're not at the end and we need a new block.
    } else {
      nextBlock = CGF.createBasicBlock("catch.fallthrough");
      nextIsEnd = false;
    }

    // Figure out the catch type's index in the LSDA's type table.
    llvm::CallInst *typeIndex =
      CGF.Builder.CreateCall(llvm_eh_typeid_for, typeValue);
    typeIndex->setDoesNotThrow();

    llvm::Value *matchesTypeIndex =
      CGF.Builder.CreateICmpEQ(selector, typeIndex, "matches");
    CGF.Builder.CreateCondBr(matchesTypeIndex, handler.Block, nextBlock);

    // If the next handler is a catch-all, we're completely done.
    if (nextIsEnd) {
      CGF.Builder.restoreIP(savedIP);
      return;
    }
    // Otherwise we need to emit and continue at that block.
    CGF.EmitBlock(nextBlock);
  }
}

void CodeGenFunction::popCatchScope() {
  EHCatchScope &catchScope = cast<EHCatchScope>(*EHStack.begin());
  if (catchScope.hasEHBranches())
    emitCatchDispatchBlock(*this, catchScope);
  EHStack.popCatch();
}

void CodeGenFunction::ExitCXXTryStmt(const CXXTryStmt &S, bool IsFnTryBlock) {
  unsigned NumHandlers = S.getNumHandlers();
  EHCatchScope &CatchScope = cast<EHCatchScope>(*EHStack.begin());
  assert(CatchScope.getNumHandlers() == NumHandlers);
  llvm::BasicBlock *DispatchBlock = CatchScope.getCachedEHDispatchBlock();

  // If the catch was not required, bail out now.
  if (!CatchScope.hasEHBranches()) {
    CatchScope.clearHandlerBlocks();
    EHStack.popCatch();
    return;
  }

  // Emit the structure of the EH dispatch for this catch.
  emitCatchDispatchBlock(*this, CatchScope);

  // Copy the handler blocks off before we pop the EH stack.  Emitting
  // the handlers might scribble on this memory.
  SmallVector<EHCatchScope::Handler, 8> Handlers(
      CatchScope.begin(), CatchScope.begin() + NumHandlers);

  EHStack.popCatch();

  // The fall-through block.
  llvm::BasicBlock *ContBB = createBasicBlock("try.cont");

  // We just emitted the body of the try; jump to the continue block.
  if (HaveInsertPoint())
    Builder.CreateBr(ContBB);

  // Determine if we need an implicit rethrow for all these catch handlers;
  // see the comment below.
  bool doImplicitRethrow = false;
  if (IsFnTryBlock)
    doImplicitRethrow = isa<CXXDestructorDecl>(CurCodeDecl) ||
                        isa<CXXConstructorDecl>(CurCodeDecl);

  // Wasm uses Windows-style EH instructions, but merges all catch clauses into
  // one big catchpad. So we save the old funclet pad here before we traverse
  // each catch handler.
  SaveAndRestore<llvm::Instruction *> RestoreCurrentFuncletPad(
      CurrentFuncletPad);
  llvm::BasicBlock *WasmCatchStartBlock = nullptr;
  if (EHPersonality::get(*this).isWasmPersonality()) {
    auto *CatchSwitch =
        cast<llvm::CatchSwitchInst>(DispatchBlock->getFirstNonPHI());
    WasmCatchStartBlock = CatchSwitch->hasUnwindDest()
                              ? CatchSwitch->getSuccessor(1)
                              : CatchSwitch->getSuccessor(0);
    auto *CPI = cast<llvm::CatchPadInst>(WasmCatchStartBlock->getFirstNonPHI());
    CurrentFuncletPad = CPI;
  }

  // Perversely, we emit the handlers backwards precisely because we
  // want them to appear in source order.  In all of these cases, the
  // catch block will have exactly one predecessor, which will be a
  // particular block in the catch dispatch.  However, in the case of
  // a catch-all, one of the dispatch blocks will branch to two
  // different handlers, and EmitBlockAfterUses will cause the second
  // handler to be moved before the first.
  bool HasCatchAll = false;
  for (unsigned I = NumHandlers; I != 0; --I) {
    HasCatchAll |= Handlers[I - 1].isCatchAll();
    llvm::BasicBlock *CatchBlock = Handlers[I-1].Block;
    EmitBlockAfterUses(CatchBlock);

    // Catch the exception if this isn't a catch-all.
    const CXXCatchStmt *C = S.getHandler(I-1);

    // Enter a cleanup scope, including the catch variable and the
    // end-catch.
    RunCleanupsScope CatchScope(*this);

    // Initialize the catch variable and set up the cleanups.
    SaveAndRestore<llvm::Instruction *> RestoreCurrentFuncletPad(
        CurrentFuncletPad);
    CGM.getCXXABI().emitBeginCatch(*this, C);

    // Emit the PGO counter increment.
    incrementProfileCounter(C);

    // Perform the body of the catch.
    EmitStmt(C->getHandlerBlock());

    // [except.handle]p11:
    //   The currently handled exception is rethrown if control
    //   reaches the end of a handler of the function-try-block of a
    //   constructor or destructor.

    // It is important that we only do this on fallthrough and not on
    // return.  Note that it's illegal to put a return in a
    // constructor function-try-block's catch handler (p14), so this
    // really only applies to destructors.
    if (doImplicitRethrow && HaveInsertPoint()) {
      CGM.getCXXABI().emitRethrow(*this, /*isNoReturn*/false);
      Builder.CreateUnreachable();
      Builder.ClearInsertionPoint();
    }

    // Fall out through the catch cleanups.
    CatchScope.ForceCleanup();

    // Branch out of the try.
    if (HaveInsertPoint())
      Builder.CreateBr(ContBB);
  }

  // Because in wasm we merge all catch clauses into one big catchpad, in case
  // none of the types in catch handlers matches after we test against each of
  // them, we should unwind to the next EH enclosing scope. We generate a call
  // to rethrow function here to do that.
  if (EHPersonality::get(*this).isWasmPersonality() && !HasCatchAll) {
    assert(WasmCatchStartBlock);
    // Navigate for the "rethrow" block we created in emitWasmCatchPadBlock().
    // Wasm uses landingpad-style conditional branches to compare selectors, so
    // we follow the false destination for each of the cond branches to reach
    // the rethrow block.
    llvm::BasicBlock *RethrowBlock = WasmCatchStartBlock;
    while (llvm::Instruction *TI = RethrowBlock->getTerminator()) {
      auto *BI = cast<llvm::BranchInst>(TI);
      assert(BI->isConditional());
      RethrowBlock = BI->getSuccessor(1);
    }
    assert(RethrowBlock != WasmCatchStartBlock && RethrowBlock->empty());
    Builder.SetInsertPoint(RethrowBlock);
    llvm::Function *RethrowInCatchFn =
        CGM.getIntrinsic(llvm::Intrinsic::wasm_rethrow);
    EmitNoreturnRuntimeCallOrInvoke(RethrowInCatchFn, {});
  }

  EmitBlock(ContBB);
  incrementProfileCounter(&S);
}

namespace {
  struct CallEndCatchForFinally final : EHScopeStack::Cleanup {
    llvm::Value *ForEHVar;
    llvm::FunctionCallee EndCatchFn;
    CallEndCatchForFinally(llvm::Value *ForEHVar,
                           llvm::FunctionCallee EndCatchFn)
        : ForEHVar(ForEHVar), EndCatchFn(EndCatchFn) {}

    void Emit(CodeGenFunction &CGF, Flags flags) override {
      llvm::BasicBlock *EndCatchBB = CGF.createBasicBlock("finally.endcatch");
      llvm::BasicBlock *CleanupContBB =
        CGF.createBasicBlock("finally.cleanup.cont");

      llvm::Value *ShouldEndCatch =
        CGF.Builder.CreateFlagLoad(ForEHVar, "finally.endcatch");
      CGF.Builder.CreateCondBr(ShouldEndCatch, EndCatchBB, CleanupContBB);
      CGF.EmitBlock(EndCatchBB);
      CGF.EmitRuntimeCallOrInvoke(EndCatchFn); // catch-all, so might throw
      CGF.EmitBlock(CleanupContBB);
    }
  };

  struct PerformFinally final : EHScopeStack::Cleanup {
    const Stmt *Body;
    llvm::Value *ForEHVar;
    llvm::FunctionCallee EndCatchFn;
    llvm::FunctionCallee RethrowFn;
    llvm::Value *SavedExnVar;

    PerformFinally(const Stmt *Body, llvm::Value *ForEHVar,
                   llvm::FunctionCallee EndCatchFn,
                   llvm::FunctionCallee RethrowFn, llvm::Value *SavedExnVar)
        : Body(Body), ForEHVar(ForEHVar), EndCatchFn(EndCatchFn),
          RethrowFn(RethrowFn), SavedExnVar(SavedExnVar) {}

    void Emit(CodeGenFunction &CGF, Flags flags) override {
      // Enter a cleanup to call the end-catch function if one was provided.
      if (EndCatchFn)
        CGF.EHStack.pushCleanup<CallEndCatchForFinally>(NormalAndEHCleanup,
                                                        ForEHVar, EndCatchFn);

      // Save the current cleanup destination in case there are
      // cleanups in the finally block.
      llvm::Value *SavedCleanupDest =
        CGF.Builder.CreateLoad(CGF.getNormalCleanupDestSlot(),
                               "cleanup.dest.saved");

      // Emit the finally block.
      CGF.EmitStmt(Body);

      // If the end of the finally is reachable, check whether this was
      // for EH.  If so, rethrow.
      if (CGF.HaveInsertPoint()) {
        llvm::BasicBlock *RethrowBB = CGF.createBasicBlock("finally.rethrow");
        llvm::BasicBlock *ContBB = CGF.createBasicBlock("finally.cont");

        llvm::Value *ShouldRethrow =
          CGF.Builder.CreateFlagLoad(ForEHVar, "finally.shouldthrow");
        CGF.Builder.CreateCondBr(ShouldRethrow, RethrowBB, ContBB);

        CGF.EmitBlock(RethrowBB);
        if (SavedExnVar) {
          CGF.EmitRuntimeCallOrInvoke(RethrowFn,
            CGF.Builder.CreateAlignedLoad(CGF.Int8PtrTy, SavedExnVar,
                                          CGF.getPointerAlign()));
        } else {
          CGF.EmitRuntimeCallOrInvoke(RethrowFn);
        }
        CGF.Builder.CreateUnreachable();

        CGF.EmitBlock(ContBB);

        // Restore the cleanup destination.
        CGF.Builder.CreateStore(SavedCleanupDest,
                                CGF.getNormalCleanupDestSlot());
      }

      // Leave the end-catch cleanup.  As an optimization, pretend that
      // the fallthrough path was inaccessible; we've dynamically proven
      // that we're not in the EH case along that path.
      if (EndCatchFn) {
        CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveAndClearIP();
        CGF.PopCleanupBlock();
        CGF.Builder.restoreIP(SavedIP);
      }

      // Now make sure we actually have an insertion point or the
      // cleanup gods will hate us.
      CGF.EnsureInsertPoint();
    }
  };
} // end anonymous namespace

/// Enters a finally block for an implementation using zero-cost
/// exceptions.  This is mostly general, but hard-codes some
/// language/ABI-specific behavior in the catch-all sections.
void CodeGenFunction::FinallyInfo::enter(CodeGenFunction &CGF, const Stmt *body,
                                         llvm::FunctionCallee beginCatchFn,
                                         llvm::FunctionCallee endCatchFn,
                                         llvm::FunctionCallee rethrowFn) {
  assert((!!beginCatchFn) == (!!endCatchFn) &&
         "begin/end catch functions not paired");
  assert(rethrowFn && "rethrow function is required");

  BeginCatchFn = beginCatchFn;

  // The rethrow function has one of the following two types:
  //   void (*)()
  //   void (*)(void*)
  // In the latter case we need to pass it the exception object.
  // But we can't use the exception slot because the @finally might
  // have a landing pad (which would overwrite the exception slot).
  llvm::FunctionType *rethrowFnTy = rethrowFn.getFunctionType();
  SavedExnVar = nullptr;
  if (rethrowFnTy->getNumParams())
    SavedExnVar = CGF.CreateTempAlloca(CGF.Int8PtrTy, "finally.exn");

  // A finally block is a statement which must be executed on any edge
  // out of a given scope.  Unlike a cleanup, the finally block may
  // contain arbitrary control flow leading out of itself.  In
  // addition, finally blocks should always be executed, even if there
  // are no catch handlers higher on the stack.  Therefore, we
  // surround the protected scope with a combination of a normal
  // cleanup (to catch attempts to break out of the block via normal
  // control flow) and an EH catch-all (semantically "outside" any try
  // statement to which the finally block might have been attached).
  // The finally block itself is generated in the context of a cleanup
  // which conditionally leaves the catch-all.

  // Jump destination for performing the finally block on an exception
  // edge.  We'll never actually reach this block, so unreachable is
  // fine.
  RethrowDest = CGF.getJumpDestInCurrentScope(CGF.getUnreachableBlock());

  // Whether the finally block is being executed for EH purposes.
  ForEHVar = CGF.CreateTempAlloca(CGF.Builder.getInt1Ty(), "finally.for-eh");
  CGF.Builder.CreateFlagStore(false, ForEHVar);

  // Enter a normal cleanup which will perform the @finally block.
  CGF.EHStack.pushCleanup<PerformFinally>(NormalCleanup, body,
                                          ForEHVar, endCatchFn,
                                          rethrowFn, SavedExnVar);

  // Enter a catch-all scope.
  llvm::BasicBlock *catchBB = CGF.createBasicBlock("finally.catchall");
  EHCatchScope *catchScope = CGF.EHStack.pushCatch(1);
  catchScope->setCatchAllHandler(0, catchBB);
}

void CodeGenFunction::FinallyInfo::exit(CodeGenFunction &CGF) {
  // Leave the finally catch-all.
  EHCatchScope &catchScope = cast<EHCatchScope>(*CGF.EHStack.begin());
  llvm::BasicBlock *catchBB = catchScope.getHandler(0).Block;

  CGF.popCatchScope();

  // If there are any references to the catch-all block, emit it.
  if (catchBB->use_empty()) {
    delete catchBB;
  } else {
    CGBuilderTy::InsertPoint savedIP = CGF.Builder.saveAndClearIP();
    CGF.EmitBlock(catchBB);

    llvm::Value *exn = nullptr;

    // If there's a begin-catch function, call it.
    if (BeginCatchFn) {
      exn = CGF.getExceptionFromSlot();
      CGF.EmitNounwindRuntimeCall(BeginCatchFn, exn);
    }

    // If we need to remember the exception pointer to rethrow later, do so.
    if (SavedExnVar) {
      if (!exn) exn = CGF.getExceptionFromSlot();
      CGF.Builder.CreateAlignedStore(exn, SavedExnVar, CGF.getPointerAlign());
    }

    // Tell the cleanups in the finally block that we're do this for EH.
    CGF.Builder.CreateFlagStore(true, ForEHVar);

    // Thread a jump through the finally cleanup.
    CGF.EmitBranchThroughCleanup(RethrowDest);

    CGF.Builder.restoreIP(savedIP);
  }

  // Finally, leave the @finally cleanup.
  CGF.PopCleanupBlock();
}

llvm::BasicBlock *CodeGenFunction::getTerminateLandingPad() {
  if (TerminateLandingPad)
    return TerminateLandingPad;

  CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();

  // This will get inserted at the end of the function.
  TerminateLandingPad = createBasicBlock("terminate.lpad");
  Builder.SetInsertPoint(TerminateLandingPad);

  // Tell the backend that this is a landing pad.
  const EHPersonality &Personality = EHPersonality::get(*this);

  if (!CurFn->hasPersonalityFn())
    CurFn->setPersonalityFn(getOpaquePersonalityFn(CGM, Personality));

  llvm::LandingPadInst *LPadInst =
      Builder.CreateLandingPad(llvm::StructType::get(Int8PtrTy, Int32Ty), 0);
  LPadInst->addClause(getCatchAllValue(*this));

  llvm::Value *Exn = nullptr;
  if (getLangOpts().CPlusPlus)
    Exn = Builder.CreateExtractValue(LPadInst, 0);
  llvm::CallInst *terminateCall =
      CGM.getCXXABI().emitTerminateForUnexpectedException(*this, Exn);
  terminateCall->setDoesNotReturn();
  Builder.CreateUnreachable();

  // Restore the saved insertion state.
  Builder.restoreIP(SavedIP);

  return TerminateLandingPad;
}

llvm::BasicBlock *CodeGenFunction::getTerminateHandler() {
  if (TerminateHandler)
    return TerminateHandler;

  // Set up the terminate handler.  This block is inserted at the very
  // end of the function by FinishFunction.
  TerminateHandler = createBasicBlock("terminate.handler");
  CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
  Builder.SetInsertPoint(TerminateHandler);

  llvm::Value *Exn = nullptr;
  if (getLangOpts().CPlusPlus)
    Exn = getExceptionFromSlot();
  llvm::CallInst *terminateCall =
      CGM.getCXXABI().emitTerminateForUnexpectedException(*this, Exn);
  terminateCall->setDoesNotReturn();
  Builder.CreateUnreachable();

  // Restore the saved insertion state.
  Builder.restoreIP(SavedIP);

  return TerminateHandler;
}

llvm::BasicBlock *CodeGenFunction::getTerminateFunclet() {
  assert(EHPersonality::get(*this).usesFuncletPads() &&
         "use getTerminateLandingPad for non-funclet EH");

  llvm::BasicBlock *&TerminateFunclet = TerminateFunclets[CurrentFuncletPad];
  if (TerminateFunclet)
    return TerminateFunclet;

  CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();

  // Set up the terminate handler.  This block is inserted at the very
  // end of the function by FinishFunction.
  TerminateFunclet = createBasicBlock("terminate.handler");
  Builder.SetInsertPoint(TerminateFunclet);

  // Create the cleanuppad using the current parent pad as its token. Use 'none'
  // if this is a top-level terminate scope, which is the common case.
  SaveAndRestore<llvm::Instruction *> RestoreCurrentFuncletPad(
      CurrentFuncletPad);
  llvm::Value *ParentPad = CurrentFuncletPad;
  if (!ParentPad)
    ParentPad = llvm::ConstantTokenNone::get(CGM.getLLVMContext());
  CurrentFuncletPad = Builder.CreateCleanupPad(ParentPad);

  // Emit the __std_terminate call.
  llvm::CallInst *terminateCall =
      CGM.getCXXABI().emitTerminateForUnexpectedException(*this, nullptr);
  terminateCall->setDoesNotReturn();
  Builder.CreateUnreachable();

  // Restore the saved insertion state.
  Builder.restoreIP(SavedIP);

  return TerminateFunclet;
}

llvm::BasicBlock *CodeGenFunction::getEHResumeBlock(bool isCleanup) {
  if (EHResumeBlock) return EHResumeBlock;

  CGBuilderTy::InsertPoint SavedIP = Builder.saveIP();

  // We emit a jump to a notional label at the outermost unwind state.
  EHResumeBlock = createBasicBlock("eh.resume");
  Builder.SetInsertPoint(EHResumeBlock);

  const EHPersonality &Personality = EHPersonality::get(*this);

  // This can always be a call because we necessarily didn't find
  // anything on the EH stack which needs our help.
  const char *RethrowName = Personality.CatchallRethrowFn;
  if (RethrowName != nullptr && !isCleanup) {
    EmitRuntimeCall(getCatchallRethrowFn(CGM, RethrowName),
                    getExceptionFromSlot())->setDoesNotReturn();
    Builder.CreateUnreachable();
    Builder.restoreIP(SavedIP);
    return EHResumeBlock;
  }

  // Recreate the landingpad's return value for the 'resume' instruction.
  llvm::Value *Exn = getExceptionFromSlot();
  llvm::Value *Sel = getSelectorFromSlot();

  llvm::Type *LPadType = llvm::StructType::get(Exn->getType(), Sel->getType());
  llvm::Value *LPadVal = llvm::UndefValue::get(LPadType);
  LPadVal = Builder.CreateInsertValue(LPadVal, Exn, 0, "lpad.val");
  LPadVal = Builder.CreateInsertValue(LPadVal, Sel, 1, "lpad.val");

  Builder.CreateResume(LPadVal);
  Builder.restoreIP(SavedIP);
  return EHResumeBlock;
}

void CodeGenFunction::EmitSEHTryStmt(const SEHTryStmt &S) {
  EnterSEHTryStmt(S);
  {
    JumpDest TryExit = getJumpDestInCurrentScope("__try.__leave");

    SEHTryEpilogueStack.push_back(&TryExit);

    llvm::BasicBlock *TryBB = nullptr;
    // IsEHa: emit an invoke to _seh_try_begin() runtime for -EHa
    if (getLangOpts().EHAsynch) {
      EmitRuntimeCallOrInvoke(getSehTryBeginFn(CGM));
      if (SEHTryEpilogueStack.size() == 1) // outermost only
        TryBB = Builder.GetInsertBlock();
    }

    EmitStmt(S.getTryBlock());

    // Volatilize all blocks in Try, till current insert point
    if (TryBB) {
      llvm::SmallPtrSet<llvm::BasicBlock *, 10> Visited;
      VolatilizeTryBlocks(TryBB, Visited);
    }

    SEHTryEpilogueStack.pop_back();

    if (!TryExit.getBlock()->use_empty())
      EmitBlock(TryExit.getBlock(), /*IsFinished=*/true);
    else
      delete TryExit.getBlock();
  }
  ExitSEHTryStmt(S);
}

//  Recursively walk through blocks in a _try
//      and make all memory instructions volatile
void CodeGenFunction::VolatilizeTryBlocks(
    llvm::BasicBlock *BB, llvm::SmallPtrSet<llvm::BasicBlock *, 10> &V) {
  if (BB == SEHTryEpilogueStack.back()->getBlock() /* end of Try */ ||
      !V.insert(BB).second /* already visited */ ||
      !BB->getParent() /* not emitted */ || BB->empty())
    return;

  if (!BB->isEHPad()) {
    for (llvm::BasicBlock::iterator J = BB->begin(), JE = BB->end(); J != JE;
         ++J) {
      if (auto LI = dyn_cast<llvm::LoadInst>(J)) {
        LI->setVolatile(true);
      } else if (auto SI = dyn_cast<llvm::StoreInst>(J)) {
        SI->setVolatile(true);
      } else if (auto* MCI = dyn_cast<llvm::MemIntrinsic>(J)) {
        MCI->setVolatile(llvm::ConstantInt::get(Builder.getInt1Ty(), 1));
      }
    }
  }
  const llvm::Instruction *TI = BB->getTerminator();
  if (TI) {
    unsigned N = TI->getNumSuccessors();
    for (unsigned I = 0; I < N; I++)
      VolatilizeTryBlocks(TI->getSuccessor(I), V);
  }
}

namespace {
struct PerformSEHFinally final : EHScopeStack::Cleanup {
  llvm::Function *OutlinedFinally;
  PerformSEHFinally(llvm::Function *OutlinedFinally)
      : OutlinedFinally(OutlinedFinally) {}

  void Emit(CodeGenFunction &CGF, Flags F) override {
    ASTContext &Context = CGF.getContext();
    CodeGenModule &CGM = CGF.CGM;

    CallArgList Args;

    // Compute the two argument values.
    QualType ArgTys[2] = {Context.UnsignedCharTy, Context.VoidPtrTy};
    llvm::Value *FP = nullptr;
    // If CFG.IsOutlinedSEHHelper is true, then we are within a finally block.
    if (CGF.IsOutlinedSEHHelper) {
      FP = &CGF.CurFn->arg_begin()[1];
    } else {
      llvm::Function *LocalAddrFn =
          CGM.getIntrinsic(llvm::Intrinsic::localaddress);
      FP = CGF.Builder.CreateCall(LocalAddrFn);
    }

    llvm::Value *IsForEH =
        llvm::ConstantInt::get(CGF.ConvertType(ArgTys[0]), F.isForEHCleanup());

    // Except _leave and fall-through at the end, all other exits in a _try
    //   (return/goto/continue/break) are considered as abnormal terminations
    //   since _leave/fall-through is always Indexed 0,
    //   just use NormalCleanupDestSlot (>= 1 for goto/return/..),
    //   as 1st Arg to indicate abnormal termination
    if (!F.isForEHCleanup() && F.hasExitSwitch()) {
      Address Addr = CGF.getNormalCleanupDestSlot();
      llvm::Value *Load = CGF.Builder.CreateLoad(Addr, "cleanup.dest");
      llvm::Value *Zero = llvm::Constant::getNullValue(CGM.Int32Ty);
      IsForEH = CGF.Builder.CreateICmpNE(Load, Zero);
    }

    Args.add(RValue::get(IsForEH), ArgTys[0]);
    Args.add(RValue::get(FP), ArgTys[1]);

    // Arrange a two-arg function info and type.
    const CGFunctionInfo &FnInfo =
        CGM.getTypes().arrangeBuiltinFunctionCall(Context.VoidTy, Args);

    auto Callee = CGCallee::forDirect(OutlinedFinally);
    CGF.EmitCall(FnInfo, Callee, ReturnValueSlot(), Args);
  }
};
} // end anonymous namespace

namespace {
/// Find all local variable captures in the statement.
struct CaptureFinder : ConstStmtVisitor<CaptureFinder> {
  CodeGenFunction &ParentCGF;
  const VarDecl *ParentThis;
  llvm::SmallSetVector<const VarDecl *, 4> Captures;
  Address SEHCodeSlot = Address::invalid();
  CaptureFinder(CodeGenFunction &ParentCGF, const VarDecl *ParentThis)
      : ParentCGF(ParentCGF), ParentThis(ParentThis) {}

  // Return true if we need to do any capturing work.
  bool foundCaptures() {
    return !Captures.empty() || SEHCodeSlot.isValid();
  }

  void Visit(const Stmt *S) {
    // See if this is a capture, then recurse.
    ConstStmtVisitor<CaptureFinder>::Visit(S);
    for (const Stmt *Child : S->children())
      if (Child)
        Visit(Child);
  }

  void VisitDeclRefExpr(const DeclRefExpr *E) {
    // If this is already a capture, just make sure we capture 'this'.
    if (E->refersToEnclosingVariableOrCapture())
      Captures.insert(ParentThis);

    const auto *D = dyn_cast<VarDecl>(E->getDecl());
    if (D && D->isLocalVarDeclOrParm() && D->hasLocalStorage())
      Captures.insert(D);
  }

  void VisitCXXThisExpr(const CXXThisExpr *E) {
    Captures.insert(ParentThis);
  }

  void VisitCallExpr(const CallExpr *E) {
    // We only need to add parent frame allocations for these builtins in x86.
    if (ParentCGF.getTarget().getTriple().getArch() != llvm::Triple::x86)
      return;

    unsigned ID = E->getBuiltinCallee();
    switch (ID) {
    case Builtin::BI__exception_code:
    case Builtin::BI_exception_code:
      // This is the simple case where we are the outermost finally. All we
      // have to do here is make sure we escape this and recover it in the
      // outlined handler.
      if (!SEHCodeSlot.isValid())
        SEHCodeSlot = ParentCGF.SEHCodeSlotStack.back();
      break;
    }
  }
};
} // end anonymous namespace

Address CodeGenFunction::recoverAddrOfEscapedLocal(CodeGenFunction &ParentCGF,
                                                   Address ParentVar,
                                                   llvm::Value *ParentFP) {
  llvm::CallInst *RecoverCall = nullptr;
  CGBuilderTy Builder(*this, AllocaInsertPt);
  if (auto *ParentAlloca = dyn_cast<llvm::AllocaInst>(ParentVar.getPointer())) {
    // Mark the variable escaped if nobody else referenced it and compute the
    // localescape index.
    auto InsertPair = ParentCGF.EscapedLocals.insert(
        std::make_pair(ParentAlloca, ParentCGF.EscapedLocals.size()));
    int FrameEscapeIdx = InsertPair.first->second;
    // call i8* @llvm.localrecover(i8* bitcast(@parentFn), i8* %fp, i32 N)
    llvm::Function *FrameRecoverFn = llvm::Intrinsic::getDeclaration(
        &CGM.getModule(), llvm::Intrinsic::localrecover);
    llvm::Constant *ParentI8Fn =
        llvm::ConstantExpr::getBitCast(ParentCGF.CurFn, Int8PtrTy);
    RecoverCall = Builder.CreateCall(
        FrameRecoverFn, {ParentI8Fn, ParentFP,
                         llvm::ConstantInt::get(Int32Ty, FrameEscapeIdx)});

  } else {
    // If the parent didn't have an alloca, we're doing some nested outlining.
    // Just clone the existing localrecover call, but tweak the FP argument to
    // use our FP value. All other arguments are constants.
    auto *ParentRecover =
        cast<llvm::IntrinsicInst>(ParentVar.getPointer()->stripPointerCasts());
    assert(ParentRecover->getIntrinsicID() == llvm::Intrinsic::localrecover &&
           "expected alloca or localrecover in parent LocalDeclMap");
    RecoverCall = cast<llvm::CallInst>(ParentRecover->clone());
    RecoverCall->setArgOperand(1, ParentFP);
    RecoverCall->insertBefore(AllocaInsertPt);
  }

  // Bitcast the variable, rename it, and insert it in the local decl map.
  llvm::Value *ChildVar =
      Builder.CreateBitCast(RecoverCall, ParentVar.getType());
  ChildVar->setName(ParentVar.getName());
  return Address(ChildVar, ParentVar.getAlignment());
}

void CodeGenFunction::EmitCapturedLocals(CodeGenFunction &ParentCGF,
                                         const Stmt *OutlinedStmt,
                                         bool IsFilter) {
  // Find all captures in the Stmt.
  CaptureFinder Finder(ParentCGF, ParentCGF.CXXABIThisDecl);
  Finder.Visit(OutlinedStmt);

  // We can exit early on x86_64 when there are no captures. We just have to
  // save the exception code in filters so that __exception_code() works.
  if (!Finder.foundCaptures() &&
      CGM.getTarget().getTriple().getArch() != llvm::Triple::x86) {
    if (IsFilter)
      EmitSEHExceptionCodeSave(ParentCGF, nullptr, nullptr);
    return;
  }

  llvm::Value *EntryFP = nullptr;
  CGBuilderTy Builder(CGM, AllocaInsertPt);
  if (IsFilter && CGM.getTarget().getTriple().getArch() == llvm::Triple::x86) {
    // 32-bit SEH filters need to be careful about FP recovery.  The end of the
    // EH registration is passed in as the EBP physical register.  We can
    // recover that with llvm.frameaddress(1).
    EntryFP = Builder.CreateCall(
        CGM.getIntrinsic(llvm::Intrinsic::frameaddress, AllocaInt8PtrTy),
        {Builder.getInt32(1)});
  } else {
    // Otherwise, for x64 and 32-bit finally functions, the parent FP is the
    // second parameter.
    auto AI = CurFn->arg_begin();
    ++AI;
    EntryFP = &*AI;
  }

  llvm::Value *ParentFP = EntryFP;
  if (IsFilter) {
    // Given whatever FP the runtime provided us in EntryFP, recover the true
    // frame pointer of the parent function. We only need to do this in filters,
    // since finally funclets recover the parent FP for us.
    llvm::Function *RecoverFPIntrin =
        CGM.getIntrinsic(llvm::Intrinsic::eh_recoverfp);
    llvm::Constant *ParentI8Fn =
        llvm::ConstantExpr::getBitCast(ParentCGF.CurFn, Int8PtrTy);
    ParentFP = Builder.CreateCall(RecoverFPIntrin, {ParentI8Fn, EntryFP});

    // if the parent is a _finally, the passed-in ParentFP is the FP
    // of parent _finally, not Establisher's FP (FP of outermost function).
    // Establkisher FP is 2nd paramenter passed into parent _finally.
    // Fortunately, it's always saved in parent's frame. The following
    // code retrieves it, and escapes it so that spill instruction won't be
    // optimized away.
    if (ParentCGF.ParentCGF != nullptr) {
      // Locate and escape Parent's frame_pointer.addr alloca
      // Depending on target, should be 1st/2nd one in LocalDeclMap.
      // Let's just scan for ImplicitParamDecl with VoidPtrTy.
      llvm::AllocaInst *FramePtrAddrAlloca = nullptr;
      for (auto &I : ParentCGF.LocalDeclMap) {
        const VarDecl *D = cast<VarDecl>(I.first);
        if (isa<ImplicitParamDecl>(D) &&
            D->getType() == getContext().VoidPtrTy) {
          assert(D->getName().startswith("frame_pointer"));
          FramePtrAddrAlloca = cast<llvm::AllocaInst>(I.second.getPointer());
          break;
        }
      }
      assert(FramePtrAddrAlloca);
      auto InsertPair = ParentCGF.EscapedLocals.insert(
          std::make_pair(FramePtrAddrAlloca, ParentCGF.EscapedLocals.size()));
      int FrameEscapeIdx = InsertPair.first->second;

      // an example of a filter's prolog::
      // %0 = call i8* @llvm.eh.recoverfp(bitcast(@"?fin$0@0@main@@"),..)
      // %1 = call i8* @llvm.localrecover(bitcast(@"?fin$0@0@main@@"),..)
      // %2 = bitcast i8* %1 to i8**
      // %3 = load i8*, i8* *%2, align 8
      //   ==> %3 is the frame-pointer of outermost host function
      llvm::Function *FrameRecoverFn = llvm::Intrinsic::getDeclaration(
          &CGM.getModule(), llvm::Intrinsic::localrecover);
      llvm::Constant *ParentI8Fn =
          llvm::ConstantExpr::getBitCast(ParentCGF.CurFn, Int8PtrTy);
      ParentFP = Builder.CreateCall(
          FrameRecoverFn, {ParentI8Fn, ParentFP,
                           llvm::ConstantInt::get(Int32Ty, FrameEscapeIdx)});
      ParentFP = Builder.CreateBitCast(ParentFP, CGM.VoidPtrPtrTy);
      ParentFP = Builder.CreateLoad(Address(ParentFP, getPointerAlign()));
    }
  }

  // Create llvm.localrecover calls for all captures.
  for (const VarDecl *VD : Finder.Captures) {
    if (VD->getType()->isVariablyModifiedType()) {
      CGM.ErrorUnsupported(VD, "VLA captured by SEH");
      continue;
    }
    assert((isa<ImplicitParamDecl>(VD) || VD->isLocalVarDeclOrParm()) &&
           "captured non-local variable");

    auto L = ParentCGF.LambdaCaptureFields.find(VD);
    if (L != ParentCGF.LambdaCaptureFields.end()) {
      LambdaCaptureFields[VD] = L->second;
      continue;
    }

    // If this decl hasn't been declared yet, it will be declared in the
    // OutlinedStmt.
    auto I = ParentCGF.LocalDeclMap.find(VD);
    if (I == ParentCGF.LocalDeclMap.end())
      continue;

    Address ParentVar = I->second;
    Address Recovered =
        recoverAddrOfEscapedLocal(ParentCGF, ParentVar, ParentFP);
    setAddrOfLocalVar(VD, Recovered);

    if (isa<ImplicitParamDecl>(VD)) {
      CXXABIThisAlignment = ParentCGF.CXXABIThisAlignment;
      CXXThisAlignment = ParentCGF.CXXThisAlignment;
      CXXABIThisValue = Builder.CreateLoad(Recovered, "this");
      if (ParentCGF.LambdaThisCaptureField) {
        LambdaThisCaptureField = ParentCGF.LambdaThisCaptureField;
        // We are in a lambda function where "this" is captured so the
        // CXXThisValue need to be loaded from the lambda capture
        LValue ThisFieldLValue =
            EmitLValueForLambdaField(LambdaThisCaptureField);
        if (!LambdaThisCaptureField->getType()->isPointerType()) {
          CXXThisValue = ThisFieldLValue.getAddress(*this).getPointer();
        } else {
          CXXThisValue = EmitLoadOfLValue(ThisFieldLValue, SourceLocation())
                             .getScalarVal();
        }
      } else {
        CXXThisValue = CXXABIThisValue;
      }
    }
  }

  if (Finder.SEHCodeSlot.isValid()) {
    SEHCodeSlotStack.push_back(
        recoverAddrOfEscapedLocal(ParentCGF, Finder.SEHCodeSlot, ParentFP));
  }

  if (IsFilter)
    EmitSEHExceptionCodeSave(ParentCGF, ParentFP, EntryFP);
}

/// Arrange a function prototype that can be called by Windows exception
/// handling personalities. On Win64, the prototype looks like:
/// RetTy func(void *EHPtrs, void *ParentFP);
void CodeGenFunction::startOutlinedSEHHelper(CodeGenFunction &ParentCGF,
                                             bool IsFilter,
                                             const Stmt *OutlinedStmt) {
  SourceLocation StartLoc = OutlinedStmt->getBeginLoc();

  // Get the mangled function name.
  SmallString<128> Name;
  {
    llvm::raw_svector_ostream OS(Name);
    const NamedDecl *ParentSEHFn = ParentCGF.CurSEHParent;
    assert(ParentSEHFn && "No CurSEHParent!");
    MangleContext &Mangler = CGM.getCXXABI().getMangleContext();
    if (IsFilter)
      Mangler.mangleSEHFilterExpression(ParentSEHFn, OS);
    else
      Mangler.mangleSEHFinallyBlock(ParentSEHFn, OS);
  }

  FunctionArgList Args;
  if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86 || !IsFilter) {
    // All SEH finally functions take two parameters. Win64 filters take two
    // parameters. Win32 filters take no parameters.
    if (IsFilter) {
      Args.push_back(ImplicitParamDecl::Create(
          getContext(), /*DC=*/nullptr, StartLoc,
          &getContext().Idents.get("exception_pointers"),
          getContext().VoidPtrTy, ImplicitParamDecl::Other));
    } else {
      Args.push_back(ImplicitParamDecl::Create(
          getContext(), /*DC=*/nullptr, StartLoc,
          &getContext().Idents.get("abnormal_termination"),
          getContext().UnsignedCharTy, ImplicitParamDecl::Other));
    }
    Args.push_back(ImplicitParamDecl::Create(
        getContext(), /*DC=*/nullptr, StartLoc,
        &getContext().Idents.get("frame_pointer"), getContext().VoidPtrTy,
        ImplicitParamDecl::Other));
  }

  QualType RetTy = IsFilter ? getContext().LongTy : getContext().VoidTy;

  const CGFunctionInfo &FnInfo =
    CGM.getTypes().arrangeBuiltinFunctionDeclaration(RetTy, Args);

  llvm::FunctionType *FnTy = CGM.getTypes().GetFunctionType(FnInfo);
  llvm::Function *Fn = llvm::Function::Create(
      FnTy, llvm::GlobalValue::InternalLinkage, Name.str(), &CGM.getModule());

  IsOutlinedSEHHelper = true;

  StartFunction(GlobalDecl(), RetTy, Fn, FnInfo, Args,
                OutlinedStmt->getBeginLoc(), OutlinedStmt->getBeginLoc());
  CurSEHParent = ParentCGF.CurSEHParent;

  CGM.SetInternalFunctionAttributes(GlobalDecl(), CurFn, FnInfo);
  EmitCapturedLocals(ParentCGF, OutlinedStmt, IsFilter);
}

/// Create a stub filter function that will ultimately hold the code of the
/// filter expression. The EH preparation passes in LLVM will outline the code
/// from the main function body into this stub.
llvm::Function *
CodeGenFunction::GenerateSEHFilterFunction(CodeGenFunction &ParentCGF,
                                           const SEHExceptStmt &Except) {
  const Expr *FilterExpr = Except.getFilterExpr();
  startOutlinedSEHHelper(ParentCGF, true, FilterExpr);

  // Emit the original filter expression, convert to i32, and return.
  llvm::Value *R = EmitScalarExpr(FilterExpr);
  R = Builder.CreateIntCast(R, ConvertType(getContext().LongTy),
                            FilterExpr->getType()->isSignedIntegerType());
  Builder.CreateStore(R, ReturnValue);

  FinishFunction(FilterExpr->getEndLoc());

  return CurFn;
}

llvm::Function *
CodeGenFunction::GenerateSEHFinallyFunction(CodeGenFunction &ParentCGF,
                                            const SEHFinallyStmt &Finally) {
  const Stmt *FinallyBlock = Finally.getBlock();
  startOutlinedSEHHelper(ParentCGF, false, FinallyBlock);

  // Emit the original filter expression, convert to i32, and return.
  EmitStmt(FinallyBlock);

  FinishFunction(FinallyBlock->getEndLoc());

  return CurFn;
}

void CodeGenFunction::EmitSEHExceptionCodeSave(CodeGenFunction &ParentCGF,
                                               llvm::Value *ParentFP,
                                               llvm::Value *EntryFP) {
  // Get the pointer to the EXCEPTION_POINTERS struct. This is returned by the
  // __exception_info intrinsic.
  if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86) {
    // On Win64, the info is passed as the first parameter to the filter.
    SEHInfo = &*CurFn->arg_begin();
    SEHCodeSlotStack.push_back(
        CreateMemTemp(getContext().IntTy, "__exception_code"));
  } else {
    // On Win32, the EBP on entry to the filter points to the end of an
    // exception registration object. It contains 6 32-bit fields, and the info
    // pointer is stored in the second field. So, GEP 20 bytes backwards and
    // load the pointer.
    SEHInfo = Builder.CreateConstInBoundsGEP1_32(Int8Ty, EntryFP, -20);
    SEHInfo = Builder.CreateBitCast(SEHInfo, Int8PtrTy->getPointerTo());
    SEHInfo = Builder.CreateAlignedLoad(Int8PtrTy, SEHInfo, getPointerAlign());
    SEHCodeSlotStack.push_back(recoverAddrOfEscapedLocal(
        ParentCGF, ParentCGF.SEHCodeSlotStack.back(), ParentFP));
  }

  // Save the exception code in the exception slot to unify exception access in
  // the filter function and the landing pad.
  // struct EXCEPTION_POINTERS {
  //   EXCEPTION_RECORD *ExceptionRecord;
  //   CONTEXT *ContextRecord;
  // };
  // int exceptioncode = exception_pointers->ExceptionRecord->ExceptionCode;
  llvm::Type *RecordTy = CGM.Int32Ty->getPointerTo();
  llvm::Type *PtrsTy = llvm::StructType::get(RecordTy, CGM.VoidPtrTy);
  llvm::Value *Ptrs = Builder.CreateBitCast(SEHInfo, PtrsTy->getPointerTo());
  llvm::Value *Rec = Builder.CreateStructGEP(PtrsTy, Ptrs, 0);
  Rec = Builder.CreateAlignedLoad(RecordTy, Rec, getPointerAlign());
  llvm::Value *Code = Builder.CreateAlignedLoad(Int32Ty, Rec, getIntAlign());
  assert(!SEHCodeSlotStack.empty() && "emitting EH code outside of __except");
  Builder.CreateStore(Code, SEHCodeSlotStack.back());
}

llvm::Value *CodeGenFunction::EmitSEHExceptionInfo() {
  // Sema should diagnose calling this builtin outside of a filter context, but
  // don't crash if we screw up.
  if (!SEHInfo)
    return llvm::UndefValue::get(Int8PtrTy);
  assert(SEHInfo->getType() == Int8PtrTy);
  return SEHInfo;
}

llvm::Value *CodeGenFunction::EmitSEHExceptionCode() {
  assert(!SEHCodeSlotStack.empty() && "emitting EH code outside of __except");
  return Builder.CreateLoad(SEHCodeSlotStack.back());
}

llvm::Value *CodeGenFunction::EmitSEHAbnormalTermination() {
  // Abnormal termination is just the first parameter to the outlined finally
  // helper.
  auto AI = CurFn->arg_begin();
  return Builder.CreateZExt(&*AI, Int32Ty);
}

void CodeGenFunction::pushSEHCleanup(CleanupKind Kind,
                                     llvm::Function *FinallyFunc) {
  EHStack.pushCleanup<PerformSEHFinally>(Kind, FinallyFunc);
}

void CodeGenFunction::EnterSEHTryStmt(const SEHTryStmt &S) {
  CodeGenFunction HelperCGF(CGM, /*suppressNewContext=*/true);
  HelperCGF.ParentCGF = this;
  if (const SEHFinallyStmt *Finally = S.getFinallyHandler()) {
    // Outline the finally block.
    llvm::Function *FinallyFunc =
        HelperCGF.GenerateSEHFinallyFunction(*this, *Finally);

    // Push a cleanup for __finally blocks.
    EHStack.pushCleanup<PerformSEHFinally>(NormalAndEHCleanup, FinallyFunc);
    return;
  }

  // Otherwise, we must have an __except block.
  const SEHExceptStmt *Except = S.getExceptHandler();
  assert(Except);
  EHCatchScope *CatchScope = EHStack.pushCatch(1);
  SEHCodeSlotStack.push_back(
      CreateMemTemp(getContext().IntTy, "__exception_code"));

  // If the filter is known to evaluate to 1, then we can use the clause
  // "catch i8* null". We can't do this on x86 because the filter has to save
  // the exception code.
  llvm::Constant *C =
    ConstantEmitter(*this).tryEmitAbstract(Except->getFilterExpr(),
                                           getContext().IntTy);
  if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86 && C &&
      C->isOneValue()) {
    CatchScope->setCatchAllHandler(0, createBasicBlock("__except"));
    return;
  }

  // In general, we have to emit an outlined filter function. Use the function
  // in place of the RTTI typeinfo global that C++ EH uses.
  llvm::Function *FilterFunc =
      HelperCGF.GenerateSEHFilterFunction(*this, *Except);
  llvm::Constant *OpaqueFunc =
      llvm::ConstantExpr::getBitCast(FilterFunc, Int8PtrTy);
  CatchScope->setHandler(0, OpaqueFunc, createBasicBlock("__except.ret"));
}

void CodeGenFunction::ExitSEHTryStmt(const SEHTryStmt &S) {
  // Just pop the cleanup if it's a __finally block.
  if (S.getFinallyHandler()) {
    PopCleanupBlock();
    return;
  }

  // IsEHa: emit an invoke _seh_try_end() to mark end of FT flow
  if (getLangOpts().EHAsynch && Builder.GetInsertBlock()) {
    llvm::FunctionCallee SehTryEnd = getSehTryEndFn(CGM);
    EmitRuntimeCallOrInvoke(SehTryEnd);
  }

  // Otherwise, we must have an __except block.
  const SEHExceptStmt *Except = S.getExceptHandler();
  assert(Except && "__try must have __finally xor __except");
  EHCatchScope &CatchScope = cast<EHCatchScope>(*EHStack.begin());

  // Don't emit the __except block if the __try block lacked invokes.
  // TODO: Model unwind edges from instructions, either with iload / istore or
  // a try body function.
  if (!CatchScope.hasEHBranches()) {
    CatchScope.clearHandlerBlocks();
    EHStack.popCatch();
    SEHCodeSlotStack.pop_back();
    return;
  }

  // The fall-through block.
  llvm::BasicBlock *ContBB = createBasicBlock("__try.cont");

  // We just emitted the body of the __try; jump to the continue block.
  if (HaveInsertPoint())
    Builder.CreateBr(ContBB);

  // Check if our filter function returned true.
  emitCatchDispatchBlock(*this, CatchScope);

  // Grab the block before we pop the handler.
  llvm::BasicBlock *CatchPadBB = CatchScope.getHandler(0).Block;
  EHStack.popCatch();

  EmitBlockAfterUses(CatchPadBB);

  // __except blocks don't get outlined into funclets, so immediately do a
  // catchret.
  llvm::CatchPadInst *CPI =
      cast<llvm::CatchPadInst>(CatchPadBB->getFirstNonPHI());
  llvm::BasicBlock *ExceptBB = createBasicBlock("__except");
  Builder.CreateCatchRet(CPI, ExceptBB);
  EmitBlock(ExceptBB);

  // On Win64, the exception code is returned in EAX. Copy it into the slot.
  if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86) {
    llvm::Function *SEHCodeIntrin =
        CGM.getIntrinsic(llvm::Intrinsic::eh_exceptioncode);
    llvm::Value *Code = Builder.CreateCall(SEHCodeIntrin, {CPI});
    Builder.CreateStore(Code, SEHCodeSlotStack.back());
  }

  // Emit the __except body.
  EmitStmt(Except->getBlock());

  // End the lifetime of the exception code.
  SEHCodeSlotStack.pop_back();

  if (HaveInsertPoint())
    Builder.CreateBr(ContBB);

  EmitBlock(ContBB);
}

void CodeGenFunction::EmitSEHLeaveStmt(const SEHLeaveStmt &S) {
  // If this code is reachable then emit a stop point (if generating
  // debug info). We have to do this ourselves because we are on the
  // "simple" statement path.
  if (HaveInsertPoint())
    EmitStopPoint(&S);

  // This must be a __leave from a __finally block, which we warn on and is UB.
  // Just emit unreachable.
  if (!isSEHTryScope()) {
    Builder.CreateUnreachable();
    Builder.ClearInsertionPoint();
    return;
  }

  EmitBranchThroughCleanup(*SEHTryEpilogueStack.back());
}