//===--- CGException.cpp - Emit LLVM Code for C++ exceptions --------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code dealing with C++ exception related code generation.
//
//===----------------------------------------------------------------------===//
#include "CodeGenFunction.h"
#include "CGCleanup.h"
#include "CGObjCRuntime.h"
#include "TargetInfo.h"
#include "clang/AST/StmtCXX.h"
#include "clang/AST/StmtObjC.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/Support/CallSite.h"
using namespace clang;
using namespace CodeGen;
static llvm::Constant *getAllocateExceptionFn(CodeGenModule &CGM) {
// void *__cxa_allocate_exception(size_t thrown_size);
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.Int8PtrTy, CGM.SizeTy, /*IsVarArgs=*/false);
return CGM.CreateRuntimeFunction(FTy, "__cxa_allocate_exception");
}
static llvm::Constant *getFreeExceptionFn(CodeGenModule &CGM) {
// void __cxa_free_exception(void *thrown_exception);
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.VoidTy, CGM.Int8PtrTy, /*IsVarArgs=*/false);
return CGM.CreateRuntimeFunction(FTy, "__cxa_free_exception");
}
static llvm::Constant *getThrowFn(CodeGenModule &CGM) {
// void __cxa_throw(void *thrown_exception, std::type_info *tinfo,
// void (*dest) (void *));
llvm::Type *Args[3] = { CGM.Int8PtrTy, CGM.Int8PtrTy, CGM.Int8PtrTy };
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.VoidTy, Args, /*IsVarArgs=*/false);
return CGM.CreateRuntimeFunction(FTy, "__cxa_throw");
}
static llvm::Constant *getReThrowFn(CodeGenModule &CGM) {
// void __cxa_rethrow();
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.VoidTy, /*IsVarArgs=*/false);
return CGM.CreateRuntimeFunction(FTy, "__cxa_rethrow");
}
static llvm::Constant *getGetExceptionPtrFn(CodeGenModule &CGM) {
// void *__cxa_get_exception_ptr(void*);
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.Int8PtrTy, CGM.Int8PtrTy, /*IsVarArgs=*/false);
return CGM.CreateRuntimeFunction(FTy, "__cxa_get_exception_ptr");
}
static llvm::Constant *getBeginCatchFn(CodeGenModule &CGM) {
// void *__cxa_begin_catch(void*);
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.Int8PtrTy, CGM.Int8PtrTy, /*IsVarArgs=*/false);
return CGM.CreateRuntimeFunction(FTy, "__cxa_begin_catch");
}
static llvm::Constant *getEndCatchFn(CodeGenModule &CGM) {
// void __cxa_end_catch();
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.VoidTy, /*IsVarArgs=*/false);
return CGM.CreateRuntimeFunction(FTy, "__cxa_end_catch");
}
static llvm::Constant *getUnexpectedFn(CodeGenModule &CGM) {
// void __cxa_call_unexpected(void *thrown_exception);
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.VoidTy, CGM.Int8PtrTy, /*IsVarArgs=*/false);
return CGM.CreateRuntimeFunction(FTy, "__cxa_call_unexpected");
}
llvm::Constant *CodeGenFunction::getUnwindResumeFn() {
llvm::FunctionType *FTy =
llvm::FunctionType::get(VoidTy, Int8PtrTy, /*IsVarArgs=*/false);
if (CGM.getLangOpts().SjLjExceptions)
return CGM.CreateRuntimeFunction(FTy, "_Unwind_SjLj_Resume");
return CGM.CreateRuntimeFunction(FTy, "_Unwind_Resume");
}
llvm::Constant *CodeGenFunction::getUnwindResumeOrRethrowFn() {
llvm::FunctionType *FTy =
llvm::FunctionType::get(VoidTy, Int8PtrTy, /*IsVarArgs=*/false);
if (CGM.getLangOpts().SjLjExceptions)
return CGM.CreateRuntimeFunction(FTy, "_Unwind_SjLj_Resume_or_Rethrow");
return CGM.CreateRuntimeFunction(FTy, "_Unwind_Resume_or_Rethrow");
}
static llvm::Constant *getTerminateFn(CodeGenModule &CGM) {
// void __terminate();
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.VoidTy, /*IsVarArgs=*/false);
StringRef name;
// In C++, use std::terminate().
if (CGM.getLangOpts().CPlusPlus)
name = "_ZSt9terminatev"; // FIXME: mangling!
else if (CGM.getLangOpts().ObjC1 &&
CGM.getLangOpts().ObjCRuntime.hasTerminate())
name = "objc_terminate";
else
name = "abort";
return CGM.CreateRuntimeFunction(FTy, name);
}
static llvm::Constant *getCatchallRethrowFn(CodeGenModule &CGM,
StringRef Name) {
llvm::FunctionType *FTy =
llvm::FunctionType::get(CGM.VoidTy, CGM.Int8PtrTy, /*IsVarArgs=*/false);
return CGM.CreateRuntimeFunction(FTy, Name);
}
namespace {
/// The exceptions personality for a function.
struct EHPersonality {
const char *PersonalityFn;
// If this is non-null, this personality requires a non-standard
// function for rethrowing an exception after a catchall cleanup.
// This function must have prototype void(void*).
const char *CatchallRethrowFn;
static const EHPersonality &get(const LangOptions &Lang);
static const EHPersonality GNU_C;
static const EHPersonality GNU_C_SJLJ;
static const EHPersonality GNU_ObjC;
static const EHPersonality GNUstep_ObjC;
static const EHPersonality GNU_ObjCXX;
static const EHPersonality NeXT_ObjC;
static const EHPersonality GNU_CPlusPlus;
static const EHPersonality GNU_CPlusPlus_SJLJ;
};
}
const EHPersonality EHPersonality::GNU_C = { "__gcc_personality_v0", 0 };
const EHPersonality EHPersonality::GNU_C_SJLJ = { "__gcc_personality_sj0", 0 };
const EHPersonality EHPersonality::NeXT_ObjC = { "__objc_personality_v0", 0 };
const EHPersonality EHPersonality::GNU_CPlusPlus = { "__gxx_personality_v0", 0};
const EHPersonality
EHPersonality::GNU_CPlusPlus_SJLJ = { "__gxx_personality_sj0", 0 };
const EHPersonality
EHPersonality::GNU_ObjC = {"__gnu_objc_personality_v0", "objc_exception_throw"};
const EHPersonality
EHPersonality::GNU_ObjCXX = { "__gnustep_objcxx_personality_v0", 0 };
const EHPersonality
EHPersonality::GNUstep_ObjC = { "__gnustep_objc_personality_v0", 0 };
static const EHPersonality &getCPersonality(const LangOptions &L) {
if (L.SjLjExceptions)
return EHPersonality::GNU_C_SJLJ;
return EHPersonality::GNU_C;
}
static const EHPersonality &getObjCPersonality(const LangOptions &L) {
switch (L.ObjCRuntime.getKind()) {
case ObjCRuntime::FragileMacOSX:
return getCPersonality(L);
case ObjCRuntime::MacOSX:
case ObjCRuntime::iOS:
return EHPersonality::NeXT_ObjC;
case ObjCRuntime::GNUstep:
if (L.ObjCRuntime.getVersion() >= VersionTuple(1, 7))
return EHPersonality::GNUstep_ObjC;
// fallthrough
case ObjCRuntime::GCC:
case ObjCRuntime::ObjFW:
return EHPersonality::GNU_ObjC;
}
llvm_unreachable("bad runtime kind");
}
static const EHPersonality &getCXXPersonality(const LangOptions &L) {
if (L.SjLjExceptions)
return EHPersonality::GNU_CPlusPlus_SJLJ;
else
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 LangOptions &L) {
switch (L.ObjCRuntime.getKind()) {
// 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:
return EHPersonality::NeXT_ObjC;
// In the fragile ABI, just use C++ exception handling and hope
// they're not doing crazy exception mixing.
case ObjCRuntime::FragileMacOSX:
return getCXXPersonality(L);
// The GCC runtime's personality function inherently doesn't support
// mixed EH. Use the C++ personality just to avoid returning null.
case ObjCRuntime::GCC:
case ObjCRuntime::ObjFW: // XXX: this will change soon
return EHPersonality::GNU_ObjC;
case ObjCRuntime::GNUstep:
return EHPersonality::GNU_ObjCXX;
}
llvm_unreachable("bad runtime kind");
}
const EHPersonality &EHPersonality::get(const LangOptions &L) {
if (L.CPlusPlus && L.ObjC1)
return getObjCXXPersonality(L);
else if (L.CPlusPlus)
return getCXXPersonality(L);
else if (L.ObjC1)
return getObjCPersonality(L);
else
return getCPersonality(L);
}
static llvm::Constant *getPersonalityFn(CodeGenModule &CGM,
const EHPersonality &Personality) {
llvm::Constant *Fn =
CGM.CreateRuntimeFunction(llvm::FunctionType::get(CGM.Int32Ty, true),
Personality.PersonalityFn);
return Fn;
}
static llvm::Constant *getOpaquePersonalityFn(CodeGenModule &CGM,
const EHPersonality &Personality) {
llvm::Constant *Fn = getPersonalityFn(CGM, Personality);
return llvm::ConstantExpr::getBitCast(Fn, CGM.Int8PtrTy);
}
/// Check whether a personality function could reasonably be swapped
/// for a C++ personality function.
static bool PersonalityHasOnlyCXXUses(llvm::Constant *Fn) {
for (llvm::Constant::use_iterator
I = Fn->use_begin(), E = Fn->use_end(); I != E; ++I) {
llvm::User *User = *I;
// Conditionally white-list bitcasts.
if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(User)) {
if (CE->getOpcode() != llvm::Instruction::BitCast) return false;
if (!PersonalityHasOnlyCXXUses(CE))
return false;
continue;
}
// Otherwise, it has to be a landingpad instruction.
llvm::LandingPadInst *LPI = dyn_cast<llvm::LandingPadInst>(User);
if (!LPI) return false;
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;
}
/// 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.ObjC1 || !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(LangOpts);
const EHPersonality &CXX = getCXXPersonality(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::Constant *CXXFn = getPersonalityFn(*this, CXX);
// This can happen if the user is screwing with us.
if (Fn->getType() != CXXFn->getType()) return;
Fn->replaceAllUsesWith(CXXFn);
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 : EHScopeStack::Cleanup {
llvm::Value *exn;
FreeException(llvm::Value *exn) : exn(exn) {}
void Emit(CodeGenFunction &CGF, Flags flags) {
CGF.EmitNounwindRuntimeCall(getFreeExceptionFn(CGF.CGM), exn);
}
};
}
// 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.
static void EmitAnyExprToExn(CodeGenFunction &CGF, const Expr *e,
llvm::Value *addr) {
// Make sure the exception object is cleaned up if there's an
// exception during initialization.
CGF.pushFullExprCleanup<FreeException>(EHCleanup, addr);
EHScopeStack::stable_iterator cleanup = CGF.EHStack.stable_begin();
// __cxa_allocate_exception returns a void*; we need to cast this
// to the appropriate type for the object.
llvm::Type *ty = CGF.ConvertTypeForMem(e->getType())->getPointerTo();
llvm::Value *typedAddr = CGF.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.
CGF.EmitAnyExprToMem(e, typedAddr, e->getType().getQualifiers(),
/*IsInit*/ true);
// Deactivate the cleanup block.
CGF.DeactivateCleanupBlock(cleanup, cast<llvm::Instruction>(typedAddr));
}
llvm::Value *CodeGenFunction::getExceptionSlot() {
if (!ExceptionSlot)
ExceptionSlot = CreateTempAlloca(Int8PtrTy, "exn.slot");
return ExceptionSlot;
}
llvm::Value *CodeGenFunction::getEHSelectorSlot() {
if (!EHSelectorSlot)
EHSelectorSlot = CreateTempAlloca(Int32Ty, "ehselector.slot");
return EHSelectorSlot;
}
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 (!E->getSubExpr()) {
EmitNoreturnRuntimeCallOrInvoke(getReThrowFn(CGM),
ArrayRef<llvm::Value*>());
// throw is an expression, and the expression emitters expect us
// to leave ourselves at a valid insertion point.
if (KeepInsertionPoint)
EmitBlock(createBasicBlock("throw.cont"));
return;
}
QualType ThrowType = E->getSubExpr()->getType();
if (ThrowType->isObjCObjectPointerType()) {
const Stmt *ThrowStmt = E->getSubExpr();
const ObjCAtThrowStmt S(E->getExprLoc(),
const_cast<Stmt *>(ThrowStmt));
CGM.getObjCRuntime().EmitThrowStmt(*this, S, false);
// This will clear insertion point which was not cleared in
// call to EmitThrowStmt.
if (KeepInsertionPoint)
EmitBlock(createBasicBlock("throw.cont"));
return;
}
// Now allocate the exception object.
llvm::Type *SizeTy = ConvertType(getContext().getSizeType());
uint64_t TypeSize = getContext().getTypeSizeInChars(ThrowType).getQuantity();
llvm::Constant *AllocExceptionFn = getAllocateExceptionFn(CGM);
llvm::CallInst *ExceptionPtr =
EmitNounwindRuntimeCall(AllocExceptionFn,
llvm::ConstantInt::get(SizeTy, TypeSize),
"exception");
EmitAnyExprToExn(*this, E->getSubExpr(), ExceptionPtr);
// Now throw the exception.
llvm::Constant *TypeInfo = CGM.GetAddrOfRTTIDescriptor(ThrowType,
/*ForEH=*/true);
// The address of the destructor. If the exception type has a
// trivial destructor (or isn't a record), we just pass null.
llvm::Constant *Dtor = 0;
if (const RecordType *RecordTy = ThrowType->getAs<RecordType>()) {
CXXRecordDecl *Record = cast<CXXRecordDecl>(RecordTy->getDecl());
if (!Record->hasTrivialDestructor()) {
CXXDestructorDecl *DtorD = Record->getDestructor();
Dtor = CGM.GetAddrOfCXXDestructor(DtorD, Dtor_Complete);
Dtor = llvm::ConstantExpr::getBitCast(Dtor, Int8PtrTy);
}
}
if (!Dtor) Dtor = llvm::Constant::getNullValue(Int8PtrTy);
llvm::Value *args[] = { ExceptionPtr, TypeInfo, Dtor };
EmitNoreturnRuntimeCallOrInvoke(getThrowFn(CGM), args);
// 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 == 0)
return;
const FunctionProtoType *Proto = FD->getType()->getAs<FunctionProtoType>();
if (Proto == 0)
return;
ExceptionSpecificationType EST = Proto->getExceptionSpecType();
if (isNoexceptExceptionSpec(EST)) {
if (Proto->getNoexceptSpec(getContext()) == FunctionProtoType::NR_Nothrow) {
// noexcept functions are simple terminate scopes.
EHStack.pushTerminate();
}
} else if (EST == EST_Dynamic || EST == EST_DynamicNone) {
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);
}
}
}
/// 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 == 0)
return;
const FunctionProtoType *Proto = FD->getType()->getAs<FunctionProtoType>();
if (Proto == 0)
return;
ExceptionSpecificationType EST = Proto->getExceptionSpecType();
if (isNoexceptExceptionSpec(EST)) {
if (Proto->getNoexceptSpec(getContext()) == FunctionProtoType::NR_Nothrow) {
EHStack.popTerminate();
}
} else if (EST == EST_Dynamic || EST == EST_DynamicNone) {
EHFilterScope &filterScope = cast<EHFilterScope>(*EHStack.begin());
emitFilterDispatchBlock(*this, filterScope);
EHStack.popFilter();
}
}
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
QualType CaughtType = C->getCaughtType();
CaughtType = CaughtType.getNonReferenceType().getUnqualifiedType();
llvm::Value *TypeInfo = 0;
if (CaughtType->isObjCObjectPointerType())
TypeInfo = CGM.getObjCRuntime().GetEHType(CaughtType);
else
TypeInfo = CGM.GetAddrOfRTTIDescriptor(CaughtType, /*ForEH=*/true);
CatchScope->setHandler(I, TypeInfo, Handler);
} else {
// No exception decl indicates '...', a catch-all.
CatchScope->setCatchAllHandler(I, Handler);
}
}
}
llvm::BasicBlock *
CodeGenFunction::getEHDispatchBlock(EHScopeStack::stable_iterator 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;
}
/// 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 (!CGM.getLangOpts().Exceptions)
return 0;
// 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;
// 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;
}
// This code contains a hack to work around a design flaw in
// LLVM's EH IR which breaks semantics after inlining. This same
// hack is implemented in llvm-gcc.
//
// The LLVM EH abstraction is basically a thin veneer over the
// traditional GCC zero-cost design: for each range of instructions
// in the function, there is (at most) one "landing pad" with an
// associated chain of EH actions. A language-specific personality
// function interprets this chain of actions and (1) decides whether
// or not to resume execution at the landing pad and (2) if so,
// provides an integer indicating why it's stopping. In LLVM IR,
// the association of a landing pad with a range of instructions is
// achieved via an invoke instruction, the chain of actions becomes
// the arguments to the @llvm.eh.selector call, and the selector
// call returns the integer indicator. Other than the required
// presence of two intrinsic function calls in the landing pad,
// the IR exactly describes the layout of the output code.
//
// A principal advantage of this design is that it is completely
// language-agnostic; in theory, the LLVM optimizers can treat
// landing pads neutrally, and targets need only know how to lower
// the intrinsics to have a functioning exceptions system (assuming
// that platform exceptions follow something approximately like the
// GCC design). Unfortunately, landing pads cannot be combined in a
// language-agnostic way: given selectors A and B, there is no way
// to make a single landing pad which faithfully represents the
// semantics of propagating an exception first through A, then
// through B, without knowing how the personality will interpret the
// (lowered form of the) selectors. This means that inlining has no
// choice but to crudely chain invokes (i.e., to ignore invokes in
// the inlined function, but to turn all unwindable calls into
// invokes), which is only semantically valid if every unwind stops
// at every landing pad.
//
// Therefore, the invoke-inline hack is to guarantee that every
// landing pad has a catch-all.
enum CleanupHackLevel_t {
/// A level of hack that requires that all landing pads have
/// catch-alls.
CHL_MandatoryCatchall,
/// A level of hack that requires that all landing pads handle
/// cleanups.
CHL_MandatoryCleanup,
/// No hacks at all; ideal IR generation.
CHL_Ideal
};
const CleanupHackLevel_t CleanupHackLevel = CHL_MandatoryCleanup;
llvm::BasicBlock *CodeGenFunction::EmitLandingPad() {
assert(EHStack.requiresLandingPad());
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();
SourceLocation SavedLocation;
if (CGDebugInfo *DI = getDebugInfo()) {
SavedLocation = DI->getLocation();
DI->EmitLocation(Builder, CurEHLocation);
}
const EHPersonality &personality = EHPersonality::get(getLangOpts());
// Create and configure the landing pad.
llvm::BasicBlock *lpad = createBasicBlock("lpad");
EmitBlock(lpad);
llvm::LandingPadInst *LPadInst =
Builder.CreateLandingPad(llvm::StructType::get(Int8PtrTy, Int32Ty, NULL),
getOpaquePersonalityFn(CGM, personality), 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);
// If this is a catch-all, register that and abort.
if (!handler.Type) {
assert(!hasCatchAll);
hasCatchAll = true;
goto done;
}
// Check whether we already have a handler for this type.
if (catchTypes.insert(handler.Type))
// If not, add it directly to the landingpad.
LPadInst->addClause(handler.Type);
}
}
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 (CleanupHackLevel == CHL_MandatoryCatchall || hasCleanup) {
if (CleanupHackLevel == CHL_MandatoryCatchall)
LPadInst->addClause(getCatchAllValue(*this));
else
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);
if (CGDebugInfo *DI = getDebugInfo())
DI->EmitLocation(Builder, SavedLocation);
return lpad;
}
namespace {
/// A cleanup to call __cxa_end_catch. In many cases, the caught
/// exception type lets us state definitively that the thrown exception
/// type does not have a destructor. In particular:
/// - Catch-alls tell us nothing, so we have to conservatively
/// assume that the thrown exception might have a destructor.
/// - Catches by reference behave according to their base types.
/// - Catches of non-record types will only trigger for exceptions
/// of non-record types, which never have destructors.
/// - Catches of record types can trigger for arbitrary subclasses
/// of the caught type, so we have to assume the actual thrown
/// exception type might have a throwing destructor, even if the
/// caught type's destructor is trivial or nothrow.
struct CallEndCatch : EHScopeStack::Cleanup {
CallEndCatch(bool MightThrow) : MightThrow(MightThrow) {}
bool MightThrow;
void Emit(CodeGenFunction &CGF, Flags flags) {
if (!MightThrow) {
CGF.EmitNounwindRuntimeCall(getEndCatchFn(CGF.CGM));
return;
}
CGF.EmitRuntimeCallOrInvoke(getEndCatchFn(CGF.CGM));
}
};
}
/// Emits a call to __cxa_begin_catch and enters a cleanup to call
/// __cxa_end_catch.
///
/// \param EndMightThrow - true if __cxa_end_catch might throw
static llvm::Value *CallBeginCatch(CodeGenFunction &CGF,
llvm::Value *Exn,
bool EndMightThrow) {
llvm::CallInst *call =
CGF.EmitNounwindRuntimeCall(getBeginCatchFn(CGF.CGM), Exn);
CGF.EHStack.pushCleanup<CallEndCatch>(NormalAndEHCleanup, EndMightThrow);
return call;
}
/// A "special initializer" callback for initializing a catch
/// parameter during catch initialization.
static void InitCatchParam(CodeGenFunction &CGF,
const VarDecl &CatchParam,
llvm::Value *ParamAddr) {
// Load the exception from where the landing pad saved it.
llvm::Value *Exn = CGF.getExceptionFromSlot();
CanQualType CatchType =
CGF.CGM.getContext().getCanonicalType(CatchParam.getType());
llvm::Type *LLVMCatchTy = CGF.ConvertTypeForMem(CatchType);
// If we're catching by reference, we can just cast the object
// pointer to the appropriate pointer.
if (isa<ReferenceType>(CatchType)) {
QualType CaughtType = cast<ReferenceType>(CatchType)->getPointeeType();
bool EndCatchMightThrow = CaughtType->isRecordType();
// __cxa_begin_catch returns the adjusted object pointer.
llvm::Value *AdjustedExn = CallBeginCatch(CGF, Exn, EndCatchMightThrow);
// We have no way to tell the personality function that we're
// catching by reference, so if we're catching a pointer,
// __cxa_begin_catch will actually return that pointer by value.
if (const PointerType *PT = dyn_cast<PointerType>(CaughtType)) {
QualType PointeeType = PT->getPointeeType();
// When catching by reference, generally we should just ignore
// this by-value pointer and use the exception object instead.
if (!PointeeType->isRecordType()) {
// Exn points to the struct _Unwind_Exception header, which
// we have to skip past in order to reach the exception data.
unsigned HeaderSize =
CGF.CGM.getTargetCodeGenInfo().getSizeOfUnwindException();
AdjustedExn = CGF.Builder.CreateConstGEP1_32(Exn, HeaderSize);
// However, if we're catching a pointer-to-record type that won't
// work, because the personality function might have adjusted
// the pointer. There's actually no way for us to fully satisfy
// the language/ABI contract here: we can't use Exn because it
// might have the wrong adjustment, but we can't use the by-value
// pointer because it's off by a level of abstraction.
//
// The current solution is to dump the adjusted pointer into an
// alloca, which breaks language semantics (because changing the
// pointer doesn't change the exception) but at least works.
// The better solution would be to filter out non-exact matches
// and rethrow them, but this is tricky because the rethrow
// really needs to be catchable by other sites at this landing
// pad. The best solution is to fix the personality function.
} else {
// Pull the pointer for the reference type off.
llvm::Type *PtrTy =
cast<llvm::PointerType>(LLVMCatchTy)->getElementType();
// Create the temporary and write the adjusted pointer into it.
llvm::Value *ExnPtrTmp = CGF.CreateTempAlloca(PtrTy, "exn.byref.tmp");
llvm::Value *Casted = CGF.Builder.CreateBitCast(AdjustedExn, PtrTy);
CGF.Builder.CreateStore(Casted, ExnPtrTmp);
// Bind the reference to the temporary.
AdjustedExn = ExnPtrTmp;
}
}
llvm::Value *ExnCast =
CGF.Builder.CreateBitCast(AdjustedExn, LLVMCatchTy, "exn.byref");
CGF.Builder.CreateStore(ExnCast, ParamAddr);
return;
}
// Scalars and complexes.
TypeEvaluationKind TEK = CGF.getEvaluationKind(CatchType);
if (TEK != TEK_Aggregate) {
llvm::Value *AdjustedExn = CallBeginCatch(CGF, Exn, false);
// If the catch type is a pointer type, __cxa_begin_catch returns
// the pointer by value.
if (CatchType->hasPointerRepresentation()) {
llvm::Value *CastExn =
CGF.Builder.CreateBitCast(AdjustedExn, LLVMCatchTy, "exn.casted");
switch (CatchType.getQualifiers().getObjCLifetime()) {
case Qualifiers::OCL_Strong:
CastExn = CGF.EmitARCRetainNonBlock(CastExn);
// fallthrough
case Qualifiers::OCL_None:
case Qualifiers::OCL_ExplicitNone:
case Qualifiers::OCL_Autoreleasing:
CGF.Builder.CreateStore(CastExn, ParamAddr);
return;
case Qualifiers::OCL_Weak:
CGF.EmitARCInitWeak(ParamAddr, CastExn);
return;
}
llvm_unreachable("bad ownership qualifier!");
}
// Otherwise, it returns a pointer into the exception object.
llvm::Type *PtrTy = LLVMCatchTy->getPointerTo(0); // addrspace 0 ok
llvm::Value *Cast = CGF.Builder.CreateBitCast(AdjustedExn, PtrTy);
LValue srcLV = CGF.MakeNaturalAlignAddrLValue(Cast, CatchType);
LValue destLV = CGF.MakeAddrLValue(ParamAddr, CatchType,
CGF.getContext().getDeclAlign(&CatchParam));
switch (TEK) {
case TEK_Complex:
CGF.EmitStoreOfComplex(CGF.EmitLoadOfComplex(srcLV), destLV,
/*init*/ true);
return;
case TEK_Scalar: {
llvm::Value *ExnLoad = CGF.EmitLoadOfScalar(srcLV);
CGF.EmitStoreOfScalar(ExnLoad, destLV, /*init*/ true);
return;
}
case TEK_Aggregate:
llvm_unreachable("evaluation kind filtered out!");
}
llvm_unreachable("bad evaluation kind");
}
assert(isa<RecordType>(CatchType) && "unexpected catch type!");
llvm::Type *PtrTy = LLVMCatchTy->getPointerTo(0); // addrspace 0 ok
// Check for a copy expression. If we don't have a copy expression,
// that means a trivial copy is okay.
const Expr *copyExpr = CatchParam.getInit();
if (!copyExpr) {
llvm::Value *rawAdjustedExn = CallBeginCatch(CGF, Exn, true);
llvm::Value *adjustedExn = CGF.Builder.CreateBitCast(rawAdjustedExn, PtrTy);
CGF.EmitAggregateCopy(ParamAddr, adjustedExn, CatchType);
return;
}
// We have to call __cxa_get_exception_ptr to get the adjusted
// pointer before copying.
llvm::CallInst *rawAdjustedExn =
CGF.EmitNounwindRuntimeCall(getGetExceptionPtrFn(CGF.CGM), Exn);
// Cast that to the appropriate type.
llvm::Value *adjustedExn = CGF.Builder.CreateBitCast(rawAdjustedExn, PtrTy);
// The copy expression is defined in terms of an OpaqueValueExpr.
// Find it and map it to the adjusted expression.
CodeGenFunction::OpaqueValueMapping
opaque(CGF, OpaqueValueExpr::findInCopyConstruct(copyExpr),
CGF.MakeAddrLValue(adjustedExn, CatchParam.getType()));
// Call the copy ctor in a terminate scope.
CGF.EHStack.pushTerminate();
// Perform the copy construction.
CharUnits Alignment = CGF.getContext().getDeclAlign(&CatchParam);
CGF.EmitAggExpr(copyExpr,
AggValueSlot::forAddr(ParamAddr, Alignment, Qualifiers(),
AggValueSlot::IsNotDestructed,
AggValueSlot::DoesNotNeedGCBarriers,
AggValueSlot::IsNotAliased));
// Leave the terminate scope.
CGF.EHStack.popTerminate();
// Undo the opaque value mapping.
opaque.pop();
// Finally we can call __cxa_begin_catch.
CallBeginCatch(CGF, Exn, true);
}
/// Begins a catch statement by initializing the catch variable and
/// calling __cxa_begin_catch.
static void BeginCatch(CodeGenFunction &CGF, const CXXCatchStmt *S) {
// We have to be very careful with the ordering of cleanups here:
// C++ [except.throw]p4:
// The destruction [of the exception temporary] occurs
// immediately after the destruction of the object declared in
// the exception-declaration in the handler.
//
// So the precise ordering is:
// 1. Construct catch variable.
// 2. __cxa_begin_catch
// 3. Enter __cxa_end_catch cleanup
// 4. Enter dtor cleanup
//
// We do this by using a slightly abnormal initialization process.
// Delegation sequence:
// - ExitCXXTryStmt opens a RunCleanupsScope
// - EmitAutoVarAlloca creates the variable and debug info
// - InitCatchParam initializes the variable from the exception
// - CallBeginCatch calls __cxa_begin_catch
// - CallBeginCatch enters the __cxa_end_catch cleanup
// - EmitAutoVarCleanups enters the variable destructor cleanup
// - EmitCXXTryStmt emits the code for the catch body
// - EmitCXXTryStmt close the RunCleanupsScope
VarDecl *CatchParam = S->getExceptionDecl();
if (!CatchParam) {
llvm::Value *Exn = CGF.getExceptionFromSlot();
CallBeginCatch(CGF, Exn, true);
return;
}
// Emit the local.
CodeGenFunction::AutoVarEmission var = CGF.EmitAutoVarAlloca(*CatchParam);
InitCatchParam(CGF, *CatchParam, var.getObjectAddress(CGF));
CGF.EmitAutoVarCleanups(var);
}
/// 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) {
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::Value *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;
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);
// If the catch was not required, bail out now.
if (!CatchScope.hasEHBranches()) {
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(NumHandlers);
memcpy(Handlers.data(), CatchScope.begin(),
NumHandlers * sizeof(EHCatchScope::Handler));
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);
// 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.
for (unsigned I = NumHandlers; I != 0; --I) {
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.
BeginCatch(*this, 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()) {
EmitRuntimeCallOrInvoke(getReThrowFn(CGM));
Builder.CreateUnreachable();
Builder.ClearInsertionPoint();
}
// Fall out through the catch cleanups.
CatchScope.ForceCleanup();
// Branch out of the try.
if (HaveInsertPoint())
Builder.CreateBr(ContBB);
}
EmitBlock(ContBB);
}
namespace {
struct CallEndCatchForFinally : EHScopeStack::Cleanup {
llvm::Value *ForEHVar;
llvm::Value *EndCatchFn;
CallEndCatchForFinally(llvm::Value *ForEHVar, llvm::Value *EndCatchFn)
: ForEHVar(ForEHVar), EndCatchFn(EndCatchFn) {}
void Emit(CodeGenFunction &CGF, Flags flags) {
llvm::BasicBlock *EndCatchBB = CGF.createBasicBlock("finally.endcatch");
llvm::BasicBlock *CleanupContBB =
CGF.createBasicBlock("finally.cleanup.cont");
llvm::Value *ShouldEndCatch =
CGF.Builder.CreateLoad(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 : EHScopeStack::Cleanup {
const Stmt *Body;
llvm::Value *ForEHVar;
llvm::Value *EndCatchFn;
llvm::Value *RethrowFn;
llvm::Value *SavedExnVar;
PerformFinally(const Stmt *Body, llvm::Value *ForEHVar,
llvm::Value *EndCatchFn,
llvm::Value *RethrowFn, llvm::Value *SavedExnVar)
: Body(Body), ForEHVar(ForEHVar), EndCatchFn(EndCatchFn),
RethrowFn(RethrowFn), SavedExnVar(SavedExnVar) {}
void Emit(CodeGenFunction &CGF, Flags flags) {
// 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.CreateLoad(ForEHVar, "finally.shouldthrow");
CGF.Builder.CreateCondBr(ShouldRethrow, RethrowBB, ContBB);
CGF.EmitBlock(RethrowBB);
if (SavedExnVar) {
CGF.EmitRuntimeCallOrInvoke(RethrowFn,
CGF.Builder.CreateLoad(SavedExnVar));
} 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();
}
};
}
/// 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::Constant *beginCatchFn,
llvm::Constant *endCatchFn,
llvm::Constant *rethrowFn) {
assert((beginCatchFn != 0) == (endCatchFn != 0) &&
"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 =
cast<llvm::FunctionType>(
cast<llvm::PointerType>(rethrowFn->getType())->getElementType());
SavedExnVar = 0;
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.CreateStore(CGF.Builder.getFalse(), 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 = 0;
// 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.CreateStore(exn, SavedExnVar);
}
// Tell the cleanups in the finally block that we're do this for EH.
CGF.Builder.CreateStore(CGF.Builder.getTrue(), ForEHVar);
// Thread a jump through the finally cleanup.
CGF.EmitBranchThroughCleanup(RethrowDest);
CGF.Builder.restoreIP(savedIP);
}
// Finally, leave the @finally cleanup.
CGF.PopCleanupBlock();
}
/// In a terminate landing pad, should we use __clang__call_terminate
/// or just a naked call to std::terminate?
///
/// __clang_call_terminate calls __cxa_begin_catch, which then allows
/// std::terminate to usefully report something about the
/// violating exception.
static bool useClangCallTerminate(CodeGenModule &CGM) {
// Only do this for Itanium-family ABIs in C++ mode.
return (CGM.getLangOpts().CPlusPlus &&
CGM.getTarget().getCXXABI().isItaniumFamily());
}
/// Get or define the following function:
/// void @__clang_call_terminate(i8* %exn) nounwind noreturn
/// This code is used only in C++.
static llvm::Constant *getClangCallTerminateFn(CodeGenModule &CGM) {
llvm::FunctionType *fnTy =
llvm::FunctionType::get(CGM.VoidTy, CGM.Int8PtrTy, /*IsVarArgs=*/false);
llvm::Constant *fnRef =
CGM.CreateRuntimeFunction(fnTy, "__clang_call_terminate");
llvm::Function *fn = dyn_cast<llvm::Function>(fnRef);
if (fn && fn->empty()) {
fn->setDoesNotThrow();
fn->setDoesNotReturn();
// What we really want is to massively penalize inlining without
// forbidding it completely. The difference between that and
// 'noinline' is negligible.
fn->addFnAttr(llvm::Attribute::NoInline);
// Allow this function to be shared across translation units, but
// we don't want it to turn into an exported symbol.
fn->setLinkage(llvm::Function::LinkOnceODRLinkage);
fn->setVisibility(llvm::Function::HiddenVisibility);
// Set up the function.
llvm::BasicBlock *entry =
llvm::BasicBlock::Create(CGM.getLLVMContext(), "", fn);
CGBuilderTy builder(entry);
// Pull the exception pointer out of the parameter list.
llvm::Value *exn = &*fn->arg_begin();
// Call __cxa_begin_catch(exn).
llvm::CallInst *catchCall = builder.CreateCall(getBeginCatchFn(CGM), exn);
catchCall->setDoesNotThrow();
catchCall->setCallingConv(CGM.getRuntimeCC());
// Call std::terminate().
llvm::CallInst *termCall = builder.CreateCall(getTerminateFn(CGM));
termCall->setDoesNotThrow();
termCall->setDoesNotReturn();
termCall->setCallingConv(CGM.getRuntimeCC());
// std::terminate cannot return.
builder.CreateUnreachable();
}
return fnRef;
}
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(CGM.getLangOpts());
llvm::LandingPadInst *LPadInst =
Builder.CreateLandingPad(llvm::StructType::get(Int8PtrTy, Int32Ty, NULL),
getOpaquePersonalityFn(CGM, Personality), 0);
LPadInst->addClause(getCatchAllValue(*this));
llvm::CallInst *terminateCall;
if (useClangCallTerminate(CGM)) {
// Extract out the exception pointer.
llvm::Value *exn = Builder.CreateExtractValue(LPadInst, 0);
terminateCall = EmitNounwindRuntimeCall(getClangCallTerminateFn(CGM), exn);
} else {
terminateCall = EmitNounwindRuntimeCall(getTerminateFn(CGM));
}
terminateCall->setDoesNotReturn();
Builder.CreateUnreachable();
// Restore the saved insertion state.
Builder.restoreIP(SavedIP);
return TerminateLandingPad;
}
llvm::BasicBlock *CodeGenFunction::getTerminateHandler() {
if (TerminateHandler)
return TerminateHandler;
CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
// Set up the terminate handler. This block is inserted at the very
// end of the function by FinishFunction.
TerminateHandler = createBasicBlock("terminate.handler");
Builder.SetInsertPoint(TerminateHandler);
llvm::CallInst *terminateCall;
if (useClangCallTerminate(CGM)) {
// Load the exception pointer.
llvm::Value *exn = getExceptionFromSlot();
terminateCall = EmitNounwindRuntimeCall(getClangCallTerminateFn(CGM), exn);
} else {
terminateCall = EmitNounwindRuntimeCall(getTerminateFn(CGM));
}
terminateCall->setDoesNotReturn();
Builder.CreateUnreachable();
// Restore the saved insertion state.
Builder.restoreIP(SavedIP);
return TerminateHandler;
}
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(CGM.getLangOpts());
// 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 != 0 && !isCleanup) {
EmitRuntimeCall(getCatchallRethrowFn(CGM, RethrowName),
getExceptionFromSlot())
->setDoesNotReturn();
} else {
switch (CleanupHackLevel) {
case CHL_MandatoryCatchall:
// In mandatory-catchall mode, we need to use
// _Unwind_Resume_or_Rethrow, or whatever the personality's
// equivalent is.
EmitRuntimeCall(getUnwindResumeOrRethrowFn(),
getExceptionFromSlot())
->setDoesNotReturn();
break;
case CHL_MandatoryCleanup: {
// In mandatory-cleanup mode, we should use 'resume'.
// 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(), NULL);
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;
}
case CHL_Ideal:
// In an idealized mode where we don't have to worry about the
// optimizer combining landing pads, we should just use
// _Unwind_Resume (or the personality's equivalent).
EmitRuntimeCall(getUnwindResumeFn(), getExceptionFromSlot())
->setDoesNotReturn();
break;
}
}
Builder.CreateUnreachable();
Builder.restoreIP(SavedIP);
return EHResumeBlock;
}