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//===--- CGCleanup.cpp - Bookkeeping and code emission for cleanups -------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file contains code dealing with the IR generation for cleanups
// and related information.
// A "cleanup" is a piece of code which needs to be executed whenever
// control transfers out of a particular scope. This can be
// conditionalized to occur only on exceptional control flow, only on
// normal control flow, or both.
#include "CGCleanup.h"
#include "CodeGenFunction.h"
#include "llvm/Support/SaveAndRestore.h"
using namespace clang;
using namespace CodeGen;
bool DominatingValue<RValue>::saved_type::needsSaving(RValue rv) {
if (rv.isScalar())
return DominatingLLVMValue::needsSaving(rv.getScalarVal());
if (rv.isAggregate())
return DominatingLLVMValue::needsSaving(rv.getAggregatePointer());
return true;
DominatingValue<RValue>::saved_type::save(CodeGenFunction &CGF, RValue rv) {
if (rv.isScalar()) {
llvm::Value *V = rv.getScalarVal();
// These automatically dominate and don't need to be saved.
if (!DominatingLLVMValue::needsSaving(V))
return saved_type(V, ScalarLiteral);
// Everything else needs an alloca.
Address addr =
CGF.CreateDefaultAlignTempAlloca(V->getType(), "saved-rvalue");
CGF.Builder.CreateStore(V, addr);
return saved_type(addr.getPointer(), ScalarAddress);
if (rv.isComplex()) {
CodeGenFunction::ComplexPairTy V = rv.getComplexVal();
llvm::Type *ComplexTy =
llvm::StructType::get(V.first->getType(), V.second->getType());
Address addr = CGF.CreateDefaultAlignTempAlloca(ComplexTy, "saved-complex");
CGF.Builder.CreateStore(V.first, CGF.Builder.CreateStructGEP(addr, 0));
CGF.Builder.CreateStore(V.second, CGF.Builder.CreateStructGEP(addr, 1));
return saved_type(addr.getPointer(), ComplexAddress);
Address V = rv.getAggregateAddress(); // TODO: volatile?
if (!DominatingLLVMValue::needsSaving(V.getPointer()))
return saved_type(V.getPointer(), AggregateLiteral,
Address addr =
CGF.CreateTempAlloca(V.getType(), CGF.getPointerAlign(), "saved-rvalue");
CGF.Builder.CreateStore(V.getPointer(), addr);
return saved_type(addr.getPointer(), AggregateAddress,
/// Given a saved r-value produced by SaveRValue, perform the code
/// necessary to restore it to usability at the current insertion
/// point.
RValue DominatingValue<RValue>::saved_type::restore(CodeGenFunction &CGF) {
auto getSavingAddress = [&](llvm::Value *value) {
auto alignment = cast<llvm::AllocaInst>(value)->getAlignment();
return Address(value, CharUnits::fromQuantity(alignment));
switch (K) {
case ScalarLiteral:
return RValue::get(Value);
case ScalarAddress:
return RValue::get(CGF.Builder.CreateLoad(getSavingAddress(Value)));
case AggregateLiteral:
return RValue::getAggregate(Address(Value, CharUnits::fromQuantity(Align)));
case AggregateAddress: {
auto addr = CGF.Builder.CreateLoad(getSavingAddress(Value));
return RValue::getAggregate(Address(addr, CharUnits::fromQuantity(Align)));
case ComplexAddress: {
Address address = getSavingAddress(Value);
llvm::Value *real =
CGF.Builder.CreateLoad(CGF.Builder.CreateStructGEP(address, 0));
llvm::Value *imag =
CGF.Builder.CreateLoad(CGF.Builder.CreateStructGEP(address, 1));
return RValue::getComplex(real, imag);
llvm_unreachable("bad saved r-value kind");
/// Push an entry of the given size onto this protected-scope stack.
char *EHScopeStack::allocate(size_t Size) {
Size = llvm::alignTo(Size, ScopeStackAlignment);
if (!StartOfBuffer) {
unsigned Capacity = 1024;
while (Capacity < Size) Capacity *= 2;
StartOfBuffer = new char[Capacity];
StartOfData = EndOfBuffer = StartOfBuffer + Capacity;
} else if (static_cast<size_t>(StartOfData - StartOfBuffer) < Size) {
unsigned CurrentCapacity = EndOfBuffer - StartOfBuffer;
unsigned UsedCapacity = CurrentCapacity - (StartOfData - StartOfBuffer);
unsigned NewCapacity = CurrentCapacity;
do {
NewCapacity *= 2;
} while (NewCapacity < UsedCapacity + Size);
char *NewStartOfBuffer = new char[NewCapacity];
char *NewEndOfBuffer = NewStartOfBuffer + NewCapacity;
char *NewStartOfData = NewEndOfBuffer - UsedCapacity;
memcpy(NewStartOfData, StartOfData, UsedCapacity);
delete [] StartOfBuffer;
StartOfBuffer = NewStartOfBuffer;
EndOfBuffer = NewEndOfBuffer;
StartOfData = NewStartOfData;
assert(StartOfBuffer + Size <= StartOfData);
StartOfData -= Size;
return StartOfData;
void EHScopeStack::deallocate(size_t Size) {
StartOfData += llvm::alignTo(Size, ScopeStackAlignment);
bool EHScopeStack::containsOnlyLifetimeMarkers(
EHScopeStack::stable_iterator Old) const {
for (EHScopeStack::iterator it = begin(); stabilize(it) != Old; it++) {
EHCleanupScope *cleanup = dyn_cast<EHCleanupScope>(&*it);
if (!cleanup || !cleanup->isLifetimeMarker())
return false;
return true;
bool EHScopeStack::requiresLandingPad() const {
for (stable_iterator si = getInnermostEHScope(); si != stable_end(); ) {
// Skip lifetime markers.
if (auto *cleanup = dyn_cast<EHCleanupScope>(&*find(si)))
if (cleanup->isLifetimeMarker()) {
si = cleanup->getEnclosingEHScope();
return true;
return false;
EHScopeStack::getInnermostActiveNormalCleanup() const {
for (stable_iterator si = getInnermostNormalCleanup(), se = stable_end();
si != se; ) {
EHCleanupScope &cleanup = cast<EHCleanupScope>(*find(si));
if (cleanup.isActive()) return si;
si = cleanup.getEnclosingNormalCleanup();
return stable_end();
void *EHScopeStack::pushCleanup(CleanupKind Kind, size_t Size) {
char *Buffer = allocate(EHCleanupScope::getSizeForCleanupSize(Size));
bool IsNormalCleanup = Kind & NormalCleanup;
bool IsEHCleanup = Kind & EHCleanup;
bool IsActive = !(Kind & InactiveCleanup);
bool IsLifetimeMarker = Kind & LifetimeMarker;
EHCleanupScope *Scope =
new (Buffer) EHCleanupScope(IsNormalCleanup,
if (IsNormalCleanup)
InnermostNormalCleanup = stable_begin();
if (IsEHCleanup)
InnermostEHScope = stable_begin();
if (IsLifetimeMarker)
return Scope->getCleanupBuffer();
void EHScopeStack::popCleanup() {
assert(!empty() && "popping exception stack when not empty");
EHCleanupScope &Cleanup = cast<EHCleanupScope>(*begin());
InnermostNormalCleanup = Cleanup.getEnclosingNormalCleanup();
InnermostEHScope = Cleanup.getEnclosingEHScope();
// Destroy the cleanup.
// Check whether we can shrink the branch-fixups stack.
if (!BranchFixups.empty()) {
// If we no longer have any normal cleanups, all the fixups are
// complete.
if (!hasNormalCleanups())
// Otherwise we can still trim out unnecessary nulls.
EHFilterScope *EHScopeStack::pushFilter(unsigned numFilters) {
assert(getInnermostEHScope() == stable_end());
char *buffer = allocate(EHFilterScope::getSizeForNumFilters(numFilters));
EHFilterScope *filter = new (buffer) EHFilterScope(numFilters);
InnermostEHScope = stable_begin();
return filter;
void EHScopeStack::popFilter() {
assert(!empty() && "popping exception stack when not empty");
EHFilterScope &filter = cast<EHFilterScope>(*begin());
InnermostEHScope = filter.getEnclosingEHScope();
EHCatchScope *EHScopeStack::pushCatch(unsigned numHandlers) {
char *buffer = allocate(EHCatchScope::getSizeForNumHandlers(numHandlers));
EHCatchScope *scope =
new (buffer) EHCatchScope(numHandlers, InnermostEHScope);
InnermostEHScope = stable_begin();
return scope;
void EHScopeStack::pushTerminate() {
char *Buffer = allocate(EHTerminateScope::getSize());
new (Buffer) EHTerminateScope(InnermostEHScope);
InnermostEHScope = stable_begin();
/// Remove any 'null' fixups on the stack. However, we can't pop more
/// fixups than the fixup depth on the innermost normal cleanup, or
/// else fixups that we try to add to that cleanup will end up in the
/// wrong place. We *could* try to shrink fixup depths, but that's
/// actually a lot of work for little benefit.
void EHScopeStack::popNullFixups() {
// We expect this to only be called when there's still an innermost
// normal cleanup; otherwise there really shouldn't be any fixups.
EHScopeStack::iterator it = find(InnermostNormalCleanup);
unsigned MinSize = cast<EHCleanupScope>(*it).getFixupDepth();
assert(BranchFixups.size() >= MinSize && "fixup stack out of order");
while (BranchFixups.size() > MinSize &&
BranchFixups.back().Destination == nullptr)
Address CodeGenFunction::createCleanupActiveFlag() {
// Create a variable to decide whether the cleanup needs to be run.
Address active = CreateTempAllocaWithoutCast(
Builder.getInt1Ty(), CharUnits::One(), "cleanup.cond");
// Initialize it to false at a site that's guaranteed to be run
// before each evaluation.
setBeforeOutermostConditional(Builder.getFalse(), active);
// Initialize it to true at the current location.
Builder.CreateStore(Builder.getTrue(), active);
return active;
void CodeGenFunction::initFullExprCleanupWithFlag(Address ActiveFlag) {
// Set that as the active flag in the cleanup.
EHCleanupScope &cleanup = cast<EHCleanupScope>(*EHStack.begin());
assert(!cleanup.hasActiveFlag() && "cleanup already has active flag?");
if (cleanup.isNormalCleanup()) cleanup.setTestFlagInNormalCleanup();
if (cleanup.isEHCleanup()) cleanup.setTestFlagInEHCleanup();
void EHScopeStack::Cleanup::anchor() {}
static void createStoreInstBefore(llvm::Value *value, Address addr,
llvm::Instruction *beforeInst) {
auto store = new llvm::StoreInst(value, addr.getPointer(), beforeInst);
static llvm::LoadInst *createLoadInstBefore(Address addr, const Twine &name,
llvm::Instruction *beforeInst) {
auto load = new llvm::LoadInst(addr.getPointer(), name, beforeInst);
return load;
/// All the branch fixups on the EH stack have propagated out past the
/// outermost normal cleanup; resolve them all by adding cases to the
/// given switch instruction.
static void ResolveAllBranchFixups(CodeGenFunction &CGF,
llvm::SwitchInst *Switch,
llvm::BasicBlock *CleanupEntry) {
llvm::SmallPtrSet<llvm::BasicBlock*, 4> CasesAdded;
for (unsigned I = 0, E = CGF.EHStack.getNumBranchFixups(); I != E; ++I) {
// Skip this fixup if its destination isn't set.
BranchFixup &Fixup = CGF.EHStack.getBranchFixup(I);
if (Fixup.Destination == nullptr) continue;
// If there isn't an OptimisticBranchBlock, then InitialBranch is
// still pointing directly to its destination; forward it to the
// appropriate cleanup entry. This is required in the specific
// case of
// { std::string s; goto lbl; }
// lbl:
// i.e. where there's an unresolved fixup inside a single cleanup
// entry which we're currently popping.
if (Fixup.OptimisticBranchBlock == nullptr) {
Fixup.InitialBranch->setSuccessor(0, CleanupEntry);
// Don't add this case to the switch statement twice.
if (!CasesAdded.insert(Fixup.Destination).second)
/// Transitions the terminator of the given exit-block of a cleanup to
/// be a cleanup switch.
static llvm::SwitchInst *TransitionToCleanupSwitch(CodeGenFunction &CGF,
llvm::BasicBlock *Block) {
// If it's a branch, turn it into a switch whose default
// destination is its original target.
llvm::Instruction *Term = Block->getTerminator();
assert(Term && "can't transition block without terminator");
if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
auto Load = createLoadInstBefore(CGF.getNormalCleanupDestSlot(),
"cleanup.dest", Term);
llvm::SwitchInst *Switch =
llvm::SwitchInst::Create(Load, Br->getSuccessor(0), 4, Block);
return Switch;
} else {
return cast<llvm::SwitchInst>(Term);
void CodeGenFunction::ResolveBranchFixups(llvm::BasicBlock *Block) {
assert(Block && "resolving a null target block");
if (!EHStack.getNumBranchFixups()) return;
assert(EHStack.hasNormalCleanups() &&
"branch fixups exist with no normal cleanups on stack");
llvm::SmallPtrSet<llvm::BasicBlock*, 4> ModifiedOptimisticBlocks;
bool ResolvedAny = false;
for (unsigned I = 0, E = EHStack.getNumBranchFixups(); I != E; ++I) {
// Skip this fixup if its destination doesn't match.
BranchFixup &Fixup = EHStack.getBranchFixup(I);
if (Fixup.Destination != Block) continue;
Fixup.Destination = nullptr;
ResolvedAny = true;
// If it doesn't have an optimistic branch block, LatestBranch is
// already pointing to the right place.
llvm::BasicBlock *BranchBB = Fixup.OptimisticBranchBlock;
if (!BranchBB)
// Don't process the same optimistic branch block twice.
if (!ModifiedOptimisticBlocks.insert(BranchBB).second)
llvm::SwitchInst *Switch = TransitionToCleanupSwitch(*this, BranchBB);
// Add a case to the switch.
Switch->addCase(Builder.getInt32(Fixup.DestinationIndex), Block);
if (ResolvedAny)
/// Pops cleanup blocks until the given savepoint is reached.
void CodeGenFunction::PopCleanupBlocks(
EHScopeStack::stable_iterator Old,
std::initializer_list<llvm::Value **> ValuesToReload) {
bool HadBranches = false;
while (EHStack.stable_begin() != Old) {
EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
HadBranches |= Scope.hasBranches();
// As long as Old strictly encloses the scope's enclosing normal
// cleanup, we're going to emit another normal cleanup which
// fallthrough can propagate through.
bool FallThroughIsBranchThrough =
// If we didn't have any branches, the insertion point before cleanups must
// dominate the current insertion point and we don't need to reload any
// values.
if (!HadBranches)
// Spill and reload all values that the caller wants to be live at the current
// insertion point.
for (llvm::Value **ReloadedValue : ValuesToReload) {
auto *Inst = dyn_cast_or_null<llvm::Instruction>(*ReloadedValue);
if (!Inst)
// Don't spill static allocas, they dominate all cleanups. These are created
// by binding a reference to a local variable or temporary.
auto *AI = dyn_cast<llvm::AllocaInst>(Inst);
if (AI && AI->isStaticAlloca())
Address Tmp =
CreateDefaultAlignTempAlloca(Inst->getType(), "tmp.exprcleanup");
// Find an insertion point after Inst and spill it to the temporary.
llvm::BasicBlock::iterator InsertBefore;
if (auto *Invoke = dyn_cast<llvm::InvokeInst>(Inst))
InsertBefore = Invoke->getNormalDest()->getFirstInsertionPt();
InsertBefore = std::next(Inst->getIterator());
CGBuilderTy(CGM, &*InsertBefore).CreateStore(Inst, Tmp);
// Reload the value at the current insertion point.
*ReloadedValue = Builder.CreateLoad(Tmp);
/// Pops cleanup blocks until the given savepoint is reached, then add the
/// cleanups from the given savepoint in the lifetime-extended cleanups stack.
void CodeGenFunction::PopCleanupBlocks(
EHScopeStack::stable_iterator Old, size_t OldLifetimeExtendedSize,
std::initializer_list<llvm::Value **> ValuesToReload) {
PopCleanupBlocks(Old, ValuesToReload);
// Move our deferred cleanups onto the EH stack.
for (size_t I = OldLifetimeExtendedSize,
E = LifetimeExtendedCleanupStack.size(); I != E; /**/) {
// Alignment should be guaranteed by the vptrs in the individual cleanups.
assert((I % alignof(LifetimeExtendedCleanupHeader) == 0) &&
"misaligned cleanup stack entry");
LifetimeExtendedCleanupHeader &Header =
I += sizeof(Header);
I += Header.getSize();
if (Header.isConditional()) {
Address ActiveFlag =
reinterpret_cast<Address &>(LifetimeExtendedCleanupStack[I]);
I += sizeof(ActiveFlag);
static llvm::BasicBlock *CreateNormalEntry(CodeGenFunction &CGF,
EHCleanupScope &Scope) {
llvm::BasicBlock *Entry = Scope.getNormalBlock();
if (!Entry) {
Entry = CGF.createBasicBlock("cleanup");
return Entry;
/// Attempts to reduce a cleanup's entry block to a fallthrough. This
/// is basically llvm::MergeBlockIntoPredecessor, except
/// simplified/optimized for the tighter constraints on cleanup blocks.
/// Returns the new block, whatever it is.
static llvm::BasicBlock *SimplifyCleanupEntry(CodeGenFunction &CGF,
llvm::BasicBlock *Entry) {
llvm::BasicBlock *Pred = Entry->getSinglePredecessor();
if (!Pred) return Entry;
llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Pred->getTerminator());
if (!Br || Br->isConditional()) return Entry;
assert(Br->getSuccessor(0) == Entry);
// If we were previously inserting at the end of the cleanup entry
// block, we'll need to continue inserting at the end of the
// predecessor.
bool WasInsertBlock = CGF.Builder.GetInsertBlock() == Entry;
assert(!WasInsertBlock || CGF.Builder.GetInsertPoint() == Entry->end());
// Kill the branch.
// Replace all uses of the entry with the predecessor, in case there
// are phis in the cleanup.
// Merge the blocks.
Pred->getInstList().splice(Pred->end(), Entry->getInstList());
// Kill the entry block.
if (WasInsertBlock)
return Pred;
static void EmitCleanup(CodeGenFunction &CGF,
EHScopeStack::Cleanup *Fn,
EHScopeStack::Cleanup::Flags flags,
Address ActiveFlag) {
// If there's an active flag, load it and skip the cleanup if it's
// false.
llvm::BasicBlock *ContBB = nullptr;
if (ActiveFlag.isValid()) {
ContBB = CGF.createBasicBlock("cleanup.done");
llvm::BasicBlock *CleanupBB = CGF.createBasicBlock("cleanup.action");
llvm::Value *IsActive
= CGF.Builder.CreateLoad(ActiveFlag, "cleanup.is_active");
CGF.Builder.CreateCondBr(IsActive, CleanupBB, ContBB);
// Ask the cleanup to emit itself.
Fn->Emit(CGF, flags);
assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
// Emit the continuation block if there was an active flag.
if (ActiveFlag.isValid())
static void ForwardPrebranchedFallthrough(llvm::BasicBlock *Exit,
llvm::BasicBlock *From,
llvm::BasicBlock *To) {
// Exit is the exit block of a cleanup, so it always terminates in
// an unconditional branch or a switch.
llvm::Instruction *Term = Exit->getTerminator();
if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
assert(Br->isUnconditional() && Br->getSuccessor(0) == From);
Br->setSuccessor(0, To);
} else {
llvm::SwitchInst *Switch = cast<llvm::SwitchInst>(Term);
for (unsigned I = 0, E = Switch->getNumSuccessors(); I != E; ++I)
if (Switch->getSuccessor(I) == From)
Switch->setSuccessor(I, To);
/// We don't need a normal entry block for the given cleanup.
/// Optimistic fixup branches can cause these blocks to come into
/// existence anyway; if so, destroy it.
/// The validity of this transformation is very much specific to the
/// exact ways in which we form branches to cleanup entries.
static void destroyOptimisticNormalEntry(CodeGenFunction &CGF,
EHCleanupScope &scope) {
llvm::BasicBlock *entry = scope.getNormalBlock();
if (!entry) return;
// Replace all the uses with unreachable.
llvm::BasicBlock *unreachableBB = CGF.getUnreachableBlock();
for (llvm::BasicBlock::use_iterator
i = entry->use_begin(), e = entry->use_end(); i != e; ) {
llvm::Use &use = *i;
// The only uses should be fixup switches.
llvm::SwitchInst *si = cast<llvm::SwitchInst>(use.getUser());
if (si->getNumCases() == 1 && si->getDefaultDest() == unreachableBB) {
// Replace the switch with a branch.
llvm::BranchInst::Create(si->case_begin()->getCaseSuccessor(), si);
// The switch operand is a load from the cleanup-dest alloca.
llvm::LoadInst *condition = cast<llvm::LoadInst>(si->getCondition());
// Destroy the switch.
// Destroy the load.
assert(condition->getOperand(0) == CGF.NormalCleanupDest.getPointer());
delete entry;
/// Pops a cleanup block. If the block includes a normal cleanup, the
/// current insertion point is threaded through the cleanup, as are
/// any branch fixups on the cleanup.
void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
assert(!EHStack.empty() && "cleanup stack is empty!");
assert(isa<EHCleanupScope>(*EHStack.begin()) && "top not a cleanup!");
EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
assert(Scope.getFixupDepth() <= EHStack.getNumBranchFixups());
// Remember activation information.
bool IsActive = Scope.isActive();
Address NormalActiveFlag =
Scope.shouldTestFlagInNormalCleanup() ? Scope.getActiveFlag()
: Address::invalid();
Address EHActiveFlag =
Scope.shouldTestFlagInEHCleanup() ? Scope.getActiveFlag()
: Address::invalid();
// Check whether we need an EH cleanup. This is only true if we've
// generated a lazy EH cleanup block.
llvm::BasicBlock *EHEntry = Scope.getCachedEHDispatchBlock();
assert(Scope.hasEHBranches() == (EHEntry != nullptr));
bool RequiresEHCleanup = (EHEntry != nullptr);
EHScopeStack::stable_iterator EHParent = Scope.getEnclosingEHScope();
// Check the three conditions which might require a normal cleanup:
// - whether there are branch fix-ups through this cleanup
unsigned FixupDepth = Scope.getFixupDepth();
bool HasFixups = EHStack.getNumBranchFixups() != FixupDepth;
// - whether there are branch-throughs or branch-afters
bool HasExistingBranches = Scope.hasBranches();
// - whether there's a fallthrough
llvm::BasicBlock *FallthroughSource = Builder.GetInsertBlock();
bool HasFallthrough = (FallthroughSource != nullptr && IsActive);
// Branch-through fall-throughs leave the insertion point set to the
// end of the last cleanup, which points to the current scope. The
// rest of IR gen doesn't need to worry about this; it only happens
// during the execution of PopCleanupBlocks().
bool HasPrebranchedFallthrough =
(FallthroughSource && FallthroughSource->getTerminator());
// If this is a normal cleanup, then having a prebranched
// fallthrough implies that the fallthrough source unconditionally
// jumps here.
assert(!Scope.isNormalCleanup() || !HasPrebranchedFallthrough ||
(Scope.getNormalBlock() &&
== Scope.getNormalBlock()));
bool RequiresNormalCleanup = false;
if (Scope.isNormalCleanup() &&
(HasFixups || HasExistingBranches || HasFallthrough)) {
RequiresNormalCleanup = true;
// If we have a prebranched fallthrough into an inactive normal
// cleanup, rewrite it so that it leads to the appropriate place.
if (Scope.isNormalCleanup() && HasPrebranchedFallthrough && !IsActive) {
llvm::BasicBlock *prebranchDest;
// If the prebranch is semantically branching through the next
// cleanup, just forward it to the next block, leaving the
// insertion point in the prebranched block.
if (FallthroughIsBranchThrough) {
EHScope &enclosing = *EHStack.find(Scope.getEnclosingNormalCleanup());
prebranchDest = CreateNormalEntry(*this, cast<EHCleanupScope>(enclosing));
// Otherwise, we need to make a new block. If the normal cleanup
// isn't being used at all, we could actually reuse the normal
// entry block, but this is simpler, and it avoids conflicts with
// dead optimistic fixup branches.
} else {
prebranchDest = createBasicBlock("forwarded-prebranch");
llvm::BasicBlock *normalEntry = Scope.getNormalBlock();
assert(normalEntry && !normalEntry->use_empty());
normalEntry, prebranchDest);
// If we don't need the cleanup at all, we're done.
if (!RequiresNormalCleanup && !RequiresEHCleanup) {
destroyOptimisticNormalEntry(*this, Scope);
EHStack.popCleanup(); // safe because there are no fixups
assert(EHStack.getNumBranchFixups() == 0 ||
// Copy the cleanup emission data out. This uses either a stack
// array or malloc'd memory, depending on the size, which is
// behavior that SmallVector would provide, if we could use it
// here. Unfortunately, if you ask for a SmallVector<char>, the
// alignment isn't sufficient.
auto *CleanupSource = reinterpret_cast<char *>(Scope.getCleanupBuffer());
alignas(EHScopeStack::ScopeStackAlignment) char
CleanupBufferStack[8 * sizeof(void *)];
std::unique_ptr<char[]> CleanupBufferHeap;
size_t CleanupSize = Scope.getCleanupSize();
EHScopeStack::Cleanup *Fn;
if (CleanupSize <= sizeof(CleanupBufferStack)) {
memcpy(CleanupBufferStack, CleanupSource, CleanupSize);
Fn = reinterpret_cast<EHScopeStack::Cleanup *>(CleanupBufferStack);
} else {
CleanupBufferHeap.reset(new char[CleanupSize]);
memcpy(CleanupBufferHeap.get(), CleanupSource, CleanupSize);
Fn = reinterpret_cast<EHScopeStack::Cleanup *>(CleanupBufferHeap.get());
EHScopeStack::Cleanup::Flags cleanupFlags;
if (Scope.isNormalCleanup())
if (Scope.isEHCleanup())
if (!RequiresNormalCleanup) {
destroyOptimisticNormalEntry(*this, Scope);
} else {
// If we have a fallthrough and no other need for the cleanup,
// emit it directly.
if (HasFallthrough && !HasPrebranchedFallthrough &&
!HasFixups && !HasExistingBranches) {
destroyOptimisticNormalEntry(*this, Scope);
EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
// Otherwise, the best approach is to thread everything through
// the cleanup block and then try to clean up after ourselves.
} else {
// Force the entry block to exist.
llvm::BasicBlock *NormalEntry = CreateNormalEntry(*this, Scope);
// I. Set up the fallthrough edge in.
CGBuilderTy::InsertPoint savedInactiveFallthroughIP;
// If there's a fallthrough, we need to store the cleanup
// destination index. For fall-throughs this is always zero.
if (HasFallthrough) {
if (!HasPrebranchedFallthrough)
Builder.CreateStore(Builder.getInt32(0), getNormalCleanupDestSlot());
// Otherwise, save and clear the IP if we don't have fallthrough
// because the cleanup is inactive.
} else if (FallthroughSource) {
assert(!IsActive && "source without fallthrough for active cleanup");
savedInactiveFallthroughIP = Builder.saveAndClearIP();
// II. Emit the entry block. This implicitly branches to it if
// we have fallthrough. All the fixups and existing branches
// should already be branched to it.
// III. Figure out where we're going and build the cleanup
// epilogue.
bool HasEnclosingCleanups =
(Scope.getEnclosingNormalCleanup() != EHStack.stable_end());
// Compute the branch-through dest if we need it:
// - if there are branch-throughs threaded through the scope
// - if fall-through is a branch-through
// - if there are fixups that will be optimistically forwarded
// to the enclosing cleanup
llvm::BasicBlock *BranchThroughDest = nullptr;
if (Scope.hasBranchThroughs() ||
(FallthroughSource && FallthroughIsBranchThrough) ||
(HasFixups && HasEnclosingCleanups)) {
EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S));
llvm::BasicBlock *FallthroughDest = nullptr;
SmallVector<llvm::Instruction*, 2> InstsToAppend;
// If there's exactly one branch-after and no other threads,
// we can route it without a switch.
if (!Scope.hasBranchThroughs() && !HasFixups && !HasFallthrough &&
Scope.getNumBranchAfters() == 1) {
assert(!BranchThroughDest || !IsActive);
// Clean up the possibly dead store to the cleanup dest slot.
llvm::Instruction *NormalCleanupDestSlot =
if (NormalCleanupDestSlot->hasOneUse()) {
NormalCleanupDest = Address::invalid();
llvm::BasicBlock *BranchAfter = Scope.getBranchAfterBlock(0);
// Build a switch-out if we need it:
// - if there are branch-afters threaded through the scope
// - if fall-through is a branch-after
// - if there are fixups that have nowhere left to go and
// so must be immediately resolved
} else if (Scope.getNumBranchAfters() ||
(HasFallthrough && !FallthroughIsBranchThrough) ||
(HasFixups && !HasEnclosingCleanups)) {
llvm::BasicBlock *Default =
(BranchThroughDest ? BranchThroughDest : getUnreachableBlock());
// TODO: base this on the number of branch-afters and fixups
const unsigned SwitchCapacity = 10;
llvm::LoadInst *Load =
createLoadInstBefore(getNormalCleanupDestSlot(), "cleanup.dest",
llvm::SwitchInst *Switch =
llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
// Branch-after fallthrough.
if (FallthroughSource && !FallthroughIsBranchThrough) {
FallthroughDest = createBasicBlock("cleanup.cont");
if (HasFallthrough)
Switch->addCase(Builder.getInt32(0), FallthroughDest);
for (unsigned I = 0, E = Scope.getNumBranchAfters(); I != E; ++I) {
// If there aren't any enclosing cleanups, we can resolve all
// the fixups now.
if (HasFixups && !HasEnclosingCleanups)
ResolveAllBranchFixups(*this, Switch, NormalEntry);
} else {
// We should always have a branch-through destination in this case.
// IV. Pop the cleanup and emit it.
assert(EHStack.hasNormalCleanups() == HasEnclosingCleanups);
EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
// Append the prepared cleanup prologue from above.
llvm::BasicBlock *NormalExit = Builder.GetInsertBlock();
for (unsigned I = 0, E = InstsToAppend.size(); I != E; ++I)
// Optimistically hope that any fixups will continue falling through.
for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
I < E; ++I) {
BranchFixup &Fixup = EHStack.getBranchFixup(I);
if (!Fixup.Destination) continue;
if (!Fixup.OptimisticBranchBlock) {
Fixup.InitialBranch->setSuccessor(0, NormalEntry);
Fixup.OptimisticBranchBlock = NormalExit;
// V. Set up the fallthrough edge out.
// Case 1: a fallthrough source exists but doesn't branch to the
// cleanup because the cleanup is inactive.
if (!HasFallthrough && FallthroughSource) {
// Prebranched fallthrough was forwarded earlier.
// Non-prebranched fallthrough doesn't need to be forwarded.
// Either way, all we need to do is restore the IP we cleared before.
// Case 2: a fallthrough source exists and should branch to the
// cleanup, but we're not supposed to branch through to the next
// cleanup.
} else if (HasFallthrough && FallthroughDest) {
// Case 3: a fallthrough source exists and should branch to the
// cleanup and then through to the next.
} else if (HasFallthrough) {
// Everything is already set up for this.
// Case 4: no fallthrough source exists.
} else {
// VI. Assorted cleaning.
// Check whether we can merge NormalEntry into a single predecessor.
// This might invalidate (non-IR) pointers to NormalEntry.
llvm::BasicBlock *NewNormalEntry =
SimplifyCleanupEntry(*this, NormalEntry);
// If it did invalidate those pointers, and NormalEntry was the same
// as NormalExit, go back and patch up the fixups.
if (NewNormalEntry != NormalEntry && NormalEntry == NormalExit)
for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
I < E; ++I)
EHStack.getBranchFixup(I).OptimisticBranchBlock = NewNormalEntry;
assert(EHStack.hasNormalCleanups() || EHStack.getNumBranchFixups() == 0);
// Emit the EH cleanup if required.
if (RequiresEHCleanup) {
CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
llvm::BasicBlock *NextAction = getEHDispatchBlock(EHParent);
// Push a terminate scope or cleanupendpad scope around the potentially
// throwing cleanups. For funclet EH personalities, the cleanupendpad models
// program termination when cleanups throw.
bool PushedTerminate = false;
SaveAndRestore<llvm::Instruction *> RestoreCurrentFuncletPad(
llvm::CleanupPadInst *CPI = nullptr;
const EHPersonality &Personality = EHPersonality::get(*this);
if (Personality.usesFuncletPads()) {
llvm::Value *ParentPad = CurrentFuncletPad;
if (!ParentPad)
ParentPad = llvm::ConstantTokenNone::get(CGM.getLLVMContext());
CurrentFuncletPad = CPI = Builder.CreateCleanupPad(ParentPad);
// Non-MSVC personalities need to terminate when an EH cleanup throws.
if (!Personality.isMSVCPersonality()) {
PushedTerminate = true;
// We only actually emit the cleanup code if the cleanup is either
// active or was used before it was deactivated.
if (EHActiveFlag.isValid() || IsActive) {
EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag);
if (CPI)
Builder.CreateCleanupRet(CPI, NextAction);
// Leave the terminate scope.
if (PushedTerminate)
SimplifyCleanupEntry(*this, EHEntry);
/// isObviouslyBranchWithoutCleanups - Return true if a branch to the
/// specified destination obviously has no cleanups to run. 'false' is always
/// a conservatively correct answer for this method.
bool CodeGenFunction::isObviouslyBranchWithoutCleanups(JumpDest Dest) const {
&& "stale jump destination");
// Calculate the innermost active normal cleanup.
EHScopeStack::stable_iterator TopCleanup =
// If we're not in an active normal cleanup scope, or if the
// destination scope is within the innermost active normal cleanup
// scope, we don't need to worry about fixups.
if (TopCleanup == EHStack.stable_end() ||
TopCleanup.encloses(Dest.getScopeDepth())) // works for invalid
return true;
// Otherwise, we might need some cleanups.
return false;
/// Terminate the current block by emitting a branch which might leave
/// the current cleanup-protected scope. The target scope may not yet
/// be known, in which case this will require a fixup.
/// As a side-effect, this method clears the insertion point.
void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) {
&& "stale jump destination");
if (!HaveInsertPoint())
// Create the branch.
llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
// Calculate the innermost active normal cleanup.
TopCleanup = EHStack.getInnermostActiveNormalCleanup();
// If we're not in an active normal cleanup scope, or if the
// destination scope is within the innermost active normal cleanup
// scope, we don't need to worry about fixups.
if (TopCleanup == EHStack.stable_end() ||
TopCleanup.encloses(Dest.getScopeDepth())) { // works for invalid
// If we can't resolve the destination cleanup scope, just add this
// to the current cleanup scope as a branch fixup.
if (!Dest.getScopeDepth().isValid()) {
BranchFixup &Fixup = EHStack.addBranchFixup();
Fixup.Destination = Dest.getBlock();
Fixup.DestinationIndex = Dest.getDestIndex();
Fixup.InitialBranch = BI;
Fixup.OptimisticBranchBlock = nullptr;
// Otherwise, thread through all the normal cleanups in scope.
// Store the index at the start.
llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
createStoreInstBefore(Index, getNormalCleanupDestSlot(), BI);
// Adjust BI to point to the first cleanup block.
EHCleanupScope &Scope =
BI->setSuccessor(0, CreateNormalEntry(*this, Scope));
// Add this destination to all the scopes involved.
EHScopeStack::stable_iterator I = TopCleanup;
EHScopeStack::stable_iterator E = Dest.getScopeDepth();
if (E.strictlyEncloses(I)) {
while (true) {
EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
I = Scope.getEnclosingNormalCleanup();
// If this is the last cleanup we're propagating through, tell it
// that there's a resolved jump moving through it.
if (!E.strictlyEncloses(I)) {
Scope.addBranchAfter(Index, Dest.getBlock());
// Otherwise, tell the scope that there's a jump propagating
// through it. If this isn't new information, all the rest of
// the work has been done before.
if (!Scope.addBranchThrough(Dest.getBlock()))
static bool IsUsedAsNormalCleanup(EHScopeStack &EHStack,
EHScopeStack::stable_iterator C) {
// If we needed a normal block for any reason, that counts.
if (cast<EHCleanupScope>(*EHStack.find(C)).getNormalBlock())
return true;
// Check whether any enclosed cleanups were needed.
for (EHScopeStack::stable_iterator
I = EHStack.getInnermostNormalCleanup();
I != C; ) {
EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I));
if (S.getNormalBlock()) return true;
I = S.getEnclosingNormalCleanup();
return false;
static bool IsUsedAsEHCleanup(EHScopeStack &EHStack,
EHScopeStack::stable_iterator cleanup) {
// If we needed an EH block for any reason, that counts.
if (EHStack.find(cleanup)->hasEHBranches())
return true;
// Check whether any enclosed cleanups were needed.
for (EHScopeStack::stable_iterator
i = EHStack.getInnermostEHScope(); i != cleanup; ) {
EHScope &scope = *EHStack.find(i);
if (scope.hasEHBranches())
return true;
i = scope.getEnclosingEHScope();
return false;
enum ForActivation_t {
/// The given cleanup block is changing activation state. Configure a
/// cleanup variable if necessary.
/// It would be good if we had some way of determining if there were
/// extra uses *after* the change-over point.
static void SetupCleanupBlockActivation(CodeGenFunction &CGF,
EHScopeStack::stable_iterator C,
ForActivation_t kind,
llvm::Instruction *dominatingIP) {
EHCleanupScope &Scope = cast<EHCleanupScope>(*CGF.EHStack.find(C));
// We always need the flag if we're activating the cleanup in a
// conditional context, because we have to assume that the current
// location doesn't necessarily dominate the cleanup's code.
bool isActivatedInConditional =
(kind == ForActivation && CGF.isInConditionalBranch());
bool needFlag = false;
// Calculate whether the cleanup was used:
// - as a normal cleanup
if (Scope.isNormalCleanup() &&
(isActivatedInConditional || IsUsedAsNormalCleanup(CGF.EHStack, C))) {
needFlag = true;
// - as an EH cleanup
if (Scope.isEHCleanup() &&
(isActivatedInConditional || IsUsedAsEHCleanup(CGF.EHStack, C))) {
needFlag = true;
// If it hasn't yet been used as either, we're done.
if (!needFlag) return;
Address var = Scope.getActiveFlag();
if (!var.isValid()) {
var = CGF.CreateTempAlloca(CGF.Builder.getInt1Ty(), CharUnits::One(),
assert(dominatingIP && "no existing variable and no dominating IP!");
// Initialize to true or false depending on whether it was
// active up to this point.
llvm::Constant *value = CGF.Builder.getInt1(kind == ForDeactivation);
// If we're in a conditional block, ignore the dominating IP and
// use the outermost conditional branch.
if (CGF.isInConditionalBranch()) {
CGF.setBeforeOutermostConditional(value, var);
} else {
createStoreInstBefore(value, var, dominatingIP);
CGF.Builder.CreateStore(CGF.Builder.getInt1(kind == ForActivation), var);
/// Activate a cleanup that was created in an inactivated state.
void CodeGenFunction::ActivateCleanupBlock(EHScopeStack::stable_iterator C,
llvm::Instruction *dominatingIP) {
assert(C != EHStack.stable_end() && "activating bottom of stack?");
EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
assert(!Scope.isActive() && "double activation");
SetupCleanupBlockActivation(*this, C, ForActivation, dominatingIP);
/// Deactive a cleanup that was created in an active state.
void CodeGenFunction::DeactivateCleanupBlock(EHScopeStack::stable_iterator C,
llvm::Instruction *dominatingIP) {
assert(C != EHStack.stable_end() && "deactivating bottom of stack?");
EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
assert(Scope.isActive() && "double deactivation");
// If it's the top of the stack, just pop it, but do so only if it belongs
// to the current RunCleanupsScope.
if (C == EHStack.stable_begin() &&
CurrentCleanupScopeDepth.strictlyEncloses(C)) {
// If it's a normal cleanup, we need to pretend that the
// fallthrough is unreachable.
CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
// Otherwise, follow the general case.
SetupCleanupBlockActivation(*this, C, ForDeactivation, dominatingIP);
Address CodeGenFunction::getNormalCleanupDestSlot() {
if (!NormalCleanupDest.isValid())
NormalCleanupDest =
CreateDefaultAlignTempAlloca(Builder.getInt32Ty(), "cleanup.dest.slot");
return NormalCleanupDest;
/// Emits all the code to cause the given temporary to be cleaned up.
void CodeGenFunction::EmitCXXTemporary(const CXXTemporary *Temporary,
QualType TempType,
Address Ptr) {
pushDestroy(NormalAndEHCleanup, Ptr, TempType, destroyCXXObject,
/*useEHCleanup*/ true);