wangtao
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity
llvm-project/clang/lib/CodeGen/CGCleanup.cpp

1168 lines
42 KiB
C++
Raw Blame History

//===--- CGCleanup.cpp - Bookkeeping and code emission for cleanups -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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 "CodeGenFunction.h"
#include "CGCleanup.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.getAggregateAddr());
return true;
}
DominatingValue<RValue>::saved_type
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.
llvm::Value *addr = CGF.CreateTempAlloca(V->getType(), "saved-rvalue");
CGF.Builder.CreateStore(V, addr);
return saved_type(addr, ScalarAddress);
}
if (rv.isComplex()) {
CodeGenFunction::ComplexPairTy V = rv.getComplexVal();
const llvm::Type *ComplexTy =
llvm::StructType::get(CGF.getLLVMContext(),
V.first->getType(), V.second->getType(),
(void*) 0);
llvm::Value *addr = CGF.CreateTempAlloca(ComplexTy, "saved-complex");
CGF.StoreComplexToAddr(V, addr, /*volatile*/ false);
return saved_type(addr, ComplexAddress);
}
assert(rv.isAggregate());
llvm::Value *V = rv.getAggregateAddr(); // TODO: volatile?
if (!DominatingLLVMValue::needsSaving(V))
return saved_type(V, AggregateLiteral);
llvm::Value *addr = CGF.CreateTempAlloca(V->getType(), "saved-rvalue");
CGF.Builder.CreateStore(V, addr);
return saved_type(addr, 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) {
switch (K) {
case ScalarLiteral:
return RValue::get(Value);
case ScalarAddress:
return RValue::get(CGF.Builder.CreateLoad(Value));
case AggregateLiteral:
return RValue::getAggregate(Value);
case AggregateAddress:
return RValue::getAggregate(CGF.Builder.CreateLoad(Value));
case ComplexAddress:
return RValue::getComplex(CGF.LoadComplexFromAddr(Value, false));
}
llvm_unreachable("bad saved r-value kind");
return RValue();
}
/// Push an entry of the given size onto this protected-scope stack.
char *EHScopeStack::allocate(size_t Size) {
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;
}
EHScopeStack::stable_iterator
EHScopeStack::getEnclosingEHCleanup(iterator it) const {
assert(it != end());
do {
if (isa<EHCleanupScope>(*it)) {
if (cast<EHCleanupScope>(*it).isEHCleanup())
return stabilize(it);
return cast<EHCleanupScope>(*it).getEnclosingEHCleanup();
}
++it;
} while (it != end());
return stable_end();
}
void *EHScopeStack::pushCleanup(CleanupKind Kind, size_t Size) {
assert(((Size % sizeof(void*)) == 0) && "cleanup type is misaligned");
char *Buffer = allocate(EHCleanupScope::getSizeForCleanupSize(Size));
bool IsNormalCleanup = Kind & NormalCleanup;
bool IsEHCleanup = Kind & EHCleanup;
bool IsActive = !(Kind & InactiveCleanup);
EHCleanupScope *Scope =
new (Buffer) EHCleanupScope(IsNormalCleanup,
IsEHCleanup,
IsActive,
Size,
BranchFixups.size(),
InnermostNormalCleanup,
InnermostEHCleanup);
if (IsNormalCleanup)
InnermostNormalCleanup = stable_begin();
if (IsEHCleanup)
InnermostEHCleanup = stable_begin();
return Scope->getCleanupBuffer();
}
void EHScopeStack::popCleanup() {
assert(!empty() && "popping exception stack when not empty");
assert(isa<EHCleanupScope>(*begin()));
EHCleanupScope &Cleanup = cast<EHCleanupScope>(*begin());
InnermostNormalCleanup = Cleanup.getEnclosingNormalCleanup();
InnermostEHCleanup = Cleanup.getEnclosingEHCleanup();
StartOfData += Cleanup.getAllocatedSize();
if (empty()) NextEHDestIndex = FirstEHDestIndex;
// Destroy the cleanup.
Cleanup.~EHCleanupScope();
// 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())
BranchFixups.clear();
// Otherwise we can still trim out unnecessary nulls.
else
popNullFixups();
}
}
EHFilterScope *EHScopeStack::pushFilter(unsigned NumFilters) {
char *Buffer = allocate(EHFilterScope::getSizeForNumFilters(NumFilters));
CatchDepth++;
return new (Buffer) EHFilterScope(NumFilters);
}
void EHScopeStack::popFilter() {
assert(!empty() && "popping exception stack when not empty");
EHFilterScope &Filter = cast<EHFilterScope>(*begin());
StartOfData += EHFilterScope::getSizeForNumFilters(Filter.getNumFilters());
if (empty()) NextEHDestIndex = FirstEHDestIndex;
assert(CatchDepth > 0 && "mismatched filter push/pop");
CatchDepth--;
}
EHCatchScope *EHScopeStack::pushCatch(unsigned NumHandlers) {
char *Buffer = allocate(EHCatchScope::getSizeForNumHandlers(NumHandlers));
CatchDepth++;
EHCatchScope *Scope = new (Buffer) EHCatchScope(NumHandlers);
for (unsigned I = 0; I != NumHandlers; ++I)
Scope->getHandlers()[I].Index = getNextEHDestIndex();
return Scope;
}
void EHScopeStack::pushTerminate() {
char *Buffer = allocate(EHTerminateScope::getSize());
CatchDepth++;
new (Buffer) EHTerminateScope(getNextEHDestIndex());
}
/// 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.
assert(hasNormalCleanups());
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 == 0)
BranchFixups.pop_back();
}
void CodeGenFunction::initFullExprCleanup() {
// Create a variable to decide whether the cleanup needs to be run.
llvm::AllocaInst *active
= CreateTempAlloca(Builder.getInt1Ty(), "cleanup.cond");
// Initialize it to false at a site that's guaranteed to be run
// before each evaluation.
llvm::BasicBlock *block = OutermostConditional->getStartingBlock();
new llvm::StoreInst(Builder.getFalse(), active, &block->back());
// Initialize it to true at the current location.
Builder.CreateStore(Builder.getTrue(), active);
// Set that as the active flag in the cleanup.
EHCleanupScope &cleanup = cast<EHCleanupScope>(*EHStack.begin());
assert(cleanup.getActiveFlag() == 0 && "cleanup already has active flag?");
cleanup.setActiveFlag(active);
if (cleanup.isNormalCleanup()) cleanup.setTestFlagInNormalCleanup();
if (cleanup.isEHCleanup()) cleanup.setTestFlagInEHCleanup();
}
EHScopeStack::Cleanup::~Cleanup() {
llvm_unreachable("Cleanup is indestructable");
}
/// 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 == 0) 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 == 0) {
new llvm::StoreInst(CGF.Builder.getInt32(Fixup.DestinationIndex),
CGF.getNormalCleanupDestSlot(),
Fixup.InitialBranch);
Fixup.InitialBranch->setSuccessor(0, CleanupEntry);
}
// Don't add this case to the switch statement twice.
if (!CasesAdded.insert(Fixup.Destination)) continue;
Switch->addCase(CGF.Builder.getInt32(Fixup.DestinationIndex),
Fixup.Destination);
}
CGF.EHStack.clearFixups();
}
/// 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::TerminatorInst *Term = Block->getTerminator();
assert(Term && "can't transition block without terminator");
if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
assert(Br->isUnconditional());
llvm::LoadInst *Load =
new llvm::LoadInst(CGF.getNormalCleanupDestSlot(), "cleanup.dest", Term);
llvm::SwitchInst *Switch =
llvm::SwitchInst::Create(Load, Br->getSuccessor(0), 4, Block);
Br->eraseFromParent();
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 = 0;
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)
continue;
// Don't process the same optimistic branch block twice.
if (!ModifiedOptimisticBlocks.insert(BranchBB))
continue;
llvm::SwitchInst *Switch = TransitionToCleanupSwitch(*this, BranchBB);
// Add a case to the switch.
Switch->addCase(Builder.getInt32(Fixup.DestinationIndex), Block);
}
if (ResolvedAny)
EHStack.popNullFixups();
}
/// Pops cleanup blocks until the given savepoint is reached.
void CodeGenFunction::PopCleanupBlocks(EHScopeStack::stable_iterator Old) {
assert(Old.isValid());
while (EHStack.stable_begin() != Old) {
EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
// 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 =
Old.strictlyEncloses(Scope.getEnclosingNormalCleanup());
PopCleanupBlock(FallThroughIsBranchThrough);
}
}
static llvm::BasicBlock *CreateNormalEntry(CodeGenFunction &CGF,
EHCleanupScope &Scope) {
assert(Scope.isNormalCleanup());
llvm::BasicBlock *Entry = Scope.getNormalBlock();
if (!Entry) {
Entry = CGF.createBasicBlock("cleanup");
Scope.setNormalBlock(Entry);
}
return Entry;
}
static llvm::BasicBlock *CreateEHEntry(CodeGenFunction &CGF,
EHCleanupScope &Scope) {
assert(Scope.isEHCleanup());
llvm::BasicBlock *Entry = Scope.getEHBlock();
if (!Entry) {
Entry = CGF.createBasicBlock("eh.cleanup");
Scope.setEHBlock(Entry);
}
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.
Br->eraseFromParent();
// Merge the blocks.
Pred->getInstList().splice(Pred->end(), Entry->getInstList());
// Replace all uses of the entry with the predecessor, in case there
// are phis in the cleanup.
Entry->replaceAllUsesWith(Pred);
// Kill the entry block.
Entry->eraseFromParent();
if (WasInsertBlock)
CGF.Builder.SetInsertPoint(Pred);
return Pred;
}
static void EmitCleanup(CodeGenFunction &CGF,
EHScopeStack::Cleanup *Fn,
bool ForEH,
llvm::Value *ActiveFlag) {
// EH cleanups always occur within a terminate scope.
if (ForEH) CGF.EHStack.pushTerminate();
// If there's an active flag, load it and skip the cleanup if it's
// false.
llvm::BasicBlock *ContBB = 0;
if (ActiveFlag) {
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);
CGF.EmitBlock(CleanupBB);
}
// Ask the cleanup to emit itself.
Fn->Emit(CGF, ForEH);
assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
// Emit the continuation block if there was an active flag.
if (ActiveFlag)
CGF.EmitBlock(ContBB);
// Leave the terminate scope.
if (ForEH) CGF.EHStack.popTerminate();
}
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::TerminatorInst *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);
}
}
/// 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();
llvm::Value *NormalActiveFlag =
Scope.shouldTestFlagInNormalCleanup() ? Scope.getActiveFlag() : 0;
llvm::Value *EHActiveFlag =
Scope.shouldTestFlagInEHCleanup() ? Scope.getActiveFlag() : 0;
// Check whether we need an EH cleanup. This is only true if we've
// generated a lazy EH cleanup block.
bool RequiresEHCleanup = Scope.hasEHBranches();
// 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 != 0 && 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() &&
FallthroughSource->getTerminator()->getSuccessor(0)
== Scope.getNormalBlock()));
bool RequiresNormalCleanup = false;
if (Scope.isNormalCleanup() &&
(HasFixups || HasExistingBranches || HasFallthrough)) {
RequiresNormalCleanup = true;
}
// Even if we don't need the normal cleanup, we might still have
// prebranched fallthrough to worry about.
if (Scope.isNormalCleanup() && !RequiresNormalCleanup &&
HasPrebranchedFallthrough) {
assert(!IsActive);
llvm::BasicBlock *NormalEntry = Scope.getNormalBlock();
// If we're branching through this cleanup, just forward the
// prebranched fallthrough to the next cleanup, leaving the insert
// point in the old block.
if (FallthroughIsBranchThrough) {
EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
llvm::BasicBlock *EnclosingEntry =
CreateNormalEntry(*this, cast<EHCleanupScope>(S));
ForwardPrebranchedFallthrough(FallthroughSource,
NormalEntry, EnclosingEntry);
assert(NormalEntry->use_empty() &&
"uses of entry remain after forwarding?");
delete NormalEntry;
// Otherwise, we're branching out; just emit the next block.
} else {
EmitBlock(NormalEntry);
SimplifyCleanupEntry(*this, NormalEntry);
}
}
// If we don't need the cleanup at all, we're done.
if (!RequiresNormalCleanup && !RequiresEHCleanup) {
EHStack.popCleanup(); // safe because there are no fixups
assert(EHStack.getNumBranchFixups() == 0 ||
EHStack.hasNormalCleanups());
return;
}
// Copy the cleanup emission data out. Note that SmallVector
// guarantees maximal alignment for its buffer regardless of its
// type parameter.
llvm::SmallVector<char, 8*sizeof(void*)> CleanupBuffer;
CleanupBuffer.reserve(Scope.getCleanupSize());
memcpy(CleanupBuffer.data(),
Scope.getCleanupBuffer(), Scope.getCleanupSize());
CleanupBuffer.set_size(Scope.getCleanupSize());
EHScopeStack::Cleanup *Fn =
reinterpret_cast<EHScopeStack::Cleanup*>(CleanupBuffer.data());
// We want to emit the EH cleanup after the normal cleanup, but go
// ahead and do the setup for the EH cleanup while the scope is still
// alive.
llvm::BasicBlock *EHEntry = 0;
llvm::SmallVector<llvm::Instruction*, 2> EHInstsToAppend;
if (RequiresEHCleanup) {
EHEntry = CreateEHEntry(*this, Scope);
// Figure out the branch-through dest if necessary.
llvm::BasicBlock *EHBranchThroughDest = 0;
if (Scope.hasEHBranchThroughs()) {
assert(Scope.getEnclosingEHCleanup() != EHStack.stable_end());
EHScope &S = *EHStack.find(Scope.getEnclosingEHCleanup());
EHBranchThroughDest = CreateEHEntry(*this, cast<EHCleanupScope>(S));
}
// If we have exactly one branch-after and no branch-throughs, we
// can dispatch it without a switch.
if (!Scope.hasEHBranchThroughs() &&
Scope.getNumEHBranchAfters() == 1) {
assert(!EHBranchThroughDest);
// TODO: remove the spurious eh.cleanup.dest stores if this edge
// never went through any switches.
llvm::BasicBlock *BranchAfterDest = Scope.getEHBranchAfterBlock(0);
EHInstsToAppend.push_back(llvm::BranchInst::Create(BranchAfterDest));
// Otherwise, if we have any branch-afters, we need a switch.
} else if (Scope.getNumEHBranchAfters()) {
// The default of the switch belongs to the branch-throughs if
// they exist.
llvm::BasicBlock *Default =
(EHBranchThroughDest ? EHBranchThroughDest : getUnreachableBlock());
const unsigned SwitchCapacity = Scope.getNumEHBranchAfters();
llvm::LoadInst *Load =
new llvm::LoadInst(getEHCleanupDestSlot(), "cleanup.dest");
llvm::SwitchInst *Switch =
llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
EHInstsToAppend.push_back(Load);
EHInstsToAppend.push_back(Switch);
for (unsigned I = 0, E = Scope.getNumEHBranchAfters(); I != E; ++I)
Switch->addCase(Scope.getEHBranchAfterIndex(I),
Scope.getEHBranchAfterBlock(I));
// Otherwise, we have only branch-throughs; jump to the next EH
// cleanup.
} else {
assert(EHBranchThroughDest);
EHInstsToAppend.push_back(llvm::BranchInst::Create(EHBranchThroughDest));
}
}
if (!RequiresNormalCleanup) {
EHStack.popCleanup();
} else {
// If we have a fallthrough and no other need for the cleanup,
// emit it directly.
if (HasFallthrough && !HasPrebranchedFallthrough &&
!HasFixups && !HasExistingBranches) {
// Fixups can cause us to optimistically create a normal block,
// only to later have no real uses for it. Just delete it in
// this case.
// TODO: we can potentially simplify all the uses after this.
if (Scope.getNormalBlock()) {
Scope.getNormalBlock()->replaceAllUsesWith(getUnreachableBlock());
delete Scope.getNormalBlock();
}
EHStack.popCleanup();
EmitCleanup(*this, Fn, /*ForEH*/ false, 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.
// 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, clear the IP if we don't have fallthrough because
// the cleanup is inactive. We don't need to save it because
// it's still just FallthroughSource.
} else if (FallthroughSource) {
assert(!IsActive && "source without fallthrough for active cleanup");
Builder.ClearInsertionPoint();
}
// 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.
EmitBlock(NormalEntry);
// 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 = 0;
if (Scope.hasBranchThroughs() ||
(FallthroughSource && FallthroughIsBranchThrough) ||
(HasFixups && HasEnclosingCleanups)) {
assert(HasEnclosingCleanups);
EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S));
}
llvm::BasicBlock *FallthroughDest = 0;
llvm::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);
// TODO: clean up the possibly dead stores to the cleanup dest slot.
llvm::BasicBlock *BranchAfter = Scope.getBranchAfterBlock(0);
InstsToAppend.push_back(llvm::BranchInst::Create(BranchAfter));
// 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 =
new llvm::LoadInst(getNormalCleanupDestSlot(), "cleanup.dest");
llvm::SwitchInst *Switch =
llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
InstsToAppend.push_back(Load);
InstsToAppend.push_back(Switch);
// 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) {
Switch->addCase(Scope.getBranchAfterIndex(I),
Scope.getBranchAfterBlock(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.
assert(BranchThroughDest);
InstsToAppend.push_back(llvm::BranchInst::Create(BranchThroughDest));
}
// IV. Pop the cleanup and emit it.
EHStack.popCleanup();
assert(EHStack.hasNormalCleanups() == HasEnclosingCleanups);
EmitCleanup(*this, Fn, /*ForEH*/ false, NormalActiveFlag);
// Append the prepared cleanup prologue from above.
llvm::BasicBlock *NormalExit = Builder.GetInsertBlock();
for (unsigned I = 0, E = InstsToAppend.size(); I != E; ++I)
NormalExit->getInstList().push_back(InstsToAppend[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) {
new llvm::StoreInst(Builder.getInt32(Fixup.DestinationIndex),
getNormalCleanupDestSlot(),
Fixup.InitialBranch);
Fixup.InitialBranch->setSuccessor(0, NormalEntry);
}
Fixup.OptimisticBranchBlock = NormalExit;
}
// V. Set up the fallthrough edge out.
// Case 1: a fallthrough source exists but shouldn't branch to
// the cleanup because the cleanup is inactive.
if (!HasFallthrough && FallthroughSource) {
assert(!IsActive);
// If we have a prebranched fallthrough, that needs to be
// forwarded to the right block.
if (HasPrebranchedFallthrough) {
llvm::BasicBlock *Next;
if (FallthroughIsBranchThrough) {
Next = BranchThroughDest;
assert(!FallthroughDest);
} else {
Next = FallthroughDest;
}
ForwardPrebranchedFallthrough(FallthroughSource, NormalEntry, Next);
}
Builder.SetInsertPoint(FallthroughSource);
// 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) {
assert(!FallthroughIsBranchThrough);
EmitBlock(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 {
Builder.ClearInsertionPoint();
}
// 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();
EmitBlock(EHEntry);
EmitCleanup(*this, Fn, /*ForEH*/ true, EHActiveFlag);
// Append the prepared cleanup prologue from above.
llvm::BasicBlock *EHExit = Builder.GetInsertBlock();
for (unsigned I = 0, E = EHInstsToAppend.size(); I != E; ++I)
EHExit->getInstList().push_back(EHInstsToAppend[I]);
Builder.restoreIP(SavedIP);
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 {
assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
&& "stale jump destination");
// Calculate the innermost active normal cleanup.
EHScopeStack::stable_iterator 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
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) {
assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
&& "stale jump destination");
if (!HaveInsertPoint())
return;
// Create the branch.
llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
// Calculate the innermost active normal cleanup.
EHScopeStack::stable_iterator
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
Builder.ClearInsertionPoint();
return;
}
// 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 = 0;
Builder.ClearInsertionPoint();
return;
}
// Otherwise, thread through all the normal cleanups in scope.
// Store the index at the start.
llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
new llvm::StoreInst(Index, getNormalCleanupDestSlot(), BI);
// Adjust BI to point to the first cleanup block.
{
EHCleanupScope &Scope =
cast<EHCleanupScope>(*EHStack.find(TopCleanup));
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));
assert(Scope.isNormalCleanup());
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());
break;
}
// Otherwise, tell the scope that there's a jump propoagating
// through it. If this isn't new information, all the rest of
// the work has been done before.
if (!Scope.addBranchThrough(Dest.getBlock()))
break;
}
}
Builder.ClearInsertionPoint();
}
void CodeGenFunction::EmitBranchThroughEHCleanup(UnwindDest Dest) {
// We should never get invalid scope depths for an UnwindDest; that
// implies that the destination wasn't set up correctly.
assert(Dest.getScopeDepth().isValid() && "invalid scope depth on EH dest?");
if (!HaveInsertPoint())
return;
// Create the branch.
llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
// Calculate the innermost active cleanup.
EHScopeStack::stable_iterator
InnermostCleanup = EHStack.getInnermostActiveEHCleanup();
// If the destination is in the same EH cleanup scope as us, we
// don't need to thread through anything.
if (InnermostCleanup.encloses(Dest.getScopeDepth())) {
Builder.ClearInsertionPoint();
return;
}
assert(InnermostCleanup != EHStack.stable_end());
// Store the index at the start.
llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
new llvm::StoreInst(Index, getEHCleanupDestSlot(), BI);
// Adjust BI to point to the first cleanup block.
{
EHCleanupScope &Scope =
cast<EHCleanupScope>(*EHStack.find(InnermostCleanup));
BI->setSuccessor(0, CreateEHEntry(*this, Scope));
}
// Add this destination to all the scopes involved.
for (EHScopeStack::stable_iterator
I = InnermostCleanup, E = Dest.getScopeDepth(); ; ) {
assert(E.strictlyEncloses(I));
EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
assert(Scope.isEHCleanup());
I = Scope.getEnclosingEHCleanup();
// If this is the last cleanup we're propagating through, add this
// as a branch-after.
if (I == E) {
Scope.addEHBranchAfter(Index, Dest.getBlock());
break;
}
// Otherwise, add it as a branch-through. If this isn't new
// information, all the rest of the work has been done before.
if (!Scope.addEHBranchThrough(Dest.getBlock()))
break;
}
Builder.ClearInsertionPoint();
}
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; ) {
assert(C.strictlyEncloses(I));
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 C) {
// If we needed an EH block for any reason, that counts.
if (cast<EHCleanupScope>(*EHStack.find(C)).getEHBlock())
return true;
// Check whether any enclosed cleanups were needed.
for (EHScopeStack::stable_iterator
I = EHStack.getInnermostEHCleanup(); I != C; ) {
assert(C.strictlyEncloses(I));
EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I));
if (S.getEHBlock()) return true;
I = S.getEnclosingEHCleanup();
}
return false;
}
enum ForActivation_t {
ForActivation,
ForDeactivation
};
/// 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) {
EHCleanupScope &Scope = cast<EHCleanupScope>(*CGF.EHStack.find(C));
// We always need the flag if we're activating the cleanup, because
// we have to assume that the current location doesn't necessarily
// dominate all future uses of the cleanup.
bool NeedFlag = (Kind == ForActivation);
// Calculate whether the cleanup was used:
// - as a normal cleanup
if (Scope.isNormalCleanup() && IsUsedAsNormalCleanup(CGF.EHStack, C)) {
Scope.setTestFlagInNormalCleanup();
NeedFlag = true;
}
// - as an EH cleanup
if (Scope.isEHCleanup() && IsUsedAsEHCleanup(CGF.EHStack, C)) {
Scope.setTestFlagInEHCleanup();
NeedFlag = true;
}
// If it hasn't yet been used as either, we're done.
if (!NeedFlag) return;
llvm::AllocaInst *Var = Scope.getActiveFlag();
if (!Var) {
Var = CGF.CreateTempAlloca(CGF.Builder.getInt1Ty(), "cleanup.isactive");
Scope.setActiveFlag(Var);
// Initialize to true or false depending on whether it was
// active up to this point.
CGF.InitTempAlloca(Var, CGF.Builder.getInt1(Kind == ForDeactivation));
}
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) {
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);
Scope.setActive(true);
}
/// Deactive a cleanup that was created in an active state.
void CodeGenFunction::DeactivateCleanupBlock(EHScopeStack::stable_iterator C) {
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.
if (C == EHStack.stable_begin()) {
// If it's a normal cleanup, we need to pretend that the
// fallthrough is unreachable.
CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
PopCleanupBlock();
Builder.restoreIP(SavedIP);
return;
}
// Otherwise, follow the general case.
SetupCleanupBlockActivation(*this, C, ForDeactivation);
Scope.setActive(false);
}
llvm::Value *CodeGenFunction::getNormalCleanupDestSlot() {
if (!NormalCleanupDest)
NormalCleanupDest =
CreateTempAlloca(Builder.getInt32Ty(), "cleanup.dest.slot");
return NormalCleanupDest;
}
llvm::Value *CodeGenFunction::getEHCleanupDestSlot() {
if (!EHCleanupDest)
EHCleanupDest =
CreateTempAlloca(Builder.getInt32Ty(), "eh.cleanup.dest.slot");
return EHCleanupDest;
}
Reference in New Issue View Git Blame Copy Permalink