//===--- 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::saved_type::needsSaving(RValue rv) { if (rv.isScalar()) return DominatingLLVMValue::needsSaving(rv.getScalarVal()); if (rv.isAggregate()) return DominatingLLVMValue::needsSaving(rv.getAggregateAddr()); return true; } DominatingValue::saved_type DominatingValue::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::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(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(*it)) { if (cast(*it).isEHCleanup()) return stabilize(it); return cast(*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(*begin())); EHCleanupScope &Cleanup = cast(*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(*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(*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(*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 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(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(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 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(*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(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(Term)) { assert(Br->isUnconditional() && Br->getSuccessor(0) == From); Br->setSuccessor(0, To); } else { llvm::SwitchInst *Switch = cast(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(*EHStack.begin()) && "top not a cleanup!"); EHCleanupScope &Scope = cast(*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(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 CleanupBuffer; CleanupBuffer.reserve(Scope.getCleanupSize()); memcpy(CleanupBuffer.data(), Scope.getCleanupBuffer(), Scope.getCleanupSize()); CleanupBuffer.set_size(Scope.getCleanupSize()); EHScopeStack::Cleanup *Fn = reinterpret_cast(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 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(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(S)); } llvm::BasicBlock *FallthroughDest = 0; llvm::SmallVector 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); } } /// 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.getInnermostNormalCleanup()) && "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(*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(*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(*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(*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(*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(*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(*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(*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(*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(*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(*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; }