diff options
Diffstat (limited to 'clang/lib/CodeGen/CGCleanup.cpp')
| -rw-r--r-- | clang/lib/CodeGen/CGCleanup.cpp | 1103 |
1 files changed, 1103 insertions, 0 deletions
diff --git a/clang/lib/CodeGen/CGCleanup.cpp b/clang/lib/CodeGen/CGCleanup.cpp new file mode 100644 index 0000000..b00e2a2 --- /dev/null +++ b/clang/lib/CodeGen/CGCleanup.cpp @@ -0,0 +1,1103 @@ +//===--- 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(); + llvm::Type *ComplexTy = + llvm::StructType::get(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"); +} + +/// 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::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(); +} + +EHScopeStack::stable_iterator EHScopeStack::getInnermostActiveEHScope() const { + for (stable_iterator si = getInnermostEHScope(), se = stable_end(); + si != se; ) { + // Skip over inactive cleanups. + EHCleanupScope *cleanup = dyn_cast<EHCleanupScope>(&*find(si)); + if (cleanup && !cleanup->isActive()) { + si = cleanup->getEnclosingEHScope(); + continue; + } + + // All other scopes are always active. + return si; + } + + 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, + InnermostEHScope); + if (IsNormalCleanup) + InnermostNormalCleanup = stable_begin(); + if (IsEHCleanup) + InnermostEHScope = 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(); + InnermostEHScope = Cleanup.getEnclosingEHScope(); + StartOfData += Cleanup.getAllocatedSize(); + + // 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) { + 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()); + StartOfData += EHFilterScope::getSizeForNumFilters(filter.getNumFilters()); + + 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. + 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. + setBeforeOutermostConditional(Builder.getFalse(), active); + + // 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(); +} + +void EHScopeStack::Cleanup::anchor() {} + +/// 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; +} + +/// 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(); + + // Replace all uses of the entry with the predecessor, in case there + // are phis in the cleanup. + Entry->replaceAllUsesWith(Pred); + + // Merge the blocks. + Pred->getInstList().splice(Pred->end(), Entry->getInstList()); + + // Kill the entry block. + Entry->eraseFromParent(); + + if (WasInsertBlock) + CGF.Builder.SetInsertPoint(Pred); + + return Pred; +} + +static void EmitCleanup(CodeGenFunction &CGF, + EHScopeStack::Cleanup *Fn, + EHScopeStack::Cleanup::Flags flags, + llvm::Value *ActiveFlag) { + // EH cleanups always occur within a terminate scope. + if (flags.isForEHCleanup()) 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, flags); + 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 (flags.isForEHCleanup()) 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); + } +} + +/// 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.getUse(); + ++i; + + use.set(unreachableBB); + + // 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. + si->eraseFromParent(); + + // Destroy the load. + assert(condition->getOperand(0) == CGF.NormalCleanupDest); + assert(condition->use_empty()); + condition->eraseFromParent(); + } + } + + assert(entry->use_empty()); + 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(); + 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. + llvm::BasicBlock *EHEntry = Scope.getCachedEHDispatchBlock(); + assert(Scope.hasEHBranches() == (EHEntry != 0)); + bool RequiresEHCleanup = (EHEntry != 0); + 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 != 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; + } + + // 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"); + EmitBlock(prebranchDest); + } + + llvm::BasicBlock *normalEntry = Scope.getNormalBlock(); + assert(normalEntry && !normalEntry->use_empty()); + + ForwardPrebranchedFallthrough(FallthroughSource, + 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 || + EHStack.hasNormalCleanups()); + return; + } + + // Copy the cleanup emission data out. Note that SmallVector + // guarantees maximal alignment for its buffer regardless of its + // type parameter. + 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()); + + EHScopeStack::Cleanup::Flags cleanupFlags; + if (Scope.isNormalCleanup()) + cleanupFlags.setIsNormalCleanupKind(); + if (Scope.isEHCleanup()) + cleanupFlags.setIsEHCleanupKind(); + + if (!RequiresNormalCleanup) { + destroyOptimisticNormalEntry(*this, Scope); + EHStack.popCleanup(); + } else { + // If we have a fallthrough and no other need for the cleanup, + // emit it directly. + if (HasFallthrough && !HasPrebranchedFallthrough && + !HasFixups && !HasExistingBranches) { + + destroyOptimisticNormalEntry(*this, Scope); + EHStack.popCleanup(); + + 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. + 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; + 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, cleanupFlags, 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 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. + assert(!IsActive); + Builder.restoreIP(savedInactiveFallthroughIP); + + // 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); + + cleanupFlags.setIsForEHCleanup(); + EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag); + + Builder.CreateBr(getEHDispatchBlock(EHParent)); + + 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(); +} + +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 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; ) { + assert(cleanup.strictlyEncloses(i)); + + EHScope &scope = *EHStack.find(i); + if (scope.hasEHBranches()) + return true; + + i = scope.getEnclosingEHScope(); + } + + 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, + 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))) { + Scope.setTestFlagInNormalCleanup(); + needFlag = true; + } + + // - as an EH cleanup + if (Scope.isEHCleanup() && + (isActivatedInConditional || 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); + + 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::Value *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 { + new llvm::StoreInst(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); + + Scope.setActive(true); +} + +/// 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. + 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, dominatingIP); + + Scope.setActive(false); +} + +llvm::Value *CodeGenFunction::getNormalCleanupDestSlot() { + if (!NormalCleanupDest) + NormalCleanupDest = + CreateTempAlloca(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, + llvm::Value *Ptr) { + pushDestroy(NormalAndEHCleanup, Ptr, TempType, destroyCXXObject, + /*useEHCleanup*/ true); +} |