CGCleanup.cpp revision 30c0d27b61e38ad6038eeb8650f0dac83056c75b
1//===--- CGCleanup.cpp - Bookkeeping and code emission for cleanups -------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file contains code dealing with the IR generation for cleanups 11// and related information. 12// 13// A "cleanup" is a piece of code which needs to be executed whenever 14// control transfers out of a particular scope. This can be 15// conditionalized to occur only on exceptional control flow, only on 16// normal control flow, or both. 17// 18//===----------------------------------------------------------------------===// 19 20#include "CodeGenFunction.h" 21#include "CGCleanup.h" 22 23using namespace clang; 24using namespace CodeGen; 25 26bool DominatingValue<RValue>::saved_type::needsSaving(RValue rv) { 27 if (rv.isScalar()) 28 return DominatingLLVMValue::needsSaving(rv.getScalarVal()); 29 if (rv.isAggregate()) 30 return DominatingLLVMValue::needsSaving(rv.getAggregateAddr()); 31 return true; 32} 33 34DominatingValue<RValue>::saved_type 35DominatingValue<RValue>::saved_type::save(CodeGenFunction &CGF, RValue rv) { 36 if (rv.isScalar()) { 37 llvm::Value *V = rv.getScalarVal(); 38 39 // These automatically dominate and don't need to be saved. 40 if (!DominatingLLVMValue::needsSaving(V)) 41 return saved_type(V, ScalarLiteral); 42 43 // Everything else needs an alloca. 44 llvm::Value *addr = CGF.CreateTempAlloca(V->getType(), "saved-rvalue"); 45 CGF.Builder.CreateStore(V, addr); 46 return saved_type(addr, ScalarAddress); 47 } 48 49 if (rv.isComplex()) { 50 CodeGenFunction::ComplexPairTy V = rv.getComplexVal(); 51 llvm::Type *ComplexTy = 52 llvm::StructType::get(V.first->getType(), V.second->getType(), 53 (void*) 0); 54 llvm::Value *addr = CGF.CreateTempAlloca(ComplexTy, "saved-complex"); 55 CGF.Builder.CreateStore(V.first, CGF.Builder.CreateStructGEP(addr, 0)); 56 CGF.Builder.CreateStore(V.second, CGF.Builder.CreateStructGEP(addr, 1)); 57 return saved_type(addr, ComplexAddress); 58 } 59 60 assert(rv.isAggregate()); 61 llvm::Value *V = rv.getAggregateAddr(); // TODO: volatile? 62 if (!DominatingLLVMValue::needsSaving(V)) 63 return saved_type(V, AggregateLiteral); 64 65 llvm::Value *addr = CGF.CreateTempAlloca(V->getType(), "saved-rvalue"); 66 CGF.Builder.CreateStore(V, addr); 67 return saved_type(addr, AggregateAddress); 68} 69 70/// Given a saved r-value produced by SaveRValue, perform the code 71/// necessary to restore it to usability at the current insertion 72/// point. 73RValue DominatingValue<RValue>::saved_type::restore(CodeGenFunction &CGF) { 74 switch (K) { 75 case ScalarLiteral: 76 return RValue::get(Value); 77 case ScalarAddress: 78 return RValue::get(CGF.Builder.CreateLoad(Value)); 79 case AggregateLiteral: 80 return RValue::getAggregate(Value); 81 case AggregateAddress: 82 return RValue::getAggregate(CGF.Builder.CreateLoad(Value)); 83 case ComplexAddress: { 84 llvm::Value *real = 85 CGF.Builder.CreateLoad(CGF.Builder.CreateStructGEP(Value, 0)); 86 llvm::Value *imag = 87 CGF.Builder.CreateLoad(CGF.Builder.CreateStructGEP(Value, 1)); 88 return RValue::getComplex(real, imag); 89 } 90 } 91 92 llvm_unreachable("bad saved r-value kind"); 93} 94 95/// Push an entry of the given size onto this protected-scope stack. 96char *EHScopeStack::allocate(size_t Size) { 97 if (!StartOfBuffer) { 98 unsigned Capacity = 1024; 99 while (Capacity < Size) Capacity *= 2; 100 StartOfBuffer = new char[Capacity]; 101 StartOfData = EndOfBuffer = StartOfBuffer + Capacity; 102 } else if (static_cast<size_t>(StartOfData - StartOfBuffer) < Size) { 103 unsigned CurrentCapacity = EndOfBuffer - StartOfBuffer; 104 unsigned UsedCapacity = CurrentCapacity - (StartOfData - StartOfBuffer); 105 106 unsigned NewCapacity = CurrentCapacity; 107 do { 108 NewCapacity *= 2; 109 } while (NewCapacity < UsedCapacity + Size); 110 111 char *NewStartOfBuffer = new char[NewCapacity]; 112 char *NewEndOfBuffer = NewStartOfBuffer + NewCapacity; 113 char *NewStartOfData = NewEndOfBuffer - UsedCapacity; 114 memcpy(NewStartOfData, StartOfData, UsedCapacity); 115 delete [] StartOfBuffer; 116 StartOfBuffer = NewStartOfBuffer; 117 EndOfBuffer = NewEndOfBuffer; 118 StartOfData = NewStartOfData; 119 } 120 121 assert(StartOfBuffer + Size <= StartOfData); 122 StartOfData -= Size; 123 return StartOfData; 124} 125 126EHScopeStack::stable_iterator 127EHScopeStack::getInnermostActiveNormalCleanup() const { 128 for (stable_iterator si = getInnermostNormalCleanup(), se = stable_end(); 129 si != se; ) { 130 EHCleanupScope &cleanup = cast<EHCleanupScope>(*find(si)); 131 if (cleanup.isActive()) return si; 132 si = cleanup.getEnclosingNormalCleanup(); 133 } 134 return stable_end(); 135} 136 137EHScopeStack::stable_iterator EHScopeStack::getInnermostActiveEHScope() const { 138 for (stable_iterator si = getInnermostEHScope(), se = stable_end(); 139 si != se; ) { 140 // Skip over inactive cleanups. 141 EHCleanupScope *cleanup = dyn_cast<EHCleanupScope>(&*find(si)); 142 if (cleanup && !cleanup->isActive()) { 143 si = cleanup->getEnclosingEHScope(); 144 continue; 145 } 146 147 // All other scopes are always active. 148 return si; 149 } 150 151 return stable_end(); 152} 153 154 155void *EHScopeStack::pushCleanup(CleanupKind Kind, size_t Size) { 156 assert(((Size % sizeof(void*)) == 0) && "cleanup type is misaligned"); 157 char *Buffer = allocate(EHCleanupScope::getSizeForCleanupSize(Size)); 158 bool IsNormalCleanup = Kind & NormalCleanup; 159 bool IsEHCleanup = Kind & EHCleanup; 160 bool IsActive = !(Kind & InactiveCleanup); 161 EHCleanupScope *Scope = 162 new (Buffer) EHCleanupScope(IsNormalCleanup, 163 IsEHCleanup, 164 IsActive, 165 Size, 166 BranchFixups.size(), 167 InnermostNormalCleanup, 168 InnermostEHScope); 169 if (IsNormalCleanup) 170 InnermostNormalCleanup = stable_begin(); 171 if (IsEHCleanup) 172 InnermostEHScope = stable_begin(); 173 174 return Scope->getCleanupBuffer(); 175} 176 177void EHScopeStack::popCleanup() { 178 assert(!empty() && "popping exception stack when not empty"); 179 180 assert(isa<EHCleanupScope>(*begin())); 181 EHCleanupScope &Cleanup = cast<EHCleanupScope>(*begin()); 182 InnermostNormalCleanup = Cleanup.getEnclosingNormalCleanup(); 183 InnermostEHScope = Cleanup.getEnclosingEHScope(); 184 StartOfData += Cleanup.getAllocatedSize(); 185 186 // Destroy the cleanup. 187 Cleanup.~EHCleanupScope(); 188 189 // Check whether we can shrink the branch-fixups stack. 190 if (!BranchFixups.empty()) { 191 // If we no longer have any normal cleanups, all the fixups are 192 // complete. 193 if (!hasNormalCleanups()) 194 BranchFixups.clear(); 195 196 // Otherwise we can still trim out unnecessary nulls. 197 else 198 popNullFixups(); 199 } 200} 201 202EHFilterScope *EHScopeStack::pushFilter(unsigned numFilters) { 203 assert(getInnermostEHScope() == stable_end()); 204 char *buffer = allocate(EHFilterScope::getSizeForNumFilters(numFilters)); 205 EHFilterScope *filter = new (buffer) EHFilterScope(numFilters); 206 InnermostEHScope = stable_begin(); 207 return filter; 208} 209 210void EHScopeStack::popFilter() { 211 assert(!empty() && "popping exception stack when not empty"); 212 213 EHFilterScope &filter = cast<EHFilterScope>(*begin()); 214 StartOfData += EHFilterScope::getSizeForNumFilters(filter.getNumFilters()); 215 216 InnermostEHScope = filter.getEnclosingEHScope(); 217} 218 219EHCatchScope *EHScopeStack::pushCatch(unsigned numHandlers) { 220 char *buffer = allocate(EHCatchScope::getSizeForNumHandlers(numHandlers)); 221 EHCatchScope *scope = 222 new (buffer) EHCatchScope(numHandlers, InnermostEHScope); 223 InnermostEHScope = stable_begin(); 224 return scope; 225} 226 227void EHScopeStack::pushTerminate() { 228 char *Buffer = allocate(EHTerminateScope::getSize()); 229 new (Buffer) EHTerminateScope(InnermostEHScope); 230 InnermostEHScope = stable_begin(); 231} 232 233/// Remove any 'null' fixups on the stack. However, we can't pop more 234/// fixups than the fixup depth on the innermost normal cleanup, or 235/// else fixups that we try to add to that cleanup will end up in the 236/// wrong place. We *could* try to shrink fixup depths, but that's 237/// actually a lot of work for little benefit. 238void EHScopeStack::popNullFixups() { 239 // We expect this to only be called when there's still an innermost 240 // normal cleanup; otherwise there really shouldn't be any fixups. 241 assert(hasNormalCleanups()); 242 243 EHScopeStack::iterator it = find(InnermostNormalCleanup); 244 unsigned MinSize = cast<EHCleanupScope>(*it).getFixupDepth(); 245 assert(BranchFixups.size() >= MinSize && "fixup stack out of order"); 246 247 while (BranchFixups.size() > MinSize && 248 BranchFixups.back().Destination == 0) 249 BranchFixups.pop_back(); 250} 251 252void CodeGenFunction::initFullExprCleanup() { 253 // Create a variable to decide whether the cleanup needs to be run. 254 llvm::AllocaInst *active 255 = CreateTempAlloca(Builder.getInt1Ty(), "cleanup.cond"); 256 257 // Initialize it to false at a site that's guaranteed to be run 258 // before each evaluation. 259 setBeforeOutermostConditional(Builder.getFalse(), active); 260 261 // Initialize it to true at the current location. 262 Builder.CreateStore(Builder.getTrue(), active); 263 264 // Set that as the active flag in the cleanup. 265 EHCleanupScope &cleanup = cast<EHCleanupScope>(*EHStack.begin()); 266 assert(cleanup.getActiveFlag() == 0 && "cleanup already has active flag?"); 267 cleanup.setActiveFlag(active); 268 269 if (cleanup.isNormalCleanup()) cleanup.setTestFlagInNormalCleanup(); 270 if (cleanup.isEHCleanup()) cleanup.setTestFlagInEHCleanup(); 271} 272 273void EHScopeStack::Cleanup::anchor() {} 274 275/// All the branch fixups on the EH stack have propagated out past the 276/// outermost normal cleanup; resolve them all by adding cases to the 277/// given switch instruction. 278static void ResolveAllBranchFixups(CodeGenFunction &CGF, 279 llvm::SwitchInst *Switch, 280 llvm::BasicBlock *CleanupEntry) { 281 llvm::SmallPtrSet<llvm::BasicBlock*, 4> CasesAdded; 282 283 for (unsigned I = 0, E = CGF.EHStack.getNumBranchFixups(); I != E; ++I) { 284 // Skip this fixup if its destination isn't set. 285 BranchFixup &Fixup = CGF.EHStack.getBranchFixup(I); 286 if (Fixup.Destination == 0) continue; 287 288 // If there isn't an OptimisticBranchBlock, then InitialBranch is 289 // still pointing directly to its destination; forward it to the 290 // appropriate cleanup entry. This is required in the specific 291 // case of 292 // { std::string s; goto lbl; } 293 // lbl: 294 // i.e. where there's an unresolved fixup inside a single cleanup 295 // entry which we're currently popping. 296 if (Fixup.OptimisticBranchBlock == 0) { 297 new llvm::StoreInst(CGF.Builder.getInt32(Fixup.DestinationIndex), 298 CGF.getNormalCleanupDestSlot(), 299 Fixup.InitialBranch); 300 Fixup.InitialBranch->setSuccessor(0, CleanupEntry); 301 } 302 303 // Don't add this case to the switch statement twice. 304 if (!CasesAdded.insert(Fixup.Destination)) continue; 305 306 Switch->addCase(CGF.Builder.getInt32(Fixup.DestinationIndex), 307 Fixup.Destination); 308 } 309 310 CGF.EHStack.clearFixups(); 311} 312 313/// Transitions the terminator of the given exit-block of a cleanup to 314/// be a cleanup switch. 315static llvm::SwitchInst *TransitionToCleanupSwitch(CodeGenFunction &CGF, 316 llvm::BasicBlock *Block) { 317 // If it's a branch, turn it into a switch whose default 318 // destination is its original target. 319 llvm::TerminatorInst *Term = Block->getTerminator(); 320 assert(Term && "can't transition block without terminator"); 321 322 if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) { 323 assert(Br->isUnconditional()); 324 llvm::LoadInst *Load = 325 new llvm::LoadInst(CGF.getNormalCleanupDestSlot(), "cleanup.dest", Term); 326 llvm::SwitchInst *Switch = 327 llvm::SwitchInst::Create(Load, Br->getSuccessor(0), 4, Block); 328 Br->eraseFromParent(); 329 return Switch; 330 } else { 331 return cast<llvm::SwitchInst>(Term); 332 } 333} 334 335void CodeGenFunction::ResolveBranchFixups(llvm::BasicBlock *Block) { 336 assert(Block && "resolving a null target block"); 337 if (!EHStack.getNumBranchFixups()) return; 338 339 assert(EHStack.hasNormalCleanups() && 340 "branch fixups exist with no normal cleanups on stack"); 341 342 llvm::SmallPtrSet<llvm::BasicBlock*, 4> ModifiedOptimisticBlocks; 343 bool ResolvedAny = false; 344 345 for (unsigned I = 0, E = EHStack.getNumBranchFixups(); I != E; ++I) { 346 // Skip this fixup if its destination doesn't match. 347 BranchFixup &Fixup = EHStack.getBranchFixup(I); 348 if (Fixup.Destination != Block) continue; 349 350 Fixup.Destination = 0; 351 ResolvedAny = true; 352 353 // If it doesn't have an optimistic branch block, LatestBranch is 354 // already pointing to the right place. 355 llvm::BasicBlock *BranchBB = Fixup.OptimisticBranchBlock; 356 if (!BranchBB) 357 continue; 358 359 // Don't process the same optimistic branch block twice. 360 if (!ModifiedOptimisticBlocks.insert(BranchBB)) 361 continue; 362 363 llvm::SwitchInst *Switch = TransitionToCleanupSwitch(*this, BranchBB); 364 365 // Add a case to the switch. 366 Switch->addCase(Builder.getInt32(Fixup.DestinationIndex), Block); 367 } 368 369 if (ResolvedAny) 370 EHStack.popNullFixups(); 371} 372 373/// Pops cleanup blocks until the given savepoint is reached. 374void CodeGenFunction::PopCleanupBlocks(EHScopeStack::stable_iterator Old, 375 SourceLocation EHLoc) { 376 assert(Old.isValid()); 377 378 while (EHStack.stable_begin() != Old) { 379 EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin()); 380 381 // As long as Old strictly encloses the scope's enclosing normal 382 // cleanup, we're going to emit another normal cleanup which 383 // fallthrough can propagate through. 384 bool FallThroughIsBranchThrough = 385 Old.strictlyEncloses(Scope.getEnclosingNormalCleanup()); 386 387 PopCleanupBlock(FallThroughIsBranchThrough, EHLoc); 388 } 389} 390 391static llvm::BasicBlock *CreateNormalEntry(CodeGenFunction &CGF, 392 EHCleanupScope &Scope) { 393 assert(Scope.isNormalCleanup()); 394 llvm::BasicBlock *Entry = Scope.getNormalBlock(); 395 if (!Entry) { 396 Entry = CGF.createBasicBlock("cleanup"); 397 Scope.setNormalBlock(Entry); 398 } 399 return Entry; 400} 401 402/// Attempts to reduce a cleanup's entry block to a fallthrough. This 403/// is basically llvm::MergeBlockIntoPredecessor, except 404/// simplified/optimized for the tighter constraints on cleanup blocks. 405/// 406/// Returns the new block, whatever it is. 407static llvm::BasicBlock *SimplifyCleanupEntry(CodeGenFunction &CGF, 408 llvm::BasicBlock *Entry) { 409 llvm::BasicBlock *Pred = Entry->getSinglePredecessor(); 410 if (!Pred) return Entry; 411 412 llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Pred->getTerminator()); 413 if (!Br || Br->isConditional()) return Entry; 414 assert(Br->getSuccessor(0) == Entry); 415 416 // If we were previously inserting at the end of the cleanup entry 417 // block, we'll need to continue inserting at the end of the 418 // predecessor. 419 bool WasInsertBlock = CGF.Builder.GetInsertBlock() == Entry; 420 assert(!WasInsertBlock || CGF.Builder.GetInsertPoint() == Entry->end()); 421 422 // Kill the branch. 423 Br->eraseFromParent(); 424 425 // Replace all uses of the entry with the predecessor, in case there 426 // are phis in the cleanup. 427 Entry->replaceAllUsesWith(Pred); 428 429 // Merge the blocks. 430 Pred->getInstList().splice(Pred->end(), Entry->getInstList()); 431 432 // Kill the entry block. 433 Entry->eraseFromParent(); 434 435 if (WasInsertBlock) 436 CGF.Builder.SetInsertPoint(Pred); 437 438 return Pred; 439} 440 441static void EmitCleanup(CodeGenFunction &CGF, 442 EHScopeStack::Cleanup *Fn, 443 EHScopeStack::Cleanup::Flags flags, 444 llvm::Value *ActiveFlag) { 445 // EH cleanups always occur within a terminate scope. 446 if (flags.isForEHCleanup()) CGF.EHStack.pushTerminate(); 447 448 // If there's an active flag, load it and skip the cleanup if it's 449 // false. 450 llvm::BasicBlock *ContBB = 0; 451 if (ActiveFlag) { 452 ContBB = CGF.createBasicBlock("cleanup.done"); 453 llvm::BasicBlock *CleanupBB = CGF.createBasicBlock("cleanup.action"); 454 llvm::Value *IsActive 455 = CGF.Builder.CreateLoad(ActiveFlag, "cleanup.is_active"); 456 CGF.Builder.CreateCondBr(IsActive, CleanupBB, ContBB); 457 CGF.EmitBlock(CleanupBB); 458 } 459 460 // Ask the cleanup to emit itself. 461 Fn->Emit(CGF, flags); 462 assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?"); 463 464 // Emit the continuation block if there was an active flag. 465 if (ActiveFlag) 466 CGF.EmitBlock(ContBB); 467 468 // Leave the terminate scope. 469 if (flags.isForEHCleanup()) CGF.EHStack.popTerminate(); 470} 471 472static void ForwardPrebranchedFallthrough(llvm::BasicBlock *Exit, 473 llvm::BasicBlock *From, 474 llvm::BasicBlock *To) { 475 // Exit is the exit block of a cleanup, so it always terminates in 476 // an unconditional branch or a switch. 477 llvm::TerminatorInst *Term = Exit->getTerminator(); 478 479 if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) { 480 assert(Br->isUnconditional() && Br->getSuccessor(0) == From); 481 Br->setSuccessor(0, To); 482 } else { 483 llvm::SwitchInst *Switch = cast<llvm::SwitchInst>(Term); 484 for (unsigned I = 0, E = Switch->getNumSuccessors(); I != E; ++I) 485 if (Switch->getSuccessor(I) == From) 486 Switch->setSuccessor(I, To); 487 } 488} 489 490/// We don't need a normal entry block for the given cleanup. 491/// Optimistic fixup branches can cause these blocks to come into 492/// existence anyway; if so, destroy it. 493/// 494/// The validity of this transformation is very much specific to the 495/// exact ways in which we form branches to cleanup entries. 496static void destroyOptimisticNormalEntry(CodeGenFunction &CGF, 497 EHCleanupScope &scope) { 498 llvm::BasicBlock *entry = scope.getNormalBlock(); 499 if (!entry) return; 500 501 // Replace all the uses with unreachable. 502 llvm::BasicBlock *unreachableBB = CGF.getUnreachableBlock(); 503 for (llvm::BasicBlock::use_iterator 504 i = entry->use_begin(), e = entry->use_end(); i != e; ) { 505 llvm::Use &use = i.getUse(); 506 ++i; 507 508 use.set(unreachableBB); 509 510 // The only uses should be fixup switches. 511 llvm::SwitchInst *si = cast<llvm::SwitchInst>(use.getUser()); 512 if (si->getNumCases() == 1 && si->getDefaultDest() == unreachableBB) { 513 // Replace the switch with a branch. 514 llvm::BranchInst::Create(si->case_begin().getCaseSuccessor(), si); 515 516 // The switch operand is a load from the cleanup-dest alloca. 517 llvm::LoadInst *condition = cast<llvm::LoadInst>(si->getCondition()); 518 519 // Destroy the switch. 520 si->eraseFromParent(); 521 522 // Destroy the load. 523 assert(condition->getOperand(0) == CGF.NormalCleanupDest); 524 assert(condition->use_empty()); 525 condition->eraseFromParent(); 526 } 527 } 528 529 assert(entry->use_empty()); 530 delete entry; 531} 532 533/// Pops a cleanup block. If the block includes a normal cleanup, the 534/// current insertion point is threaded through the cleanup, as are 535/// any branch fixups on the cleanup. 536void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough, 537 SourceLocation EHLoc) { 538 assert(!EHStack.empty() && "cleanup stack is empty!"); 539 assert(isa<EHCleanupScope>(*EHStack.begin()) && "top not a cleanup!"); 540 EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin()); 541 assert(Scope.getFixupDepth() <= EHStack.getNumBranchFixups()); 542 543 // Remember activation information. 544 bool IsActive = Scope.isActive(); 545 llvm::Value *NormalActiveFlag = 546 Scope.shouldTestFlagInNormalCleanup() ? Scope.getActiveFlag() : 0; 547 llvm::Value *EHActiveFlag = 548 Scope.shouldTestFlagInEHCleanup() ? Scope.getActiveFlag() : 0; 549 550 // Check whether we need an EH cleanup. This is only true if we've 551 // generated a lazy EH cleanup block. 552 llvm::BasicBlock *EHEntry = Scope.getCachedEHDispatchBlock(); 553 assert(Scope.hasEHBranches() == (EHEntry != 0)); 554 bool RequiresEHCleanup = (EHEntry != 0); 555 EHScopeStack::stable_iterator EHParent = Scope.getEnclosingEHScope(); 556 557 // Check the three conditions which might require a normal cleanup: 558 559 // - whether there are branch fix-ups through this cleanup 560 unsigned FixupDepth = Scope.getFixupDepth(); 561 bool HasFixups = EHStack.getNumBranchFixups() != FixupDepth; 562 563 // - whether there are branch-throughs or branch-afters 564 bool HasExistingBranches = Scope.hasBranches(); 565 566 // - whether there's a fallthrough 567 llvm::BasicBlock *FallthroughSource = Builder.GetInsertBlock(); 568 bool HasFallthrough = (FallthroughSource != 0 && IsActive); 569 570 // Branch-through fall-throughs leave the insertion point set to the 571 // end of the last cleanup, which points to the current scope. The 572 // rest of IR gen doesn't need to worry about this; it only happens 573 // during the execution of PopCleanupBlocks(). 574 bool HasPrebranchedFallthrough = 575 (FallthroughSource && FallthroughSource->getTerminator()); 576 577 // If this is a normal cleanup, then having a prebranched 578 // fallthrough implies that the fallthrough source unconditionally 579 // jumps here. 580 assert(!Scope.isNormalCleanup() || !HasPrebranchedFallthrough || 581 (Scope.getNormalBlock() && 582 FallthroughSource->getTerminator()->getSuccessor(0) 583 == Scope.getNormalBlock())); 584 585 bool RequiresNormalCleanup = false; 586 if (Scope.isNormalCleanup() && 587 (HasFixups || HasExistingBranches || HasFallthrough)) { 588 RequiresNormalCleanup = true; 589 } 590 591 // If we have a prebranched fallthrough into an inactive normal 592 // cleanup, rewrite it so that it leads to the appropriate place. 593 if (Scope.isNormalCleanup() && HasPrebranchedFallthrough && !IsActive) { 594 llvm::BasicBlock *prebranchDest; 595 596 // If the prebranch is semantically branching through the next 597 // cleanup, just forward it to the next block, leaving the 598 // insertion point in the prebranched block. 599 if (FallthroughIsBranchThrough) { 600 EHScope &enclosing = *EHStack.find(Scope.getEnclosingNormalCleanup()); 601 prebranchDest = CreateNormalEntry(*this, cast<EHCleanupScope>(enclosing)); 602 603 // Otherwise, we need to make a new block. If the normal cleanup 604 // isn't being used at all, we could actually reuse the normal 605 // entry block, but this is simpler, and it avoids conflicts with 606 // dead optimistic fixup branches. 607 } else { 608 prebranchDest = createBasicBlock("forwarded-prebranch"); 609 EmitBlock(prebranchDest); 610 } 611 612 llvm::BasicBlock *normalEntry = Scope.getNormalBlock(); 613 assert(normalEntry && !normalEntry->use_empty()); 614 615 ForwardPrebranchedFallthrough(FallthroughSource, 616 normalEntry, prebranchDest); 617 } 618 619 // If we don't need the cleanup at all, we're done. 620 if (!RequiresNormalCleanup && !RequiresEHCleanup) { 621 destroyOptimisticNormalEntry(*this, Scope); 622 EHStack.popCleanup(); // safe because there are no fixups 623 assert(EHStack.getNumBranchFixups() == 0 || 624 EHStack.hasNormalCleanups()); 625 return; 626 } 627 628 // Copy the cleanup emission data out. Note that SmallVector 629 // guarantees maximal alignment for its buffer regardless of its 630 // type parameter. 631 SmallVector<char, 8*sizeof(void*)> CleanupBuffer; 632 CleanupBuffer.reserve(Scope.getCleanupSize()); 633 memcpy(CleanupBuffer.data(), 634 Scope.getCleanupBuffer(), Scope.getCleanupSize()); 635 CleanupBuffer.set_size(Scope.getCleanupSize()); 636 EHScopeStack::Cleanup *Fn = 637 reinterpret_cast<EHScopeStack::Cleanup*>(CleanupBuffer.data()); 638 639 EHScopeStack::Cleanup::Flags cleanupFlags; 640 if (Scope.isNormalCleanup()) 641 cleanupFlags.setIsNormalCleanupKind(); 642 if (Scope.isEHCleanup()) 643 cleanupFlags.setIsEHCleanupKind(); 644 645 if (!RequiresNormalCleanup) { 646 destroyOptimisticNormalEntry(*this, Scope); 647 EHStack.popCleanup(); 648 } else { 649 // If we have a fallthrough and no other need for the cleanup, 650 // emit it directly. 651 if (HasFallthrough && !HasPrebranchedFallthrough && 652 !HasFixups && !HasExistingBranches) { 653 654 destroyOptimisticNormalEntry(*this, Scope); 655 EHStack.popCleanup(); 656 657 EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag); 658 659 // Otherwise, the best approach is to thread everything through 660 // the cleanup block and then try to clean up after ourselves. 661 } else { 662 // Force the entry block to exist. 663 llvm::BasicBlock *NormalEntry = CreateNormalEntry(*this, Scope); 664 665 // I. Set up the fallthrough edge in. 666 667 CGBuilderTy::InsertPoint savedInactiveFallthroughIP; 668 669 // If there's a fallthrough, we need to store the cleanup 670 // destination index. For fall-throughs this is always zero. 671 if (HasFallthrough) { 672 if (!HasPrebranchedFallthrough) 673 Builder.CreateStore(Builder.getInt32(0), getNormalCleanupDestSlot()); 674 675 // Otherwise, save and clear the IP if we don't have fallthrough 676 // because the cleanup is inactive. 677 } else if (FallthroughSource) { 678 assert(!IsActive && "source without fallthrough for active cleanup"); 679 savedInactiveFallthroughIP = Builder.saveAndClearIP(); 680 } 681 682 // II. Emit the entry block. This implicitly branches to it if 683 // we have fallthrough. All the fixups and existing branches 684 // should already be branched to it. 685 EmitBlock(NormalEntry); 686 687 // III. Figure out where we're going and build the cleanup 688 // epilogue. 689 690 bool HasEnclosingCleanups = 691 (Scope.getEnclosingNormalCleanup() != EHStack.stable_end()); 692 693 // Compute the branch-through dest if we need it: 694 // - if there are branch-throughs threaded through the scope 695 // - if fall-through is a branch-through 696 // - if there are fixups that will be optimistically forwarded 697 // to the enclosing cleanup 698 llvm::BasicBlock *BranchThroughDest = 0; 699 if (Scope.hasBranchThroughs() || 700 (FallthroughSource && FallthroughIsBranchThrough) || 701 (HasFixups && HasEnclosingCleanups)) { 702 assert(HasEnclosingCleanups); 703 EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup()); 704 BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S)); 705 } 706 707 llvm::BasicBlock *FallthroughDest = 0; 708 SmallVector<llvm::Instruction*, 2> InstsToAppend; 709 710 // If there's exactly one branch-after and no other threads, 711 // we can route it without a switch. 712 if (!Scope.hasBranchThroughs() && !HasFixups && !HasFallthrough && 713 Scope.getNumBranchAfters() == 1) { 714 assert(!BranchThroughDest || !IsActive); 715 716 // TODO: clean up the possibly dead stores to the cleanup dest slot. 717 llvm::BasicBlock *BranchAfter = Scope.getBranchAfterBlock(0); 718 InstsToAppend.push_back(llvm::BranchInst::Create(BranchAfter)); 719 720 // Build a switch-out if we need it: 721 // - if there are branch-afters threaded through the scope 722 // - if fall-through is a branch-after 723 // - if there are fixups that have nowhere left to go and 724 // so must be immediately resolved 725 } else if (Scope.getNumBranchAfters() || 726 (HasFallthrough && !FallthroughIsBranchThrough) || 727 (HasFixups && !HasEnclosingCleanups)) { 728 729 llvm::BasicBlock *Default = 730 (BranchThroughDest ? BranchThroughDest : getUnreachableBlock()); 731 732 // TODO: base this on the number of branch-afters and fixups 733 const unsigned SwitchCapacity = 10; 734 735 llvm::LoadInst *Load = 736 new llvm::LoadInst(getNormalCleanupDestSlot(), "cleanup.dest"); 737 llvm::SwitchInst *Switch = 738 llvm::SwitchInst::Create(Load, Default, SwitchCapacity); 739 740 InstsToAppend.push_back(Load); 741 InstsToAppend.push_back(Switch); 742 743 // Branch-after fallthrough. 744 if (FallthroughSource && !FallthroughIsBranchThrough) { 745 FallthroughDest = createBasicBlock("cleanup.cont"); 746 if (HasFallthrough) 747 Switch->addCase(Builder.getInt32(0), FallthroughDest); 748 } 749 750 for (unsigned I = 0, E = Scope.getNumBranchAfters(); I != E; ++I) { 751 Switch->addCase(Scope.getBranchAfterIndex(I), 752 Scope.getBranchAfterBlock(I)); 753 } 754 755 // If there aren't any enclosing cleanups, we can resolve all 756 // the fixups now. 757 if (HasFixups && !HasEnclosingCleanups) 758 ResolveAllBranchFixups(*this, Switch, NormalEntry); 759 } else { 760 // We should always have a branch-through destination in this case. 761 assert(BranchThroughDest); 762 InstsToAppend.push_back(llvm::BranchInst::Create(BranchThroughDest)); 763 } 764 765 // IV. Pop the cleanup and emit it. 766 EHStack.popCleanup(); 767 assert(EHStack.hasNormalCleanups() == HasEnclosingCleanups); 768 769 EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag); 770 771 // Append the prepared cleanup prologue from above. 772 llvm::BasicBlock *NormalExit = Builder.GetInsertBlock(); 773 for (unsigned I = 0, E = InstsToAppend.size(); I != E; ++I) 774 NormalExit->getInstList().push_back(InstsToAppend[I]); 775 776 // Optimistically hope that any fixups will continue falling through. 777 for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups(); 778 I < E; ++I) { 779 BranchFixup &Fixup = EHStack.getBranchFixup(I); 780 if (!Fixup.Destination) continue; 781 if (!Fixup.OptimisticBranchBlock) { 782 new llvm::StoreInst(Builder.getInt32(Fixup.DestinationIndex), 783 getNormalCleanupDestSlot(), 784 Fixup.InitialBranch); 785 Fixup.InitialBranch->setSuccessor(0, NormalEntry); 786 } 787 Fixup.OptimisticBranchBlock = NormalExit; 788 } 789 790 // V. Set up the fallthrough edge out. 791 792 // Case 1: a fallthrough source exists but doesn't branch to the 793 // cleanup because the cleanup is inactive. 794 if (!HasFallthrough && FallthroughSource) { 795 // Prebranched fallthrough was forwarded earlier. 796 // Non-prebranched fallthrough doesn't need to be forwarded. 797 // Either way, all we need to do is restore the IP we cleared before. 798 assert(!IsActive); 799 Builder.restoreIP(savedInactiveFallthroughIP); 800 801 // Case 2: a fallthrough source exists and should branch to the 802 // cleanup, but we're not supposed to branch through to the next 803 // cleanup. 804 } else if (HasFallthrough && FallthroughDest) { 805 assert(!FallthroughIsBranchThrough); 806 EmitBlock(FallthroughDest); 807 808 // Case 3: a fallthrough source exists and should branch to the 809 // cleanup and then through to the next. 810 } else if (HasFallthrough) { 811 // Everything is already set up for this. 812 813 // Case 4: no fallthrough source exists. 814 } else { 815 Builder.ClearInsertionPoint(); 816 } 817 818 // VI. Assorted cleaning. 819 820 // Check whether we can merge NormalEntry into a single predecessor. 821 // This might invalidate (non-IR) pointers to NormalEntry. 822 llvm::BasicBlock *NewNormalEntry = 823 SimplifyCleanupEntry(*this, NormalEntry); 824 825 // If it did invalidate those pointers, and NormalEntry was the same 826 // as NormalExit, go back and patch up the fixups. 827 if (NewNormalEntry != NormalEntry && NormalEntry == NormalExit) 828 for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups(); 829 I < E; ++I) 830 EHStack.getBranchFixup(I).OptimisticBranchBlock = NewNormalEntry; 831 } 832 } 833 834 assert(EHStack.hasNormalCleanups() || EHStack.getNumBranchFixups() == 0); 835 836 // Emit the EH cleanup if required. 837 if (RequiresEHCleanup) { 838 if (CGDebugInfo *DI = getDebugInfo()) 839 DI->EmitLocation(Builder, EHLoc); 840 841 CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP(); 842 843 EmitBlock(EHEntry); 844 845 // We only actually emit the cleanup code if the cleanup is either 846 // active or was used before it was deactivated. 847 if (EHActiveFlag || IsActive) { 848 849 cleanupFlags.setIsForEHCleanup(); 850 EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag); 851 } 852 853 Builder.CreateBr(getEHDispatchBlock(EHParent)); 854 855 Builder.restoreIP(SavedIP); 856 857 SimplifyCleanupEntry(*this, EHEntry); 858 } 859} 860 861/// isObviouslyBranchWithoutCleanups - Return true if a branch to the 862/// specified destination obviously has no cleanups to run. 'false' is always 863/// a conservatively correct answer for this method. 864bool CodeGenFunction::isObviouslyBranchWithoutCleanups(JumpDest Dest) const { 865 assert(Dest.getScopeDepth().encloses(EHStack.stable_begin()) 866 && "stale jump destination"); 867 868 // Calculate the innermost active normal cleanup. 869 EHScopeStack::stable_iterator TopCleanup = 870 EHStack.getInnermostActiveNormalCleanup(); 871 872 // If we're not in an active normal cleanup scope, or if the 873 // destination scope is within the innermost active normal cleanup 874 // scope, we don't need to worry about fixups. 875 if (TopCleanup == EHStack.stable_end() || 876 TopCleanup.encloses(Dest.getScopeDepth())) // works for invalid 877 return true; 878 879 // Otherwise, we might need some cleanups. 880 return false; 881} 882 883 884/// Terminate the current block by emitting a branch which might leave 885/// the current cleanup-protected scope. The target scope may not yet 886/// be known, in which case this will require a fixup. 887/// 888/// As a side-effect, this method clears the insertion point. 889void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) { 890 assert(Dest.getScopeDepth().encloses(EHStack.stable_begin()) 891 && "stale jump destination"); 892 893 if (!HaveInsertPoint()) 894 return; 895 896 // Create the branch. 897 llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock()); 898 899 // Calculate the innermost active normal cleanup. 900 EHScopeStack::stable_iterator 901 TopCleanup = EHStack.getInnermostActiveNormalCleanup(); 902 903 // If we're not in an active normal cleanup scope, or if the 904 // destination scope is within the innermost active normal cleanup 905 // scope, we don't need to worry about fixups. 906 if (TopCleanup == EHStack.stable_end() || 907 TopCleanup.encloses(Dest.getScopeDepth())) { // works for invalid 908 Builder.ClearInsertionPoint(); 909 return; 910 } 911 912 // If we can't resolve the destination cleanup scope, just add this 913 // to the current cleanup scope as a branch fixup. 914 if (!Dest.getScopeDepth().isValid()) { 915 BranchFixup &Fixup = EHStack.addBranchFixup(); 916 Fixup.Destination = Dest.getBlock(); 917 Fixup.DestinationIndex = Dest.getDestIndex(); 918 Fixup.InitialBranch = BI; 919 Fixup.OptimisticBranchBlock = 0; 920 921 Builder.ClearInsertionPoint(); 922 return; 923 } 924 925 // Otherwise, thread through all the normal cleanups in scope. 926 927 // Store the index at the start. 928 llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex()); 929 new llvm::StoreInst(Index, getNormalCleanupDestSlot(), BI); 930 931 // Adjust BI to point to the first cleanup block. 932 { 933 EHCleanupScope &Scope = 934 cast<EHCleanupScope>(*EHStack.find(TopCleanup)); 935 BI->setSuccessor(0, CreateNormalEntry(*this, Scope)); 936 } 937 938 // Add this destination to all the scopes involved. 939 EHScopeStack::stable_iterator I = TopCleanup; 940 EHScopeStack::stable_iterator E = Dest.getScopeDepth(); 941 if (E.strictlyEncloses(I)) { 942 while (true) { 943 EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I)); 944 assert(Scope.isNormalCleanup()); 945 I = Scope.getEnclosingNormalCleanup(); 946 947 // If this is the last cleanup we're propagating through, tell it 948 // that there's a resolved jump moving through it. 949 if (!E.strictlyEncloses(I)) { 950 Scope.addBranchAfter(Index, Dest.getBlock()); 951 break; 952 } 953 954 // Otherwise, tell the scope that there's a jump propoagating 955 // through it. If this isn't new information, all the rest of 956 // the work has been done before. 957 if (!Scope.addBranchThrough(Dest.getBlock())) 958 break; 959 } 960 } 961 962 Builder.ClearInsertionPoint(); 963} 964 965static bool IsUsedAsNormalCleanup(EHScopeStack &EHStack, 966 EHScopeStack::stable_iterator C) { 967 // If we needed a normal block for any reason, that counts. 968 if (cast<EHCleanupScope>(*EHStack.find(C)).getNormalBlock()) 969 return true; 970 971 // Check whether any enclosed cleanups were needed. 972 for (EHScopeStack::stable_iterator 973 I = EHStack.getInnermostNormalCleanup(); 974 I != C; ) { 975 assert(C.strictlyEncloses(I)); 976 EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I)); 977 if (S.getNormalBlock()) return true; 978 I = S.getEnclosingNormalCleanup(); 979 } 980 981 return false; 982} 983 984static bool IsUsedAsEHCleanup(EHScopeStack &EHStack, 985 EHScopeStack::stable_iterator cleanup) { 986 // If we needed an EH block for any reason, that counts. 987 if (EHStack.find(cleanup)->hasEHBranches()) 988 return true; 989 990 // Check whether any enclosed cleanups were needed. 991 for (EHScopeStack::stable_iterator 992 i = EHStack.getInnermostEHScope(); i != cleanup; ) { 993 assert(cleanup.strictlyEncloses(i)); 994 995 EHScope &scope = *EHStack.find(i); 996 if (scope.hasEHBranches()) 997 return true; 998 999 i = scope.getEnclosingEHScope(); 1000 } 1001 1002 return false; 1003} 1004 1005enum ForActivation_t { 1006 ForActivation, 1007 ForDeactivation 1008}; 1009 1010/// The given cleanup block is changing activation state. Configure a 1011/// cleanup variable if necessary. 1012/// 1013/// It would be good if we had some way of determining if there were 1014/// extra uses *after* the change-over point. 1015static void SetupCleanupBlockActivation(CodeGenFunction &CGF, 1016 EHScopeStack::stable_iterator C, 1017 ForActivation_t kind, 1018 llvm::Instruction *dominatingIP) { 1019 EHCleanupScope &Scope = cast<EHCleanupScope>(*CGF.EHStack.find(C)); 1020 1021 // We always need the flag if we're activating the cleanup in a 1022 // conditional context, because we have to assume that the current 1023 // location doesn't necessarily dominate the cleanup's code. 1024 bool isActivatedInConditional = 1025 (kind == ForActivation && CGF.isInConditionalBranch()); 1026 1027 bool needFlag = false; 1028 1029 // Calculate whether the cleanup was used: 1030 1031 // - as a normal cleanup 1032 if (Scope.isNormalCleanup() && 1033 (isActivatedInConditional || IsUsedAsNormalCleanup(CGF.EHStack, C))) { 1034 Scope.setTestFlagInNormalCleanup(); 1035 needFlag = true; 1036 } 1037 1038 // - as an EH cleanup 1039 if (Scope.isEHCleanup() && 1040 (isActivatedInConditional || IsUsedAsEHCleanup(CGF.EHStack, C))) { 1041 Scope.setTestFlagInEHCleanup(); 1042 needFlag = true; 1043 } 1044 1045 // If it hasn't yet been used as either, we're done. 1046 if (!needFlag) return; 1047 1048 llvm::AllocaInst *var = Scope.getActiveFlag(); 1049 if (!var) { 1050 var = CGF.CreateTempAlloca(CGF.Builder.getInt1Ty(), "cleanup.isactive"); 1051 Scope.setActiveFlag(var); 1052 1053 assert(dominatingIP && "no existing variable and no dominating IP!"); 1054 1055 // Initialize to true or false depending on whether it was 1056 // active up to this point. 1057 llvm::Value *value = CGF.Builder.getInt1(kind == ForDeactivation); 1058 1059 // If we're in a conditional block, ignore the dominating IP and 1060 // use the outermost conditional branch. 1061 if (CGF.isInConditionalBranch()) { 1062 CGF.setBeforeOutermostConditional(value, var); 1063 } else { 1064 new llvm::StoreInst(value, var, dominatingIP); 1065 } 1066 } 1067 1068 CGF.Builder.CreateStore(CGF.Builder.getInt1(kind == ForActivation), var); 1069} 1070 1071/// Activate a cleanup that was created in an inactivated state. 1072void CodeGenFunction::ActivateCleanupBlock(EHScopeStack::stable_iterator C, 1073 llvm::Instruction *dominatingIP) { 1074 assert(C != EHStack.stable_end() && "activating bottom of stack?"); 1075 EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C)); 1076 assert(!Scope.isActive() && "double activation"); 1077 1078 SetupCleanupBlockActivation(*this, C, ForActivation, dominatingIP); 1079 1080 Scope.setActive(true); 1081} 1082 1083/// Deactive a cleanup that was created in an active state. 1084void CodeGenFunction::DeactivateCleanupBlock(EHScopeStack::stable_iterator C, 1085 llvm::Instruction *dominatingIP) { 1086 assert(C != EHStack.stable_end() && "deactivating bottom of stack?"); 1087 EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C)); 1088 assert(Scope.isActive() && "double deactivation"); 1089 1090 // If it's the top of the stack, just pop it. 1091 if (C == EHStack.stable_begin()) { 1092 // If it's a normal cleanup, we need to pretend that the 1093 // fallthrough is unreachable. 1094 CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP(); 1095 PopCleanupBlock(); 1096 Builder.restoreIP(SavedIP); 1097 return; 1098 } 1099 1100 // Otherwise, follow the general case. 1101 SetupCleanupBlockActivation(*this, C, ForDeactivation, dominatingIP); 1102 1103 Scope.setActive(false); 1104} 1105 1106llvm::Value *CodeGenFunction::getNormalCleanupDestSlot() { 1107 if (!NormalCleanupDest) 1108 NormalCleanupDest = 1109 CreateTempAlloca(Builder.getInt32Ty(), "cleanup.dest.slot"); 1110 return NormalCleanupDest; 1111} 1112 1113/// Emits all the code to cause the given temporary to be cleaned up. 1114void CodeGenFunction::EmitCXXTemporary(const CXXTemporary *Temporary, 1115 QualType TempType, 1116 llvm::Value *Ptr) { 1117 pushDestroy(NormalAndEHCleanup, Ptr, TempType, destroyCXXObject, 1118 /*useEHCleanup*/ true); 1119} 1120