contrib/llvm/tools/clang/lib/CodeGen/CGCleanup.cpp

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