DwarfEHPrepare.cpp revision 445560881898fe212c185bd4c0485140d7b4fc88
1//===-- DwarfEHPrepare - Prepare exception handling for code generation ---===// 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 pass mulches exception handling code into a form adapted to code 11// generation. Required if using dwarf exception handling. 12// 13//===----------------------------------------------------------------------===// 14 15#define DEBUG_TYPE "dwarfehprepare" 16#include "llvm/Function.h" 17#include "llvm/Instructions.h" 18#include "llvm/IntrinsicInst.h" 19#include "llvm/Module.h" 20#include "llvm/Pass.h" 21#include "llvm/ADT/Statistic.h" 22#include "llvm/Analysis/Dominators.h" 23#include "llvm/CodeGen/Passes.h" 24#include "llvm/MC/MCAsmInfo.h" 25#include "llvm/Support/CallSite.h" 26#include "llvm/Target/TargetLowering.h" 27#include "llvm/Transforms/Utils/BasicBlockUtils.h" 28#include "llvm/Transforms/Utils/PromoteMemToReg.h" 29#include "llvm/Transforms/Utils/SSAUpdater.h" 30using namespace llvm; 31 32STATISTIC(NumLandingPadsSplit, "Number of landing pads split"); 33STATISTIC(NumUnwindsLowered, "Number of unwind instructions lowered"); 34STATISTIC(NumExceptionValuesMoved, "Number of eh.exception calls moved"); 35STATISTIC(NumStackTempsIntroduced, "Number of stack temporaries introduced"); 36 37static void PromoteAlloca(AllocaInst *AI); 38 39namespace { 40 class DwarfEHPrepare : public FunctionPass { 41 const TargetMachine *TM; 42 const TargetLowering *TLI; 43 bool CompileFast; 44 45 // The eh.exception intrinsic. 46 Function *ExceptionValueIntrinsic; 47 48 // The eh.selector intrinsic. 49 Function *SelectorIntrinsic; 50 51 // _Unwind_Resume_or_Rethrow call. 52 Constant *URoR; 53 54 // The EH language-specific catch-all type. 55 GlobalVariable *EHCatchAllValue; 56 57 // _Unwind_Resume or the target equivalent. 58 Constant *RewindFunction; 59 60 // Dominator info is used when turning stack temporaries into registers. 61 DominatorTree *DT; 62 63 // The function we are running on. 64 Function *F; 65 66 // The landing pads for this function. 67 typedef SmallPtrSet<BasicBlock*, 8> BBSet; 68 BBSet LandingPads; 69 70 // Stack temporary used to hold eh.exception values. 71 AllocaInst *ExceptionValueVar; 72 73 bool NormalizeLandingPads(); 74 bool LowerUnwinds(); 75 bool MoveExceptionValueCalls(); 76 bool FinishStackTemporaries(); 77 bool PromoteStackTemporaries(); 78 79 Instruction *CreateExceptionValueCall(BasicBlock *BB); 80 Instruction *CreateValueLoad(BasicBlock *BB); 81 82 /// CreateReadOfExceptionValue - Return the result of the eh.exception 83 /// intrinsic by calling the intrinsic if in a landing pad, or loading it 84 /// from the exception value variable otherwise. 85 Instruction *CreateReadOfExceptionValue(BasicBlock *BB) { 86 return LandingPads.count(BB) ? 87 CreateExceptionValueCall(BB) : CreateValueLoad(BB); 88 } 89 90 /// CleanupSelectors - Any remaining eh.selector intrinsic calls which still 91 /// use the "llvm.eh.catch.all.value" call need to convert to using its 92 /// initializer instead. 93 bool CleanupSelectors(SmallPtrSet<IntrinsicInst*, 32> &Sels); 94 95 bool HasCatchAllInSelector(IntrinsicInst *); 96 97 /// FindAllCleanupSelectors - Find all eh.selector calls that are clean-ups. 98 void FindAllCleanupSelectors(SmallPtrSet<IntrinsicInst*, 32> &Sels, 99 SmallPtrSet<IntrinsicInst*, 32> &CatchAllSels); 100 101 /// FindAllURoRInvokes - Find all URoR invokes in the function. 102 void FindAllURoRInvokes(SmallPtrSet<InvokeInst*, 32> &URoRInvokes); 103 104 /// HandleURoRInvokes - Handle invokes of "_Unwind_Resume_or_Rethrow" 105 /// calls. The "unwind" part of these invokes jump to a landing pad within 106 /// the current function. This is a candidate to merge the selector 107 /// associated with the URoR invoke with the one from the URoR's landing 108 /// pad. 109 bool HandleURoRInvokes(); 110 111 /// FindSelectorAndURoR - Find the eh.selector call and URoR call associated 112 /// with the eh.exception call. This recursively looks past instructions 113 /// which don't change the EH pointer value, like casts or PHI nodes. 114 bool FindSelectorAndURoR(Instruction *Inst, bool &URoRInvoke, 115 SmallPtrSet<IntrinsicInst*, 8> &SelCalls); 116 117 /// PromoteStoreInst - Perform Mem2Reg on a StoreInst. 118 bool PromoteStoreInst(StoreInst *SI) { 119 AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1)); 120 if (!AI || !isAllocaPromotable(AI)) return false; 121 122 PromoteAlloca(AI); 123 return true; 124 } 125 126 /// PromoteEHPtrStore - Promote the storing of an EH pointer into a 127 /// register. This should get rid of the store and subsequent loads. 128 bool PromoteEHPtrStore(IntrinsicInst *II) { 129 if (!CompileFast) return false; 130 131 bool Changed = false; 132 StoreInst *SI; 133 134 while (1) { 135 SI = 0; 136 for (Value::use_iterator 137 I = II->use_begin(), E = II->use_end(); I != E; ++I) { 138 SI = dyn_cast<StoreInst>(*I); 139 if (SI) break; 140 } 141 142 if (SI && !PromoteStoreInst(SI)) 143 break; 144 145 Changed = true; 146 } 147 148 return Changed; 149 } 150 151 public: 152 static char ID; // Pass identification, replacement for typeid. 153 DwarfEHPrepare(const TargetMachine *tm, bool fast) : 154 FunctionPass(ID), TM(tm), TLI(TM->getTargetLowering()), 155 CompileFast(fast), 156 ExceptionValueIntrinsic(0), SelectorIntrinsic(0), 157 URoR(0), EHCatchAllValue(0), RewindFunction(0) {} 158 159 virtual bool runOnFunction(Function &Fn); 160 161 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 162 AU.addPreserved<DominatorTree>(); 163 } 164 165 const char *getPassName() const { 166 return "Exception handling preparation"; 167 } 168 169 }; 170} // end anonymous namespace 171 172char DwarfEHPrepare::ID = 0; 173 174FunctionPass *llvm::createDwarfEHPass(const TargetMachine *tm, bool fast) { 175 return new DwarfEHPrepare(tm, fast); 176} 177 178/// PromoteAlloca - This promotes an alloca to registers when we know that it 179/// only has non-volatile loads and stores to it. 180static void PromoteAlloca(AllocaInst *AI) { 181 assert(isAllocaPromotable(AI)); 182 183 // First step: bucket up uses of the pointers by the block they occur in. 184 // This is important because we have to handle multiple defs/uses in a block 185 // ourselves: SSAUpdater is purely for cross-block references. 186 // FIXME: Want a TinyVector<Instruction*> since there is usually 0/1 element. 187 DenseMap<BasicBlock*, std::vector<Instruction*> > UsesByBlock; 188 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 189 UI != E; ++UI) { 190 Instruction *User = cast<Instruction>(*UI); 191 UsesByBlock[User->getParent()].push_back(User); 192 } 193 194 SSAUpdater SSA; 195 196 // It wants to know some value of the same type as what we'll be inserting. 197 Value *SomeValue; 198 if (isa<LoadInst>(*AI->use_begin())) 199 SomeValue = *AI->use_begin(); 200 else 201 SomeValue = cast<StoreInst>(*AI->use_begin())->getOperand(0); 202 SSA.Initialize(SomeValue); 203 204 // Okay, now we can iterate over all the blocks in the loop with uses, 205 // processing them. Keep track of which loads are loading a live-in value. 206 SmallVector<LoadInst*, 32> LiveInLoads; 207 208 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 209 UI != E; ++UI) { 210 Instruction *User = cast<Instruction>(*UI); 211 std::vector<Instruction*> &BlockUses = UsesByBlock[User->getParent()]; 212 213 // If this block has already been processed, ignore this repeat use. 214 if (BlockUses.empty()) continue; 215 216 // Okay, this is the first use in the block. If this block just has a 217 // single user in it, we can rewrite it trivially. 218 if (BlockUses.size() == 1) { 219 // If it is a store, it is a trivial def of the value in the block. 220 if (isa<StoreInst>(User)) { 221 SSA.AddAvailableValue(User->getParent(), 222 cast<StoreInst>(User)->getOperand(0)); 223 } else { 224 // Otherwise it is a load, queue it to rewrite as a live-in load. 225 LiveInLoads.push_back(cast<LoadInst>(User)); 226 } 227 BlockUses.clear(); 228 continue; 229 } 230 231 // Otherwise, check to see if this block is all loads. If so, we can queue 232 // them all as live in loads. 233 bool HasStore = false; 234 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) { 235 if (isa<StoreInst>(BlockUses[i])) { 236 HasStore = true; 237 break; 238 } 239 } 240 241 if (!HasStore) { 242 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) 243 LiveInLoads.push_back(cast<LoadInst>(BlockUses[i])); 244 BlockUses.clear(); 245 continue; 246 } 247 248 // Otherwise, we have mixed loads and stores (or just a bunch of stores). 249 // Since SSAUpdater is purely for cross-block values, we need to determine 250 // the order of these instructions in the block. If the first use in the 251 // block is a load, then it uses the live in value. The last store defines 252 // the live out value. We handle this by doing a linear scan of the block. 253 BasicBlock *BB = User->getParent(); 254 Value *StoredValue = 0; 255 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) { 256 if (LoadInst *L = dyn_cast<LoadInst>(II)) { 257 // If this is a load to an unrelated pointer, ignore it. 258 if (L->getOperand(0) != AI) continue; 259 260 // If we haven't seen a store yet, this is a live in use, otherwise 261 // use the stored value. 262 if (StoredValue) 263 L->replaceAllUsesWith(StoredValue); 264 else 265 LiveInLoads.push_back(L); 266 continue; 267 } 268 269 if (StoreInst *S = dyn_cast<StoreInst>(II)) { 270 // If this is a store to an unrelated pointer, ignore it. 271 if (S->getOperand(1) != AI) continue; 272 273 // Remember that this is the active value in the block. 274 StoredValue = S->getOperand(0); 275 } 276 } 277 278 // The last stored value that happened is the live-out for the block. 279 assert(StoredValue && "Already checked that there is a store in block"); 280 SSA.AddAvailableValue(BB, StoredValue); 281 BlockUses.clear(); 282 } 283 284 // Okay, now we rewrite all loads that use live-in values in the loop, 285 // inserting PHI nodes as necessary. 286 for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) { 287 LoadInst *ALoad = LiveInLoads[i]; 288 ALoad->replaceAllUsesWith(SSA.GetValueInMiddleOfBlock(ALoad->getParent())); 289 } 290 291 // Now that everything is rewritten, delete the old instructions from the body 292 // of the loop. They should all be dead now. 293 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 294 UI != E; ++UI) 295 cast<Instruction>(*UI)->eraseFromParent(); 296} 297 298 299 300/// HasCatchAllInSelector - Return true if the intrinsic instruction has a 301/// catch-all. 302bool DwarfEHPrepare::HasCatchAllInSelector(IntrinsicInst *II) { 303 if (!EHCatchAllValue) return false; 304 305 unsigned ArgIdx = II->getNumArgOperands() - 1; 306 GlobalVariable *GV = dyn_cast<GlobalVariable>(II->getArgOperand(ArgIdx)); 307 return GV == EHCatchAllValue; 308} 309 310/// FindAllCleanupSelectors - Find all eh.selector calls that are clean-ups. 311void DwarfEHPrepare:: 312FindAllCleanupSelectors(SmallPtrSet<IntrinsicInst*, 32> &Sels, 313 SmallPtrSet<IntrinsicInst*, 32> &CatchAllSels) { 314 for (Value::use_iterator 315 I = SelectorIntrinsic->use_begin(), 316 E = SelectorIntrinsic->use_end(); I != E; ++I) { 317 IntrinsicInst *II = cast<IntrinsicInst>(*I); 318 319 if (II->getParent()->getParent() != F) 320 continue; 321 322 if (!HasCatchAllInSelector(II)) 323 Sels.insert(II); 324 else 325 CatchAllSels.insert(II); 326 } 327} 328 329/// FindAllURoRInvokes - Find all URoR invokes in the function. 330void DwarfEHPrepare:: 331FindAllURoRInvokes(SmallPtrSet<InvokeInst*, 32> &URoRInvokes) { 332 for (Value::use_iterator 333 I = URoR->use_begin(), 334 E = URoR->use_end(); I != E; ++I) { 335 if (InvokeInst *II = dyn_cast<InvokeInst>(*I)) 336 URoRInvokes.insert(II); 337 } 338} 339 340/// CleanupSelectors - Any remaining eh.selector intrinsic calls which still use 341/// the "llvm.eh.catch.all.value" call need to convert to using its 342/// initializer instead. 343bool DwarfEHPrepare::CleanupSelectors(SmallPtrSet<IntrinsicInst*, 32> &Sels) { 344 if (!EHCatchAllValue) return false; 345 346 if (!SelectorIntrinsic) { 347 SelectorIntrinsic = 348 Intrinsic::getDeclaration(F->getParent(), Intrinsic::eh_selector); 349 if (!SelectorIntrinsic) return false; 350 } 351 352 bool Changed = false; 353 for (SmallPtrSet<IntrinsicInst*, 32>::iterator 354 I = Sels.begin(), E = Sels.end(); I != E; ++I) { 355 IntrinsicInst *Sel = *I; 356 357 // Index of the "llvm.eh.catch.all.value" variable. 358 unsigned OpIdx = Sel->getNumArgOperands() - 1; 359 GlobalVariable *GV = dyn_cast<GlobalVariable>(Sel->getArgOperand(OpIdx)); 360 if (GV != EHCatchAllValue) continue; 361 Sel->setArgOperand(OpIdx, EHCatchAllValue->getInitializer()); 362 Changed = true; 363 } 364 365 return Changed; 366} 367 368/// FindSelectorAndURoR - Find the eh.selector call associated with the 369/// eh.exception call. And indicate if there is a URoR "invoke" associated with 370/// the eh.exception call. This recursively looks past instructions which don't 371/// change the EH pointer value, like casts or PHI nodes. 372bool 373DwarfEHPrepare::FindSelectorAndURoR(Instruction *Inst, bool &URoRInvoke, 374 SmallPtrSet<IntrinsicInst*, 8> &SelCalls) { 375 SmallPtrSet<PHINode*, 32> SeenPHIs; 376 bool Changed = false; 377 378 restart: 379 for (Value::use_iterator 380 I = Inst->use_begin(), E = Inst->use_end(); I != E; ++I) { 381 Instruction *II = dyn_cast<Instruction>(*I); 382 if (!II || II->getParent()->getParent() != F) continue; 383 384 if (IntrinsicInst *Sel = dyn_cast<IntrinsicInst>(II)) { 385 if (Sel->getIntrinsicID() == Intrinsic::eh_selector) 386 SelCalls.insert(Sel); 387 } else if (InvokeInst *Invoke = dyn_cast<InvokeInst>(II)) { 388 if (Invoke->getCalledFunction() == URoR) 389 URoRInvoke = true; 390 } else if (CastInst *CI = dyn_cast<CastInst>(II)) { 391 Changed |= FindSelectorAndURoR(CI, URoRInvoke, SelCalls); 392 } else if (StoreInst *SI = dyn_cast<StoreInst>(II)) { 393 if (!PromoteStoreInst(SI)) continue; 394 Changed = true; 395 SeenPHIs.clear(); 396 goto restart; // Uses may have changed, restart loop. 397 } else if (PHINode *PN = dyn_cast<PHINode>(II)) { 398 if (SeenPHIs.insert(PN)) 399 // Don't process a PHI node more than once. 400 Changed |= FindSelectorAndURoR(PN, URoRInvoke, SelCalls); 401 } 402 } 403 404 return Changed; 405} 406 407/// HandleURoRInvokes - Handle invokes of "_Unwind_Resume_or_Rethrow" calls. The 408/// "unwind" part of these invokes jump to a landing pad within the current 409/// function. This is a candidate to merge the selector associated with the URoR 410/// invoke with the one from the URoR's landing pad. 411bool DwarfEHPrepare::HandleURoRInvokes() { 412 if (!EHCatchAllValue) { 413 EHCatchAllValue = 414 F->getParent()->getNamedGlobal("llvm.eh.catch.all.value"); 415 if (!EHCatchAllValue) return false; 416 } 417 418 if (!SelectorIntrinsic) { 419 SelectorIntrinsic = 420 Intrinsic::getDeclaration(F->getParent(), Intrinsic::eh_selector); 421 if (!SelectorIntrinsic) return false; 422 } 423 424 SmallPtrSet<IntrinsicInst*, 32> Sels; 425 SmallPtrSet<IntrinsicInst*, 32> CatchAllSels; 426 FindAllCleanupSelectors(Sels, CatchAllSels); 427 428 if (!DT) 429 // We require DominatorTree information. 430 return CleanupSelectors(CatchAllSels); 431 432 if (!URoR) { 433 URoR = F->getParent()->getFunction("_Unwind_Resume_or_Rethrow"); 434 if (!URoR) return CleanupSelectors(CatchAllSels); 435 } 436 437 SmallPtrSet<InvokeInst*, 32> URoRInvokes; 438 FindAllURoRInvokes(URoRInvokes); 439 440 SmallPtrSet<IntrinsicInst*, 32> SelsToConvert; 441 442 for (SmallPtrSet<IntrinsicInst*, 32>::iterator 443 SI = Sels.begin(), SE = Sels.end(); SI != SE; ++SI) { 444 const BasicBlock *SelBB = (*SI)->getParent(); 445 for (SmallPtrSet<InvokeInst*, 32>::iterator 446 UI = URoRInvokes.begin(), UE = URoRInvokes.end(); UI != UE; ++UI) { 447 const BasicBlock *URoRBB = (*UI)->getParent(); 448 if (DT->dominates(SelBB, URoRBB)) { 449 SelsToConvert.insert(*SI); 450 break; 451 } 452 } 453 } 454 455 bool Changed = false; 456 457 if (Sels.size() != SelsToConvert.size()) { 458 // If we haven't been able to convert all of the clean-up selectors, then 459 // loop through the slow way to see if they still need to be converted. 460 if (!ExceptionValueIntrinsic) { 461 ExceptionValueIntrinsic = 462 Intrinsic::getDeclaration(F->getParent(), Intrinsic::eh_exception); 463 if (!ExceptionValueIntrinsic) 464 return CleanupSelectors(CatchAllSels); 465 } 466 467 for (Value::use_iterator 468 I = ExceptionValueIntrinsic->use_begin(), 469 E = ExceptionValueIntrinsic->use_end(); I != E; ++I) { 470 IntrinsicInst *EHPtr = dyn_cast<IntrinsicInst>(*I); 471 if (!EHPtr || EHPtr->getParent()->getParent() != F) continue; 472 473 Changed |= PromoteEHPtrStore(EHPtr); 474 475 bool URoRInvoke = false; 476 SmallPtrSet<IntrinsicInst*, 8> SelCalls; 477 Changed |= FindSelectorAndURoR(EHPtr, URoRInvoke, SelCalls); 478 479 if (URoRInvoke) { 480 // This EH pointer is being used by an invoke of an URoR instruction and 481 // an eh.selector intrinsic call. If the eh.selector is a 'clean-up', we 482 // need to convert it to a 'catch-all'. 483 for (SmallPtrSet<IntrinsicInst*, 8>::iterator 484 SI = SelCalls.begin(), SE = SelCalls.end(); SI != SE; ++SI) 485 if (!HasCatchAllInSelector(*SI)) 486 SelsToConvert.insert(*SI); 487 } 488 } 489 } 490 491 if (!SelsToConvert.empty()) { 492 // Convert all clean-up eh.selectors, which are associated with "invokes" of 493 // URoR calls, into catch-all eh.selectors. 494 Changed = true; 495 496 for (SmallPtrSet<IntrinsicInst*, 8>::iterator 497 SI = SelsToConvert.begin(), SE = SelsToConvert.end(); 498 SI != SE; ++SI) { 499 IntrinsicInst *II = *SI; 500 501 // Use the exception object pointer and the personality function 502 // from the original selector. 503 CallSite CS(II); 504 IntrinsicInst::op_iterator I = CS.arg_begin(); 505 IntrinsicInst::op_iterator E = CS.arg_end(); 506 IntrinsicInst::op_iterator B = prior(E); 507 508 // Exclude last argument if it is an integer. 509 if (isa<ConstantInt>(B)) E = B; 510 511 // Add exception object pointer (front). 512 // Add personality function (next). 513 // Add in any filter IDs (rest). 514 SmallVector<Value*, 8> Args(I, E); 515 516 Args.push_back(EHCatchAllValue->getInitializer()); // Catch-all indicator. 517 518 CallInst *NewSelector = 519 CallInst::Create(SelectorIntrinsic, Args.begin(), Args.end(), 520 "eh.sel.catch.all", II); 521 522 NewSelector->setTailCall(II->isTailCall()); 523 NewSelector->setAttributes(II->getAttributes()); 524 NewSelector->setCallingConv(II->getCallingConv()); 525 526 II->replaceAllUsesWith(NewSelector); 527 II->eraseFromParent(); 528 } 529 } 530 531 Changed |= CleanupSelectors(CatchAllSels); 532 return Changed; 533} 534 535/// NormalizeLandingPads - Normalize and discover landing pads, noting them 536/// in the LandingPads set. A landing pad is normal if the only CFG edges 537/// that end at it are unwind edges from invoke instructions. If we inlined 538/// through an invoke we could have a normal branch from the previous 539/// unwind block through to the landing pad for the original invoke. 540/// Abnormal landing pads are fixed up by redirecting all unwind edges to 541/// a new basic block which falls through to the original. 542bool DwarfEHPrepare::NormalizeLandingPads() { 543 bool Changed = false; 544 545 const MCAsmInfo *MAI = TM->getMCAsmInfo(); 546 bool usingSjLjEH = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj; 547 548 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) { 549 TerminatorInst *TI = I->getTerminator(); 550 if (!isa<InvokeInst>(TI)) 551 continue; 552 BasicBlock *LPad = TI->getSuccessor(1); 553 // Skip landing pads that have already been normalized. 554 if (LandingPads.count(LPad)) 555 continue; 556 557 // Check that only invoke unwind edges end at the landing pad. 558 bool OnlyUnwoundTo = true; 559 bool SwitchOK = usingSjLjEH; 560 for (pred_iterator PI = pred_begin(LPad), PE = pred_end(LPad); 561 PI != PE; ++PI) { 562 TerminatorInst *PT = (*PI)->getTerminator(); 563 // The SjLj dispatch block uses a switch instruction. This is effectively 564 // an unwind edge, so we can disregard it here. There will only ever 565 // be one dispatch, however, so if there are multiple switches, one 566 // of them truly is a normal edge, not an unwind edge. 567 if (SwitchOK && isa<SwitchInst>(PT)) { 568 SwitchOK = false; 569 continue; 570 } 571 if (!isa<InvokeInst>(PT) || LPad == PT->getSuccessor(0)) { 572 OnlyUnwoundTo = false; 573 break; 574 } 575 } 576 577 if (OnlyUnwoundTo) { 578 // Only unwind edges lead to the landing pad. Remember the landing pad. 579 LandingPads.insert(LPad); 580 continue; 581 } 582 583 // At least one normal edge ends at the landing pad. Redirect the unwind 584 // edges to a new basic block which falls through into this one. 585 586 // Create the new basic block. 587 BasicBlock *NewBB = BasicBlock::Create(F->getContext(), 588 LPad->getName() + "_unwind_edge"); 589 590 // Insert it into the function right before the original landing pad. 591 LPad->getParent()->getBasicBlockList().insert(LPad, NewBB); 592 593 // Redirect unwind edges from the original landing pad to NewBB. 594 for (pred_iterator PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ) { 595 TerminatorInst *PT = (*PI++)->getTerminator(); 596 if (isa<InvokeInst>(PT) && PT->getSuccessor(1) == LPad) 597 // Unwind to the new block. 598 PT->setSuccessor(1, NewBB); 599 } 600 601 // If there are any PHI nodes in LPad, we need to update them so that they 602 // merge incoming values from NewBB instead. 603 for (BasicBlock::iterator II = LPad->begin(); isa<PHINode>(II); ++II) { 604 PHINode *PN = cast<PHINode>(II); 605 pred_iterator PB = pred_begin(NewBB), PE = pred_end(NewBB); 606 607 // Check to see if all of the values coming in via unwind edges are the 608 // same. If so, we don't need to create a new PHI node. 609 Value *InVal = PN->getIncomingValueForBlock(*PB); 610 for (pred_iterator PI = PB; PI != PE; ++PI) { 611 if (PI != PB && InVal != PN->getIncomingValueForBlock(*PI)) { 612 InVal = 0; 613 break; 614 } 615 } 616 617 if (InVal == 0) { 618 // Different unwind edges have different values. Create a new PHI node 619 // in NewBB. 620 PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".unwind", 621 NewBB); 622 // Add an entry for each unwind edge, using the value from the old PHI. 623 for (pred_iterator PI = PB; PI != PE; ++PI) 624 NewPN->addIncoming(PN->getIncomingValueForBlock(*PI), *PI); 625 626 // Now use this new PHI as the common incoming value for NewBB in PN. 627 InVal = NewPN; 628 } 629 630 // Revector exactly one entry in the PHI node to come from NewBB 631 // and delete all other entries that come from unwind edges. If 632 // there are both normal and unwind edges from the same predecessor, 633 // this leaves an entry for the normal edge. 634 for (pred_iterator PI = PB; PI != PE; ++PI) 635 PN->removeIncomingValue(*PI); 636 PN->addIncoming(InVal, NewBB); 637 } 638 639 // Add a fallthrough from NewBB to the original landing pad. 640 BranchInst::Create(LPad, NewBB); 641 642 // Now update DominatorTree analysis information if it is around. 643 if (DT) 644 DT->splitBlock(NewBB); 645 646 // Remember the newly constructed landing pad. The original landing pad 647 // LPad is no longer a landing pad now that all unwind edges have been 648 // revectored to NewBB. 649 LandingPads.insert(NewBB); 650 ++NumLandingPadsSplit; 651 Changed = true; 652 } 653 654 return Changed; 655} 656 657/// LowerUnwinds - Turn unwind instructions into calls to _Unwind_Resume, 658/// rethrowing any previously caught exception. This will crash horribly 659/// at runtime if there is no such exception: using unwind to throw a new 660/// exception is currently not supported. 661bool DwarfEHPrepare::LowerUnwinds() { 662 SmallVector<TerminatorInst*, 16> UnwindInsts; 663 664 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) { 665 TerminatorInst *TI = I->getTerminator(); 666 if (isa<UnwindInst>(TI)) 667 UnwindInsts.push_back(TI); 668 } 669 670 if (UnwindInsts.empty()) return false; 671 672 // Find the rewind function if we didn't already. 673 if (!RewindFunction) { 674 LLVMContext &Ctx = UnwindInsts[0]->getContext(); 675 std::vector<const Type*> 676 Params(1, Type::getInt8PtrTy(Ctx)); 677 FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx), 678 Params, false); 679 const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME); 680 RewindFunction = F->getParent()->getOrInsertFunction(RewindName, FTy); 681 } 682 683 bool Changed = false; 684 685 for (SmallVectorImpl<TerminatorInst*>::iterator 686 I = UnwindInsts.begin(), E = UnwindInsts.end(); I != E; ++I) { 687 TerminatorInst *TI = *I; 688 689 // Replace the unwind instruction with a call to _Unwind_Resume (or the 690 // appropriate target equivalent) followed by an UnreachableInst. 691 692 // Create the call... 693 CallInst *CI = CallInst::Create(RewindFunction, 694 CreateReadOfExceptionValue(TI->getParent()), 695 "", TI); 696 CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME)); 697 // ...followed by an UnreachableInst. 698 new UnreachableInst(TI->getContext(), TI); 699 700 // Nuke the unwind instruction. 701 TI->eraseFromParent(); 702 ++NumUnwindsLowered; 703 Changed = true; 704 } 705 706 return Changed; 707} 708 709/// MoveExceptionValueCalls - Ensure that eh.exception is only ever called from 710/// landing pads by replacing calls outside of landing pads with loads from a 711/// stack temporary. Move eh.exception calls inside landing pads to the start 712/// of the landing pad (optional, but may make things simpler for later passes). 713bool DwarfEHPrepare::MoveExceptionValueCalls() { 714 // If the eh.exception intrinsic is not declared in the module then there is 715 // nothing to do. Speed up compilation by checking for this common case. 716 if (!ExceptionValueIntrinsic && 717 !F->getParent()->getFunction(Intrinsic::getName(Intrinsic::eh_exception))) 718 return false; 719 720 bool Changed = false; 721 722 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) { 723 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) 724 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) 725 if (CI->getIntrinsicID() == Intrinsic::eh_exception) { 726 if (!CI->use_empty()) { 727 Value *ExceptionValue = CreateReadOfExceptionValue(BB); 728 if (CI == ExceptionValue) { 729 // The call was at the start of a landing pad - leave it alone. 730 assert(LandingPads.count(BB) && 731 "Created eh.exception call outside landing pad!"); 732 continue; 733 } 734 CI->replaceAllUsesWith(ExceptionValue); 735 } 736 CI->eraseFromParent(); 737 ++NumExceptionValuesMoved; 738 Changed = true; 739 } 740 } 741 742 return Changed; 743} 744 745/// FinishStackTemporaries - If we introduced a stack variable to hold the 746/// exception value then initialize it in each landing pad. 747bool DwarfEHPrepare::FinishStackTemporaries() { 748 if (!ExceptionValueVar) 749 // Nothing to do. 750 return false; 751 752 bool Changed = false; 753 754 // Make sure that there is a store of the exception value at the start of 755 // each landing pad. 756 for (BBSet::iterator LI = LandingPads.begin(), LE = LandingPads.end(); 757 LI != LE; ++LI) { 758 Instruction *ExceptionValue = CreateReadOfExceptionValue(*LI); 759 Instruction *Store = new StoreInst(ExceptionValue, ExceptionValueVar); 760 Store->insertAfter(ExceptionValue); 761 Changed = true; 762 } 763 764 return Changed; 765} 766 767/// PromoteStackTemporaries - Turn any stack temporaries we introduced into 768/// registers if possible. 769bool DwarfEHPrepare::PromoteStackTemporaries() { 770 // Turn the exception temporary into registers and phi nodes if possible. 771 if (ExceptionValueVar && isAllocaPromotable(ExceptionValueVar)) { 772 PromoteAlloca(ExceptionValueVar); 773 return true; 774 } 775 return false; 776} 777 778/// CreateExceptionValueCall - Insert a call to the eh.exception intrinsic at 779/// the start of the basic block (unless there already is one, in which case 780/// the existing call is returned). 781Instruction *DwarfEHPrepare::CreateExceptionValueCall(BasicBlock *BB) { 782 Instruction *Start = BB->getFirstNonPHIOrDbg(); 783 // Is this a call to eh.exception? 784 if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(Start)) 785 if (CI->getIntrinsicID() == Intrinsic::eh_exception) 786 // Reuse the existing call. 787 return Start; 788 789 // Find the eh.exception intrinsic if we didn't already. 790 if (!ExceptionValueIntrinsic) 791 ExceptionValueIntrinsic = Intrinsic::getDeclaration(F->getParent(), 792 Intrinsic::eh_exception); 793 794 // Create the call. 795 return CallInst::Create(ExceptionValueIntrinsic, "eh.value.call", Start); 796} 797 798/// CreateValueLoad - Insert a load of the exception value stack variable 799/// (creating it if necessary) at the start of the basic block (unless 800/// there already is a load, in which case the existing load is returned). 801Instruction *DwarfEHPrepare::CreateValueLoad(BasicBlock *BB) { 802 Instruction *Start = BB->getFirstNonPHIOrDbg(); 803 // Is this a load of the exception temporary? 804 if (ExceptionValueVar) 805 if (LoadInst* LI = dyn_cast<LoadInst>(Start)) 806 if (LI->getPointerOperand() == ExceptionValueVar) 807 // Reuse the existing load. 808 return Start; 809 810 // Create the temporary if we didn't already. 811 if (!ExceptionValueVar) { 812 ExceptionValueVar = new AllocaInst(PointerType::getUnqual( 813 Type::getInt8Ty(BB->getContext())), "eh.value", F->begin()->begin()); 814 ++NumStackTempsIntroduced; 815 } 816 817 // Load the value. 818 return new LoadInst(ExceptionValueVar, "eh.value.load", Start); 819} 820 821bool DwarfEHPrepare::runOnFunction(Function &Fn) { 822 bool Changed = false; 823 824 // Initialize internal state. 825 DT = getAnalysisIfAvailable<DominatorTree>(); 826 ExceptionValueVar = 0; 827 F = &Fn; 828 829 // Ensure that only unwind edges end at landing pads (a landing pad is a 830 // basic block where an invoke unwind edge ends). 831 Changed |= NormalizeLandingPads(); 832 833 // Turn unwind instructions into libcalls. 834 Changed |= LowerUnwinds(); 835 836 // TODO: Move eh.selector calls to landing pads and combine them. 837 838 // Move eh.exception calls to landing pads. 839 Changed |= MoveExceptionValueCalls(); 840 841 // Initialize any stack temporaries we introduced. 842 Changed |= FinishStackTemporaries(); 843 844 // Turn any stack temporaries into registers. 845 if (!CompileFast) 846 Changed |= PromoteStackTemporaries(); 847 848 Changed |= HandleURoRInvokes(); 849 850 LandingPads.clear(); 851 852 return Changed; 853} 854