1 //===- DwarfEHPrepare - Prepare exception handling for code generation ----===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This pass mulches exception handling code into a form adapted to code 10 // generation. Required if using dwarf exception handling. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/ADT/BitVector.h" 15 #include "llvm/ADT/SmallVector.h" 16 #include "llvm/ADT/Statistic.h" 17 #include "llvm/ADT/Triple.h" 18 #include "llvm/Analysis/CFG.h" 19 #include "llvm/Analysis/DomTreeUpdater.h" 20 #include "llvm/Analysis/EHPersonalities.h" 21 #include "llvm/Analysis/TargetTransformInfo.h" 22 #include "llvm/CodeGen/RuntimeLibcalls.h" 23 #include "llvm/CodeGen/TargetLowering.h" 24 #include "llvm/CodeGen/TargetPassConfig.h" 25 #include "llvm/CodeGen/TargetSubtargetInfo.h" 26 #include "llvm/IR/BasicBlock.h" 27 #include "llvm/IR/Constants.h" 28 #include "llvm/IR/DebugInfoMetadata.h" 29 #include "llvm/IR/DerivedTypes.h" 30 #include "llvm/IR/Dominators.h" 31 #include "llvm/IR/Function.h" 32 #include "llvm/IR/Instructions.h" 33 #include "llvm/IR/Module.h" 34 #include "llvm/IR/Type.h" 35 #include "llvm/InitializePasses.h" 36 #include "llvm/Pass.h" 37 #include "llvm/Support/Casting.h" 38 #include "llvm/Target/TargetMachine.h" 39 #include "llvm/Transforms/Utils/Local.h" 40 #include <cstddef> 41 42 using namespace llvm; 43 44 #define DEBUG_TYPE "dwarfehprepare" 45 46 STATISTIC(NumResumesLowered, "Number of resume calls lowered"); 47 STATISTIC(NumCleanupLandingPadsUnreachable, 48 "Number of cleanup landing pads found unreachable"); 49 STATISTIC(NumCleanupLandingPadsRemaining, 50 "Number of cleanup landing pads remaining"); 51 STATISTIC(NumNoUnwind, "Number of functions with nounwind"); 52 STATISTIC(NumUnwind, "Number of functions with unwind"); 53 54 namespace { 55 56 class DwarfEHPrepare { 57 CodeGenOpt::Level OptLevel; 58 59 Function &F; 60 const TargetLowering &TLI; 61 DomTreeUpdater *DTU; 62 const TargetTransformInfo *TTI; 63 const Triple &TargetTriple; 64 65 /// Return the exception object from the value passed into 66 /// the 'resume' instruction (typically an aggregate). Clean up any dead 67 /// instructions, including the 'resume' instruction. 68 Value *GetExceptionObject(ResumeInst *RI); 69 70 /// Replace resumes that are not reachable from a cleanup landing pad with 71 /// unreachable and then simplify those blocks. 72 size_t 73 pruneUnreachableResumes(SmallVectorImpl<ResumeInst *> &Resumes, 74 SmallVectorImpl<LandingPadInst *> &CleanupLPads); 75 76 /// Convert the ResumeInsts that are still present 77 /// into calls to the appropriate _Unwind_Resume function. 78 bool InsertUnwindResumeCalls(); 79 80 public: 81 DwarfEHPrepare(CodeGenOpt::Level OptLevel_, Function &F_, 82 const TargetLowering &TLI_, DomTreeUpdater *DTU_, 83 const TargetTransformInfo *TTI_, const Triple &TargetTriple_) 84 : OptLevel(OptLevel_), F(F_), TLI(TLI_), DTU(DTU_), TTI(TTI_), 85 TargetTriple(TargetTriple_) {} 86 87 bool run(); 88 }; 89 90 } // namespace 91 92 Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) { 93 Value *V = RI->getOperand(0); 94 Value *ExnObj = nullptr; 95 InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V); 96 LoadInst *SelLoad = nullptr; 97 InsertValueInst *ExcIVI = nullptr; 98 bool EraseIVIs = false; 99 100 if (SelIVI) { 101 if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) { 102 ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0)); 103 if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) && 104 ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) { 105 ExnObj = ExcIVI->getOperand(1); 106 SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1)); 107 EraseIVIs = true; 108 } 109 } 110 } 111 112 if (!ExnObj) 113 ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI); 114 115 RI->eraseFromParent(); 116 117 if (EraseIVIs) { 118 if (SelIVI->use_empty()) 119 SelIVI->eraseFromParent(); 120 if (ExcIVI->use_empty()) 121 ExcIVI->eraseFromParent(); 122 if (SelLoad && SelLoad->use_empty()) 123 SelLoad->eraseFromParent(); 124 } 125 126 return ExnObj; 127 } 128 129 size_t DwarfEHPrepare::pruneUnreachableResumes( 130 SmallVectorImpl<ResumeInst *> &Resumes, 131 SmallVectorImpl<LandingPadInst *> &CleanupLPads) { 132 assert(DTU && "Should have DomTreeUpdater here."); 133 134 BitVector ResumeReachable(Resumes.size()); 135 size_t ResumeIndex = 0; 136 for (auto *RI : Resumes) { 137 for (auto *LP : CleanupLPads) { 138 if (isPotentiallyReachable(LP, RI, nullptr, &DTU->getDomTree())) { 139 ResumeReachable.set(ResumeIndex); 140 break; 141 } 142 } 143 ++ResumeIndex; 144 } 145 146 // If everything is reachable, there is no change. 147 if (ResumeReachable.all()) 148 return Resumes.size(); 149 150 LLVMContext &Ctx = F.getContext(); 151 152 // Otherwise, insert unreachable instructions and call simplifycfg. 153 size_t ResumesLeft = 0; 154 for (size_t I = 0, E = Resumes.size(); I < E; ++I) { 155 ResumeInst *RI = Resumes[I]; 156 if (ResumeReachable[I]) { 157 Resumes[ResumesLeft++] = RI; 158 } else { 159 BasicBlock *BB = RI->getParent(); 160 new UnreachableInst(Ctx, RI); 161 RI->eraseFromParent(); 162 simplifyCFG(BB, *TTI, DTU); 163 } 164 } 165 Resumes.resize(ResumesLeft); 166 return ResumesLeft; 167 } 168 169 bool DwarfEHPrepare::InsertUnwindResumeCalls() { 170 SmallVector<ResumeInst *, 16> Resumes; 171 SmallVector<LandingPadInst *, 16> CleanupLPads; 172 if (F.doesNotThrow()) 173 NumNoUnwind++; 174 else 175 NumUnwind++; 176 for (BasicBlock &BB : F) { 177 if (auto *RI = dyn_cast<ResumeInst>(BB.getTerminator())) 178 Resumes.push_back(RI); 179 if (auto *LP = BB.getLandingPadInst()) 180 if (LP->isCleanup()) 181 CleanupLPads.push_back(LP); 182 } 183 184 NumCleanupLandingPadsRemaining += CleanupLPads.size(); 185 186 if (Resumes.empty()) 187 return false; 188 189 // Check the personality, don't do anything if it's scope-based. 190 EHPersonality Pers = classifyEHPersonality(F.getPersonalityFn()); 191 if (isScopedEHPersonality(Pers)) 192 return false; 193 194 LLVMContext &Ctx = F.getContext(); 195 196 size_t ResumesLeft = Resumes.size(); 197 if (OptLevel != CodeGenOpt::None) { 198 ResumesLeft = pruneUnreachableResumes(Resumes, CleanupLPads); 199 #if LLVM_ENABLE_STATS 200 unsigned NumRemainingLPs = 0; 201 for (BasicBlock &BB : F) { 202 if (auto *LP = BB.getLandingPadInst()) 203 if (LP->isCleanup()) 204 NumRemainingLPs++; 205 } 206 NumCleanupLandingPadsUnreachable += CleanupLPads.size() - NumRemainingLPs; 207 NumCleanupLandingPadsRemaining -= CleanupLPads.size() - NumRemainingLPs; 208 #endif 209 } 210 211 if (ResumesLeft == 0) 212 return true; // We pruned them all. 213 214 // RewindFunction - _Unwind_Resume or the target equivalent. 215 FunctionCallee RewindFunction; 216 CallingConv::ID RewindFunctionCallingConv; 217 FunctionType *FTy; 218 const char *RewindName; 219 bool DoesRewindFunctionNeedExceptionObject; 220 221 if ((Pers == EHPersonality::GNU_CXX || Pers == EHPersonality::GNU_CXX_SjLj) && 222 TargetTriple.isTargetEHABICompatible()) { 223 RewindName = TLI.getLibcallName(RTLIB::CXA_END_CLEANUP); 224 FTy = FunctionType::get(Type::getVoidTy(Ctx), false); 225 RewindFunctionCallingConv = 226 TLI.getLibcallCallingConv(RTLIB::CXA_END_CLEANUP); 227 DoesRewindFunctionNeedExceptionObject = false; 228 } else { 229 RewindName = TLI.getLibcallName(RTLIB::UNWIND_RESUME); 230 FTy = 231 FunctionType::get(Type::getVoidTy(Ctx), Type::getInt8PtrTy(Ctx), false); 232 RewindFunctionCallingConv = TLI.getLibcallCallingConv(RTLIB::UNWIND_RESUME); 233 DoesRewindFunctionNeedExceptionObject = true; 234 } 235 RewindFunction = F.getParent()->getOrInsertFunction(RewindName, FTy); 236 237 // Create the basic block where the _Unwind_Resume call will live. 238 if (ResumesLeft == 1) { 239 // Instead of creating a new BB and PHI node, just append the call to 240 // _Unwind_Resume to the end of the single resume block. 241 ResumeInst *RI = Resumes.front(); 242 BasicBlock *UnwindBB = RI->getParent(); 243 Value *ExnObj = GetExceptionObject(RI); 244 llvm::SmallVector<Value *, 1> RewindFunctionArgs; 245 if (DoesRewindFunctionNeedExceptionObject) 246 RewindFunctionArgs.push_back(ExnObj); 247 248 // Call the rewind function. 249 CallInst *CI = 250 CallInst::Create(RewindFunction, RewindFunctionArgs, "", UnwindBB); 251 // The verifier requires that all calls of debug-info-bearing functions 252 // from debug-info-bearing functions have a debug location (for inlining 253 // purposes). Assign a dummy location to satisfy the constraint. 254 Function *RewindFn = dyn_cast<Function>(RewindFunction.getCallee()); 255 if (RewindFn && RewindFn->getSubprogram()) 256 if (DISubprogram *SP = F.getSubprogram()) 257 CI->setDebugLoc(DILocation::get(SP->getContext(), 0, 0, SP)); 258 CI->setCallingConv(RewindFunctionCallingConv); 259 260 // We never expect _Unwind_Resume to return. 261 CI->setDoesNotReturn(); 262 new UnreachableInst(Ctx, UnwindBB); 263 return true; 264 } 265 266 std::vector<DominatorTree::UpdateType> Updates; 267 Updates.reserve(Resumes.size()); 268 269 llvm::SmallVector<Value *, 1> RewindFunctionArgs; 270 271 BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &F); 272 PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesLeft, "exn.obj", 273 UnwindBB); 274 275 // Extract the exception object from the ResumeInst and add it to the PHI node 276 // that feeds the _Unwind_Resume call. 277 for (ResumeInst *RI : Resumes) { 278 BasicBlock *Parent = RI->getParent(); 279 BranchInst::Create(UnwindBB, Parent); 280 Updates.push_back({DominatorTree::Insert, Parent, UnwindBB}); 281 282 Value *ExnObj = GetExceptionObject(RI); 283 PN->addIncoming(ExnObj, Parent); 284 285 ++NumResumesLowered; 286 } 287 288 if (DoesRewindFunctionNeedExceptionObject) 289 RewindFunctionArgs.push_back(PN); 290 291 // Call the function. 292 CallInst *CI = 293 CallInst::Create(RewindFunction, RewindFunctionArgs, "", UnwindBB); 294 CI->setCallingConv(RewindFunctionCallingConv); 295 296 // We never expect _Unwind_Resume to return. 297 CI->setDoesNotReturn(); 298 new UnreachableInst(Ctx, UnwindBB); 299 300 if (DTU) 301 DTU->applyUpdates(Updates); 302 303 return true; 304 } 305 306 bool DwarfEHPrepare::run() { 307 bool Changed = InsertUnwindResumeCalls(); 308 309 return Changed; 310 } 311 312 static bool prepareDwarfEH(CodeGenOpt::Level OptLevel, Function &F, 313 const TargetLowering &TLI, DominatorTree *DT, 314 const TargetTransformInfo *TTI, 315 const Triple &TargetTriple) { 316 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy); 317 318 return DwarfEHPrepare(OptLevel, F, TLI, DT ? &DTU : nullptr, TTI, 319 TargetTriple) 320 .run(); 321 } 322 323 namespace { 324 325 class DwarfEHPrepareLegacyPass : public FunctionPass { 326 327 CodeGenOpt::Level OptLevel; 328 329 public: 330 static char ID; // Pass identification, replacement for typeid. 331 332 DwarfEHPrepareLegacyPass(CodeGenOpt::Level OptLevel = CodeGenOpt::Default) 333 : FunctionPass(ID), OptLevel(OptLevel) {} 334 335 bool runOnFunction(Function &F) override { 336 const TargetMachine &TM = 337 getAnalysis<TargetPassConfig>().getTM<TargetMachine>(); 338 const TargetLowering &TLI = *TM.getSubtargetImpl(F)->getTargetLowering(); 339 DominatorTree *DT = nullptr; 340 const TargetTransformInfo *TTI = nullptr; 341 if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>()) 342 DT = &DTWP->getDomTree(); 343 if (OptLevel != CodeGenOpt::None) { 344 if (!DT) 345 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 346 TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); 347 } 348 return prepareDwarfEH(OptLevel, F, TLI, DT, TTI, TM.getTargetTriple()); 349 } 350 351 void getAnalysisUsage(AnalysisUsage &AU) const override { 352 AU.addRequired<TargetPassConfig>(); 353 AU.addRequired<TargetTransformInfoWrapperPass>(); 354 if (OptLevel != CodeGenOpt::None) { 355 AU.addRequired<DominatorTreeWrapperPass>(); 356 AU.addRequired<TargetTransformInfoWrapperPass>(); 357 } 358 AU.addPreserved<DominatorTreeWrapperPass>(); 359 } 360 361 StringRef getPassName() const override { 362 return "Exception handling preparation"; 363 } 364 }; 365 366 } // end anonymous namespace 367 368 char DwarfEHPrepareLegacyPass::ID = 0; 369 370 INITIALIZE_PASS_BEGIN(DwarfEHPrepareLegacyPass, DEBUG_TYPE, 371 "Prepare DWARF exceptions", false, false) 372 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) 373 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig) 374 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) 375 INITIALIZE_PASS_END(DwarfEHPrepareLegacyPass, DEBUG_TYPE, 376 "Prepare DWARF exceptions", false, false) 377 378 FunctionPass *llvm::createDwarfEHPass(CodeGenOpt::Level OptLevel) { 379 return new DwarfEHPrepareLegacyPass(OptLevel); 380 } 381