410 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// This pass mulches exception handling code into a form adapted to code10// generation. Required if using dwarf exception handling.11//12//===----------------------------------------------------------------------===//13 14#include "llvm/CodeGen/DwarfEHPrepare.h"15#include "llvm/ADT/BitVector.h"16#include "llvm/ADT/SmallVector.h"17#include "llvm/ADT/Statistic.h"18#include "llvm/Analysis/CFG.h"19#include "llvm/Analysis/DomTreeUpdater.h"20#include "llvm/Analysis/TargetTransformInfo.h"21#include "llvm/CodeGen/TargetLowering.h"22#include "llvm/CodeGen/TargetPassConfig.h"23#include "llvm/CodeGen/TargetSubtargetInfo.h"24#include "llvm/IR/BasicBlock.h"25#include "llvm/IR/Constants.h"26#include "llvm/IR/DebugInfoMetadata.h"27#include "llvm/IR/DerivedTypes.h"28#include "llvm/IR/Dominators.h"29#include "llvm/IR/EHPersonalities.h"30#include "llvm/IR/Function.h"31#include "llvm/IR/Instructions.h"32#include "llvm/IR/Module.h"33#include "llvm/IR/Type.h"34#include "llvm/InitializePasses.h"35#include "llvm/Pass.h"36#include "llvm/Support/Casting.h"37#include "llvm/Target/TargetMachine.h"38#include "llvm/TargetParser/Triple.h"39#include "llvm/Transforms/Utils/Local.h"40#include <cstddef>41 42using namespace llvm;43 44#define DEBUG_TYPE "dwarf-eh-prepare"45 46STATISTIC(NumResumesLowered, "Number of resume calls lowered");47STATISTIC(NumCleanupLandingPadsUnreachable,48 "Number of cleanup landing pads found unreachable");49STATISTIC(NumCleanupLandingPadsRemaining,50 "Number of cleanup landing pads remaining");51STATISTIC(NumNoUnwind, "Number of functions with nounwind");52STATISTIC(NumUnwind, "Number of functions with unwind");53 54namespace {55 56class DwarfEHPrepare {57 CodeGenOptLevel 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 into66 /// the 'resume' instruction (typically an aggregate). Clean up any dead67 /// instructions, including the 'resume' instruction.68 Value *GetExceptionObject(ResumeInst *RI);69 70 /// Replace resumes that are not reachable from a cleanup landing pad with71 /// unreachable and then simplify those blocks.72 size_t73 pruneUnreachableResumes(SmallVectorImpl<ResumeInst *> &Resumes,74 SmallVectorImpl<LandingPadInst *> &CleanupLPads);75 76 /// Convert the ResumeInsts that are still present77 /// into calls to the appropriate _Unwind_Resume function.78 bool InsertUnwindResumeCalls();79 80public:81 DwarfEHPrepare(CodeGenOptLevel 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} // namespace91 92Value *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",114 RI->getIterator());115 116 RI->eraseFromParent();117 118 if (EraseIVIs) {119 if (SelIVI->use_empty())120 SelIVI->eraseFromParent();121 if (ExcIVI->use_empty())122 ExcIVI->eraseFromParent();123 if (SelLoad && SelLoad->use_empty())124 SelLoad->eraseFromParent();125 }126 127 return ExnObj;128}129 130size_t DwarfEHPrepare::pruneUnreachableResumes(131 SmallVectorImpl<ResumeInst *> &Resumes,132 SmallVectorImpl<LandingPadInst *> &CleanupLPads) {133 assert(DTU && "Should have DomTreeUpdater here.");134 135 BitVector ResumeReachable(Resumes.size());136 size_t ResumeIndex = 0;137 for (auto *RI : Resumes) {138 for (auto *LP : CleanupLPads) {139 if (isPotentiallyReachable(LP, RI, nullptr, &DTU->getDomTree())) {140 ResumeReachable.set(ResumeIndex);141 break;142 }143 }144 ++ResumeIndex;145 }146 147 // If everything is reachable, there is no change.148 if (ResumeReachable.all())149 return Resumes.size();150 151 LLVMContext &Ctx = F.getContext();152 153 // Otherwise, insert unreachable instructions and call simplifycfg.154 size_t ResumesLeft = 0;155 for (size_t I = 0, E = Resumes.size(); I < E; ++I) {156 ResumeInst *RI = Resumes[I];157 if (ResumeReachable[I]) {158 Resumes[ResumesLeft++] = RI;159 } else {160 BasicBlock *BB = RI->getParent();161 new UnreachableInst(Ctx, RI->getIterator());162 RI->eraseFromParent();163 simplifyCFG(BB, *TTI, DTU);164 }165 }166 Resumes.resize(ResumesLeft);167 return ResumesLeft;168}169 170bool DwarfEHPrepare::InsertUnwindResumeCalls() {171 SmallVector<ResumeInst *, 16> Resumes;172 SmallVector<LandingPadInst *, 16> CleanupLPads;173 if (F.doesNotThrow())174 NumNoUnwind++;175 else176 NumUnwind++;177 for (BasicBlock &BB : F) {178 if (auto *RI = dyn_cast<ResumeInst>(BB.getTerminator()))179 Resumes.push_back(RI);180 if (auto *LP = BB.getLandingPadInst())181 if (LP->isCleanup())182 CleanupLPads.push_back(LP);183 }184 185 NumCleanupLandingPadsRemaining += CleanupLPads.size();186 187 if (Resumes.empty())188 return false;189 190 // Check the personality, don't do anything if it's scope-based.191 EHPersonality Pers = classifyEHPersonality(F.getPersonalityFn());192 if (isScopedEHPersonality(Pers))193 return false;194 195 LLVMContext &Ctx = F.getContext();196 197 size_t ResumesLeft = Resumes.size();198 if (OptLevel != CodeGenOptLevel::None) {199 ResumesLeft = pruneUnreachableResumes(Resumes, CleanupLPads);200#if LLVM_ENABLE_STATS201 unsigned NumRemainingLPs = 0;202 for (BasicBlock &BB : F) {203 if (auto *LP = BB.getLandingPadInst())204 if (LP->isCleanup())205 NumRemainingLPs++;206 }207 NumCleanupLandingPadsUnreachable += CleanupLPads.size() - NumRemainingLPs;208 NumCleanupLandingPadsRemaining -= CleanupLPads.size() - NumRemainingLPs;209#endif210 }211 212 if (ResumesLeft == 0)213 return true; // We pruned them all.214 215 // RewindFunction - _Unwind_Resume or the target equivalent.216 FunctionCallee RewindFunction;217 CallingConv::ID RewindFunctionCallingConv;218 FunctionType *FTy;219 const char *RewindName;220 bool DoesRewindFunctionNeedExceptionObject;221 222 if ((Pers == EHPersonality::GNU_CXX || Pers == EHPersonality::GNU_CXX_SjLj) &&223 TargetTriple.isTargetEHABICompatible()) {224 RewindName = TLI.getLibcallName(RTLIB::CXA_END_CLEANUP);225 FTy = FunctionType::get(Type::getVoidTy(Ctx), false);226 RewindFunctionCallingConv =227 TLI.getLibcallCallingConv(RTLIB::CXA_END_CLEANUP);228 DoesRewindFunctionNeedExceptionObject = false;229 } else {230 RewindName = TLI.getLibcallName(RTLIB::UNWIND_RESUME);231 FTy = FunctionType::get(Type::getVoidTy(Ctx), PointerType::getUnqual(Ctx),232 false);233 RewindFunctionCallingConv = TLI.getLibcallCallingConv(RTLIB::UNWIND_RESUME);234 DoesRewindFunctionNeedExceptionObject = true;235 }236 RewindFunction = F.getParent()->getOrInsertFunction(RewindName, FTy);237 238 // Create the basic block where the _Unwind_Resume call will live.239 if (ResumesLeft == 1) {240 // Instead of creating a new BB and PHI node, just append the call to241 // _Unwind_Resume to the end of the single resume block.242 ResumeInst *RI = Resumes.front();243 BasicBlock *UnwindBB = RI->getParent();244 Value *ExnObj = GetExceptionObject(RI);245 llvm::SmallVector<Value *, 1> RewindFunctionArgs;246 if (DoesRewindFunctionNeedExceptionObject)247 RewindFunctionArgs.push_back(ExnObj);248 249 // Call the rewind function.250 CallInst *CI =251 CallInst::Create(RewindFunction, RewindFunctionArgs, "", UnwindBB);252 // The verifier requires that all calls of debug-info-bearing functions253 // from debug-info-bearing functions have a debug location (for inlining254 // purposes). Assign a dummy location to satisfy the constraint.255 Function *RewindFn = dyn_cast<Function>(RewindFunction.getCallee());256 if (RewindFn && RewindFn->getSubprogram())257 if (DISubprogram *SP = F.getSubprogram())258 CI->setDebugLoc(DILocation::get(SP->getContext(), 0, 0, SP));259 CI->setCallingConv(RewindFunctionCallingConv);260 261 // We never expect _Unwind_Resume to return.262 CI->setDoesNotReturn();263 new UnreachableInst(Ctx, UnwindBB);264 return true;265 }266 267 std::vector<DominatorTree::UpdateType> Updates;268 Updates.reserve(Resumes.size());269 270 llvm::SmallVector<Value *, 1> RewindFunctionArgs;271 272 BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &F);273 PHINode *PN = PHINode::Create(PointerType::getUnqual(Ctx), ResumesLeft,274 "exn.obj", UnwindBB);275 276 // Extract the exception object from the ResumeInst and add it to the PHI node277 // that feeds the _Unwind_Resume call.278 for (ResumeInst *RI : Resumes) {279 BasicBlock *Parent = RI->getParent();280 BranchInst::Create(UnwindBB, Parent);281 Updates.push_back({DominatorTree::Insert, Parent, UnwindBB});282 283 Value *ExnObj = GetExceptionObject(RI);284 PN->addIncoming(ExnObj, Parent);285 286 ++NumResumesLowered;287 }288 289 if (DoesRewindFunctionNeedExceptionObject)290 RewindFunctionArgs.push_back(PN);291 292 // Call the function.293 CallInst *CI =294 CallInst::Create(RewindFunction, RewindFunctionArgs, "", UnwindBB);295 // The verifier requires that all calls of debug-info-bearing functions296 // from debug-info-bearing functions have a debug location (for inlining297 // purposes). Assign a dummy location to satisfy the constraint.298 Function *RewindFn = dyn_cast<Function>(RewindFunction.getCallee());299 if (RewindFn && RewindFn->getSubprogram())300 if (DISubprogram *SP = F.getSubprogram())301 CI->setDebugLoc(DILocation::get(SP->getContext(), 0, 0, SP));302 CI->setCallingConv(RewindFunctionCallingConv);303 304 // We never expect _Unwind_Resume to return.305 CI->setDoesNotReturn();306 new UnreachableInst(Ctx, UnwindBB);307 308 if (DTU)309 DTU->applyUpdates(Updates);310 311 return true;312}313 314bool DwarfEHPrepare::run() {315 bool Changed = InsertUnwindResumeCalls();316 317 return Changed;318}319 320static bool prepareDwarfEH(CodeGenOptLevel OptLevel, Function &F,321 const TargetLowering &TLI, DominatorTree *DT,322 const TargetTransformInfo *TTI,323 const Triple &TargetTriple) {324 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);325 326 return DwarfEHPrepare(OptLevel, F, TLI, DT ? &DTU : nullptr, TTI,327 TargetTriple)328 .run();329}330 331namespace {332 333class DwarfEHPrepareLegacyPass : public FunctionPass {334 335 CodeGenOptLevel OptLevel;336 337public:338 static char ID; // Pass identification, replacement for typeid.339 340 DwarfEHPrepareLegacyPass(CodeGenOptLevel OptLevel = CodeGenOptLevel::Default)341 : FunctionPass(ID), OptLevel(OptLevel) {}342 343 bool runOnFunction(Function &F) override {344 const TargetMachine &TM =345 getAnalysis<TargetPassConfig>().getTM<TargetMachine>();346 const TargetLowering &TLI = *TM.getSubtargetImpl(F)->getTargetLowering();347 DominatorTree *DT = nullptr;348 const TargetTransformInfo *TTI = nullptr;349 if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>())350 DT = &DTWP->getDomTree();351 if (OptLevel != CodeGenOptLevel::None) {352 if (!DT)353 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();354 TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);355 }356 return prepareDwarfEH(OptLevel, F, TLI, DT, TTI, TM.getTargetTriple());357 }358 359 void getAnalysisUsage(AnalysisUsage &AU) const override {360 AU.addRequired<TargetPassConfig>();361 AU.addRequired<TargetTransformInfoWrapperPass>();362 if (OptLevel != CodeGenOptLevel::None) {363 AU.addRequired<DominatorTreeWrapperPass>();364 AU.addRequired<TargetTransformInfoWrapperPass>();365 }366 AU.addPreserved<DominatorTreeWrapperPass>();367 }368 369 StringRef getPassName() const override {370 return "Exception handling preparation";371 }372};373 374} // end anonymous namespace375 376PreservedAnalyses DwarfEHPreparePass::run(Function &F,377 FunctionAnalysisManager &FAM) {378 const auto &TLI = *TM->getSubtargetImpl(F)->getTargetLowering();379 auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(F);380 const TargetTransformInfo *TTI = nullptr;381 auto OptLevel = TM->getOptLevel();382 if (OptLevel != CodeGenOptLevel::None) {383 if (!DT)384 DT = &FAM.getResult<DominatorTreeAnalysis>(F);385 TTI = &FAM.getResult<TargetIRAnalysis>(F);386 }387 bool Changed =388 prepareDwarfEH(OptLevel, F, TLI, DT, TTI, TM->getTargetTriple());389 390 if (!Changed)391 return PreservedAnalyses::all();392 PreservedAnalyses PA;393 PA.preserve<DominatorTreeAnalysis>();394 return PA;395}396 397char DwarfEHPrepareLegacyPass::ID = 0;398 399INITIALIZE_PASS_BEGIN(DwarfEHPrepareLegacyPass, DEBUG_TYPE,400 "Prepare DWARF exceptions", false, false)401INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)402INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)403INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)404INITIALIZE_PASS_END(DwarfEHPrepareLegacyPass, DEBUG_TYPE,405 "Prepare DWARF exceptions", false, false)406 407FunctionPass *llvm::createDwarfEHPass(CodeGenOptLevel OptLevel) {408 return new DwarfEHPrepareLegacyPass(OptLevel);409}410