forked from OSchip/llvm-project
351 lines
11 KiB
C++
351 lines
11 KiB
C++
//===- DwarfEHPrepare - Prepare exception handling for code generation ----===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass mulches exception handling code into a form adapted to code
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// generation. Required if using dwarf exception handling.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/BitVector.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/CFG.h"
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#include "llvm/Analysis/DomTreeUpdater.h"
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#include "llvm/Analysis/EHPersonalities.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/CodeGen/RuntimeLibcalls.h"
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#include "llvm/CodeGen/TargetLowering.h"
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#include "llvm/CodeGen/TargetPassConfig.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Type.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include <cstddef>
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using namespace llvm;
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#define DEBUG_TYPE "dwarfehprepare"
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STATISTIC(NumResumesLowered, "Number of resume calls lowered");
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STATISTIC(NumCleanupLandingPadsUnreachable,
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"Number of cleanup landing pads found unreachable");
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STATISTIC(NumCleanupLandingPadsRemaining,
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"Number of cleanup landing pads remaining");
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STATISTIC(NumNoUnwind, "Number of functions with nounwind");
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STATISTIC(NumUnwind, "Number of functions with unwind");
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namespace {
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class DwarfEHPrepare {
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CodeGenOpt::Level OptLevel;
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// RewindFunction - _Unwind_Resume or the target equivalent.
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FunctionCallee &RewindFunction;
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Function &F;
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const TargetLowering &TLI;
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DomTreeUpdater *DTU;
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const TargetTransformInfo *TTI;
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/// Return the exception object from the value passed into
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/// the 'resume' instruction (typically an aggregate). Clean up any dead
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/// instructions, including the 'resume' instruction.
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Value *GetExceptionObject(ResumeInst *RI);
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/// Replace resumes that are not reachable from a cleanup landing pad with
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/// unreachable and then simplify those blocks.
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size_t
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pruneUnreachableResumes(SmallVectorImpl<ResumeInst *> &Resumes,
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SmallVectorImpl<LandingPadInst *> &CleanupLPads);
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/// Convert the ResumeInsts that are still present
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/// into calls to the appropriate _Unwind_Resume function.
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bool InsertUnwindResumeCalls();
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public:
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DwarfEHPrepare(CodeGenOpt::Level OptLevel_, FunctionCallee &RewindFunction_,
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Function &F_, const TargetLowering &TLI_, DomTreeUpdater *DTU_,
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const TargetTransformInfo *TTI_)
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: OptLevel(OptLevel_), RewindFunction(RewindFunction_), F(F_), TLI(TLI_),
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DTU(DTU_), TTI(TTI_) {}
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bool run();
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};
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} // namespace
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Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
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Value *V = RI->getOperand(0);
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Value *ExnObj = nullptr;
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InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
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LoadInst *SelLoad = nullptr;
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InsertValueInst *ExcIVI = nullptr;
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bool EraseIVIs = false;
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if (SelIVI) {
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if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
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ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0));
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if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) &&
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ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
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ExnObj = ExcIVI->getOperand(1);
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SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
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EraseIVIs = true;
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}
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}
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}
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if (!ExnObj)
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ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
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RI->eraseFromParent();
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if (EraseIVIs) {
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if (SelIVI->use_empty())
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SelIVI->eraseFromParent();
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if (ExcIVI->use_empty())
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ExcIVI->eraseFromParent();
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if (SelLoad && SelLoad->use_empty())
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SelLoad->eraseFromParent();
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}
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return ExnObj;
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}
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size_t DwarfEHPrepare::pruneUnreachableResumes(
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SmallVectorImpl<ResumeInst *> &Resumes,
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SmallVectorImpl<LandingPadInst *> &CleanupLPads) {
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assert(DTU && "Should have DomTreeUpdater here.");
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BitVector ResumeReachable(Resumes.size());
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size_t ResumeIndex = 0;
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for (auto *RI : Resumes) {
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for (auto *LP : CleanupLPads) {
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if (isPotentiallyReachable(LP, RI, nullptr, &DTU->getDomTree())) {
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ResumeReachable.set(ResumeIndex);
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break;
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}
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}
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++ResumeIndex;
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}
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// If everything is reachable, there is no change.
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if (ResumeReachable.all())
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return Resumes.size();
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LLVMContext &Ctx = F.getContext();
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// Otherwise, insert unreachable instructions and call simplifycfg.
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size_t ResumesLeft = 0;
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for (size_t I = 0, E = Resumes.size(); I < E; ++I) {
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ResumeInst *RI = Resumes[I];
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if (ResumeReachable[I]) {
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Resumes[ResumesLeft++] = RI;
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} else {
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BasicBlock *BB = RI->getParent();
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new UnreachableInst(Ctx, RI);
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RI->eraseFromParent();
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simplifyCFG(BB, *TTI, DTU);
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}
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}
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Resumes.resize(ResumesLeft);
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return ResumesLeft;
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}
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bool DwarfEHPrepare::InsertUnwindResumeCalls() {
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SmallVector<ResumeInst *, 16> Resumes;
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SmallVector<LandingPadInst *, 16> CleanupLPads;
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if (F.doesNotThrow())
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NumNoUnwind++;
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else
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NumUnwind++;
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for (BasicBlock &BB : F) {
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if (auto *RI = dyn_cast<ResumeInst>(BB.getTerminator()))
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Resumes.push_back(RI);
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if (auto *LP = BB.getLandingPadInst())
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if (LP->isCleanup())
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CleanupLPads.push_back(LP);
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}
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NumCleanupLandingPadsRemaining += CleanupLPads.size();
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if (Resumes.empty())
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return false;
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// Check the personality, don't do anything if it's scope-based.
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EHPersonality Pers = classifyEHPersonality(F.getPersonalityFn());
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if (isScopedEHPersonality(Pers))
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return false;
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LLVMContext &Ctx = F.getContext();
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size_t ResumesLeft = Resumes.size();
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if (OptLevel != CodeGenOpt::None) {
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ResumesLeft = pruneUnreachableResumes(Resumes, CleanupLPads);
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#if LLVM_ENABLE_STATS
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unsigned NumRemainingLPs = 0;
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for (BasicBlock &BB : F) {
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if (auto *LP = BB.getLandingPadInst())
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if (LP->isCleanup())
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NumRemainingLPs++;
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}
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NumCleanupLandingPadsUnreachable += CleanupLPads.size() - NumRemainingLPs;
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NumCleanupLandingPadsRemaining -= CleanupLPads.size() - NumRemainingLPs;
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#endif
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}
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if (ResumesLeft == 0)
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return true; // We pruned them all.
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// Find the rewind function if we didn't already.
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if (!RewindFunction) {
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FunctionType *FTy =
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FunctionType::get(Type::getVoidTy(Ctx), Type::getInt8PtrTy(Ctx), false);
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const char *RewindName = TLI.getLibcallName(RTLIB::UNWIND_RESUME);
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RewindFunction = F.getParent()->getOrInsertFunction(RewindName, FTy);
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}
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// Create the basic block where the _Unwind_Resume call will live.
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if (ResumesLeft == 1) {
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// Instead of creating a new BB and PHI node, just append the call to
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// _Unwind_Resume to the end of the single resume block.
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ResumeInst *RI = Resumes.front();
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BasicBlock *UnwindBB = RI->getParent();
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Value *ExnObj = GetExceptionObject(RI);
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// Call the _Unwind_Resume function.
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CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
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CI->setCallingConv(TLI.getLibcallCallingConv(RTLIB::UNWIND_RESUME));
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// We never expect _Unwind_Resume to return.
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CI->setDoesNotReturn();
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new UnreachableInst(Ctx, UnwindBB);
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return true;
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}
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std::vector<DominatorTree::UpdateType> Updates;
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Updates.reserve(Resumes.size());
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BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &F);
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PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesLeft, "exn.obj",
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UnwindBB);
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// Extract the exception object from the ResumeInst and add it to the PHI node
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// that feeds the _Unwind_Resume call.
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for (ResumeInst *RI : Resumes) {
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BasicBlock *Parent = RI->getParent();
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BranchInst::Create(UnwindBB, Parent);
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Updates.push_back({DominatorTree::Insert, Parent, UnwindBB});
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Value *ExnObj = GetExceptionObject(RI);
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PN->addIncoming(ExnObj, Parent);
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++NumResumesLowered;
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}
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// Call the function.
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CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
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CI->setCallingConv(TLI.getLibcallCallingConv(RTLIB::UNWIND_RESUME));
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// We never expect _Unwind_Resume to return.
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CI->setDoesNotReturn();
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new UnreachableInst(Ctx, UnwindBB);
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if (DTU)
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DTU->applyUpdates(Updates);
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return true;
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}
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bool DwarfEHPrepare::run() {
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bool Changed = InsertUnwindResumeCalls();
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return Changed;
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}
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static bool prepareDwarfEH(CodeGenOpt::Level OptLevel,
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FunctionCallee &RewindFunction, Function &F,
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const TargetLowering &TLI, DominatorTree *DT,
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const TargetTransformInfo *TTI) {
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DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
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return DwarfEHPrepare(OptLevel, RewindFunction, F, TLI, DT ? &DTU : nullptr,
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TTI)
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.run();
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}
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namespace {
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class DwarfEHPrepareLegacyPass : public FunctionPass {
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// RewindFunction - _Unwind_Resume or the target equivalent.
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FunctionCallee RewindFunction = nullptr;
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CodeGenOpt::Level OptLevel;
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public:
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static char ID; // Pass identification, replacement for typeid.
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DwarfEHPrepareLegacyPass(CodeGenOpt::Level OptLevel = CodeGenOpt::Default)
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: FunctionPass(ID), OptLevel(OptLevel) {}
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bool runOnFunction(Function &F) override {
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const TargetMachine &TM =
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getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
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const TargetLowering &TLI = *TM.getSubtargetImpl(F)->getTargetLowering();
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DominatorTree *DT = nullptr;
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const TargetTransformInfo *TTI = nullptr;
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if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>())
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DT = &DTWP->getDomTree();
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if (OptLevel != CodeGenOpt::None) {
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if (!DT)
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DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
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TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
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}
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return prepareDwarfEH(OptLevel, RewindFunction, F, TLI, DT, TTI);
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<TargetPassConfig>();
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AU.addRequired<TargetTransformInfoWrapperPass>();
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if (OptLevel != CodeGenOpt::None) {
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<TargetTransformInfoWrapperPass>();
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}
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AU.addPreserved<DominatorTreeWrapperPass>();
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}
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StringRef getPassName() const override {
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return "Exception handling preparation";
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}
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};
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} // end anonymous namespace
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char DwarfEHPrepareLegacyPass::ID = 0;
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INITIALIZE_PASS_BEGIN(DwarfEHPrepareLegacyPass, DEBUG_TYPE,
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"Prepare DWARF exceptions", false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
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INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
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INITIALIZE_PASS_END(DwarfEHPrepareLegacyPass, DEBUG_TYPE,
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"Prepare DWARF exceptions", false, false)
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FunctionPass *llvm::createDwarfEHPass(CodeGenOpt::Level OptLevel) {
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return new DwarfEHPrepareLegacyPass(OptLevel);
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}
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