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The personality routine currently lives in the LandingPadInst. This isn't desirable because: - All LandingPadInsts in the same function must have the same personality routine. This means that each LandingPadInst beyond the first has an operand which produces no additional information. - There is ongoing work to introduce EH IR constructs other than LandingPadInst. Moving the personality routine off of any one particular Instruction and onto the parent function seems a lot better than have N different places a personality function can sneak onto an exceptional function. Differential Revision: http://reviews.llvm.org/D10429 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239940 91177308-0d34-0410-b5e6-96231b3b80d8
265 lines
8.6 KiB
C++
265 lines
8.6 KiB
C++
//===-- DwarfEHPrepare - Prepare exception handling for code generation ---===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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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/CodeGen/Passes.h"
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#include "llvm/ADT/BitVector.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/LibCallSemantics.h"
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#include "llvm/Analysis/TargetTransformInfo.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/Pass.h"
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#include "llvm/Target/TargetLowering.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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#include "llvm/Transforms/Utils/Local.h"
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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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namespace {
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class DwarfEHPrepare : public FunctionPass {
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const TargetMachine *TM;
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// RewindFunction - _Unwind_Resume or the target equivalent.
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Constant *RewindFunction;
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DominatorTree *DT;
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const TargetLowering *TLI;
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bool InsertUnwindResumeCalls(Function &Fn);
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Value *GetExceptionObject(ResumeInst *RI);
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size_t
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pruneUnreachableResumes(Function &Fn,
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SmallVectorImpl<ResumeInst *> &Resumes,
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SmallVectorImpl<LandingPadInst *> &CleanupLPads);
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public:
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static char ID; // Pass identification, replacement for typeid.
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// INITIALIZE_TM_PASS requires a default constructor, but it isn't used in
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// practice.
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DwarfEHPrepare()
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: FunctionPass(ID), TM(nullptr), RewindFunction(nullptr), DT(nullptr),
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TLI(nullptr) {}
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DwarfEHPrepare(const TargetMachine *TM)
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: FunctionPass(ID), TM(TM), RewindFunction(nullptr), DT(nullptr),
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TLI(nullptr) {}
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bool runOnFunction(Function &Fn) override;
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bool doFinalization(Module &M) override {
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RewindFunction = nullptr;
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return false;
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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const char *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 DwarfEHPrepare::ID = 0;
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INITIALIZE_TM_PASS_BEGIN(DwarfEHPrepare, "dwarfehprepare",
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"Prepare DWARF exceptions", false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
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INITIALIZE_TM_PASS_END(DwarfEHPrepare, "dwarfehprepare",
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"Prepare DWARF exceptions", false, false)
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FunctionPass *llvm::createDwarfEHPass(const TargetMachine *TM) {
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return new DwarfEHPrepare(TM);
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}
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void DwarfEHPrepare::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<TargetTransformInfoWrapperPass>();
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AU.addRequired<DominatorTreeWrapperPass>();
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}
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/// GetExceptionObject - 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 *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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/// 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 DwarfEHPrepare::pruneUnreachableResumes(
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Function &Fn, SmallVectorImpl<ResumeInst *> &Resumes,
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SmallVectorImpl<LandingPadInst *> &CleanupLPads) {
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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, DT)) {
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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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const TargetTransformInfo &TTI =
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getAnalysis<TargetTransformInfoWrapperPass>().getTTI(Fn);
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LLVMContext &Ctx = Fn.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, 1);
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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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/// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
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/// into calls to the appropriate _Unwind_Resume function.
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bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
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SmallVector<ResumeInst*, 16> Resumes;
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SmallVector<LandingPadInst*, 16> CleanupLPads;
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for (BasicBlock &BB : Fn) {
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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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if (Resumes.empty())
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return false;
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// Check the personality, don't do anything if it's for MSVC.
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EHPersonality Pers = classifyEHPersonality(Fn.getPersonalityFn());
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if (isMSVCEHPersonality(Pers))
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return false;
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LLVMContext &Ctx = Fn.getContext();
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size_t ResumesLeft = pruneUnreachableResumes(Fn, Resumes, CleanupLPads);
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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 = FunctionType::get(Type::getVoidTy(Ctx),
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Type::getInt8PtrTy(Ctx), false);
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const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
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RewindFunction = Fn.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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new UnreachableInst(Ctx, UnwindBB);
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return true;
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}
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BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
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PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesLeft,
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"exn.obj", 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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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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new UnreachableInst(Ctx, UnwindBB);
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return true;
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}
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bool DwarfEHPrepare::runOnFunction(Function &Fn) {
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assert(TM && "DWARF EH preparation requires a target machine");
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DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
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TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
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bool Changed = InsertUnwindResumeCalls(Fn);
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DT = nullptr;
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TLI = nullptr;
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return Changed;
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}
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