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1 //===-- WinEHPrepare - Prepare exception handling for code generation ---===//
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2 //
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3 // The LLVM Compiler Infrastructure
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4 //
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5 // This file is distributed under the University of Illinois Open Source
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6 // License. See LICENSE.TXT for details.
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7 //
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8 //===----------------------------------------------------------------------===//
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9 //
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10 // This pass lowers LLVM IR exception handling into something closer to what the
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11 // backend wants. It snifs the personality function to see which kind of
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12 // preparation is necessary. If the personality function uses the Itanium LSDA,
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13 // this pass delegates to the DWARF EH preparation pass.
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14 //
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15 //===----------------------------------------------------------------------===//
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16
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17 #include "llvm/CodeGen/Passes.h"
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18 #include "llvm/Analysis/LibCallSemantics.h"
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19 #include "llvm/IR/Function.h"
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20 #include "llvm/IR/IRBuilder.h"
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21 #include "llvm/IR/Instructions.h"
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22 #include "llvm/Pass.h"
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23 #include <memory>
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24
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25 using namespace llvm;
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26
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27 #define DEBUG_TYPE "winehprepare"
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28
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29 namespace {
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30 class WinEHPrepare : public FunctionPass {
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31 std::unique_ptr<FunctionPass> DwarfPrepare;
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32
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33 public:
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34 static char ID; // Pass identification, replacement for typeid.
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35 WinEHPrepare(const TargetMachine *TM = nullptr)
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36 : FunctionPass(ID), DwarfPrepare(createDwarfEHPass(TM)) {}
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37
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38 bool runOnFunction(Function &Fn) override;
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39
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40 bool doFinalization(Module &M) override;
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41
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42 void getAnalysisUsage(AnalysisUsage &AU) const override;
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43
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44 const char *getPassName() const override {
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45 return "Windows exception handling preparation";
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46 }
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47 };
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48 } // end anonymous namespace
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49
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50 char WinEHPrepare::ID = 0;
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51 INITIALIZE_TM_PASS(WinEHPrepare, "winehprepare",
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52 "Prepare Windows exceptions", false, false)
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53
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54 FunctionPass *llvm::createWinEHPass(const TargetMachine *TM) {
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55 return new WinEHPrepare(TM);
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56 }
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57
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58 static bool isMSVCPersonality(EHPersonality Pers) {
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59 return Pers == EHPersonality::MSVC_Win64SEH ||
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60 Pers == EHPersonality::MSVC_CXX;
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61 }
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62
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63 bool WinEHPrepare::runOnFunction(Function &Fn) {
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64 SmallVector<LandingPadInst *, 4> LPads;
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65 SmallVector<ResumeInst *, 4> Resumes;
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66 for (BasicBlock &BB : Fn) {
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67 if (auto *LP = BB.getLandingPadInst())
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68 LPads.push_back(LP);
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69 if (auto *Resume = dyn_cast<ResumeInst>(BB.getTerminator()))
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70 Resumes.push_back(Resume);
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71 }
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72
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73 // No need to prepare functions that lack landing pads.
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74 if (LPads.empty())
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75 return false;
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76
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77 // Classify the personality to see what kind of preparation we need.
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78 EHPersonality Pers = classifyEHPersonality(LPads.back()->getPersonalityFn());
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79
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80 // Delegate through to the DWARF pass if this is unrecognized.
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81 if (!isMSVCPersonality(Pers))
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82 return DwarfPrepare->runOnFunction(Fn);
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83
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84 // FIXME: Cleanups are unimplemented. Replace them with unreachable.
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85 if (Resumes.empty())
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86 return false;
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87
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88 for (ResumeInst *Resume : Resumes) {
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89 IRBuilder<>(Resume).CreateUnreachable();
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90 Resume->eraseFromParent();
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91 }
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92
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93 return true;
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94 }
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95
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96 bool WinEHPrepare::doFinalization(Module &M) {
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97 return DwarfPrepare->doFinalization(M);
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98 }
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99
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100 void WinEHPrepare::getAnalysisUsage(AnalysisUsage &AU) const {
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101 DwarfPrepare->getAnalysisUsage(AU);
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102 }
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