1 //===-- WinEHPrepare - Prepare exception handling for code generation ---===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This pass lowers LLVM IR exception handling into something closer to what the
11 // backend wants. It snifs the personality function to see which kind of
12 // preparation is necessary. If the personality function uses the Itanium LSDA,
13 // this pass delegates to the DWARF EH preparation pass.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "llvm/CodeGen/Passes.h"
18 #include "llvm/Analysis/LibCallSemantics.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/IRBuilder.h"
21 #include "llvm/IR/Instructions.h"
22 #include "llvm/Pass.h"
23 #include <memory>
24 
25 using namespace llvm;
26 
27 #define DEBUG_TYPE "winehprepare"
28 
29 namespace {
30 class WinEHPrepare : public FunctionPass {
31   std::unique_ptr<FunctionPass> DwarfPrepare;
32 
33 public:
34   static char ID; // Pass identification, replacement for typeid.
35   WinEHPrepare(const TargetMachine *TM = nullptr)
36       : FunctionPass(ID), DwarfPrepare(createDwarfEHPass(TM)) {}
37 
38   bool runOnFunction(Function &Fn) override;
39 
40   bool doFinalization(Module &M) override;
41 
42   void getAnalysisUsage(AnalysisUsage &AU) const override;
43 
44   const char *getPassName() const override {
45     return "Windows exception handling preparation";
46   }
47 };
48 } // end anonymous namespace
49 
50 char WinEHPrepare::ID = 0;
51 INITIALIZE_TM_PASS(WinEHPrepare, "winehprepare",
52                    "Prepare Windows exceptions", false, false)
53 
54 FunctionPass *llvm::createWinEHPass(const TargetMachine *TM) {
55   return new WinEHPrepare(TM);
56 }
57 
58 static bool isMSVCPersonality(EHPersonality Pers) {
59   return Pers == EHPersonality::MSVC_Win64SEH ||
60          Pers == EHPersonality::MSVC_CXX;
61 }
62 
63 bool WinEHPrepare::runOnFunction(Function &Fn) {
64   SmallVector<LandingPadInst *, 4> LPads;
65   SmallVector<ResumeInst *, 4> Resumes;
66   for (BasicBlock &BB : Fn) {
67     if (auto *LP = BB.getLandingPadInst())
68       LPads.push_back(LP);
69     if (auto *Resume = dyn_cast<ResumeInst>(BB.getTerminator()))
70       Resumes.push_back(Resume);
71   }
72 
73   // No need to prepare functions that lack landing pads.
74   if (LPads.empty())
75     return false;
76 
77   // Classify the personality to see what kind of preparation we need.
78   EHPersonality Pers = ClassifyEHPersonality(LPads.back()->getPersonalityFn());
79 
80   // Delegate through to the DWARF pass if this is unrecognized.
81   if (!isMSVCPersonality(Pers))
82     return DwarfPrepare->runOnFunction(Fn);
83 
84   // FIXME: Cleanups are unimplemented. Replace them with unreachable.
85   if (Resumes.empty())
86     return false;
87 
88   for (ResumeInst *Resume : Resumes) {
89     IRBuilder<>(Resume).CreateUnreachable();
90     Resume->eraseFromParent();
91   }
92 
93   return true;
94 }
95 
96 bool WinEHPrepare::doFinalization(Module &M) {
97   return DwarfPrepare->doFinalization(M);
98 }
99 
100 void WinEHPrepare::getAnalysisUsage(AnalysisUsage &AU) const {
101   DwarfPrepare->getAnalysisUsage(AU);
102 }
103