DwarfEHPrepare.cpp revision dce4a407a24b04eebc6a376f8e62b41aaa7b071f 
1//===-- DwarfEHPrepare - 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 mulches exception handling code into a form adapted to code
11// generation. Required if using dwarf exception handling.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/CodeGen/Passes.h"
16#include "llvm/ADT/Statistic.h"
17#include "llvm/IR/CallSite.h"
18#include "llvm/IR/Dominators.h"
19#include "llvm/IR/Function.h"
20#include "llvm/IR/Instructions.h"
21#include "llvm/IR/IntrinsicInst.h"
22#include "llvm/IR/Module.h"
23#include "llvm/MC/MCAsmInfo.h"
24#include "llvm/Pass.h"
25#include "llvm/Target/TargetLowering.h"
26#include "llvm/Transforms/Utils/BasicBlockUtils.h"
27#include "llvm/Transforms/Utils/SSAUpdater.h"
28using namespace llvm;
29
30#define DEBUG_TYPE "dwarfehprepare"
31
32STATISTIC(NumResumesLowered, "Number of resume calls lowered");
33
34namespace {
35  class DwarfEHPrepare : public FunctionPass {
36    const TargetMachine *TM;
37
38    // RewindFunction - _Unwind_Resume or the target equivalent.
39    Constant *RewindFunction;
40
41    bool InsertUnwindResumeCalls(Function &Fn);
42    Value *GetExceptionObject(ResumeInst *RI);
43
44  public:
45    static char ID; // Pass identification, replacement for typeid.
46    DwarfEHPrepare(const TargetMachine *TM)
47        : FunctionPass(ID), TM(TM), RewindFunction(nullptr) {
48      initializeDominatorTreeWrapperPassPass(*PassRegistry::getPassRegistry());
49    }
50
51    bool runOnFunction(Function &Fn) override;
52
53    void getAnalysisUsage(AnalysisUsage &AU) const override { }
54
55    const char *getPassName() const override {
56      return "Exception handling preparation";
57    }
58  };
59} // end anonymous namespace
60
61char DwarfEHPrepare::ID = 0;
62
63FunctionPass *llvm::createDwarfEHPass(const TargetMachine *TM) {
64  return new DwarfEHPrepare(TM);
65}
66
67/// GetExceptionObject - Return the exception object from the value passed into
68/// the 'resume' instruction (typically an aggregate). Clean up any dead
69/// instructions, including the 'resume' instruction.
70Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
71  Value *V = RI->getOperand(0);
72  Value *ExnObj = nullptr;
73  InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
74  LoadInst *SelLoad = nullptr;
75  InsertValueInst *ExcIVI = nullptr;
76  bool EraseIVIs = false;
77
78  if (SelIVI) {
79    if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
80      ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0));
81      if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) &&
82          ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
83        ExnObj = ExcIVI->getOperand(1);
84        SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
85        EraseIVIs = true;
86      }
87    }
88  }
89
90  if (!ExnObj)
91    ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
92
93  RI->eraseFromParent();
94
95  if (EraseIVIs) {
96    if (SelIVI->getNumUses() == 0)
97      SelIVI->eraseFromParent();
98    if (ExcIVI->getNumUses() == 0)
99      ExcIVI->eraseFromParent();
100    if (SelLoad && SelLoad->getNumUses() == 0)
101      SelLoad->eraseFromParent();
102  }
103
104  return ExnObj;
105}
106
107/// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
108/// into calls to the appropriate _Unwind_Resume function.
109bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
110  SmallVector<ResumeInst*, 16> Resumes;
111  for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
112    TerminatorInst *TI = I->getTerminator();
113    if (ResumeInst *RI = dyn_cast<ResumeInst>(TI))
114      Resumes.push_back(RI);
115  }
116
117  if (Resumes.empty())
118    return false;
119
120  // Find the rewind function if we didn't already.
121  const TargetLowering *TLI = TM->getTargetLowering();
122  if (!RewindFunction) {
123    LLVMContext &Ctx = Resumes[0]->getContext();
124    FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
125                                          Type::getInt8PtrTy(Ctx), false);
126    const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
127    RewindFunction = Fn.getParent()->getOrInsertFunction(RewindName, FTy);
128  }
129
130  // Create the basic block where the _Unwind_Resume call will live.
131  LLVMContext &Ctx = Fn.getContext();
132  unsigned ResumesSize = Resumes.size();
133
134  if (ResumesSize == 1) {
135    // Instead of creating a new BB and PHI node, just append the call to
136    // _Unwind_Resume to the end of the single resume block.
137    ResumeInst *RI = Resumes.front();
138    BasicBlock *UnwindBB = RI->getParent();
139    Value *ExnObj = GetExceptionObject(RI);
140
141    // Call the _Unwind_Resume function.
142    CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
143    CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
144
145    // We never expect _Unwind_Resume to return.
146    new UnreachableInst(Ctx, UnwindBB);
147    return true;
148  }
149
150  BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
151  PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesSize,
152                                "exn.obj", UnwindBB);
153
154  // Extract the exception object from the ResumeInst and add it to the PHI node
155  // that feeds the _Unwind_Resume call.
156  for (SmallVectorImpl<ResumeInst*>::iterator
157         I = Resumes.begin(), E = Resumes.end(); I != E; ++I) {
158    ResumeInst *RI = *I;
159    BasicBlock *Parent = RI->getParent();
160    BranchInst::Create(UnwindBB, Parent);
161
162    Value *ExnObj = GetExceptionObject(RI);
163    PN->addIncoming(ExnObj, Parent);
164
165    ++NumResumesLowered;
166  }
167
168  // Call the function.
169  CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
170  CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
171
172  // We never expect _Unwind_Resume to return.
173  new UnreachableInst(Ctx, UnwindBB);
174  return true;
175}
176
177bool DwarfEHPrepare::runOnFunction(Function &Fn) {
178  bool Changed = InsertUnwindResumeCalls(Fn);
179  return Changed;
180}
181