DwarfEHPrepare.cpp revision afcb5b5ee854474a50dc4642a6e6ecc15acfe8cc 
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#define DEBUG_TYPE "dwarfehprepare"
16#include "llvm/Function.h"
17#include "llvm/Instructions.h"
18#include "llvm/IntrinsicInst.h"
19#include "llvm/Module.h"
20#include "llvm/Pass.h"
21#include "llvm/ADT/Statistic.h"
22#include "llvm/Analysis/Dominators.h"
23#include "llvm/CodeGen/Passes.h"
24#include "llvm/MC/MCAsmInfo.h"
25#include "llvm/Support/CallSite.h"
26#include "llvm/Target/TargetLowering.h"
27#include "llvm/Transforms/Utils/BasicBlockUtils.h"
28#include "llvm/Transforms/Utils/SSAUpdater.h"
29using namespace llvm;
30
31STATISTIC(NumResumesLowered, "Number of resume calls lowered");
32
33namespace {
34  class DwarfEHPrepare : public FunctionPass {
35    const TargetMachine *TM;
36    const TargetLowering *TLI;
37
38    // RewindFunction - _Unwind_Resume or the target equivalent.
39    Constant *RewindFunction;
40
41    bool InsertUnwindResumeCalls(Function &Fn);
42
43  public:
44    static char ID; // Pass identification, replacement for typeid.
45    DwarfEHPrepare(const TargetMachine *tm) :
46      FunctionPass(ID), TM(tm), TLI(TM->getTargetLowering()),
47      RewindFunction(0) {
48        initializeDominatorTreePass(*PassRegistry::getPassRegistry());
49      }
50
51    virtual bool runOnFunction(Function &Fn);
52
53    virtual void getAnalysisUsage(AnalysisUsage &AU) const { }
54
55    const char *getPassName() const {
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/// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
68/// into calls to the appropriate _Unwind_Resume function.
69bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
70  bool UsesNewEH = false;
71  SmallVector<ResumeInst*, 16> Resumes;
72  for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
73    TerminatorInst *TI = I->getTerminator();
74    if (ResumeInst *RI = dyn_cast<ResumeInst>(TI))
75      Resumes.push_back(RI);
76    else if (InvokeInst *II = dyn_cast<InvokeInst>(TI))
77      UsesNewEH = II->getUnwindDest()->isLandingPad();
78  }
79
80  if (Resumes.empty())
81    return UsesNewEH;
82
83  // Find the rewind function if we didn't already.
84  if (!RewindFunction) {
85    LLVMContext &Ctx = Resumes[0]->getContext();
86    FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
87                                          Type::getInt8PtrTy(Ctx), false);
88    const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
89    RewindFunction = Fn.getParent()->getOrInsertFunction(RewindName, FTy);
90  }
91
92  // Create the basic block where the _Unwind_Resume call will live.
93  LLVMContext &Ctx = Fn.getContext();
94  BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
95  PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), Resumes.size(),
96                                "exn.obj", UnwindBB);
97
98  // Extract the exception object from the ResumeInst and add it to the PHI node
99  // that feeds the _Unwind_Resume call.
100  for (SmallVectorImpl<ResumeInst*>::iterator
101         I = Resumes.begin(), E = Resumes.end(); I != E; ++I) {
102    ResumeInst *RI = *I;
103    BranchInst::Create(UnwindBB, RI->getParent());
104
105    Value *V = RI->getOperand(0);
106    Instruction *ExnObj = 0;
107    InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
108    LoadInst *SelLoad = 0;
109    InsertValueInst *ExcIVI = 0;
110    bool EraseIVIs = false;
111    if (SelIVI) {
112      if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
113        ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0));
114        if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) &&
115            ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
116          ExnObj = cast<Instruction>(ExcIVI->getOperand(1));
117          SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
118          EraseIVIs = true;
119        }
120      }
121    }
122
123    if (!ExnObj)
124      ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
125
126    PN->addIncoming(ExnObj, RI->getParent());
127    RI->eraseFromParent();
128
129    if (EraseIVIs) {
130      if (SelIVI->getNumUses() == 0)
131        SelIVI->eraseFromParent();
132      if (ExcIVI->getNumUses() == 0)
133        ExcIVI->eraseFromParent();
134      if (SelLoad && SelLoad->getNumUses() == 0)
135        SelLoad->eraseFromParent();
136    }
137
138    ++NumResumesLowered;
139  }
140
141  // Call the function.
142  CallInst *CI = CallInst::Create(RewindFunction, PN, "", 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
150bool DwarfEHPrepare::runOnFunction(Function &Fn) {
151  bool Changed = InsertUnwindResumeCalls(Fn);
152  return Changed;
153}
154