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/CodeGen/Passes.h"
17 #include "llvm/ADT/Statistic.h"
18 #include "llvm/Analysis/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/Support/CallSite.h"
26 #include "llvm/Target/TargetLowering.h"
27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
28 #include "llvm/Transforms/Utils/SSAUpdater.h"
29 using namespace llvm;
30
31 STATISTIC(NumResumesLowered, "Number of resume calls lowered");
32
33 namespace {
34 class DwarfEHPrepare : public FunctionPass {
35 const TargetMachine *TM;
36
37 // RewindFunction - _Unwind_Resume or the target equivalent.
38 Constant *RewindFunction;
39
40 bool InsertUnwindResumeCalls(Function &Fn);
41 Value *GetExceptionObject(ResumeInst *RI);
42
43 public:
44 static char ID; // Pass identification, replacement for typeid.
DwarfEHPrepare(const TargetMachine * TM)45 DwarfEHPrepare(const TargetMachine *TM) :
46 FunctionPass(ID), TM(TM), RewindFunction(0) {
47 initializeDominatorTreePass(*PassRegistry::getPassRegistry());
48 }
49
50 virtual bool runOnFunction(Function &Fn);
51
getAnalysisUsage(AnalysisUsage & AU) const52 virtual void getAnalysisUsage(AnalysisUsage &AU) const { }
53
getPassName() const54 const char *getPassName() const {
55 return "Exception handling preparation";
56 }
57 };
58 } // end anonymous namespace
59
60 char DwarfEHPrepare::ID = 0;
61
createDwarfEHPass(const TargetMachine * TM)62 FunctionPass *llvm::createDwarfEHPass(const TargetMachine *TM) {
63 return new DwarfEHPrepare(TM);
64 }
65
66 /// GetExceptionObject - Return the exception object from the value passed into
67 /// the 'resume' instruction (typically an aggregate). Clean up any dead
68 /// instructions, including the 'resume' instruction.
GetExceptionObject(ResumeInst * RI)69 Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
70 Value *V = RI->getOperand(0);
71 Value *ExnObj = 0;
72 InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
73 LoadInst *SelLoad = 0;
74 InsertValueInst *ExcIVI = 0;
75 bool EraseIVIs = false;
76
77 if (SelIVI) {
78 if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
79 ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0));
80 if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) &&
81 ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
82 ExnObj = ExcIVI->getOperand(1);
83 SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
84 EraseIVIs = true;
85 }
86 }
87 }
88
89 if (!ExnObj)
90 ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
91
92 RI->eraseFromParent();
93
94 if (EraseIVIs) {
95 if (SelIVI->getNumUses() == 0)
96 SelIVI->eraseFromParent();
97 if (ExcIVI->getNumUses() == 0)
98 ExcIVI->eraseFromParent();
99 if (SelLoad && SelLoad->getNumUses() == 0)
100 SelLoad->eraseFromParent();
101 }
102
103 return ExnObj;
104 }
105
106 /// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
107 /// into calls to the appropriate _Unwind_Resume function.
InsertUnwindResumeCalls(Function & Fn)108 bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
109 SmallVector<ResumeInst*, 16> Resumes;
110 for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
111 TerminatorInst *TI = I->getTerminator();
112 if (ResumeInst *RI = dyn_cast<ResumeInst>(TI))
113 Resumes.push_back(RI);
114 }
115
116 if (Resumes.empty())
117 return false;
118
119 // Find the rewind function if we didn't already.
120 const TargetLowering *TLI = TM->getTargetLowering();
121 if (!RewindFunction) {
122 LLVMContext &Ctx = Resumes[0]->getContext();
123 FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
124 Type::getInt8PtrTy(Ctx), false);
125 const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
126 RewindFunction = Fn.getParent()->getOrInsertFunction(RewindName, FTy);
127 }
128
129 // Create the basic block where the _Unwind_Resume call will live.
130 LLVMContext &Ctx = Fn.getContext();
131 unsigned ResumesSize = Resumes.size();
132
133 if (ResumesSize == 1) {
134 // Instead of creating a new BB and PHI node, just append the call to
135 // _Unwind_Resume to the end of the single resume block.
136 ResumeInst *RI = Resumes.front();
137 BasicBlock *UnwindBB = RI->getParent();
138 Value *ExnObj = GetExceptionObject(RI);
139
140 // Call the _Unwind_Resume function.
141 CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
142 CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
143
144 // We never expect _Unwind_Resume to return.
145 new UnreachableInst(Ctx, UnwindBB);
146 return true;
147 }
148
149 BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
150 PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesSize,
151 "exn.obj", UnwindBB);
152
153 // Extract the exception object from the ResumeInst and add it to the PHI node
154 // that feeds the _Unwind_Resume call.
155 for (SmallVectorImpl<ResumeInst*>::iterator
156 I = Resumes.begin(), E = Resumes.end(); I != E; ++I) {
157 ResumeInst *RI = *I;
158 BasicBlock *Parent = RI->getParent();
159 BranchInst::Create(UnwindBB, Parent);
160
161 Value *ExnObj = GetExceptionObject(RI);
162 PN->addIncoming(ExnObj, Parent);
163
164 ++NumResumesLowered;
165 }
166
167 // Call the function.
168 CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
169 CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
170
171 // We never expect _Unwind_Resume to return.
172 new UnreachableInst(Ctx, UnwindBB);
173 return true;
174 }
175
runOnFunction(Function & Fn)176 bool DwarfEHPrepare::runOnFunction(Function &Fn) {
177 bool Changed = InsertUnwindResumeCalls(Fn);
178 return Changed;
179 }
180