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"
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 const TargetLowering *TLI;
37
38 // RewindFunction - _Unwind_Resume or the target equivalent.
39 Constant *RewindFunction;
40
41 bool InsertUnwindResumeCalls(Function &Fn);
42 Instruction *GetExceptionObject(ResumeInst *RI);
43
44 public:
45 static char ID; // Pass identification, replacement for typeid.
DwarfEHPrepare(const TargetMachine * tm)46 DwarfEHPrepare(const TargetMachine *tm) :
47 FunctionPass(ID), TM(tm), TLI(TM->getTargetLowering()),
48 RewindFunction(0) {
49 initializeDominatorTreePass(*PassRegistry::getPassRegistry());
50 }
51
52 virtual bool runOnFunction(Function &Fn);
53
getAnalysisUsage(AnalysisUsage & AU) const54 virtual void getAnalysisUsage(AnalysisUsage &AU) const { }
55
getPassName() const56 const char *getPassName() const {
57 return "Exception handling preparation";
58 }
59 };
60 } // end anonymous namespace
61
62 char DwarfEHPrepare::ID = 0;
63
createDwarfEHPass(const TargetMachine * tm)64 FunctionPass *llvm::createDwarfEHPass(const TargetMachine *tm) {
65 return new DwarfEHPrepare(tm);
66 }
67
68 /// GetExceptionObject - Return the exception object from the value passed into
69 /// the 'resume' instruction (typically an aggregate). Clean up any dead
70 /// instructions, including the 'resume' instruction.
GetExceptionObject(ResumeInst * RI)71 Instruction *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
72 Value *V = RI->getOperand(0);
73 Instruction *ExnObj = 0;
74 InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
75 LoadInst *SelLoad = 0;
76 InsertValueInst *ExcIVI = 0;
77 bool EraseIVIs = false;
78
79 if (SelIVI) {
80 if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
81 ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0));
82 if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) &&
83 ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
84 ExnObj = cast<Instruction>(ExcIVI->getOperand(1));
85 SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
86 EraseIVIs = true;
87 }
88 }
89 }
90
91 if (!ExnObj)
92 ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
93
94 RI->eraseFromParent();
95
96 if (EraseIVIs) {
97 if (SelIVI->getNumUses() == 0)
98 SelIVI->eraseFromParent();
99 if (ExcIVI->getNumUses() == 0)
100 ExcIVI->eraseFromParent();
101 if (SelLoad && SelLoad->getNumUses() == 0)
102 SelLoad->eraseFromParent();
103 }
104
105 return ExnObj;
106 }
107
108 /// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
109 /// into calls to the appropriate _Unwind_Resume function.
InsertUnwindResumeCalls(Function & Fn)110 bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
111 bool UsesNewEH = false;
112 SmallVector<ResumeInst*, 16> Resumes;
113 for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
114 TerminatorInst *TI = I->getTerminator();
115 if (ResumeInst *RI = dyn_cast<ResumeInst>(TI))
116 Resumes.push_back(RI);
117 else if (InvokeInst *II = dyn_cast<InvokeInst>(TI))
118 UsesNewEH = II->getUnwindDest()->isLandingPad();
119 }
120
121 if (Resumes.empty())
122 return UsesNewEH;
123
124 // Find the rewind function if we didn't already.
125 if (!RewindFunction) {
126 LLVMContext &Ctx = Resumes[0]->getContext();
127 FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
128 Type::getInt8PtrTy(Ctx), false);
129 const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
130 RewindFunction = Fn.getParent()->getOrInsertFunction(RewindName, FTy);
131 }
132
133 // Create the basic block where the _Unwind_Resume call will live.
134 LLVMContext &Ctx = Fn.getContext();
135 unsigned ResumesSize = Resumes.size();
136
137 if (ResumesSize == 1) {
138 // Instead of creating a new BB and PHI node, just append the call to
139 // _Unwind_Resume to the end of the single resume block.
140 ResumeInst *RI = Resumes.front();
141 BasicBlock *UnwindBB = RI->getParent();
142 Instruction *ExnObj = GetExceptionObject(RI);
143
144 // Call the _Unwind_Resume function.
145 CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
146 CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
147
148 // We never expect _Unwind_Resume to return.
149 new UnreachableInst(Ctx, UnwindBB);
150 return true;
151 }
152
153 BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
154 PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesSize,
155 "exn.obj", UnwindBB);
156
157 // Extract the exception object from the ResumeInst and add it to the PHI node
158 // that feeds the _Unwind_Resume call.
159 for (SmallVectorImpl<ResumeInst*>::iterator
160 I = Resumes.begin(), E = Resumes.end(); I != E; ++I) {
161 ResumeInst *RI = *I;
162 BasicBlock *Parent = RI->getParent();
163 BranchInst::Create(UnwindBB, Parent);
164
165 Instruction *ExnObj = GetExceptionObject(RI);
166 PN->addIncoming(ExnObj, Parent);
167
168 ++NumResumesLowered;
169 }
170
171 // Call the function.
172 CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
173 CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
174
175 // We never expect _Unwind_Resume to return.
176 new UnreachableInst(Ctx, UnwindBB);
177 return true;
178 }
179
runOnFunction(Function & Fn)180 bool DwarfEHPrepare::runOnFunction(Function &Fn) {
181 bool Changed = InsertUnwindResumeCalls(Fn);
182 return Changed;
183 }
184