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"
28 using namespace llvm;
29
30 #define DEBUG_TYPE "dwarfehprepare"
31
32 STATISTIC(NumResumesLowered, "Number of resume calls lowered");
33
34 namespace {
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.
DwarfEHPrepare(const TargetMachine * TM)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
getAnalysisUsage(AnalysisUsage & AU) const53 void getAnalysisUsage(AnalysisUsage &AU) const override { }
54
getPassName() const55 const char *getPassName() const override {
56 return "Exception handling preparation";
57 }
58 };
59 } // end anonymous namespace
60
61 char DwarfEHPrepare::ID = 0;
62
createDwarfEHPass(const TargetMachine * TM)63 FunctionPass *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.
GetExceptionObject(ResumeInst * RI)70 Value *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.
InsertUnwindResumeCalls(Function & Fn)109 bool 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
runOnFunction(Function & Fn)177 bool DwarfEHPrepare::runOnFunction(Function &Fn) {
178 bool Changed = InsertUnwindResumeCalls(Fn);
179 return Changed;
180 }
181