1 //===-- DwarfEHPrepare - Prepare exception handling for code generation ---===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass mulches exception handling code into a form adapted to code
11 // generation. Required if using dwarf exception handling.
13 //===----------------------------------------------------------------------===//
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/Target/TargetSubtargetInfo.h"
27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
28 #include "llvm/Transforms/Utils/SSAUpdater.h"
31 #define DEBUG_TYPE "dwarfehprepare"
33 STATISTIC(NumResumesLowered, "Number of resume calls lowered");
36 class DwarfEHPrepare : public FunctionPass {
37 const TargetMachine *TM;
39 // RewindFunction - _Unwind_Resume or the target equivalent.
40 Constant *RewindFunction;
42 bool InsertUnwindResumeCalls(Function &Fn);
43 Value *GetExceptionObject(ResumeInst *RI);
46 static char ID; // Pass identification, replacement for typeid.
47 DwarfEHPrepare(const TargetMachine *TM)
48 : FunctionPass(ID), TM(TM), RewindFunction(nullptr) {
49 initializeDominatorTreeWrapperPassPass(*PassRegistry::getPassRegistry());
52 bool runOnFunction(Function &Fn) override;
54 void getAnalysisUsage(AnalysisUsage &AU) const override { }
56 const char *getPassName() const override {
57 return "Exception handling preparation";
60 } // end anonymous namespace
62 char DwarfEHPrepare::ID = 0;
64 FunctionPass *llvm::createDwarfEHPass(const TargetMachine *TM) {
65 return new DwarfEHPrepare(TM);
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.
71 Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
72 Value *V = RI->getOperand(0);
73 Value *ExnObj = nullptr;
74 InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
75 LoadInst *SelLoad = nullptr;
76 InsertValueInst *ExcIVI = nullptr;
77 bool EraseIVIs = false;
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 = ExcIVI->getOperand(1);
85 SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
92 ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
94 RI->eraseFromParent();
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();
108 /// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
109 /// into calls to the appropriate _Unwind_Resume function.
110 bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
111 SmallVector<ResumeInst*, 16> Resumes;
112 for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
113 TerminatorInst *TI = I->getTerminator();
114 if (ResumeInst *RI = dyn_cast<ResumeInst>(TI))
115 Resumes.push_back(RI);
121 // Find the rewind function if we didn't already.
122 const TargetLowering *TLI = TM->getSubtargetImpl()->getTargetLowering();
123 if (!RewindFunction) {
124 LLVMContext &Ctx = Resumes[0]->getContext();
125 FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
126 Type::getInt8PtrTy(Ctx), false);
127 const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
128 RewindFunction = Fn.getParent()->getOrInsertFunction(RewindName, FTy);
131 // Create the basic block where the _Unwind_Resume call will live.
132 LLVMContext &Ctx = Fn.getContext();
133 unsigned ResumesSize = Resumes.size();
135 if (ResumesSize == 1) {
136 // Instead of creating a new BB and PHI node, just append the call to
137 // _Unwind_Resume to the end of the single resume block.
138 ResumeInst *RI = Resumes.front();
139 BasicBlock *UnwindBB = RI->getParent();
140 Value *ExnObj = GetExceptionObject(RI);
142 // Call the _Unwind_Resume function.
143 CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
144 CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
146 // We never expect _Unwind_Resume to return.
147 new UnreachableInst(Ctx, UnwindBB);
151 BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
152 PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesSize,
153 "exn.obj", UnwindBB);
155 // Extract the exception object from the ResumeInst and add it to the PHI node
156 // that feeds the _Unwind_Resume call.
157 for (SmallVectorImpl<ResumeInst*>::iterator
158 I = Resumes.begin(), E = Resumes.end(); I != E; ++I) {
160 BasicBlock *Parent = RI->getParent();
161 BranchInst::Create(UnwindBB, Parent);
163 Value *ExnObj = GetExceptionObject(RI);
164 PN->addIncoming(ExnObj, Parent);
169 // Call the function.
170 CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
171 CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
173 // We never expect _Unwind_Resume to return.
174 new UnreachableInst(Ctx, UnwindBB);
178 bool DwarfEHPrepare::runOnFunction(Function &Fn) {
179 bool Changed = InsertUnwindResumeCalls(Fn);