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 
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 
61 char DwarfEHPrepare::ID = 0;
62 
63 FunctionPass *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.
69 bool 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     ExtractValueInst *ExnObj = ExtractValueInst::Create(RI->getOperand(0),
105                                                         0, "exn.obj", RI);
106     PN->addIncoming(ExnObj, RI->getParent());
107     RI->eraseFromParent();
108     ++NumResumesLowered;
109   }
110 
111   // Call the function.
112   CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
113   CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
114 
115   // We never expect _Unwind_Resume to return.
116   new UnreachableInst(Ctx, UnwindBB);
117   return true;
118 }
119 
120 bool DwarfEHPrepare::runOnFunction(Function &Fn) {
121   bool Changed = InsertUnwindResumeCalls(Fn);
122   return Changed;
123 }
124