src/llvm/lib/CodeGen/DwarfEHPrepare.cpp

   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/Target/TargetSubtargetInfo.h"
  27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  28 #include "llvm/Transforms/Utils/SSAUpdater.h"
  29 using namespace llvm;
  30
  31 #define DEBUG_TYPE "dwarfehprepare"
  32
  33 STATISTIC(NumResumesLowered, "Number of resume calls lowered");
  34
  35 namespace {
  36   class DwarfEHPrepare : public FunctionPass {
  37     const TargetMachine *TM;
  38
  39     // RewindFunction - _Unwind_Resume or the target equivalent.
  40     Constant *RewindFunction;
  41
  42     bool InsertUnwindResumeCalls(Function &Fn);
  43     Value *GetExceptionObject(ResumeInst *RI);
  44
  45   public:
  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());
  50     }
  51
  52     bool runOnFunction(Function &Fn) override;
  53
  54     bool doFinalization(Module &M) override {
  55       RewindFunction = nullptr;
  56       return false;
  57     }
  58
  59     void getAnalysisUsage(AnalysisUsage &AU) const override { }
  60
  61     const char *getPassName() const override {
  62       return "Exception handling preparation";
  63     }
  64   };
  65 } // end anonymous namespace
  66
  67 char DwarfEHPrepare::ID = 0;
  68
  69 FunctionPass *llvm::createDwarfEHPass(const TargetMachine *TM) {
  70   return new DwarfEHPrepare(TM);
  71 }
  72
  73 /// GetExceptionObject - Return the exception object from the value passed into
  74 /// the 'resume' instruction (typically an aggregate). Clean up any dead
  75 /// instructions, including the 'resume' instruction.
  76 Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
  77   Value *V = RI->getOperand(0);
  78   Value *ExnObj = nullptr;
  79   InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
  80   LoadInst *SelLoad = nullptr;
  81   InsertValueInst *ExcIVI = nullptr;
  82   bool EraseIVIs = false;
  83
  84   if (SelIVI) {
  85     if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
  86       ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0));
  87       if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) &&
  88           ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
  89         ExnObj = ExcIVI->getOperand(1);
  90         SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
  91         EraseIVIs = true;
  92       }
  93     }
  94   }
  95
  96   if (!ExnObj)
  97     ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
  98
  99   RI->eraseFromParent();
 100
 101   if (EraseIVIs) {
 102     if (SelIVI->getNumUses() == 0)
 103       SelIVI->eraseFromParent();
 104     if (ExcIVI->getNumUses() == 0)
 105       ExcIVI->eraseFromParent();
 106     if (SelLoad && SelLoad->getNumUses() == 0)
 107       SelLoad->eraseFromParent();
 108   }
 109
 110   return ExnObj;
 111 }
 112
 113 /// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
 114 /// into calls to the appropriate _Unwind_Resume function.
 115 bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
 116   SmallVector<ResumeInst*, 16> Resumes;
 117   for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
 118     TerminatorInst *TI = I->getTerminator();
 119     if (ResumeInst *RI = dyn_cast<ResumeInst>(TI))
 120       Resumes.push_back(RI);
 121   }
 122
 123   if (Resumes.empty())
 124     return false;
 125
 126   // Find the rewind function if we didn't already.
 127   const TargetLowering *TLI = TM->getSubtargetImpl()->getTargetLowering();
 128   if (!RewindFunction) {
 129     LLVMContext &Ctx = Resumes[0]->getContext();
 130     FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
 131                                           Type::getInt8PtrTy(Ctx), false);
 132     const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
 133     RewindFunction = Fn.getParent()->getOrInsertFunction(RewindName, FTy);
 134   }
 135
 136   // Create the basic block where the _Unwind_Resume call will live.
 137   LLVMContext &Ctx = Fn.getContext();
 138   unsigned ResumesSize = Resumes.size();
 139
 140   if (ResumesSize == 1) {
 141     // Instead of creating a new BB and PHI node, just append the call to
 142     // _Unwind_Resume to the end of the single resume block.
 143     ResumeInst *RI = Resumes.front();
 144     BasicBlock *UnwindBB = RI->getParent();
 145     Value *ExnObj = GetExceptionObject(RI);
 146
 147     // Call the _Unwind_Resume function.
 148     CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
 149     CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
 150
 151     // We never expect _Unwind_Resume to return.
 152     new UnreachableInst(Ctx, UnwindBB);
 153     return true;
 154   }
 155
 156   BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
 157   PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesSize,
 158                                 "exn.obj", UnwindBB);
 159
 160   // Extract the exception object from the ResumeInst and add it to the PHI node
 161   // that feeds the _Unwind_Resume call.
 162   for (SmallVectorImpl<ResumeInst*>::iterator
 163          I = Resumes.begin(), E = Resumes.end(); I != E; ++I) {
 164     ResumeInst *RI = *I;
 165     BasicBlock *Parent = RI->getParent();
 166     BranchInst::Create(UnwindBB, Parent);
 167
 168     Value *ExnObj = GetExceptionObject(RI);
 169     PN->addIncoming(ExnObj, Parent);
 170
 171     ++NumResumesLowered;
 172   }
 173
 174   // Call the function.
 175   CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
 176   CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
 177
 178   // We never expect _Unwind_Resume to return.
 179   new UnreachableInst(Ctx, UnwindBB);
 180   return true;
 181 }
 182
 183 bool DwarfEHPrepare::runOnFunction(Function &Fn) {
 184   bool Changed = InsertUnwindResumeCalls(Fn);
 185   return Changed;
 186 }