C++ ExtractValueInst::replaceAllUsesWith方法代码示例

/// substituteLPadValues - Substitute the values returned by the landingpad
/// instruction with those returned by the personality function.
void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
                                         Value *SelVal) {
  SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
  while (!UseWorkList.empty()) {
    Value *Val = UseWorkList.pop_back_val();
    ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Val);
    if (!EVI)
      continue;
    if (EVI->getNumIndices() != 1)
      continue;
    if (*EVI->idx_begin() == 0)
      EVI->replaceAllUsesWith(ExnVal);
    else if (*EVI->idx_begin() == 1)
      EVI->replaceAllUsesWith(SelVal);
    if (EVI->getNumUses() == 0)
      EVI->eraseFromParent();
  }

  if (LPI->getNumUses() == 0)
    return;

  // There are still some uses of LPI. Construct an aggregate with the exception
  // values and replace the LPI with that aggregate.
  Type *LPadType = LPI->getType();
  Value *LPadVal = UndefValue::get(LPadType);
  auto *SelI = cast<Instruction>(SelVal);
  IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
  LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
  LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");

  LPI->replaceAllUsesWith(LPadVal);
}

//.........这里部分代码省略.........
  auto FailureBB = BasicBlock::Create(Ctx, "cmpxchg.failure", F, ExitBB);
  auto NoStoreBB = BasicBlock::Create(Ctx, "cmpxchg.nostore", F, FailureBB);
  auto SuccessBB = BasicBlock::Create(Ctx, "cmpxchg.success", F, NoStoreBB);
  auto TryStoreBB = BasicBlock::Create(Ctx, "cmpxchg.trystore", F, SuccessBB);
  auto LoopBB = BasicBlock::Create(Ctx, "cmpxchg.start", F, TryStoreBB);

  // This grabs the DebugLoc from CI
  IRBuilder<> Builder(CI);

  // The split call above "helpfully" added a branch at the end of BB (to the
  // wrong place), but we might want a fence too. It's easiest to just remove
  // the branch entirely.
  std::prev(BB->end())->eraseFromParent();
  Builder.SetInsertPoint(BB);
  TLI->emitLeadingFence(Builder, SuccessOrder, /*IsStore=*/true,
                        /*IsLoad=*/true);
  Builder.CreateBr(LoopBB);

  // Start the main loop block now that we've taken care of the preliminaries.
  Builder.SetInsertPoint(LoopBB);
  Value *Loaded = TLI->emitLoadLinked(Builder, Addr, MemOpOrder);
  Value *ShouldStore =
      Builder.CreateICmpEQ(Loaded, CI->getCompareOperand(), "should_store");

  // If the cmpxchg doesn't actually need any ordering when it fails, we can
  // jump straight past that fence instruction (if it exists).
  Builder.CreateCondBr(ShouldStore, TryStoreBB, NoStoreBB);

  Builder.SetInsertPoint(TryStoreBB);
  Value *StoreSuccess = TLI->emitStoreConditional(
      Builder, CI->getNewValOperand(), Addr, MemOpOrder);
  StoreSuccess = Builder.CreateICmpEQ(
      StoreSuccess, ConstantInt::get(Type::getInt32Ty(Ctx), 0), "success");
  Builder.CreateCondBr(StoreSuccess, SuccessBB,
                       CI->isWeak() ? FailureBB : LoopBB);

  // Make sure later instructions don't get reordered with a fence if necessary.
  Builder.SetInsertPoint(SuccessBB);
  TLI->emitTrailingFence(Builder, SuccessOrder, /*IsStore=*/true,
                         /*IsLoad=*/true);
  Builder.CreateBr(ExitBB);

  Builder.SetInsertPoint(NoStoreBB);
  // In the failing case, where we don't execute the store-conditional, the
  // target might want to balance out the load-linked with a dedicated
  // instruction (e.g., on ARM, clearing the exclusive monitor).
  TLI->emitAtomicCmpXchgNoStoreLLBalance(Builder);
  Builder.CreateBr(FailureBB);

  Builder.SetInsertPoint(FailureBB);
  TLI->emitTrailingFence(Builder, FailureOrder, /*IsStore=*/true,
                         /*IsLoad=*/true);
  Builder.CreateBr(ExitBB);

  // Finally, we have control-flow based knowledge of whether the cmpxchg
  // succeeded or not. We expose this to later passes by converting any
  // subsequent "icmp eq/ne %loaded, %oldval" into a use of an appropriate PHI.

  // Setup the builder so we can create any PHIs we need.
  Builder.SetInsertPoint(ExitBB, ExitBB->begin());
  PHINode *Success = Builder.CreatePHI(Type::getInt1Ty(Ctx), 2);
  Success->addIncoming(ConstantInt::getTrue(Ctx), SuccessBB);
  Success->addIncoming(ConstantInt::getFalse(Ctx), FailureBB);

  // Look for any users of the cmpxchg that are just comparing the loaded value
  // against the desired one, and replace them with the CFG-derived version.
  SmallVector<ExtractValueInst *, 2> PrunedInsts;
  for (auto User : CI->users()) {
    ExtractValueInst *EV = dyn_cast<ExtractValueInst>(User);
    if (!EV)
      continue;

    assert(EV->getNumIndices() == 1 && EV->getIndices()[0] <= 1 &&
           "weird extraction from { iN, i1 }");

    if (EV->getIndices()[0] == 0)
      EV->replaceAllUsesWith(Loaded);
    else
      EV->replaceAllUsesWith(Success);

    PrunedInsts.push_back(EV);
  }

  // We can remove the instructions now we're no longer iterating through them.
  for (auto EV : PrunedInsts)
    EV->eraseFromParent();

  if (!CI->use_empty()) {
    // Some use of the full struct return that we don't understand has happened,
    // so we've got to reconstruct it properly.
    Value *Res;
    Res = Builder.CreateInsertValue(UndefValue::get(CI->getType()), Loaded, 0);
    Res = Builder.CreateInsertValue(Res, Success, 1);

    CI->replaceAllUsesWith(Res);
  }

  CI->eraseFromParent();
  return true;
}

//
// Method: runOnModule()
//
// Description:
//  Entry point for this LLVM pass. Search for insert/extractvalue instructions
//  that can be simplified.
//
// Inputs:
//  M - A reference to the LLVM module to transform.
//
// Outputs:
//  M - The transformed LLVM module.
//
// Return value:
// true  - The module was modified.
// false - The module was not modified.
//
bool SimplifyEV::runOnModule(Module& M) {
  // Repeat till no change
  bool changed;
  do {
    changed = false;
    for (Module::iterator F = M.begin(); F != M.end(); ++F) {
      for (Function::iterator B = F->begin(), FE = F->end(); B != FE; ++B) {      
        for (BasicBlock::iterator I = B->begin(), BE = B->end(); I != BE;) {
          ExtractValueInst *EV = dyn_cast<ExtractValueInst>(I++);
          if(!EV)
            continue;
          Value *Agg = EV->getAggregateOperand();
          if (!EV->hasIndices()) {
            EV->replaceAllUsesWith(Agg);
            DEBUG(errs() << "EV:");
            DEBUG(errs() << "ERASE:");
            DEBUG(EV->dump());
            EV->eraseFromParent();
            numErased++;
            changed = true;
            continue;
          }
          if (Constant *C = dyn_cast<Constant>(Agg)) {
            if (isa<UndefValue>(C)) {
              EV->replaceAllUsesWith(UndefValue::get(EV->getType()));
              DEBUG(errs() << "EV:");
              DEBUG(errs() << "ERASE:");
              DEBUG(EV->dump());
              EV->eraseFromParent();
              numErased++;
              changed = true;
              continue;
            }
            if (isa<ConstantAggregateZero>(C)) {
              EV->replaceAllUsesWith(Constant::getNullValue(EV->getType()));
              DEBUG(errs() << "EV:");
              DEBUG(errs() << "ERASE:");
              DEBUG(EV->dump());
              EV->eraseFromParent();
              numErased++;
              changed = true;
              continue;
            }
            if (isa<ConstantArray>(C) || isa<ConstantStruct>(C)) {
              // Extract the element indexed by the first index out of the constant
              Value *V = C->getOperand(*EV->idx_begin());
              if (EV->getNumIndices() > 1) {
                // Extract the remaining indices out of the constant indexed by the
                // first index
                ExtractValueInst *EV_new = ExtractValueInst::Create(V, 
                                                                    EV->getIndices().slice(1), 
                                                                    "", EV);
                EV->replaceAllUsesWith(EV_new);
                DEBUG(errs() << "EV:");
                DEBUG(errs() << "ERASE:");
                DEBUG(EV->dump());
                EV->eraseFromParent();
                numErased++;
                changed = true;
                continue;
              }  else {
                EV->replaceAllUsesWith(V);
                DEBUG(errs() << "EV:");
                DEBUG(errs() << "ERASE:");
                DEBUG(EV->dump());
                EV->eraseFromParent();
                numErased++;
                changed = true;
                continue;
              }
            }
            continue;
          }
          if (LoadInst * LI = dyn_cast<LoadInst>(Agg)) {
            // if the Agg value came from a load instruction
            // replace the extract value intruction with
            // a gep and a load.
            SmallVector<Value*, 8> Indices;
            Type *Int32Ty = Type::getInt32Ty(M.getContext());
            Indices.push_back(Constant::getNullValue(Int32Ty));
            for (ExtractValueInst::idx_iterator I = EV->idx_begin(), E = EV->idx_end();
                 I != E; ++I) {
              Indices.push_back(ConstantInt::get(Int32Ty, *I));
//.........这里部分代码省略.........