C++ AllocaInst::isUsedByMetadata方法代码示例

void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
  unsigned FixedInstr = 0;
  unsigned FixedMemOp = 0;
  unsigned FixedDbg = 0;
  MachineModuleInfo *MMI = &MF->getMMI();

  // Remap debug information that refers to stack slots.
  for (auto &VI : MMI->getVariableDbgInfo()) {
    if (!VI.Var)
      continue;
    if (SlotRemap.count(VI.Slot)) {
      DEBUG(dbgs() << "Remapping debug info for ["
                   << cast<DILocalVariable>(VI.Var)->getName() << "].\n");
      VI.Slot = SlotRemap[VI.Slot];
      FixedDbg++;
    }
  }

  // Keep a list of *allocas* which need to be remapped.
  DenseMap<const AllocaInst*, const AllocaInst*> Allocas;
  for (const std::pair<int, int> &SI : SlotRemap) {
    const AllocaInst *From = MFI->getObjectAllocation(SI.first);
    const AllocaInst *To = MFI->getObjectAllocation(SI.second);
    assert(To && From && "Invalid allocation object");
    Allocas[From] = To;

    // AA might be used later for instruction scheduling, and we need it to be
    // able to deduce the correct aliasing releationships between pointers
    // derived from the alloca being remapped and the target of that remapping.
    // The only safe way, without directly informing AA about the remapping
    // somehow, is to directly update the IR to reflect the change being made
    // here.
    Instruction *Inst = const_cast<AllocaInst *>(To);
    if (From->getType() != To->getType()) {
      BitCastInst *Cast = new BitCastInst(Inst, From->getType());
      Cast->insertAfter(Inst);
      Inst = Cast;
    }

    // Allow the stack protector to adjust its value map to account for the
    // upcoming replacement.
    SP->adjustForColoring(From, To);

    // The new alloca might not be valid in a llvm.dbg.declare for this
    // variable, so undef out the use to make the verifier happy.
    AllocaInst *FromAI = const_cast<AllocaInst *>(From);
    if (FromAI->isUsedByMetadata())
      ValueAsMetadata::handleRAUW(FromAI, UndefValue::get(FromAI->getType()));
    for (auto &Use : FromAI->uses()) {
      if (BitCastInst *BCI = dyn_cast<BitCastInst>(Use.get()))
        if (BCI->isUsedByMetadata())
          ValueAsMetadata::handleRAUW(BCI, UndefValue::get(BCI->getType()));
    }

    // Note that this will not replace uses in MMOs (which we'll update below),
    // or anywhere else (which is why we won't delete the original
    // instruction).
    FromAI->replaceAllUsesWith(Inst);
  }

  // Remap all instructions to the new stack slots.
  for (MachineBasicBlock &BB : *MF)
    for (MachineInstr &I : BB) {
      // Skip lifetime markers. We'll remove them soon.
      if (I.getOpcode() == TargetOpcode::LIFETIME_START ||
          I.getOpcode() == TargetOpcode::LIFETIME_END)
        continue;

      // Update the MachineMemOperand to use the new alloca.
      for (MachineMemOperand *MMO : I.memoperands()) {
        // FIXME: In order to enable the use of TBAA when using AA in CodeGen,
        // we'll also need to update the TBAA nodes in MMOs with values
        // derived from the merged allocas. When doing this, we'll need to use
        // the same variant of GetUnderlyingObjects that is used by the
        // instruction scheduler (that can look through ptrtoint/inttoptr
        // pairs).

        // We've replaced IR-level uses of the remapped allocas, so we only
        // need to replace direct uses here.
        const AllocaInst *AI = dyn_cast_or_null<AllocaInst>(MMO->getValue());
        if (!AI)
          continue;

        if (!Allocas.count(AI))
          continue;

        MMO->setValue(Allocas[AI]);
        FixedMemOp++;
      }

      // Update all of the machine instruction operands.
      for (MachineOperand &MO : I.operands()) {
        if (!MO.isFI())
          continue;
        int FromSlot = MO.getIndex();

        // Don't touch arguments.
        if (FromSlot<0)
          continue;

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