C++ mop_iterator::readsReg方法代码示例

/// Find all live intervals that need to shrink, then remove the instruction.
void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
  assert(MI->allDefsAreDead() && "Def isn't really dead");
  SlotIndex Idx = LIS.getInstructionIndex(MI).getRegSlot();

  // Never delete a bundled instruction.
  if (MI->isBundled()) {
    return;
  }
  // Never delete inline asm.
  if (MI->isInlineAsm()) {
    DEBUG(dbgs() << "Won't delete: " << Idx << '\t' << *MI);
    return;
  }

  // Use the same criteria as DeadMachineInstructionElim.
  bool SawStore = false;
  if (!MI->isSafeToMove(&TII, 0, SawStore)) {
    DEBUG(dbgs() << "Can't delete: " << Idx << '\t' << *MI);
    return;
  }

  DEBUG(dbgs() << "Deleting dead def " << Idx << '\t' << *MI);

  // Collect virtual registers to be erased after MI is gone.
  SmallVector<unsigned, 8> RegsToErase;
  bool ReadsPhysRegs = false;

  // Check for live intervals that may shrink
  for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
         MOE = MI->operands_end(); MOI != MOE; ++MOI) {
    if (!MOI->isReg())
      continue;
    unsigned Reg = MOI->getReg();
    if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
      // Check if MI reads any unreserved physregs.
      if (Reg && MOI->readsReg() && !MRI.isReserved(Reg))
        ReadsPhysRegs = true;
      else if (MOI->isDef()) {
        for (MCRegUnitIterator Units(Reg, MRI.getTargetRegisterInfo());
             Units.isValid(); ++Units) {
          if (LiveRange *LR = LIS.getCachedRegUnit(*Units)) {
            if (VNInfo *VNI = LR->getVNInfoAt(Idx))
              LR->removeValNo(VNI);
          }
        }
      }
      continue;
    }
    LiveInterval &LI = LIS.getInterval(Reg);

    // Shrink read registers, unless it is likely to be expensive and
    // unlikely to change anything. We typically don't want to shrink the
    // PIC base register that has lots of uses everywhere.
    // Always shrink COPY uses that probably come from live range splitting.
    if (MI->readsVirtualRegister(Reg) &&
        (MI->isCopy() || MOI->isDef() || MRI.hasOneNonDBGUse(Reg) ||
         LI.Query(Idx).isKill()))
      ToShrink.insert(&LI);

    // Remove defined value.
    if (MOI->isDef()) {
      if (VNInfo *VNI = LI.getVNInfoAt(Idx)) {
        if (TheDelegate)
          TheDelegate->LRE_WillShrinkVirtReg(LI.reg);
        LI.removeValNo(VNI);
        if (LI.empty())
          RegsToErase.push_back(Reg);
      }
    }
  }

  // Currently, we don't support DCE of physreg live ranges. If MI reads
  // any unreserved physregs, don't erase the instruction, but turn it into
  // a KILL instead. This way, the physreg live ranges don't end up
  // dangling.
  // FIXME: It would be better to have something like shrinkToUses() for
  // physregs. That could potentially enable more DCE and it would free up
  // the physreg. It would not happen often, though.
  if (ReadsPhysRegs) {
    MI->setDesc(TII.get(TargetOpcode::KILL));
    // Remove all operands that aren't physregs.
    for (unsigned i = MI->getNumOperands(); i; --i) {
      const MachineOperand &MO = MI->getOperand(i-1);
      if (MO.isReg() && TargetRegisterInfo::isPhysicalRegister(MO.getReg()))
        continue;
      MI->RemoveOperand(i-1);
    }
    DEBUG(dbgs() << "Converted physregs to:\t" << *MI);
  } else {
    if (TheDelegate)
      TheDelegate->LRE_WillEraseInstruction(MI);
    LIS.RemoveMachineInstrFromMaps(MI);
    MI->eraseFromParent();
    ++NumDCEDeleted;
  }

  // Erase any virtregs that are now empty and unused. There may be <undef>
  // uses around. Keep the empty live range in that case.
  for (unsigned i = 0, e = RegsToErase.size(); i != e; ++i) {
//.........这里部分代码省略.........