bool ExpandPostRA::LowerSubregToReg(MachineInstr *MI) {
  MachineBasicBlock *MBB = MI->getParent();
  assert((MI->getOperand(0).isReg() && MI->getOperand(0).isDef()) &&
         MI->getOperand(1).isImm() &&
         (MI->getOperand(2).isReg() && MI->getOperand(2).isUse()) &&
          MI->getOperand(3).isImm() && "Invalid subreg_to_reg");

  unsigned DstReg  = MI->getOperand(0).getReg();
  unsigned InsReg  = MI->getOperand(2).getReg();
  assert(!MI->getOperand(2).getSubReg() && "SubIdx on physreg?");
  unsigned SubIdx  = MI->getOperand(3).getImm();

  assert(SubIdx != 0 && "Invalid index for insert_subreg");
  unsigned DstSubReg = TRI->getSubReg(DstReg, SubIdx);

  assert(TargetRegisterInfo::isPhysicalRegister(DstReg) &&
         "Insert destination must be in a physical register");
  assert(TargetRegisterInfo::isPhysicalRegister(InsReg) &&
         "Inserted value must be in a physical register");

  LLVM_DEBUG(dbgs() << "subreg: CONVERTING: " << *MI);

  if (MI->allDefsAreDead()) {
    MI->setDesc(TII->get(TargetOpcode::KILL));
    MI->RemoveOperand(3); // SubIdx
    MI->RemoveOperand(1); // Imm
    LLVM_DEBUG(dbgs() << "subreg: replaced by: " << *MI);
    return true;
  }

  if (DstSubReg == InsReg) {
    // No need to insert an identity copy instruction.
    // Watch out for case like this:
    // %rax = SUBREG_TO_REG 0, killed %eax, 3
    // We must leave %rax live.
    if (DstReg != InsReg) {
      MI->setDesc(TII->get(TargetOpcode::KILL));
      MI->RemoveOperand(3);     // SubIdx
      MI->RemoveOperand(1);     // Imm
      LLVM_DEBUG(dbgs() << "subreg: replace by: " << *MI);
      return true;
    }
    LLVM_DEBUG(dbgs() << "subreg: eliminated!");
  } else {
    TII->copyPhysReg(*MBB, MI, MI->getDebugLoc(), DstSubReg, InsReg,
                     MI->getOperand(2).isKill());

    // Implicitly define DstReg for subsequent uses.
    MachineBasicBlock::iterator CopyMI = MI;
    --CopyMI;
    CopyMI->addRegisterDefined(DstReg);
    LLVM_DEBUG(dbgs() << "subreg: " << *CopyMI);
  }

  LLVM_DEBUG(dbgs() << '\n');
  MBB->erase(MI);
  return true;
}
Exemple #2
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void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
                                             MachineBasicBlock::iterator mi,
                                             SlotIndex MIIdx,
                                             MachineOperand& MO,
                                             unsigned MOIdx,
                                             LiveInterval &interval) {
  DEBUG(dbgs() << "\t\tregister: " << PrintReg(interval.reg, tri_));

  // Virtual registers may be defined multiple times (due to phi
  // elimination and 2-addr elimination).  Much of what we do only has to be
  // done once for the vreg.  We use an empty interval to detect the first
  // time we see a vreg.
  LiveVariables::VarInfo& vi = lv_->getVarInfo(interval.reg);
  if (interval.empty()) {
    // Get the Idx of the defining instructions.
    SlotIndex defIndex = MIIdx.getRegSlot(MO.isEarlyClobber());

    // Make sure the first definition is not a partial redefinition. Add an
    // <imp-def> of the full register.
    // FIXME: LiveIntervals shouldn't modify the code like this.  Whoever
    // created the machine instruction should annotate it with <undef> flags
    // as needed.  Then we can simply assert here.  The REG_SEQUENCE lowering
    // is the main suspect.
    if (MO.getSubReg()) {
      mi->addRegisterDefined(interval.reg);
      // Mark all defs of interval.reg on this instruction as reading <undef>.
      for (unsigned i = MOIdx, e = mi->getNumOperands(); i != e; ++i) {
        MachineOperand &MO2 = mi->getOperand(i);
        if (MO2.isReg() && MO2.getReg() == interval.reg && MO2.getSubReg())
          MO2.setIsUndef();
      }
    }

    MachineInstr *CopyMI = NULL;
    if (mi->isCopyLike()) {
      CopyMI = mi;
    }

    VNInfo *ValNo = interval.getNextValue(defIndex, CopyMI, VNInfoAllocator);
    assert(ValNo->id == 0 && "First value in interval is not 0?");

    // Loop over all of the blocks that the vreg is defined in.  There are
    // two cases we have to handle here.  The most common case is a vreg
    // whose lifetime is contained within a basic block.  In this case there
    // will be a single kill, in MBB, which comes after the definition.
    if (vi.Kills.size() == 1 && vi.Kills[0]->getParent() == mbb) {
      // FIXME: what about dead vars?
      SlotIndex killIdx;
      if (vi.Kills[0] != mi)
        killIdx = getInstructionIndex(vi.Kills[0]).getRegSlot();
      else
        killIdx = defIndex.getDeadSlot();

      // If the kill happens after the definition, we have an intra-block
      // live range.
      if (killIdx > defIndex) {
        assert(vi.AliveBlocks.empty() &&
               "Shouldn't be alive across any blocks!");
        LiveRange LR(defIndex, killIdx, ValNo);
        interval.addRange(LR);
        DEBUG(dbgs() << " +" << LR << "\n");
        return;
      }
    }

    // The other case we handle is when a virtual register lives to the end
    // of the defining block, potentially live across some blocks, then is
    // live into some number of blocks, but gets killed.  Start by adding a
    // range that goes from this definition to the end of the defining block.
    LiveRange NewLR(defIndex, getMBBEndIdx(mbb), ValNo);
    DEBUG(dbgs() << " +" << NewLR);
    interval.addRange(NewLR);

    bool PHIJoin = lv_->isPHIJoin(interval.reg);

    if (PHIJoin) {
      // A phi join register is killed at the end of the MBB and revived as a new
      // valno in the killing blocks.
      assert(vi.AliveBlocks.empty() && "Phi join can't pass through blocks");
      DEBUG(dbgs() << " phi-join");
      ValNo->setHasPHIKill(true);
    } else {
      // Iterate over all of the blocks that the variable is completely
      // live in, adding [insrtIndex(begin), instrIndex(end)+4) to the
      // live interval.
      for (SparseBitVector<>::iterator I = vi.AliveBlocks.begin(),
               E = vi.AliveBlocks.end(); I != E; ++I) {
        MachineBasicBlock *aliveBlock = mf_->getBlockNumbered(*I);
        LiveRange LR(getMBBStartIdx(aliveBlock), getMBBEndIdx(aliveBlock), ValNo);
        interval.addRange(LR);
        DEBUG(dbgs() << " +" << LR);
      }
    }

    // Finally, this virtual register is live from the start of any killing
    // block to the 'use' slot of the killing instruction.
    for (unsigned i = 0, e = vi.Kills.size(); i != e; ++i) {
      MachineInstr *Kill = vi.Kills[i];
      SlotIndex Start = getMBBStartIdx(Kill->getParent());
      SlotIndex killIdx = getInstructionIndex(Kill).getRegSlot();

      // Create interval with one of a NEW value number.  Note that this value
      // number isn't actually defined by an instruction, weird huh? :)
      if (PHIJoin) {
        assert(getInstructionFromIndex(Start) == 0 &&
               "PHI def index points at actual instruction.");
        ValNo = interval.getNextValue(Start, 0, VNInfoAllocator);
        ValNo->setIsPHIDef(true);
      }
      LiveRange LR(Start, killIdx, ValNo);
      interval.addRange(LR);
      DEBUG(dbgs() << " +" << LR);
    }

  } else {
    if (MultipleDefsBySameMI(*mi, MOIdx))
      // Multiple defs of the same virtual register by the same instruction.
      // e.g. %reg1031:5<def>, %reg1031:6<def> = VLD1q16 %reg1024<kill>, ...
      // This is likely due to elimination of REG_SEQUENCE instructions. Return
      // here since there is nothing to do.
      return;

    // If this is the second time we see a virtual register definition, it
    // must be due to phi elimination or two addr elimination.  If this is
    // the result of two address elimination, then the vreg is one of the
    // def-and-use register operand.

    // It may also be partial redef like this:
    // 80  %reg1041:6<def> = VSHRNv4i16 %reg1034<kill>, 12, pred:14, pred:%reg0
    // 120 %reg1041:5<def> = VSHRNv4i16 %reg1039<kill>, 12, pred:14, pred:%reg0
    bool PartReDef = isPartialRedef(MIIdx, MO, interval);
    if (PartReDef || mi->isRegTiedToUseOperand(MOIdx)) {
      // If this is a two-address definition, then we have already processed
      // the live range.  The only problem is that we didn't realize there
      // are actually two values in the live interval.  Because of this we
      // need to take the LiveRegion that defines this register and split it
      // into two values.
      SlotIndex RedefIndex = MIIdx.getRegSlot(MO.isEarlyClobber());

      const LiveRange *OldLR =
        interval.getLiveRangeContaining(RedefIndex.getRegSlot(true));
      VNInfo *OldValNo = OldLR->valno;
      SlotIndex DefIndex = OldValNo->def.getRegSlot();

      // Delete the previous value, which should be short and continuous,
      // because the 2-addr copy must be in the same MBB as the redef.
      interval.removeRange(DefIndex, RedefIndex);

      // The new value number (#1) is defined by the instruction we claimed
      // defined value #0.
      VNInfo *ValNo = interval.createValueCopy(OldValNo, VNInfoAllocator);

      // Value#0 is now defined by the 2-addr instruction.
      OldValNo->def  = RedefIndex;
      OldValNo->setCopy(0);

      // A re-def may be a copy. e.g. %reg1030:6<def> = VMOVD %reg1026, ...
      if (PartReDef && mi->isCopyLike())
        OldValNo->setCopy(&*mi);

      // Add the new live interval which replaces the range for the input copy.
      LiveRange LR(DefIndex, RedefIndex, ValNo);
      DEBUG(dbgs() << " replace range with " << LR);
      interval.addRange(LR);

      // If this redefinition is dead, we need to add a dummy unit live
      // range covering the def slot.
      if (MO.isDead())
        interval.addRange(LiveRange(RedefIndex, RedefIndex.getDeadSlot(),
                                    OldValNo));

      DEBUG({
          dbgs() << " RESULT: ";
          interval.print(dbgs(), tri_);
        });
    } else if (lv_->isPHIJoin(interval.reg)) {