C++ (Cpp) TargetInstrInfo::isMoveInstr示例

/// EmitLiveInCopy - Emit a copy for a live in physical register. If the
/// physical register has only a single copy use, then coalesced the copy
/// if possible.
static void EmitLiveInCopy(MachineBasicBlock *MBB,
                           MachineBasicBlock::iterator &InsertPos,
                           unsigned VirtReg, unsigned PhysReg,
                           const TargetRegisterClass *RC,
                           DenseMap<MachineInstr*, unsigned> &CopyRegMap,
                           const MachineRegisterInfo &MRI,
                           const TargetRegisterInfo &TRI,
                           const TargetInstrInfo &TII) {
  unsigned NumUses = 0;
  MachineInstr *UseMI = NULL;
  for (MachineRegisterInfo::use_iterator UI = MRI.use_begin(VirtReg),
         UE = MRI.use_end(); UI != UE; ++UI) {
    UseMI = &*UI;
    if (++NumUses > 1)
      break;
  }

  // If the number of uses is not one, or the use is not a move instruction,
  // don't coalesce. Also, only coalesce away a virtual register to virtual
  // register copy.
  bool Coalesced = false;
  unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
  if (NumUses == 1 &&
      TII.isMoveInstr(*UseMI, SrcReg, DstReg, SrcSubReg, DstSubReg) &&
      TargetRegisterInfo::isVirtualRegister(DstReg)) {
    VirtReg = DstReg;
    Coalesced = true;
  }

  // Now find an ideal location to insert the copy.
  MachineBasicBlock::iterator Pos = InsertPos;
  while (Pos != MBB->begin()) {
    MachineInstr *PrevMI = prior(Pos);
    DenseMap<MachineInstr*, unsigned>::iterator RI = CopyRegMap.find(PrevMI);
    // copyRegToReg might emit multiple instructions to do a copy.
    unsigned CopyDstReg = (RI == CopyRegMap.end()) ? 0 : RI->second;
    if (CopyDstReg && !TRI.regsOverlap(CopyDstReg, PhysReg))
      // This is what the BB looks like right now:
      // r1024 = mov r0
      // ...
      // r1    = mov r1024
      //
      // We want to insert "r1025 = mov r1". Inserting this copy below the
      // move to r1024 makes it impossible for that move to be coalesced.
      //
      // r1025 = mov r1
      // r1024 = mov r0
      // ...
      // r1    = mov 1024
      // r2    = mov 1025
      break; // Woot! Found a good location.
    --Pos;
  }

  bool Emitted = TII.copyRegToReg(*MBB, Pos, VirtReg, PhysReg, RC, RC);
  assert(Emitted && "Unable to issue a live-in copy instruction!\n");
  (void) Emitted;

  CopyRegMap.insert(std::make_pair(prior(Pos), VirtReg));
  if (Coalesced) {
    if (&*InsertPos == UseMI) ++InsertPos;
    MBB->erase(UseMI);
  }
}