VirtRegMap.cpp

          // indicates it is safe to use R1 for the reload instead of R0.
          //
          // To further complicate matters, we might conflict with an alias,
          // or R0 and R1 might not be compatible with each other.  In this
          // case, we actually insert a reload for V1 in R1, ensuring that
          // we can get at R0 or its alias.
          ReusedOperands.addReuse(i, ReuseSlot, PhysReg,
                                  VRM.getPhys(VirtReg), VirtReg);
          if (ti != -1)
            // Only mark it clobbered if this is a use&def operand.
            ReusedOperands.markClobbered(PhysReg);
          ++NumReused;

          if (MI.getOperand(i).isKill() &&
              ReuseSlot <= VirtRegMap::MAX_STACK_SLOT) {
            // This was the last use and the spilled value is still available
            // for reuse. That means the spill was unnecessary!
            MachineInstr* DeadStore = MaybeDeadStores[ReuseSlot];
            if (DeadStore) {
              DOUT << "Removed dead store:\t" << *DeadStore;
              InvalidateKills(*DeadStore, RegKills, KillOps);
              VRM.RemoveFromFoldedVirtMap(DeadStore);
              MBB.erase(DeadStore);
              MaybeDeadStores[ReuseSlot] = NULL;
              ++NumDSE;
            }
          }
          continue;
        }  // CanReuse
        
        // Otherwise we have a situation where we have a two-address instruction
        // whose mod/ref operand needs to be reloaded.  This reload is already
        // available in some register "PhysReg", but if we used PhysReg as the
        // operand to our 2-addr instruction, the instruction would modify
        // PhysReg.  This isn't cool if something later uses PhysReg and expects
        // to get its initial value.
        //
        // To avoid this problem, and to avoid doing a load right after a store,
        // we emit a copy from PhysReg into the designated register for this
        // operand.
        unsigned DesignatedReg = VRM.getPhys(VirtReg);
        assert(DesignatedReg && "Must map virtreg to physreg!");

        // Note that, if we reused a register for a previous operand, the
        // register we want to reload into might not actually be
        // available.  If this occurs, use the register indicated by the
        // reuser.
        if (ReusedOperands.hasReuses())
          DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI, 
                               Spills, MaybeDeadStores, RegKills, KillOps, VRM);
        
        // If the mapped designated register is actually the physreg we have
        // incoming, we don't need to inserted a dead copy.
        if (DesignatedReg == PhysReg) {
          // If this stack slot value is already available, reuse it!
          if (ReuseSlot > VirtRegMap::MAX_STACK_SLOT)
            DOUT << "Reusing RM#" << ReuseSlot-VirtRegMap::MAX_STACK_SLOT-1;
          else
            DOUT << "Reusing SS#" << ReuseSlot;
          DOUT << " from physreg " << MRI->getName(PhysReg) << " for vreg"
               << VirtReg
               << " instead of reloading into same physreg.\n";
          unsigned RReg = SubIdx ? MRI->getSubReg(PhysReg, SubIdx) : PhysReg;
          MI.getOperand(i).setReg(RReg);
          ReusedOperands.markClobbered(RReg);
          ++NumReused;
          continue;
        }
        
        const TargetRegisterClass* RC = RegMap->getRegClass(VirtReg);
        MF.setPhysRegUsed(DesignatedReg);
        ReusedOperands.markClobbered(DesignatedReg);
        MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC, RC);

        MachineInstr *CopyMI = prior(MII);
        UpdateKills(*CopyMI, RegKills, KillOps);

        // This invalidates DesignatedReg.
        Spills.ClobberPhysReg(DesignatedReg);
        
        Spills.addAvailable(ReuseSlot, &MI, DesignatedReg);
        unsigned RReg =
          SubIdx ? MRI->getSubReg(DesignatedReg, SubIdx) : DesignatedReg;
        MI.getOperand(i).setReg(RReg);
        DOUT << '\t' << *prior(MII);
        ++NumReused;
        continue;
      } // if (PhysReg)
      
      // Otherwise, reload it and remember that we have it.
      PhysReg = VRM.getPhys(VirtReg);
      assert(PhysReg && "Must map virtreg to physreg!");

      // Note that, if we reused a register for a previous operand, the
      // register we want to reload into might not actually be
      // available.  If this occurs, use the register indicated by the
      // reuser.
      if (ReusedOperands.hasReuses())
        PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, 
                               Spills, MaybeDeadStores, RegKills, KillOps, VRM);
      
      MF.setPhysRegUsed(PhysReg);
      ReusedOperands.markClobbered(PhysReg);
      if (DoReMat) {
        MRI->reMaterialize(MBB, &MI, PhysReg, VRM.getReMaterializedMI(VirtReg));
        ++NumReMats;
      } else {
        const TargetRegisterClass* RC = RegMap->getRegClass(VirtReg);
        MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, SSorRMId, RC);
        ++NumLoads;
      }
      // This invalidates PhysReg.
      Spills.ClobberPhysReg(PhysReg);

      // Any stores to this stack slot are not dead anymore.
      if (!DoReMat)
        MaybeDeadStores[SSorRMId] = NULL;
      Spills.addAvailable(SSorRMId, &MI, PhysReg);
      // Assumes this is the last use. IsKill will be unset if reg is reused
      // unless it's a two-address operand.
      if (TID->getOperandConstraint(i, TOI::TIED_TO) == -1)
        MI.getOperand(i).setIsKill();
      unsigned RReg = SubIdx ? MRI->getSubReg(PhysReg, SubIdx) : PhysReg;
      MI.getOperand(i).setReg(RReg);
      UpdateKills(*prior(MII), RegKills, KillOps);
      DOUT << '\t' << *prior(MII);
    }

    DOUT << '\t' << MI;

    // If we have folded references to memory operands, make sure we clear all
    // physical registers that may contain the value of the spilled virtual
    // register
    SmallSet<int, 2> FoldedSS;
    for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
      unsigned VirtReg = I->second.first;
      VirtRegMap::ModRef MR = I->second.second;
      DOUT << "Folded vreg: " << VirtReg << "  MR: " << MR;
      if (VRM.isAssignedReg(VirtReg)) {
        DOUT << ": No stack slot!\n";
        continue;
      }
      int SS = VRM.getStackSlot(VirtReg);
      FoldedSS.insert(SS);
      DOUT << " - StackSlot: " << SS << "\n";
      
      // If this folded instruction is just a use, check to see if it's a
      // straight load from the virt reg slot.
      if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
        int FrameIdx;
        unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx);
        if (DestReg && FrameIdx == SS) {
          // If this spill slot is available, turn it into a copy (or nothing)
          // instead of leaving it as a load!
          if (unsigned InReg = Spills.getSpillSlotOrReMatPhysReg(SS)) {
            DOUT << "Promoted Load To Copy: " << MI;
            if (DestReg != InReg) {
              const TargetRegisterClass *RC = RegMap->getRegClass(VirtReg);
              MRI->copyRegToReg(MBB, &MI, DestReg, InReg, RC, RC);
              // Revisit the copy so we make sure to notice the effects of the
              // operation on the destreg (either needing to RA it if it's 
              // virtual or needing to clobber any values if it's physical).
              NextMII = &MI;
              --NextMII;  // backtrack to the copy.
              BackTracked = true;
            } else
              DOUT << "Removing now-noop copy: " << MI;

            VRM.RemoveFromFoldedVirtMap(&MI);
            MBB.erase(&MI);
            Erased = true;
            goto ProcessNextInst;
          }
        } else {
          unsigned PhysReg = Spills.getSpillSlotOrReMatPhysReg(SS);
          SmallVector<MachineInstr*, 4> NewMIs;
          if (PhysReg &&
              MRI->unfoldMemoryOperand(MF, &MI, PhysReg, false, false, NewMIs)) {
            MBB.insert(MII, NewMIs[0]);
            VRM.RemoveFromFoldedVirtMap(&MI);
            MBB.erase(&MI);
            Erased = true;
            --NextMII;  // backtrack to the unfolded instruction.
            BackTracked = true;
            goto ProcessNextInst;
          }
        }
      }

      // If this reference is not a use, any previous store is now dead.
      // Otherwise, the store to this stack slot is not dead anymore.
      MachineInstr* DeadStore = MaybeDeadStores[SS];
      if (DeadStore) {
        bool isDead = !(MR & VirtRegMap::isRef);
        MachineInstr *NewStore = NULL;
        if (MR & VirtRegMap::isModRef) {
          unsigned PhysReg = Spills.getSpillSlotOrReMatPhysReg(SS);
          SmallVector<MachineInstr*, 4> NewMIs;
          if (PhysReg &&
              DeadStore->findRegisterUseOperandIdx(PhysReg, true) != -1 &&
              MRI->unfoldMemoryOperand(MF, &MI, PhysReg, false, true, NewMIs)) {
            MBB.insert(MII, NewMIs[0]);
            NewStore = NewMIs[1];
            MBB.insert(MII, NewStore);
            VRM.RemoveFromFoldedVirtMap(&MI);
            MBB.erase(&MI);
            Erased = true;
            --NextMII;
            --NextMII;  // backtrack to the unfolded instruction.
            BackTracked = true;
            isDead = true;
          }
        }

        if (isDead) {  // Previous store is dead.
          // If we get here, the store is dead, nuke it now.
          DOUT << "Removed dead store:\t" << *DeadStore;
          InvalidateKills(*DeadStore, RegKills, KillOps);
          VRM.RemoveFromFoldedVirtMap(DeadStore);
          MBB.erase(DeadStore);
          if (!NewStore)
            ++NumDSE;
        }

        MaybeDeadStores[SS] = NULL;
        if (NewStore) {
          // Treat this store as a spill merged into a copy. That makes the
          // stack slot value available.
          VRM.virtFolded(VirtReg, NewStore, VirtRegMap::isMod);
          goto ProcessNextInst;
        }
      }

      // If the spill slot value is available, and this is a new definition of
      // the value, the value is not available anymore.
      if (MR & VirtRegMap::isMod) {
        // Notice that the value in this stack slot has been modified.
        Spills.ModifyStackSlotOrReMat(SS);
        
        // If this is *just* a mod of the value, check to see if this is just a
        // store to the spill slot (i.e. the spill got merged into the copy). If
        // so, realize that the vreg is available now, and add the store to the
        // MaybeDeadStore info.
        int StackSlot;
        if (!(MR & VirtRegMap::isRef)) {
          if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
            assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
                   "Src hasn't been allocated yet?");
            // Okay, this is certainly a store of SrcReg to [StackSlot].  Mark
            // this as a potentially dead store in case there is a subsequent
            // store into the stack slot without a read from it.
            MaybeDeadStores[StackSlot] = &MI;

            // If the stack slot value was previously available in some other
            // register, change it now.  Otherwise, make the register available,
            // in PhysReg.
            Spills.addAvailable(StackSlot, &MI, SrcReg, false/*don't clobber*/);
          }
        }
      }
    }

    // Process all of the spilled defs.
    for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
      MachineOperand &MO = MI.getOperand(i);
      if (!(MO.isRegister() && MO.getReg() && MO.isDef()))
        continue;

      unsigned VirtReg = MO.getReg();
      if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
        // Check to see if this is a noop copy.  If so, eliminate the
        // instruction before considering the dest reg to be changed.
        unsigned Src, Dst;
        if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
          ++NumDCE;
          DOUT << "Removing now-noop copy: " << MI;
          MBB.erase(&MI);
          Erased = true;
          VRM.RemoveFromFoldedVirtMap(&MI);
          Spills.disallowClobberPhysReg(VirtReg);
          goto ProcessNextInst;
        }
          
        // If it's not a no-op copy, it clobbers the value in the destreg.
        Spills.ClobberPhysReg(VirtReg);
        ReusedOperands.markClobbered(VirtReg);
 
        // Check to see if this instruction is a load from a stack slot into
        // a register.  If so, this provides the stack slot value in the reg.
        int FrameIdx;
        if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
          assert(DestReg == VirtReg && "Unknown load situation!");

          // If it is a folded reference, then it's not safe to clobber.
          bool Folded = FoldedSS.count(FrameIdx);
          // Otherwise, if it wasn't available, remember that it is now!
          Spills.addAvailable(FrameIdx, &MI, DestReg, !Folded);
          goto ProcessNextInst;
        }
            
        continue;
      }

      unsigned SubIdx = MO.getSubReg();
      bool DoReMat = VRM.isReMaterialized(VirtReg);
      if (DoReMat)
        ReMatDefs.insert(&MI);

      // The only vregs left are stack slot definitions.
      int StackSlot = VRM.getStackSlot(VirtReg);
      const TargetRegisterClass *RC = RegMap->getRegClass(VirtReg);

      // If this def is part of a two-address operand, make sure to execute
      // the store from the correct physical register.
      unsigned PhysReg;
      int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i);
      if (TiedOp != -1) {
        PhysReg = MI.getOperand(TiedOp).getReg();
        if (SubIdx) {
          unsigned SuperReg = findSuperReg(RC, PhysReg, SubIdx, MRI);
          assert(SuperReg && MRI->getSubReg(SuperReg, SubIdx) == PhysReg &&
                 "Can't find corresponding super-register!");
          PhysReg = SuperReg;
        }
      } else {
        PhysReg = VRM.getPhys(VirtReg);
        if (ReusedOperands.isClobbered(PhysReg)) {
          // Another def has taken the assigned physreg. It must have been a
          // use&def which got it due to reuse. Undo the reuse!
          PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, 
                               Spills, MaybeDeadStores, RegKills, KillOps, VRM);
        }
      }

      MF.setPhysRegUsed(PhysReg);
      unsigned RReg = SubIdx ? MRI->getSubReg(PhysReg, SubIdx) : PhysReg;
      ReusedOperands.markClobbered(RReg);
      MI.getOperand(i).setReg(RReg);

      if (!MO.isDead()) {
        MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
        DOUT << "Store:\t" << *next(MII);

        // If there is a dead store to this stack slot, nuke it now.
        MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
        if (LastStore) {
          DOUT << "Removed dead store:\t" << *LastStore;
          ++NumDSE;
          SmallVector<unsigned, 2> KillRegs;
          InvalidateKills(*LastStore, RegKills, KillOps, &KillRegs);
          MachineBasicBlock::iterator PrevMII = LastStore;
          bool CheckDef = PrevMII != MBB.begin();
          if (CheckDef)
            --PrevMII;
          MBB.erase(LastStore);
          VRM.RemoveFromFoldedVirtMap(LastStore);
          if (CheckDef) {
            // Look at defs of killed registers on the store. Mark the defs
            // as dead since the store has been deleted and they aren't
            // being reused.
            for (unsigned j = 0, ee = KillRegs.size(); j != ee; ++j) {
              bool HasOtherDef = false;
              if (InvalidateRegDef(PrevMII, MI, KillRegs[j], HasOtherDef)) {
                MachineInstr *DeadDef = PrevMII;
                if (ReMatDefs.count(DeadDef) && !HasOtherDef) {
                  // FIXME: This assumes a remat def does not have side
                  // effects.
                  MBB.erase(DeadDef);
                  VRM.RemoveFromFoldedVirtMap(DeadDef);
                  ++NumDRM;
                }
              }
            }
          }
        }
        LastStore = next(MII);

        // If the stack slot value was previously available in some other
        // register, change it now.  Otherwise, make the register available,
        // in PhysReg.
        Spills.ModifyStackSlotOrReMat(StackSlot);
        Spills.ClobberPhysReg(PhysReg);
        Spills.addAvailable(StackSlot, LastStore, PhysReg);
        ++NumStores;

        // Check to see if this is a noop copy.  If so, eliminate the
        // instruction before considering the dest reg to be changed.
        {
          unsigned Src, Dst;
          if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
            ++NumDCE;
            DOUT << "Removing now-noop copy: " << MI;
            MBB.erase(&MI);
            Erased = true;
            VRM.RemoveFromFoldedVirtMap(&MI);
            UpdateKills(*LastStore, RegKills, KillOps);
            goto ProcessNextInst;
          }
        }
      }    
    }
  ProcessNextInst:
    if (!Erased && !BackTracked)
      for (MachineBasicBlock::iterator II = MI; II != NextMII; ++II)
        UpdateKills(*II, RegKills, KillOps);
    MII = NextMII;
  }
}


llvm::Spiller* llvm::createSpiller() {
  switch (SpillerOpt) {
  default: assert(0 && "Unreachable!");
  case local:
    return new LocalSpiller();
  case simple:
    return new SimpleSpiller();
  }
}