unsigned RegScavenger::scavengeRegisterBackwards(const TargetRegisterClass &RC,
MachineBasicBlock::iterator To,
bool RestoreAfter, int SPAdj) {
const MachineBasicBlock &MBB = *To->getParent();
const MachineFunction &MF = *MBB.getParent();
// Find the register whose use is furthest away.
MachineBasicBlock::iterator UseMI;
ArrayRef<MCPhysReg> AllocationOrder = RC.getRawAllocationOrder(MF);
std::pair<MCPhysReg, MachineBasicBlock::iterator> P =
findSurvivorBackwards(*MRI, MBBI, To, LiveUnits, AllocationOrder);
MCPhysReg Reg = P.first;
MachineBasicBlock::iterator SpillBefore = P.second;
assert(Reg != 0 && "No register left to scavenge!");
// Found an available register?
if (SpillBefore != MBB.end()) {
MachineBasicBlock::iterator ReloadAfter =
RestoreAfter ? std::next(MBBI) : MBBI;
MachineBasicBlock::iterator ReloadBefore = std::next(ReloadAfter);
DEBUG(dbgs() << "Reload before: " << *ReloadBefore << '\n');
ScavengedInfo &Scavenged = spill(Reg, RC, SPAdj, SpillBefore, ReloadBefore);
Scavenged.Restore = &*std::prev(SpillBefore);
LiveUnits.removeReg(Reg);
DEBUG(dbgs() << "Scavenged register with spill: " << PrintReg(Reg, TRI)
<< " until " << *SpillBefore);
} else {
DEBUG(dbgs() << "Scavenged free register: " << PrintReg(Reg, TRI) << '\n');
}
return Reg;
}
