+
+// Compute target-independent register allocator hints to help eliminate copies.
+void
+TargetRegisterInfo::getRegAllocationHints(unsigned VirtReg,
+ ArrayRef<MCPhysReg> Order,
+ SmallVectorImpl<MCPhysReg> &Hints,
+ const MachineFunction &MF,
+ const VirtRegMap *VRM) const {
+ const MachineRegisterInfo &MRI = MF.getRegInfo();
+ std::pair<unsigned, unsigned> Hint = MRI.getRegAllocationHint(VirtReg);
+
+ // Hints with HintType != 0 were set by target-dependent code.
+ // Such targets must provide their own implementation of
+ // TRI::getRegAllocationHints to interpret those hint types.
+ assert(Hint.first == 0 && "Target must implement TRI::getRegAllocationHints");
+
+ // Target-independent hints are either a physical or a virtual register.
+ unsigned Phys = Hint.second;
+ if (VRM && isVirtualRegister(Phys))
+ Phys = VRM->getPhys(Phys);
+
+ // Check that Phys is a valid hint in VirtReg's register class.
+ if (!isPhysicalRegister(Phys))
+ return;
+ if (MRI.isReserved(Phys))
+ return;
+ // Check that Phys is in the allocation order. We shouldn't heed hints
+ // from VirtReg's register class if they aren't in the allocation order. The
+ // target probably has a reason for removing the register.
+ if (std::find(Order.begin(), Order.end(), Phys) == Order.end())
+ return;
+
+ // All clear, tell the register allocator to prefer this register.
+ Hints.push_back(Phys);
+}