[NFC] Expose isRematerializable and copyHint from CalcSpillWeights

[mtrofin]

Summary

We need to reuse them for the ML regalloc eviction advisor, as we
'explode' the weight calculation into sub-features.

llvm/include/llvm/CodeGen/CalcSpillWeights.h

public:
     /// \return The expected spill weight of the split artifact. Returns
     /// negative weight for unspillable LI.
     float futureWeight(LiveInterval &LI, SlotIndex Start, SlotIndex End);
 
     /// Compute spill weights and allocation hints for all virtual register
     /// live intervals.
     void calculateSpillWeightsAndHints();
 
+    /// Return the preferred allocation register for reg, given a COPY
+    /// instruction.
+    static Register copyHint(const MachineInstr *MI, unsigned Reg,
+                             const TargetRegisterInfo &TRI,
+                             const MachineRegisterInfo &MRI);
+
+    /// Determine if all values in LI are rematerializable.
+    static bool isRematerializable(const LiveInterval &LI,
+                                   const LiveIntervals &LIS,
+                                   const VirtRegMap &VRM,
+                                   const TargetInstrInfo &TII);
+
   protected:
     /// Helper function for weight calculations.
     /// (Re)compute LI's spill weight and allocation hint, or, for non null
     /// start and end - compute future expected spill weight of a split
     /// artifact of LI that will span between start and end slot indexes.
     /// \param LI     The live interval for which to compute the weight.
     /// \param Start  The expected beginning of the split artifact. Instructions
     ///               before start will not affect the weight. Relevant for

llvm/lib/CodeGen/CalcSpillWeights.cpp

for (unsigned I = 0, E = MRI.getNumVirtRegs(); I != E; ++I) {
     Register Reg = Register::index2VirtReg(I);
     if (MRI.reg_nodbg_empty(Reg))
       continue;
     calculateSpillWeightAndHint(LIS.getInterval(Reg));
   }
 }
 
 // Return the preferred allocation register for reg, given a COPY instruction.
-static Register copyHint(const MachineInstr *MI, unsigned Reg,
+Register VirtRegAuxInfo::copyHint(const MachineInstr *MI, unsigned Reg,
                                   const TargetRegisterInfo &TRI,
                                   const MachineRegisterInfo &MRI) {
   unsigned Sub, HSub;
   Register HReg;
   if (MI->getOperand(0).getReg() == Reg) {
     Sub = MI->getOperand(0).getSubReg();
     HReg = MI->getOperand(1).getReg();
     HSub = MI->getOperand(1).getSubReg();
   } else {
     Sub = MI->getOperand(1).getSubReg();
Register VirtRegAuxInfo::copyHint(const MachineInstr *MI, unsigned Reg,
   // Check if reg:sub matches so that a super register could be hinted.
   if (Sub)
     return TRI.getMatchingSuperReg(CopiedPReg, Sub, RC);
 
   return 0;
 }
 
 // Check if all values in LI are rematerializable
-static bool isRematerializable(const LiveInterval &LI, const LiveIntervals &LIS,
+bool VirtRegAuxInfo::isRematerializable(const LiveInterval &LI,
+                                        const LiveIntervals &LIS,
                                         const VirtRegMap &VRM,
                                         const TargetInstrInfo &TII) {
   Register Reg = LI.reg();
   Register Original = VRM.getOriginal(Reg);
   for (LiveInterval::const_vni_iterator I = LI.vni_begin(), E = LI.vni_end();
        I != E; ++I) {
     const VNInfo *VNI = *I;
     if (VNI->isUnused())
       continue;
     if (VNI->isPHIDef())