RegAllocGreedy-ForceGlobal should use number of Allocatable registers

[smohser]

Summary

RegAllocGreedy decides to allocate global and split ranges based on registers number in the register class, which includes preassigned registers and some cases unusable registers (if your register class includes registers for multiple cores), when it should only consider the allocatable registers only.

[smohser]

delete personal mail

[lebedev.ri]

Test?

[smohser]

i have no unit test, neither was one provided in the original commit

lib/CodeGen/RegAllocGreedy.cpp

if (ExtraRegInfo[Reg].Stage == RS_Split) {
     static unsigned MemOp = 0;
     Prio = MemOp++;
   } else {
     // Giant live ranges fall back to the global assignment heuristic, which
     // prevents excessive spilling in pathological cases.
     bool ReverseLocal = TRI->reverseLocalAssignment();
     const TargetRegisterClass &RC = *MRI->getRegClass(Reg);
     bool ForceGlobal = !ReverseLocal &&
-      (Size / SlotIndex::InstrDist) > (2 * RC.getNumRegs());
+      (Size / SlotIndex::InstrDist) > (2 * RegClassInfo.getNumAllocatableRegs(&RC));
 
     if (ExtraRegInfo[Reg].Stage == RS_Assign && !ForceGlobal && !LI->empty() &&
         LIS->intervalIsInOneMBB(*LI)) {
       // Allocate original local ranges in linear instruction order. Since they
       // are singly defined, this produces optimal coloring in the absence of
       // global interference and other constraints.
       if (!ReverseLocal)
         Prio = LI->beginIndex().getInstrDistance(Indexes->getLastIndex());