RegAlloc: Use SmallSet instead of std::set

[arsenm]

Summary

There shouldn't be more than a small handful of hints at most.

[arsenm]

6c44a7179f1747ec38d580e6b50bde98555ad811

llvm/lib/CodeGen/CalcSpillWeights.cpp

float VirtRegAuxInfo::weightCalcHelper(LiveInterval &LI, SlotIndex *Start,
   }
 
   // Pass all the sorted copy hints to mri.
   if (ShouldUpdateLI && CopyHints.size()) {
     // Remove a generic hint if previously added by target.
     if (TargetHint.first == 0 && TargetHint.second)
       MRI.clearSimpleHint(LI.reg());
 
-    std::set<Register> HintedRegs;
+    SmallSet<Register, 4> HintedRegs;
     for (const auto &Hint : CopyHints) {
       if (!HintedRegs.insert(Hint.Reg).second ||
           (TargetHint.first != 0 && Hint.Reg == TargetHint.second))
         // Don't add the same reg twice or the target-type hint again.
         continue;
       MRI.addRegAllocationHint(LI.reg(), Hint.Reg);
     }