[mi-sched] Update comment and add break.

Author: lcvon007

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -3281,14 +3281,16 @@ void GenericScheduler::initPolicy(MachineBasicBlock::iterator Begin,
 
   // Avoid setting up the register pressure tracker for small regions to save
   // compile time. As a rough heuristic, only track pressure when the number of
-  // schedulable instructions exceeds half the integer register file.
+  // schedulable instructions exceeds half the allocatable integer register file
+  // that is the largest legal integer regiser type.
   RegionPolicy.ShouldTrackPressure = true;
   for (unsigned VT = MVT::i64; VT > (unsigned)MVT::i1; --VT) {
     MVT::SimpleValueType LegalIntVT = (MVT::SimpleValueType)VT;
     if (TLI->isTypeLegal(LegalIntVT)) {
       unsigned NIntRegs = Context->RegClassInfo->getNumAllocatableRegs(
         TLI->getRegClassFor(LegalIntVT));
       RegionPolicy.ShouldTrackPressure = NumRegionInstrs > (NIntRegs / 2);
+      break;
     }
   }