LiveRangeCalc: Rewrite subrange calculation

This changes subrange calculation to calculate subranges sequentially
instead of in parallel. The code is easier to understand that way and
addresses the code review issues raised about LiveOutData being
hard to understand/needing more comments by removing them :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224313 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveIntervalAnalysis.cpp

@@ -192,8 +192,7 @@ void LiveIntervals::computeVirtRegInterval(LiveInterval &LI) {
   assert(LRCalc && "LRCalc not initialized.");
   assert(LI.empty() && "Should only compute empty intervals.");
   LRCalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
-  LRCalc->createDeadDefs(LI);
-  LRCalc->extendToUses(LI);
+  LRCalc->calculate(LI);
   computeDeadValues(LI, LI);
 }