Add a -new-live-intervals experimental option.

This option replaces the existing live interval computation with one
based on LiveRangeCalc.cpp. The new algorithm does not depend on
LiveVariables, and it can be run at any time, before or after leaving
SSA form.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160892 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveIntervalAnalysis.h

@@ -375,6 +375,7 @@ namespace llvm {
 
     void computeLiveInRegUnits();
     void computeRegUnitInterval(LiveInterval*);
+    void computeVirtRegInterval(LiveInterval*);
 
     class HMEditor;
   };