Only update regunit live ranges that have been precomputed.

Regunit live ranges are computed on demand, so when mi-sched calls
handleMove, some regunits may not have live ranges yet.

That makes updating them easier: Just skip the non-existing ranges. They
will be computed correctly from the rescheduled machine code when they
are needed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158831 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveIntervalAnalysis.h

@@ -347,6 +347,12 @@ namespace llvm {
       return *LI;
     }
 
+    /// getCachedRegUnit - Return the live range for Unit if it has already
+    /// been computed, or NULL if it hasn't been computed yet.
+    LiveInterval *getCachedRegUnit(unsigned Unit) {
+      return RegUnitIntervals[Unit];
+    }
+
     /// trackingRegUnits - Does LiveIntervals curently track register units?
     /// This function will be removed when regunit tracking is permanently
     /// enabled.