MergeValueInto is too smart: it might choose to do the merge the opposite direction.

Live interval reconstruction needs to account for this, and scour its maps to
prevent dangling references.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@63558 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveInterval.cpp

@@ -591,7 +591,7 @@ void LiveInterval::MergeInClobberRanges(const LiveInterval &Clobbers,
 /// are found to be equivalent.  This eliminates V1, replacing all
 /// LiveRanges with the V1 value number with the V2 value number.  This can
 /// cause merging of V1/V2 values numbers and compaction of the value space.
-void LiveInterval::MergeValueNumberInto(VNInfo *V1, VNInfo *V2) {
+VNInfo* LiveInterval::MergeValueNumberInto(VNInfo *V1, VNInfo *V2) {
   assert(V1 != V2 && "Identical value#'s are always equivalent!");
 
   // This code actually merges the (numerically) larger value number into the
@@ -652,6 +652,8 @@ void LiveInterval::MergeValueNumberInto(VNInfo *V1, VNInfo *V2) {
   } else {
     V1->def = ~1U;
   }
+  
+  return V2;
 }
 
 void LiveInterval::Copy(const LiveInterval &RHS,