Add a default constructor for LiveRange.

It is useful to be able to create temporary LiveRange object whose
members are filled in later.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175639 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveInterval.h

@@ -86,9 +86,10 @@ namespace llvm {
     SlotIndex end;    // End point of the interval (exclusive)
     VNInfo *valno;   // identifier for the value contained in this interval.
 
+    LiveRange() : valno(0) {}
+
     LiveRange(SlotIndex S, SlotIndex E, VNInfo *V)
       : start(S), end(E), valno(V) {
-
       assert(S < E && "Cannot create empty or backwards range");
     }