MachineInstr can change. Store indexes instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44612 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/VirtRegMap.cpp b/lib/CodeGen/VirtRegMap.cpp
index e39f6a7..d0fd62a 100644
--- a/lib/CodeGen/VirtRegMap.cpp
+++ b/lib/CodeGen/VirtRegMap.cpp
@@ -64,7 +64,7 @@
   : TII(*mf.getTarget().getInstrInfo()), MF(mf), 
     Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT),
     Virt2ReMatIdMap(NO_STACK_SLOT), Virt2SplitMap(0),
-    Virt2SplitKillMap(NULL), ReMatMap(NULL), ReMatId(MAX_STACK_SLOT+1) {
+    Virt2SplitKillMap(0), ReMatMap(NULL), ReMatId(MAX_STACK_SLOT+1) {
   grow();
 }