Tag cached interference with a user-provided tag instead of the virtual register number.

The live range of a virtual register may change which invalidates the cached
interference information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127772 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveIntervalUnion.h b/lib/CodeGen/LiveIntervalUnion.h
index 3734c7f..4ae2667 100644
--- a/lib/CodeGen/LiveIntervalUnion.h
+++ b/lib/CodeGen/LiveIntervalUnion.h
@@ -163,7 +163,7 @@
     bool CheckedFirstInterference;
     bool SeenAllInterferences;
     bool SeenUnspillableVReg;
-    unsigned Tag, VTag;
+    unsigned Tag, UserTag;
 
   public:
     Query(): LiveUnion(), VirtReg() {}
@@ -181,12 +181,13 @@
       SeenAllInterferences = false;
       SeenUnspillableVReg = false;
       Tag = 0;
-      VTag = 0;
+      UserTag = 0;
     }
 
-    void init(LiveInterval *VReg, LiveIntervalUnion *LIU) {
+    void init(unsigned UTag, LiveInterval *VReg, LiveIntervalUnion *LIU) {
       assert(VReg && LIU && "Invalid arguments");
-      if (VReg->reg == VTag && LiveUnion == LIU && !LIU->changedSince(Tag)) {
+      if (UserTag == UTag && VirtReg == VReg &&
+          LiveUnion == LIU && !LIU->changedSince(Tag)) {
         // Retain cached results, e.g. firstInterference.
         return;
       }
@@ -194,7 +195,7 @@
       LiveUnion = LIU;
       VirtReg = VReg;
       Tag = LIU->getTag();
-      VTag = VReg->reg;
+      UserTag = UTag;
     }
 
     LiveInterval &virtReg() const {