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 {
diff --git a/lib/CodeGen/RegAllocBase.h b/lib/CodeGen/RegAllocBase.h
index 5af0ce7..f431d5a 100644
--- a/lib/CodeGen/RegAllocBase.h
+++ b/lib/CodeGen/RegAllocBase.h
@@ -61,6 +61,11 @@
 /// assignment order.
 class RegAllocBase {
   LiveIntervalUnion::Allocator UnionAllocator;
+
+  // Cache tag for PhysReg2LiveUnion entries. Increment whenever virtual
+  // registers may have changed.
+  unsigned UserTag;
+
 protected:
   // Array of LiveIntervalUnions indexed by physical register.
   class LiveUnionArray {
@@ -92,7 +97,7 @@
   // query on a new live virtual register.
   OwningArrayPtr<LiveIntervalUnion::Query> Queries;
 
-  RegAllocBase(): TRI(0), MRI(0), VRM(0), LIS(0) {}
+  RegAllocBase(): UserTag(0), TRI(0), MRI(0), VRM(0), LIS(0) {}
 
   virtual ~RegAllocBase() {}
 
@@ -104,7 +109,7 @@
   // before querying a new live virtual register. This ties Queries and
   // PhysReg2LiveUnion together.
   LiveIntervalUnion::Query &query(LiveInterval &VirtReg, unsigned PhysReg) {
-    Queries[PhysReg].init(&VirtReg, &PhysReg2LiveUnion[PhysReg]);
+    Queries[PhysReg].init(UserTag, &VirtReg, &PhysReg2LiveUnion[PhysReg]);
     return Queries[PhysReg];
   }
 
diff --git a/lib/CodeGen/RegAllocBasic.cpp b/lib/CodeGen/RegAllocBasic.cpp
index d51be52..ce92f3d 100644
--- a/lib/CodeGen/RegAllocBasic.cpp
+++ b/lib/CodeGen/RegAllocBasic.cpp
@@ -296,6 +296,9 @@
       continue;
     }
 
+    // Invalidate all interference queries, live ranges could have changed.
+    ++UserTag;
+
     // selectOrSplit requests the allocator to return an available physical
     // register if possible and populate a list of new live intervals that
     // result from splitting.