diff --git a/lib/CodeGen/LiveIntervalUnion.cpp b/lib/CodeGen/LiveIntervalUnion.cpp
index 9c579af..dadd02b 100644
--- a/lib/CodeGen/LiveIntervalUnion.cpp
+++ b/lib/CodeGen/LiveIntervalUnion.cpp
@@ -208,3 +208,26 @@
     VRI = VirtReg->advanceTo(VRI, Overlaps.start());
   }
 }
+
+void LiveIntervalUnion::Array::init(LiveIntervalUnion::Allocator &Alloc,
+                                    unsigned NSize) {
+  // Reuse existing allocation.
+  if (NSize == Size)
+    return;
+  clear();
+  Size = NSize;
+  LIUs = static_cast<LiveIntervalUnion*>(
+    malloc(sizeof(LiveIntervalUnion)*NSize));
+  for (unsigned i = 0; i != Size; ++i)
+    new(LIUs + i) LiveIntervalUnion(Alloc);
+}
+
+void LiveIntervalUnion::Array::clear() {
+  if (!LIUs)
+    return;
+  for (unsigned i = 0; i != Size; ++i)
+    LIUs[i].~LiveIntervalUnion();
+  free(LIUs);
+  Size =  0;
+  LIUs = 0;
+}
diff --git a/lib/CodeGen/LiveIntervalUnion.h b/lib/CodeGen/LiveIntervalUnion.h
index 4925abf..cd4e690 100644
--- a/lib/CodeGen/LiveIntervalUnion.h
+++ b/lib/CodeGen/LiveIntervalUnion.h
@@ -181,6 +181,28 @@
     Query(const Query&);          // DO NOT IMPLEMENT
     void operator=(const Query&); // DO NOT IMPLEMENT
   };
+
+  // Array of LiveIntervalUnions.
+  class Array {
+    unsigned Size;
+    LiveIntervalUnion *LIUs;
+  public:
+    Array() : Size(0), LIUs(0) {}
+    ~Array() { clear(); }
+
+    // Initialize the array to have Size entries.
+    // Reuse an existing allocation if the size matches.
+    void init(LiveIntervalUnion::Allocator&, unsigned Size);
+
+    unsigned size() const { return Size; }
+
+    void clear();
+
+    LiveIntervalUnion& operator[](unsigned idx) {
+      assert(idx <  Size && "idx out of bounds");
+      return LIUs[idx];
+    }
+  };
 };
 
 } // end namespace llvm
diff --git a/lib/CodeGen/RegAllocBase.cpp b/lib/CodeGen/RegAllocBase.cpp
index 5b2ec5e..3349b44 100644
--- a/lib/CodeGen/RegAllocBase.cpp
+++ b/lib/CodeGen/RegAllocBase.cpp
@@ -52,10 +52,11 @@
 void RegAllocBase::verify() {
   LiveVirtRegBitSet VisitedVRegs;
   OwningArrayPtr<LiveVirtRegBitSet>
-    unionVRegs(new LiveVirtRegBitSet[PhysReg2LiveUnion.numRegs()]);
+    unionVRegs(new LiveVirtRegBitSet[TRI->getNumRegs()]);
 
   // Verify disjoint unions.
-  for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
+  for (unsigned PhysReg = 0, NumRegs = TRI->getNumRegs(); PhysReg != NumRegs;
+       ++PhysReg) {
     DEBUG(PhysReg2LiveUnion[PhysReg].print(dbgs(), TRI));
     LiveVirtRegBitSet &VRegs = unionVRegs[PhysReg];
     PhysReg2LiveUnion[PhysReg].verify(VRegs);
@@ -89,16 +90,6 @@
 //                         RegAllocBase Implementation
 //===----------------------------------------------------------------------===//
 
-// Instantiate a LiveIntervalUnion for each physical register.
-void RegAllocBase::LiveUnionArray::init(LiveIntervalUnion::Allocator &allocator,
-                                        unsigned NRegs) {
-  NumRegs = NRegs;
-  Array =
-    static_cast<LiveIntervalUnion*>(malloc(sizeof(LiveIntervalUnion)*NRegs));
-  for (unsigned r = 0; r != NRegs; ++r)
-    new(Array + r) LiveIntervalUnion(allocator);
-}
-
 void RegAllocBase::init(VirtRegMap &vrm, LiveIntervals &lis) {
   NamedRegionTimer T("Initialize", TimerGroupName, TimePassesIsEnabled);
   TRI = &vrm.getTargetRegInfo();
@@ -109,25 +100,15 @@
   RegClassInfo.runOnMachineFunction(vrm.getMachineFunction());
 
   const unsigned NumRegs = TRI->getNumRegs();
-  if (NumRegs != PhysReg2LiveUnion.numRegs()) {
+  if (NumRegs != PhysReg2LiveUnion.size()) {
     PhysReg2LiveUnion.init(UnionAllocator, NumRegs);
     // Cache an interferece query for each physical reg
-    Queries.reset(new LiveIntervalUnion::Query[PhysReg2LiveUnion.numRegs()]);
+    Queries.reset(new LiveIntervalUnion::Query[NumRegs]);
   }
 }
 
-void RegAllocBase::LiveUnionArray::clear() {
-  if (!Array)
-    return;
-  for (unsigned r = 0; r != NumRegs; ++r)
-    Array[r].~LiveIntervalUnion();
-  free(Array);
-  NumRegs =  0;
-  Array = 0;
-}
-
 void RegAllocBase::releaseMemory() {
-  for (unsigned r = 0, e = PhysReg2LiveUnion.numRegs(); r != e; ++r)
+  for (unsigned r = 0, e = PhysReg2LiveUnion.size(); r != e; ++r)
     PhysReg2LiveUnion[r].clear();
 }
 
@@ -253,7 +234,8 @@
     return;
 
   LiveIntervalUnion::SegmentIter SI;
-  for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
+  for (unsigned PhysReg = 0, NumRegs = TRI->getNumRegs(); PhysReg != NumRegs;
+       ++PhysReg) {
     LiveIntervalUnion &LiveUnion = PhysReg2LiveUnion[PhysReg];
     if (LiveUnion.empty())
       continue;
diff --git a/lib/CodeGen/RegAllocBase.h b/lib/CodeGen/RegAllocBase.h
index 072fe2b..d55484f 100644
--- a/lib/CodeGen/RegAllocBase.h
+++ b/lib/CodeGen/RegAllocBase.h
@@ -62,27 +62,7 @@
   // registers may have changed.
   unsigned UserTag;
 
-  // Array of LiveIntervalUnions indexed by physical register.
-  class LiveUnionArray {
-    unsigned NumRegs;
-    LiveIntervalUnion *Array;
-  public:
-    LiveUnionArray(): NumRegs(0), Array(0) {}
-    ~LiveUnionArray() { clear(); }
-
-    unsigned numRegs() const { return NumRegs; }
-
-    void init(LiveIntervalUnion::Allocator &, unsigned NRegs);
-
-    void clear();
-
-    LiveIntervalUnion& operator[](unsigned PhysReg) {
-      assert(PhysReg <  NumRegs && "physReg out of bounds");
-      return Array[PhysReg];
-    }
-  };
-
-  LiveUnionArray PhysReg2LiveUnion;
+  LiveIntervalUnion::Array PhysReg2LiveUnion;
 
   // Current queries, one per physreg. They must be reinitialized each time we
   // query on a new live virtual register.