diff --git a/llvm/lib/CodeGen/InterferenceCache.cpp b/llvm/lib/CodeGen/InterferenceCache.cpp
new file mode 100644
index 0000000..512b4b3
--- /dev/null
+++ b/llvm/lib/CodeGen/InterferenceCache.cpp
@@ -0,0 +1,139 @@
+//===-- InterferenceCache.h - Caching per-block interference ---*- C++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// InterferenceCache remembers per-block interference in LiveIntervalUnions.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "regalloc"
+#include "InterferenceCache.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+
+using namespace llvm;
+
+void InterferenceCache::init(MachineFunction *mf,
+                             LiveIntervalUnion *liuarray,
+                             SlotIndexes *indexes,
+                            const TargetRegisterInfo *tri) {
+  MF = mf;
+  LIUArray = liuarray;
+  TRI = tri;
+  PhysRegEntries.assign(TRI->getNumRegs(), 0);
+  for (unsigned i = 0; i != CacheEntries; ++i)
+    Entries[i].clear(indexes);
+}
+
+InterferenceCache::Entry *InterferenceCache::get(unsigned PhysReg) {
+  unsigned E = PhysRegEntries[PhysReg];
+  if (E < CacheEntries && Entries[E].getPhysReg() == PhysReg) {
+    if (!Entries[E].valid(LIUArray, TRI))
+      Entries[E].revalidate();
+    return &Entries[E];
+  }
+  // No valid entry exists, pick the next round-robin entry.
+  E = RoundRobin;
+  if (++RoundRobin == CacheEntries)
+    RoundRobin = 0;
+  Entries[E].reset(PhysReg, LIUArray, TRI, MF);
+  PhysRegEntries[PhysReg] = E;
+  return &Entries[E];
+}
+
+/// revalidate - LIU contents have changed, update tags.
+void InterferenceCache::Entry::revalidate() {
+  // Invalidate all block entries.
+  ++Tag;
+  // Invalidate all iterators.
+  PrevPos = SlotIndex();
+  for (unsigned i = 0, e = Aliases.size(); i != e; ++i)
+    Aliases[i].second = Aliases[i].first->getTag();
+}
+
+void InterferenceCache::Entry::reset(unsigned physReg,
+                                     LiveIntervalUnion *LIUArray,
+                                     const TargetRegisterInfo *TRI,
+                                     const MachineFunction *MF) {
+  // LIU's changed, invalidate cache.
+  ++Tag;
+  PhysReg = physReg;
+  Blocks.resize(MF->getNumBlockIDs());
+  Aliases.clear();
+  for (const unsigned *AS = TRI->getOverlaps(PhysReg); *AS; ++AS) {
+    LiveIntervalUnion *LIU = LIUArray + *AS;
+    Aliases.push_back(std::make_pair(LIU, LIU->getTag()));
+  }
+
+  // Reset iterators.
+  PrevPos = SlotIndex();
+  unsigned e = Aliases.size();
+  Iters.resize(e);
+  for (unsigned i = 0; i != e; ++i)
+    Iters[i].setMap(Aliases[i].first->getMap());
+}
+
+bool InterferenceCache::Entry::valid(LiveIntervalUnion *LIUArray,
+                                     const TargetRegisterInfo *TRI) {
+  unsigned i = 0, e = Aliases.size();
+  for (const unsigned *AS = TRI->getOverlaps(PhysReg); *AS; ++AS, ++i) {
+    LiveIntervalUnion *LIU = LIUArray + *AS;
+    if (i == e ||  Aliases[i].first != LIU)
+      return false;
+    if (LIU->changedSince(Aliases[i].second))
+      return false;
+  }
+  return i == e;
+}
+
+void InterferenceCache::Entry::update(unsigned MBBNum) {
+  BlockInterference *BI = &Blocks[MBBNum];
+  BI->Tag = Tag;
+  BI->First = BI->Last = SlotIndex();
+
+  SlotIndex Start, Stop;
+  tie(Start, Stop) = Indexes->getMBBRange(MBBNum);
+
+  // Use advanceTo only when possible.
+  if (!PrevPos.isValid() || Start < PrevPos)
+    for (unsigned i = 0, e = Iters.size(); i != e; ++i)
+      Iters[i].find(Start);
+  else
+    for (unsigned i = 0, e = Iters.size(); i != e; ++i)
+      Iters[i].advanceTo(Start);
+  PrevPos = Start;
+
+  // Check for first interference.
+  for (unsigned i = 0, e = Iters.size(); i != e; ++i) {
+    Iter &I = Iters[i];
+    if (!I.valid())
+      continue;
+    SlotIndex StartI = I.start();
+    if (StartI >= Stop)
+      continue;
+    if (!BI->First.isValid() || StartI < BI->First)
+      BI->First = StartI;
+  }
+
+  // No interference in block.
+  if (!BI->First.isValid())
+    return;
+
+  // Check for last interference.
+  for (unsigned i = 0, e = Iters.size(); i != e; ++i) {
+    Iter &I = Iters[i];
+    if (!I.valid() || I.start() >= Stop)
+      continue;
+    I.advanceTo(Stop);
+    if (!I.valid() || I.start() >= Stop)
+      --I;
+    SlotIndex StopI = I.stop();
+    if (!BI->Last.isValid() || StopI > BI->Last)
+      BI->Last = StopI;
+  }
+  PrevPos = Stop;
+}