diff --git a/include/llvm/CodeGen/LiveIntervalAnalysis.h b/include/llvm/CodeGen/LiveIntervalAnalysis.h
index a344b1ff1b5..fe22d8af027 100644
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -375,6 +375,7 @@ namespace llvm {
 
     void computeLiveInRegUnits();
     void computeRegUnitInterval(LiveInterval*);
+    void computeVirtRegInterval(LiveInterval*);
 
     class HMEditor;
   };
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 819707f59f5..bc0ec157f62 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -27,6 +27,7 @@
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetMachine.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
@@ -38,6 +39,11 @@
 #include <cmath>
 using namespace llvm;
 
+// Switch to the new experimental algorithm for computing live intervals.
+static cl::opt<bool>
+NewLiveIntervals("new-live-intervals", cl::Hidden,
+                 cl::desc("Use new algorithm forcomputing live intervals"));
+
 char LiveIntervals::ID = 0;
 INITIALIZE_PASS_BEGIN(LiveIntervals, "liveintervals",
                 "Live Interval Analysis", false, false)
@@ -105,7 +111,25 @@ bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
   AllocatableRegs = TRI->getAllocatableSet(fn);
   ReservedRegs = TRI->getReservedRegs(fn);
 
-  computeIntervals();
+  // Allocate space for all virtual registers.
+  VirtRegIntervals.resize(MRI->getNumVirtRegs());
+
+  if (NewLiveIntervals) {
+    // This is the new way of computing live intervals.
+    // It is independent of LiveVariables, and it can run at any time.
+    for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
+      unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
+      if (MRI->reg_nodbg_empty(Reg))
+        continue;
+      LiveInterval *LI = createInterval(Reg);
+      VirtRegIntervals[Reg] = LI;
+      computeVirtRegInterval(LI);
+    }
+  } else {
+    // This is the old way of computing live intervals.
+    // It depends on LiveVariables.
+    computeIntervals();
+  }
   computeLiveInRegUnits();
 
   DEBUG(dump());
@@ -442,6 +466,17 @@ LiveInterval* LiveIntervals::createInterval(unsigned reg) {
 }
 
 
+/// computeVirtRegInterval - Compute the live interval of a virtual register,
+/// based on defs and uses.
+void LiveIntervals::computeVirtRegInterval(LiveInterval *LI) {
+  assert(LRCalc && "LRCalc not initialized.");
+  assert(LI->empty() && "Should only compute empty intervals.");
+  LRCalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
+  LRCalc->createDeadDefs(LI);
+  LRCalc->extendToUses(LI);
+}
+
+
 //===----------------------------------------------------------------------===//
 //                           Register Unit Liveness
 //===----------------------------------------------------------------------===//