diff --git a/include/llvm/CodeGen/LiveVariables.h b/include/llvm/CodeGen/LiveVariables.h
index aae7687..26c0362 100644
--- a/include/llvm/CodeGen/LiveVariables.h
+++ b/include/llvm/CodeGen/LiveVariables.h
@@ -33,6 +33,7 @@
 #include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/SparseBitVector.h"
 
 namespace llvm {
 
@@ -75,7 +76,7 @@
     /// through.  This is a bit set which uses the basic block number as an
     /// index.
     ///
-    BitVector AliveBlocks;
+    SparseBitVector<> AliveBlocks;
 
     /// NumUses - Number of uses of this register across the entire function.
     ///
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 612b9ac..bf18015 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -422,7 +422,7 @@
       // If the kill happens after the definition, we have an intra-block
       // live range.
       if (killIdx > defIndex) {
-        assert(vi.AliveBlocks.none() &&
+        assert(vi.AliveBlocks.empty() &&
                "Shouldn't be alive across any blocks!");
         LiveRange LR(defIndex, killIdx, ValNo);
         interval.addRange(LR);
@@ -443,10 +443,10 @@
     // Iterate over all of the blocks that the variable is completely
     // live in, adding [insrtIndex(begin), instrIndex(end)+4) to the
     // live interval.
-    for (int i = vi.AliveBlocks.find_first(); i != -1;
-         i = vi.AliveBlocks.find_next(i)) {
-      LiveRange LR(getMBBStartIdx(i),
-                   getMBBEndIdx(i)+1,  // MBB ends at -1.
+    for (SparseBitVector<>::iterator I = vi.AliveBlocks.begin(), 
+             E = vi.AliveBlocks.end(); I != E; ++I) {
+      LiveRange LR(getMBBStartIdx(*I),
+                   getMBBEndIdx(*I)+1,  // MBB ends at -1.
                    ValNo);
       interval.addRange(LR);
       DOUT << " +" << LR;
diff --git a/lib/CodeGen/LiveVariables.cpp b/lib/CodeGen/LiveVariables.cpp
index 9453aa4..c33d81e 100644
--- a/lib/CodeGen/LiveVariables.cpp
+++ b/lib/CodeGen/LiveVariables.cpp
@@ -52,8 +52,9 @@
 
 void LiveVariables::VarInfo::dump() const {
   cerr << "  Alive in blocks: ";
-  for (int i = AliveBlocks.find_first(); i != -1; i = AliveBlocks.find_next(i))
-    cerr << i << ", ";
+  for (SparseBitVector<>::iterator I = AliveBlocks.begin(),
+           E = AliveBlocks.end(); I != E; ++I)
+    cerr << *I << ", ";
   cerr << "\n  Killed by:";
   if (Kills.empty())
     cerr << " No instructions.\n";
@@ -75,9 +76,7 @@
     else
       VirtRegInfo.resize(2*VirtRegInfo.size());
   }
-  VarInfo &VI = VirtRegInfo[RegIdx];
-  VI.AliveBlocks.resize(MF->getNumBlockIDs());
-  return VI;
+  return VirtRegInfo[RegIdx];
 }
 
 void LiveVariables::MarkVirtRegAliveInBlock(VarInfo& VRInfo,
@@ -96,11 +95,11 @@
   
   if (MBB == DefBlock) return;  // Terminate recursion
 
-  if (VRInfo.AliveBlocks[BBNum])
+  if (VRInfo.AliveBlocks.test(BBNum))
     return;  // We already know the block is live
 
   // Mark the variable known alive in this bb
-  VRInfo.AliveBlocks[BBNum] = true;
+  VRInfo.AliveBlocks.set(BBNum);
 
   for (MachineBasicBlock::const_pred_reverse_iterator PI = MBB->pred_rbegin(),
          E = MBB->pred_rend(); PI != E; ++PI)
@@ -163,7 +162,7 @@
   // Add a new kill entry for this basic block. If this virtual register is
   // already marked as alive in this basic block, that means it is alive in at
   // least one of the successor blocks, it's not a kill.
-  if (!VRInfo.AliveBlocks[BBNum])
+  if (!VRInfo.AliveBlocks.test(BBNum))
     VRInfo.Kills.push_back(MI);
 
   // Update all dominating blocks to mark them as "known live".
@@ -175,7 +174,7 @@
 void LiveVariables::HandleVirtRegDef(unsigned Reg, MachineInstr *MI) {
   VarInfo &VRInfo = getVarInfo(Reg);
 
-  if (VRInfo.AliveBlocks.none())
+  if (VRInfo.AliveBlocks.empty())
     // If vr is not alive in any block, then defaults to dead.
     VRInfo.Kills.push_back(MI);
 }
diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp
index 2eacb08..c5c76fc 100644
--- a/lib/CodeGen/PHIElimination.cpp
+++ b/lib/CodeGen/PHIElimination.cpp
@@ -334,8 +334,7 @@
 
       // Is it alive in this successor?
       unsigned SuccIdx = SuccMBB->getNumber();
-      if (SuccIdx < InRegVI.AliveBlocks.size() &&
-          InRegVI.AliveBlocks[SuccIdx]) {
+      if (InRegVI.AliveBlocks.test(SuccIdx)) {
         ValueIsLive = true;
         break;
       }
@@ -407,8 +406,7 @@
 
       // This vreg no longer lives all of the way through opBlock.
       unsigned opBlockNum = opBlock.getNumber();
-      if (opBlockNum < InRegVI.AliveBlocks.size())
-        InRegVI.AliveBlocks[opBlockNum] = false;
+      InRegVI.AliveBlocks.reset(opBlockNum);
     }
   }