diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp
index dc799e8..1cbe798 100644
--- a/lib/CodeGen/PHIElimination.cpp
+++ b/lib/CodeGen/PHIElimination.cpp
@@ -182,6 +182,10 @@
     TII->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC, RC);
   }
 
+  // Record PHI def.
+  //assert(!hasPHIDef(DestReg) && "Vreg has multiple phi-defs?"); 
+  //PHIDefs[DestReg] = &MBB;
+
   // Update live variable information if there is any.
   LiveVariables *LV = getAnalysisIfAvailable<LiveVariables>();
   if (LV) {
@@ -223,6 +227,13 @@
     assert(TargetRegisterInfo::isVirtualRegister(SrcReg) &&
            "Machine PHI Operands must all be virtual registers!");
 
+    // Get the MachineBasicBlock equivalent of the BasicBlock that is the source
+    // path the PHI.
+    MachineBasicBlock &opBlock = *MPhi->getOperand(i*2+2).getMBB();
+
+    // Record the kill.
+    //PHIKills[SrcReg].insert(&opBlock);
+
     // If source is defined by an implicit def, there is no need to insert a
     // copy.
     MachineInstr *DefMI = MRI->getVRegDef(SrcReg);
@@ -231,10 +242,6 @@
       continue;
     }
 
-    // Get the MachineBasicBlock equivalent of the BasicBlock that is the source
-    // path the PHI.
-    MachineBasicBlock &opBlock = *MPhi->getOperand(i*2+2).getMBB();
-
     // Check to make sure we haven't already emitted the copy for this block.
     // This can happen because PHI nodes may have multiple entries for the same
     // basic block.
diff --git a/lib/CodeGen/PHIElimination.h b/lib/CodeGen/PHIElimination.h
index 26a3731..b06435f 100644
--- a/lib/CodeGen/PHIElimination.h
+++ b/lib/CodeGen/PHIElimination.h
@@ -10,6 +10,8 @@
 #ifndef LLVM_CODEGEN_PHIELIMINATION_HPP
 #define LLVM_CODEGEN_PHIELIMINATION_HPP
 
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/Target/TargetInstrInfo.h"
@@ -21,8 +23,17 @@
   /// Lower PHI instructions to copies.  
   class PHIElimination : public MachineFunctionPass {
     MachineRegisterInfo  *MRI; // Machine register information
+  private:
+
+    typedef SmallSet<MachineBasicBlock*, 4> PHIKillList;
+    typedef DenseMap<unsigned, PHIKillList> PHIKillMap;
+    typedef DenseMap<unsigned, MachineBasicBlock*> PHIDefMap;
 
   public:
+
+    typedef PHIKillList::iterator phi_kill_iterator;
+    typedef PHIKillList::const_iterator const_phi_kill_iterator;
+
     static char ID; // Pass identification, replacement for typeid
     PHIElimination() : MachineFunctionPass(&ID) {}
 
@@ -30,6 +41,38 @@
     
     virtual void getAnalysisUsage(AnalysisUsage &AU) const;
 
+    /// Return true if the given vreg was defined by a PHI intsr prior to
+    /// lowering.
+    bool hasPHIDef(unsigned vreg) const {
+      return PHIDefs.count(vreg);
+    }
+
+    /// Returns the block in which the PHI instruction which defined the
+    /// given vreg used to reside. 
+    MachineBasicBlock* getPHIDefBlock(unsigned vreg) {
+      PHIDefMap::iterator phiDefItr = PHIDefs.find(vreg);
+      assert(phiDefItr != PHIDefs.end() && "vreg has no phi-def.");
+      return phiDefItr->second;
+    }
+
+    /// Returns true if the given vreg was killed by a PHI instr.
+    bool hasPHIKills(unsigned vreg) const {
+      return PHIKills.count(vreg);
+    }
+
+    /// Returns an iterator over the BasicBlocks which contained PHI
+    /// kills of this register prior to lowering.
+    phi_kill_iterator phiKillsBegin(unsigned vreg) {
+      PHIKillMap::iterator phiKillItr = PHIKills.find(vreg);
+      assert(phiKillItr != PHIKills.end() && "vreg has no phi-kills.");
+      return phiKillItr->second.begin();
+    } 
+    phi_kill_iterator phiKillsEnd(unsigned vreg) {
+      PHIKillMap::iterator phiKillItr = PHIKills.find(vreg);
+      assert(phiKillItr != PHIKills.end() && "vreg has no phi-kills.");
+      return phiKillItr->second.end();
+    }
+
   private:
     /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions
     /// in predecessor basic blocks.
@@ -70,6 +113,8 @@
     typedef std::map<BBVRegPair, unsigned> VRegPHIUse;
 
     VRegPHIUse VRegPHIUseCount;
+    PHIDefMap PHIDefs;
+    PHIKillMap PHIKills;
 
     // Defs of PHI sources which are implicit_def.
     SmallPtrSet<MachineInstr*, 4> ImpDefs;