diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 9f8f0c4..833173f 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -698,6 +698,7 @@
 /// consumed.
 void SelectionDAGBuilder::clear() {
   NodeMap.clear();
+  UnusedArgNodeMap.clear();
   PendingLoads.clear();
   PendingExports.clear();
   CurDebugLoc = DebugLoc();
@@ -4063,7 +4064,10 @@
     } else {
       bool createUndef = false;
       // FIXME : Why not use getValue() directly ?
-      SDValue &N = NodeMap[V];
+      SDValue N = NodeMap[V];
+      if (!N.getNode() && isa<Argument>(V))
+        // Check unused arguments map.
+        N = UnusedArgNodeMap[V];
       if (N.getNode()) {
         if (!EmitFuncArgumentDbgValue(DI, V, Variable, Offset, N)) {
           SDV = DAG.getDbgValue(Variable, N.getNode(),
@@ -6032,6 +6036,12 @@
     SmallVector<EVT, 4> ValueVTs;
     ComputeValueVTs(TLI, I->getType(), ValueVTs);
     unsigned NumValues = ValueVTs.size();
+
+    // If this argument is unused then remember its value. It is used to generate
+    // debugging information.
+    if (I->use_empty() && NumValues)
+      SDB->setUnusedArgValue(I, InVals[i]);
+
     for (unsigned Value = 0; Value != NumValues; ++Value) {
       EVT VT = ValueVTs[Value];
       EVT PartVT = TLI.getRegisterType(*CurDAG->getContext(), VT);
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
index 3fcd4b9..86903ca 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -88,6 +88,10 @@
   DebugLoc CurDebugLoc;
 
   DenseMap<const Value*, SDValue> NodeMap;
+  
+  /// UnusedArgNodeMap - Maps argument value for unused arguments. This is used
+  /// to preserve debug information for incoming arguments.
+  DenseMap<const Value*, SDValue> UnusedArgNodeMap;
 
 public:
   /// PendingLoads - Loads are not emitted to the program immediately.  We bunch
@@ -349,6 +353,12 @@
     N = NewN;
   }
   
+  void setUnusedArgValue(const Value *V, SDValue NewN) {
+    SDValue &N = UnusedArgNodeMap[V];
+    assert(N.getNode() == 0 && "Already set a value for this node!");
+    N = NewN;
+  }
+  
   void GetRegistersForValue(SDISelAsmOperandInfo &OpInfo,
                             std::set<unsigned> &OutputRegs, 
                             std::set<unsigned> &InputRegs);