diff --git a/lib/Transforms/IPO/SimplifyLibCalls.cpp b/lib/Transforms/IPO/SimplifyLibCalls.cpp
index c7038ccd798..0f19740e2de 100644
--- a/lib/Transforms/IPO/SimplifyLibCalls.cpp
+++ b/lib/Transforms/IPO/SimplifyLibCalls.cpp
@@ -688,82 +688,72 @@ public:
       "Number of 'strncmp' calls simplified") {}
 
   /// @brief Make sure that the "strncmp" function has the right prototype
-  virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC){
-    if (f->getReturnType() == Type::Int32Ty && f->arg_size() == 3)
-      return true;
+  virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &SLC){
+    const FunctionType *FT = F->getFunctionType();
+    return FT->getReturnType() == Type::Int32Ty && FT->getNumParams() == 3 &&
+           FT->getParamType(0) == FT->getParamType(1) &&
+           FT->getParamType(0) == PointerType::get(Type::Int8Ty) &&
+           isa<IntegerType>(FT->getParamType(2));
     return false;
   }
 
-  /// @brief Perform the strncpy optimization
-  virtual bool OptimizeCall(CallInst *ci, SimplifyLibCalls &SLC) {
+  /// @brief Perform the strncmp optimization
+  virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &SLC) {
     // First, check to see if src and destination are the same. If they are,
     // then the optimization is to replace the CallInst with a constant 0
     // because the call is a no-op.
-    Value* s1 = ci->getOperand(1);
-    Value* s2 = ci->getOperand(2);
-    if (s1 == s2) {
-      // strncmp(x,x,l)  -> 0
-      ci->replaceAllUsesWith(ConstantInt::get(Type::Int32Ty,0));
-      ci->eraseFromParent();
+    Value *Str1P = CI->getOperand(1);
+    Value *Str2P = CI->getOperand(2);
+    if (Str1P == Str2P) {
+      // strcmp(x,x)  -> 0
+      CI->replaceAllUsesWith(ConstantInt::get(CI->getType(), 0));
+      CI->eraseFromParent();
       return true;
     }
-
+    
     // Check the length argument, if it is Constant zero then the strings are
     // considered equal.
-    uint64_t len_arg = 0;
-    bool len_arg_is_const = false;
-    if (ConstantInt* len_CI = dyn_cast<ConstantInt>(ci->getOperand(3))) {
-      len_arg_is_const = true;
-      len_arg = len_CI->getZExtValue();
-      if (len_arg == 0) {
-        // strncmp(x,y,0)   -> 0
-        ci->replaceAllUsesWith(ConstantInt::get(Type::Int32Ty,0));
-        ci->eraseFromParent();
-        return true;
-      }
+    ConstantInt *LengthArg = dyn_cast<ConstantInt>(CI->getOperand(3));
+    if (LengthArg && LengthArg->isZero()) {
+      // strncmp(x,y,0)   -> 0
+      CI->replaceAllUsesWith(ConstantInt::get(CI->getType(), 0));
+      CI->eraseFromParent();
+      return true;
     }
-
-    bool isstr_1 = false;
-    uint64_t len_1 = 0, StartIdx;
-    ConstantArray* A1;
-    if (GetConstantStringInfo(s1, A1, len_1, StartIdx)) {
-      isstr_1 = true;
-      if (len_1 == 0) {
-        // strncmp("",x) -> *x
-        LoadInst* load = new LoadInst(s1,ci->getName()+".load",ci);
-        CastInst* cast =
-          CastInst::create(Instruction::SExt, load, Type::Int32Ty, 
-                           ci->getName()+".int", ci);
-        ci->replaceAllUsesWith(cast);
-        ci->eraseFromParent();
-        return true;
-      }
+    
+    uint64_t Str1Len, Str1StartIdx;
+    ConstantArray *A1;
+    bool Str1IsCst = GetConstantStringInfo(Str1P, A1, Str1Len, Str1StartIdx);
+    if (Str1IsCst && Str1Len == 0) {
+      // strcmp("", x) -> *x
+      Value *V = new LoadInst(Str2P, CI->getName()+".load", CI);
+      V = new ZExtInst(V, CI->getType(), CI->getName()+".int", CI);
+      CI->replaceAllUsesWith(V);
+      CI->eraseFromParent();
+      return true;
     }
-
-    bool isstr_2 = false;
-    uint64_t len_2 = 0;
+    
+    uint64_t Str2Len, Str2StartIdx;
     ConstantArray* A2;
-    if (GetConstantStringInfo(s2, A2, len_2, StartIdx)) {
-      isstr_2 = true;
-      if (len_2 == 0) {
-        // strncmp(x,"") -> *x
-        LoadInst* load = new LoadInst(s2,ci->getName()+".val",ci);
-        CastInst* cast =
-          CastInst::create(Instruction::SExt, load, Type::Int32Ty, 
-                           ci->getName()+".int", ci);
-        ci->replaceAllUsesWith(cast);
-        ci->eraseFromParent();
-        return true;
-      }
+    bool Str2IsCst = GetConstantStringInfo(Str2P, A2, Str2Len, Str2StartIdx);
+    if (Str2IsCst && Str2Len == 0) {
+      // strcmp(x,"") -> *x
+      Value *V = new LoadInst(Str1P, CI->getName()+".load", CI);
+      V = new ZExtInst(V, CI->getType(), CI->getName()+".int", CI);
+      CI->replaceAllUsesWith(V);
+      CI->eraseFromParent();
+      return true;
     }
-
-    if (isstr_1 && isstr_2 && len_arg_is_const) {
-      // strncmp(x,y,const) -> constant
-      std::string str1 = A1->getAsString();
-      std::string str2 = A2->getAsString();
-      int result = strncmp(str1.c_str(), str2.c_str(), len_arg);
-      ci->replaceAllUsesWith(ConstantInt::get(Type::Int32Ty,result));
-      ci->eraseFromParent();
+    
+    if (LengthArg && Str1IsCst && Str2IsCst && A1->isCString() &&
+        A2->isCString()) {
+      // strcmp(x, y)  -> cnst  (if both x and y are constant strings)
+      std::string S1 = A1->getAsString();
+      std::string S2 = A2->getAsString();
+      int R = strncmp(S1.c_str()+Str1StartIdx, S2.c_str()+Str2StartIdx,
+                      LengthArg->getZExtValue());
+      CI->replaceAllUsesWith(ConstantInt::get(CI->getType(), R));
+      CI->eraseFromParent();
       return true;
     }
     return false;