diff --git a/include/llvm/Intrinsics.td b/include/llvm/Intrinsics.td
index 84a39ad0c87..7ceeb9c7d5d 100644
--- a/include/llvm/Intrinsics.td
+++ b/include/llvm/Intrinsics.td
@@ -284,8 +284,8 @@ def int_expect : Intrinsic<[llvm_anyint_ty], [LLVMMatchType<0>,
 let Properties = [IntrNoMem] in {
   def int_bswap: Intrinsic<[llvm_anyint_ty], [LLVMMatchType<0>]>;
   def int_ctpop: Intrinsic<[llvm_anyint_ty], [LLVMMatchType<0>]>;
-  def int_ctlz : Intrinsic<[llvm_anyint_ty], [LLVMMatchType<0>]>;
-  def int_cttz : Intrinsic<[llvm_anyint_ty], [LLVMMatchType<0>]>;
+  def int_ctlz : Intrinsic<[llvm_anyint_ty], [LLVMMatchType<0>, llvm_i1_ty]>;
+  def int_cttz : Intrinsic<[llvm_anyint_ty], [LLVMMatchType<0>, llvm_i1_ty]>;
 }
 
 //===------------------------ Debugger Intrinsics -------------------------===//
diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 7e98b218884..8e2f263cd4c 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -1290,10 +1290,6 @@ llvm::ConstantFoldCall(Function *F, ArrayRef<Constant *> Operands,
         return ConstantInt::get(F->getContext(), Op->getValue().byteSwap());
       case Intrinsic::ctpop:
         return ConstantInt::get(Ty, Op->getValue().countPopulation());
-      case Intrinsic::cttz:
-        return ConstantInt::get(Ty, Op->getValue().countTrailingZeros());
-      case Intrinsic::ctlz:
-        return ConstantInt::get(Ty, Op->getValue().countLeadingZeros());
       case Intrinsic::convert_from_fp16: {
         APFloat Val(Op->getValue());
 
@@ -1418,6 +1414,14 @@ llvm::ConstantFoldCall(Function *F, ArrayRef<Constant *> Operands,
           };
           return ConstantStruct::get(cast<StructType>(F->getReturnType()), Ops);
         }
+        case Intrinsic::cttz:
+          // FIXME: This should check for Op2 == 1, and become unreachable if
+          // Op1 == 0.
+          return ConstantInt::get(Ty, Op1->getValue().countTrailingZeros());
+        case Intrinsic::ctlz:
+          // FIXME: This should check for Op2 == 1, and become unreachable if
+          // Op1 == 0.
+          return ConstantInt::get(Ty, Op1->getValue().countLeadingZeros());
         }
       }
       
diff --git a/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index 6e169de8291..075adc01873 100644
--- a/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -999,7 +999,7 @@ struct FFSOpt : public LibCallOptimization {
     Type *ArgType = Op->getType();
     Value *F = Intrinsic::getDeclaration(Callee->getParent(),
                                          Intrinsic::cttz, ArgType);
-    Value *V = B.CreateCall(F, Op, "cttz");
+    Value *V = B.CreateCall2(F, Op, B.getFalse(), "cttz");
     V = B.CreateAdd(V, ConstantInt::get(V->getType(), 1));
     V = B.CreateIntCast(V, B.getInt32Ty(), false);
 
diff --git a/lib/VMCore/AutoUpgrade.cpp b/lib/VMCore/AutoUpgrade.cpp
index 373524cdf38..6bdb115a9aa 100644
--- a/lib/VMCore/AutoUpgrade.cpp
+++ b/lib/VMCore/AutoUpgrade.cpp
@@ -40,7 +40,20 @@ static bool UpgradeIntrinsicFunction1(Function *F, Function *&NewFn) {
 
   switch (Name[0]) {
   default: break;
-  // SOMEDAY: Add some.
+  case 'c': {
+    Type *Tys[] = { F->arg_begin()->getType() };
+    if (Name.startswith("ctlz.") && F->arg_size() == 1) {
+      F->setName(Name + ".old");
+      NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::ctlz, Tys);
+      return true;
+    }
+    if (Name.startswith("cttz.") && F->arg_size() == 1) {
+      F->setName(Name + ".old");
+      NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::cttz, Tys);
+      return true;
+    }
+    break;
+  }
   }
 
   //  This may not belong here. This function is effectively being overloaded 
@@ -72,15 +85,29 @@ bool llvm::UpgradeGlobalVariable(GlobalVariable *GV) {
 // order to seamlessly integrate with existing context.
 void llvm::UpgradeIntrinsicCall(CallInst *CI, Function *NewFn) {
   Function *F = CI->getCalledFunction();
+  LLVMContext &C = CI->getContext();
 
   assert(F && "CallInst has no function associated with it.");
 
-  if (NewFn) return;
-  
-  if (F->getName() == "llvm.something eventually") {
-    // UPGRADE HERE.
-  } else {
+  if (!NewFn) return;
+
+  IRBuilder<> Builder(C);
+  Builder.SetInsertPoint(CI->getParent(), CI);
+
+  switch (NewFn->getIntrinsicID()) {
+  default:
     llvm_unreachable("Unknown function for CallInst upgrade.");
+
+  case Intrinsic::ctlz:
+  case Intrinsic::cttz:
+    assert(CI->getNumArgOperands() == 1 &&
+           "Mismatch between function args and call args");
+    StringRef Name = CI->getName();
+    CI->setName(Name + ".old");
+    CI->replaceAllUsesWith(Builder.CreateCall2(NewFn, CI->getArgOperand(0),
+                                               Builder.getFalse(), Name));
+    CI->eraseFromParent();
+    return;
   }
 }