Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1394,12 +1394,21 @@
 
 Value *LibCallSimplifier::optimizeSqrt(CallInst *CI, IRBuilder<> &B) {
   Function *Callee = CI->getCalledFunction();
-  
+
   Value *Ret = nullptr;
   if (TLI->has(LibFunc::sqrtf) && (Callee->getName() == "sqrt" ||
                                    Callee->getIntrinsicID() == Intrinsic::sqrt))
     Ret = optimizeUnaryDoubleFP(CI, B, true);
 
+  // FIXME: Refactor - this check is repeated all over this file and even in the
+  // preceding call to shrink double -> float.
+
+  // Make sure this has 1 argument of FP type, which matches the result type.
+  FunctionType *FT = Callee->getFunctionType();
+  if (FT->getNumParams() != 1 || FT->getReturnType() != FT->getParamType(0) ||
+      !FT->getParamType(0)->isFloatingPointTy())
+    return Ret;
+
   if (!CI->hasUnsafeAlgebra())
     return Ret;
 
Index: test/Transforms/InstCombine/cos-2.ll
===================================================================
--- test/Transforms/InstCombine/cos-2.ll
+++ test/Transforms/InstCombine/cos-2.ll
@@ -1,12 +1,11 @@
-; Test that the cos library call simplifier works correctly.
-;
 ; RUN: opt < %s -instcombine -S | FileCheck %s
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
 declare float @cos(double)
+declare signext i8 @sqrt(...)
 
-; Check that cos functions with the wrong prototype aren't simplified.
+; Check that functions with the wrong prototype aren't simplified.
 
 define float @test_no_simplify1(double %d) {
 ; CHECK-LABEL: @test_no_simplify1(
@@ -15,3 +14,14 @@
 ; CHECK: call float @cos(double %neg)
   ret float %cos
 }
+
+
+define i8 @bogus_sqrt() {
+  %fake_sqrt = call signext i8 (...) @sqrt()
+  ret i8 %fake_sqrt
+
+; CHECK-LABEL: bogus_sqrt(
+; CHECK-NEXT:  %fake_sqrt = call signext i8 (...) @sqrt()
+; CHECK-NEXT:  ret i8 %fake_sqrt
+}
+