diff --git a/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index 7d652dea48ed..370b81849df9 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -118,41 +118,6 @@ static bool IsOnlyUsedInEqualityComparison(Value *V, Value *With) {
 //===----------------------------------------------------------------------===//
 
 namespace {
-//===---------------------------------------===//
-// 'strcspn' Optimizations
-
-struct StrCSpnOpt : public LibCallOptimization {
-  virtual Value *CallOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
-    FunctionType *FT = Callee->getFunctionType();
-    if (FT->getNumParams() != 2 ||
-        FT->getParamType(0) != B.getInt8PtrTy() ||
-        FT->getParamType(1) != FT->getParamType(0) ||
-        !FT->getReturnType()->isIntegerTy())
-      return 0;
-
-    StringRef S1, S2;
-    bool HasS1 = getConstantStringInfo(CI->getArgOperand(0), S1);
-    bool HasS2 = getConstantStringInfo(CI->getArgOperand(1), S2);
-
-    // strcspn("", s) -> 0
-    if (HasS1 && S1.empty())
-      return Constant::getNullValue(CI->getType());
-
-    // Constant folding.
-    if (HasS1 && HasS2) {
-      size_t Pos = S1.find_first_of(S2);
-      if (Pos == StringRef::npos) Pos = S1.size();
-      return ConstantInt::get(CI->getType(), Pos);
-    }
-
-    // strcspn(s, "") -> strlen(s)
-    if (TD && HasS2 && S2.empty())
-      return EmitStrLen(CI->getArgOperand(0), B, TD, TLI);
-
-    return 0;
-  }
-};
-
 //===---------------------------------------===//
 // 'strstr' Optimizations
 
@@ -1005,7 +970,7 @@ namespace {
 
     StringMap<LibCallOptimization*> Optimizations;
     // String and Memory LibCall Optimizations
-    StrCSpnOpt StrCSpn; StrStrOpt StrStr;
+    StrStrOpt StrStr;
     MemCmpOpt MemCmp; MemCpyOpt MemCpy; MemMoveOpt MemMove; MemSetOpt MemSet;
     // Math Library Optimizations
     CosOpt Cos; PowOpt Pow; Exp2Opt Exp2;
@@ -1073,7 +1038,6 @@ void SimplifyLibCalls::AddOpt(LibFunc::Func F1, LibFunc::Func F2,
 /// we know.
 void SimplifyLibCalls::InitOptimizations() {
   // String and Memory LibCall Optimizations
-  Optimizations["strcspn"] = &StrCSpn;
   Optimizations["strstr"] = &StrStr;
   Optimizations["memcmp"] = &MemCmp;
   AddOpt(LibFunc::memcpy, &MemCpy);
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index f0d5491f9031..74d4e22fa446 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -801,6 +801,38 @@ struct StrSpnOpt : public LibCallOptimization {
   }
 };
 
+struct StrCSpnOpt : public LibCallOptimization {
+  virtual Value *callOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
+    FunctionType *FT = Callee->getFunctionType();
+    if (FT->getNumParams() != 2 ||
+        FT->getParamType(0) != B.getInt8PtrTy() ||
+        FT->getParamType(1) != FT->getParamType(0) ||
+        !FT->getReturnType()->isIntegerTy())
+      return 0;
+
+    StringRef S1, S2;
+    bool HasS1 = getConstantStringInfo(CI->getArgOperand(0), S1);
+    bool HasS2 = getConstantStringInfo(CI->getArgOperand(1), S2);
+
+    // strcspn("", s) -> 0
+    if (HasS1 && S1.empty())
+      return Constant::getNullValue(CI->getType());
+
+    // Constant folding.
+    if (HasS1 && HasS2) {
+      size_t Pos = S1.find_first_of(S2);
+      if (Pos == StringRef::npos) Pos = S1.size();
+      return ConstantInt::get(CI->getType(), Pos);
+    }
+
+    // strcspn(s, "") -> strlen(s)
+    if (TD && HasS2 && S2.empty())
+      return EmitStrLen(CI->getArgOperand(0), B, TD, TLI);
+
+    return 0;
+  }
+};
+
 } // End anonymous namespace.
 
 namespace llvm {
@@ -832,6 +864,7 @@ class LibCallSimplifierImpl {
   StrPBrkOpt StrPBrk;
   StrToOpt StrTo;
   StrSpnOpt StrSpn;
+  StrCSpnOpt StrCSpn;
 
   void initOptimizations();
   void addOpt(LibFunc::Func F, LibCallOptimization* Opt);
@@ -874,6 +907,7 @@ void LibCallSimplifierImpl::initOptimizations() {
   addOpt(LibFunc::strtold, &StrTo);
   addOpt(LibFunc::strtoull, &StrTo);
   addOpt(LibFunc::strspn, &StrSpn);
+  addOpt(LibFunc::strcspn, &StrCSpn);
 }
 
 Value *LibCallSimplifierImpl::optimizeCall(CallInst *CI) {
diff --git a/llvm/test/Transforms/InstCombine/disable-simplify-libcalls.ll b/llvm/test/Transforms/InstCombine/disable-simplify-libcalls.ll
index 155c97c0104c..d81e9ae5bd73 100644
--- a/llvm/test/Transforms/InstCombine/disable-simplify-libcalls.ll
+++ b/llvm/test/Transforms/InstCombine/disable-simplify-libcalls.ll
@@ -36,6 +36,7 @@ declare i64 @strtol(i8*, i8**, i32)
 declare i64 @strtoll(i8*, i8**, i32)
 declare i64 @strtoul(i8*, i8**, i32)
 declare i64 @strtoull(i8*, i8**, i32)
+declare i64 @strcspn(i8*, i8*)
 
 define double @t1(double %x) {
 ; CHECK: @t1
@@ -225,3 +226,11 @@ define i64 @t24(i8** %y) {
   ret i64 %ret
 ; CHECK: call i64 @strtoull
 }
+
+define i64 @t25(i8* %y) {
+; CHECK: @t25
+  %x = getelementptr [1 x i8]* @empty, i32 0, i32 0
+  %ret = call i64 @strcspn(i8* %x, i8* %y)
+  ret i64 %ret
+; CHECK: call i64 @strcspn
+}
diff --git a/llvm/test/Transforms/InstCombine/strcspn-1.ll b/llvm/test/Transforms/InstCombine/strcspn-1.ll
new file mode 100644
index 000000000000..60fad897b2c8
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/strcspn-1.ll
@@ -0,0 +1,57 @@
+; Test that the strcspn 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"
+
+@abcba = constant [6 x i8] c"abcba\00"
+@abc = constant [4 x i8] c"abc\00"
+@null = constant [1 x i8] zeroinitializer
+
+declare i64 @strcspn(i8*, i8*)
+
+; Check strcspn(s, "") -> strlen(s).
+
+define i64 @test_simplify1(i8* %str) {
+; CHECK: @test_simplify1
+  %pat = getelementptr [1 x i8]* @null, i32 0, i32 0
+
+  %ret = call i64 @strcspn(i8* %str, i8* %pat)
+; CHECK-NEXT: [[VAR:%[a-z]+]] = call i64 @strlen(i8* %str)
+  ret i64 %ret
+; CHECK-NEXT: ret i64 [[VAR]]
+}
+
+; Check strcspn("", s) -> 0.
+
+define i64 @test_simplify2(i8* %pat) {
+; CHECK: @test_simplify2
+  %str = getelementptr [1 x i8]* @null, i32 0, i32 0
+
+  %ret = call i64 @strcspn(i8* %str, i8* %pat)
+  ret i64 %ret
+; CHECK-NEXT: ret i64 0
+}
+
+; Check strcspn(s1, s2), where s1 and s2 are constants.
+
+define i64 @test_simplify3() {
+; CHECK: @test_simplify3
+  %str = getelementptr [6 x i8]* @abcba, i32 0, i32 0
+  %pat = getelementptr [4 x i8]* @abc, i32 0, i32 0
+
+  %ret = call i64 @strcspn(i8* %str, i8* %pat)
+  ret i64 %ret
+; CHECK-NEXT: ret i64 0
+}
+
+; Check cases that shouldn't be simplified.
+
+define i64 @test_no_simplify1(i8* %str, i8* %pat) {
+; CHECK: @test_no_simplify1
+
+  %ret = call i64 @strcspn(i8* %str, i8* %pat)
+; CHECK-NEXT: %ret = call i64 @strcspn(i8* %str, i8* %pat)
+  ret i64 %ret
+; CHECK-NEXT: ret i64 %ret
+}
diff --git a/llvm/test/Transforms/InstCombine/strcspn-2.ll b/llvm/test/Transforms/InstCombine/strcspn-2.ll
new file mode 100644
index 000000000000..4e2393686c7d
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/strcspn-2.ll
@@ -0,0 +1,21 @@
+; Test that the strcspn 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"
+
+@null = constant [1 x i8] zeroinitializer
+
+declare double @strcspn(i8*, i8*)
+
+; Check that strcspn functions with the wrong prototype aren't simplified.
+
+define double @test_no_simplify1(i8* %pat) {
+; CHECK: @test_no_simplify1
+  %str = getelementptr [1 x i8]* @null, i32 0, i32 0
+
+  %ret = call double @strcspn(i8* %str, i8* %pat)
+; CHECK-NEXT: call double @strcspn
+  ret double %ret
+; CHECK-NEXT: ret double %ret
+}
diff --git a/llvm/test/Transforms/SimplifyLibCalls/StrSpn.ll b/llvm/test/Transforms/SimplifyLibCalls/StrSpn.ll
deleted file mode 100644
index 2660ee9800a6..000000000000
--- a/llvm/test/Transforms/SimplifyLibCalls/StrSpn.ll
+++ /dev/null
@@ -1,25 +0,0 @@
-; RUN: opt < %s -simplify-libcalls -S | FileCheck %s
-
-target datalayout = "-p:64:64:64"
-
-@abcba = constant [6 x i8] c"abcba\00"
-@abc = constant [4 x i8] c"abc\00"
-@null = constant [1 x i8] zeroinitializer
-
-declare i64 @strcspn(i8*, i8*)
-
-define i64 @testcspn(i8* %s1, i8* %s2) {
-  	%abcba_p = getelementptr [6 x i8]* @abcba, i32 0, i32 0
-	%abc_p = getelementptr [4 x i8]* @abc, i32 0, i32 0
-	%null_p = getelementptr [1 x i8]* @null, i32 0, i32 0
-	%test1 = call i64 @strcspn(i8* %s1, i8* %null_p)
-; CHECK: call i64 @strlen(i8* %s1)
-	%test2 = call i64 @strcspn(i8* %null_p, i8* %s2)
-	%test3 = call i64 @strcspn(i8* %abcba_p, i8* %abc_p)
-; CHECK-NOT: call i64 @strcspn
-	%test4 = call i64 @strcspn(i8* %s1, i8* %s2)
-; CHECK: call i64 @strcspn(i8* %s1, i8* %s2)
-        %add0 = add i64 %test1, %test3
-; CHECK: add i64 %{{.+}}, 0
-	ret i64 %add0
-}