diff --git a/clang/test/CodeGen/nofpclass.c b/clang/test/CodeGen/nofpclass.c
diff --git a/llvm/include/llvm/IR/Attributes.h b/llvm/include/llvm/IR/Attributes.h
@@ -1265,6 +1265,10 @@ enum AttributeSafetyKind : uint8_t {
   ASK_ALL = ASK_SAFE_TO_DROP | ASK_UNSAFE_TO_DROP,
 };
 
+/// Returns true if this is a type legal for the 'nofpclass' attribute. This
+/// follows the same type rules as FPMathOperator.
+bool isNoFPClassCompatibleType(Type *Ty);
+
 /// Which attributes cannot be applied to a type. The argument \p ASK indicates,
 /// if only attributes that are known to be safely droppable are contained in
 /// the mask; only attributes that might be unsafe to drop (e.g., ABI-related

diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
@@ -266,16 +266,6 @@ bool Attribute::isExistingAttribute(StringRef Name) {
       .Default(false);
 }
 
-/// Returns true if this is a type legal for the 'nofpclass' attribute. This
-/// follows the same type rules as FPMathOperator.
-///
-/// TODO: Consider relaxing to any FP type struct fields.
-static bool isNoFPClassCompatibleType(Type *Ty) {
-  while (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty))
-    Ty = ArrTy->getElementType();
-  return Ty->isFPOrFPVectorTy();
-}
-
 //===----------------------------------------------------------------------===//
 // Attribute Accessor Methods
 //===----------------------------------------------------------------------===//
@@ -1850,6 +1840,9 @@ AttrBuilder &AttrBuilder::addMemoryAttr(MemoryEffects ME) {
 }
 
 AttrBuilder &AttrBuilder::addNoFPClassAttr(FPClassTest Mask) {
+  if (Mask == fcNone)
+    return *this;
+
   return addRawIntAttr(Attribute::NoFPClass, Mask);
 }
 
@@ -1935,6 +1928,16 @@ bool AttrBuilder::operator==(const AttrBuilder &B) const {
 // AttributeFuncs Function Defintions
 //===----------------------------------------------------------------------===//
 
+/// Returns true if this is a type legal for the 'nofpclass' attribute. This
+/// follows the same type rules as FPMathOperator.
+///
+/// TODO: Consider relaxing to any FP type struct fields.
+bool AttributeFuncs::isNoFPClassCompatibleType(Type *Ty) {
+  while (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty))
+    Ty = ArrTy->getElementType();
+  return Ty->isFPOrFPVectorTy();
+}
+
 /// Which attributes cannot be applied to a type.
 AttributeMask AttributeFuncs::typeIncompatible(Type *Ty,
                                                AttributeSafetyKind ASK) {

diff --git a/llvm/test/CodeGen/AMDGPU/llvm.is.fpclass.f16.ll b/llvm/test/CodeGen/AMDGPU/llvm.is.fpclass.f16.ll
diff --git a/llvm/test/CodeGen/X86/is_fpclass.ll b/llvm/test/CodeGen/X86/is_fpclass.ll
diff --git a/llvm/test/Linker/Inputs/nofpclass.ll b/llvm/test/Linker/Inputs/nofpclass.ll
@@ -0,0 +1,4 @@
+define float @declared_as_nonan(float %arg) {
+  %add = fadd float %arg, 1.0
+  ret float %add
+}
diff --git a/llvm/test/Linker/nofpclass.ll b/llvm/test/Linker/nofpclass.ll
@@ -0,0 +1,30 @@
+; RUN: llvm-link %s %S/Inputs/nofpclass.ll -S -o - | FileCheck -check-prefix=ORDER1 %s
+; RUN: llvm-link %S/Inputs/nofpclass.ll %s -S -o - | FileCheck -check-prefix=ORDER2 %s
+
+; Make sure nofpclass is dropped if the function was declared as
+; nofpclass, but not defined with nofpclass.
+
+; ORDER1: define float @caller(float %arg) {
+; ORDER1-NEXT: %result = call float @declared_as_nonan(float %arg)
+; ORDER1-NEXT: ret float %result
+
+; ORDER1: define float @declared_as_nonan(float %arg) {
+; ORDER1-NEXT: %add = fadd float %arg, 1.000000e+00
+; ORDER1-NEXT: ret float %add
+
+
+; ORDER2: define float @declared_as_nonan(float %arg) {
+; ORDER2-NEXT: %add = fadd float %arg, 1.000000e+00
+; ORDER2-NEXT: ret float %add
+
+; ORDER2: define float @caller(float %arg) {
+; ORDER2-NEXT: %result = call float @declared_as_nonan(float %arg)
+; ORDER2-NEXT: ret float %result
+
+
+declare nofpclass(nan) float @declared_as_nonan(float nofpclass(nan))
+
+define float @caller(float %arg) {
+  %result = call float @declared_as_nonan(float %arg)
+  ret float %result
+}
diff --git a/llvm/test/Transforms/Attributor/nofpclass.ll b/llvm/test/Transforms/Attributor/nofpclass.ll