Index: lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3282,6 +3282,13 @@
       return replaceInstUsesWith(*II, FCmp);
     }
 
+    // fp_class (nnan x), qnan|snan|other -> fp_class (nnan x), other
+    if (((Mask & S_NAN) || (Mask & Q_NAN)) && isKnownNeverNaN(Src0, &TLI)) {
+      II->setArgOperand(1, ConstantInt::get(Src1->getType(),
+                                            Mask & ~(S_NAN | Q_NAN)));
+      return II;
+    }
+
     const ConstantFP *CVal = dyn_cast<ConstantFP>(Src0);
     if (!CVal) {
       if (isa<UndefValue>(Src0))
Index: test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll
===================================================================
--- test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll
+++ test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll
@@ -625,6 +625,39 @@
   ret i1 %val
 }
 
+; CHECK-LABEL: @test_class_is_snan_nnan_src(
+; CHECK-NEXT: ret i1 false
+define i1 @test_class_is_snan_nnan_src(float %x) {
+  %nnan = fadd nnan float %x, 1.0
+  %class = call i1 @llvm.amdgcn.class.f32(float %nnan, i32 1)
+  ret i1 %class
+}
+
+; CHECK-LABEL: @test_class_is_qnan_nnan_src(
+; CHECK-NEXT: ret i1 false
+define i1 @test_class_is_qnan_nnan_src(float %x) {
+  %nnan = fadd nnan float %x, 1.0
+  %class = call i1 @llvm.amdgcn.class.f32(float %nnan, i32 2)
+  ret i1 %class
+}
+
+; CHECK-LABEL: @test_class_is_nan_nnan_src(
+; CHECK-NEXT: ret i1 false
+define i1 @test_class_is_nan_nnan_src(float %x) {
+  %nnan = fadd nnan float %x, 1.0
+  %class = call i1 @llvm.amdgcn.class.f32(float %nnan, i32 3)
+  ret i1 %class
+}
+
+; CHECK-LABEL: @test_class_is_nan_other_nnan_src(
+; CHECK-NEXT: %nnan = fadd nnan float %x, 1.000000e+00
+; CHECK-NEXT: %class = call i1 @llvm.amdgcn.class.f32(float %nnan, i32 264)
+define i1 @test_class_is_nan_other_nnan_src(float %x) {
+  %nnan = fadd nnan float %x, 1.0
+  %class = call i1 @llvm.amdgcn.class.f32(float %nnan, i32 267)
+  ret i1 %class
+}
+
 ; --------------------------------------------------------------------
 ; llvm.amdgcn.cos
 ; --------------------------------------------------------------------