Index: clang/lib/AST/Interp/ByteCodeExprGen.cpp
===================================================================
--- clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -1856,6 +1856,9 @@
   case UO_Real:   // __real x
   case UO_Imag:   // __imag x
   case UO_Extension:
+    if (DiscardResult)
+      return this->discard(SubExpr);
+    return this->visit(SubExpr);
   case UO_Coawait:
     assert(false && "Unhandled opcode");
   }
Index: clang/test/AST/Interp/literals.cpp
===================================================================
--- clang/test/AST/Interp/literals.cpp
+++ clang/test/AST/Interp/literals.cpp
@@ -782,6 +782,12 @@
 
 namespace PredefinedExprs {
   constexpr char heh(unsigned index) {
+#if __cplusplus >= 201402L
+    __FUNCTION__;               // ref-warning {{result unused}} \
+                                // expected-warning {{result unused}}
+    __extension__ __FUNCTION__; // ref-warning {{result unused}} \
+                                // expected-warning {{result unused}}
+#endif
     return __FUNCTION__[index];
   }
   static_assert(heh(0) == 'h', "");