diff --git a/clang/include/clang/Basic/Builtins.def b/clang/include/clang/Basic/Builtins.def
--- a/clang/include/clang/Basic/Builtins.def
+++ b/clang/include/clang/Basic/Builtins.def
@@ -788,6 +788,9 @@
 BUILTIN(__builtin_index, "c*cC*i", "Fn")
 BUILTIN(__builtin_rindex, "c*cC*i", "Fn")
 
+// ignored glibc builtin, see https://sourceware.org/bugzilla/show_bug.cgi?id=25399
+BUILTIN(__warn_memset_zero_len, "v", "nU")
+
 // Microsoft builtins.  These are only active with -fms-extensions.
 LANGBUILTIN(_alloca,          "v*z", "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(__annotation,     "wC*.","n", ALL_MS_LANGUAGES)
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -3222,6 +3222,8 @@
         Builder.CreateZExt(EmitSignBit(*this, EmitScalarExpr(E->getArg(0))),
                            ConvertType(E->getType())));
   }
+  case Builtin::BI__warn_memset_zero_len:
+    return RValue::getIgnored();
   case Builtin::BI__annotation: {
     // Re-encode each wide string to UTF8 and make an MDString.
     SmallVector<Metadata *, 1> Strings;