Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -231,9 +231,12 @@
   let KnownToGCC = 1;
 }
 
-// The Clang spelling implies GNU<name> and CXX11<"clang", name>. This spelling
-// should be used for any Clang-specific attributes.
-class Clang<string name> : Spelling<name, "Clang">;
+// The Clang spelling implies GNU<name>, CXX11<"clang", name>, and optionally,
+// C2x<"clang", name>. This spelling should be used for any Clang-specific
+// attributes.
+class Clang<string name, bit includeC = 0> : Spelling<name, "Clang"> {
+  bit IncludeC = includeC;
+}
 
 class Accessor<string name, list<Spelling> spellings> {
   string Name = name;
@@ -604,7 +607,7 @@
 }
 
 def Annotate : InheritableParamAttr {
-  let Spellings = [Clang<"annotate">];
+  let Spellings = [Clang<"annotate", 1>];
   let Args = [StringArgument<"Annotation">];
   // Ensure that the annotate attribute can be used with
   // '#pragma clang attribute' even though it has no subject list.
Index: test/Sema/annotate.c
===================================================================
--- test/Sema/annotate.c
+++ test/Sema/annotate.c
@@ -1,9 +1,13 @@
-// RUN: %clang_cc1 %s -fsyntax-only -verify
+// RUN: %clang_cc1 %s -fsyntax-only -fdouble-square-bracket-attributes -verify
 
 void __attribute__((annotate("foo"))) foo(float *a) {
   __attribute__((annotate("bar"))) int x;
+  [[clang::annotate("bar")]] int x2;
   __attribute__((annotate(1))) int y; // expected-error {{'annotate' attribute requires a string}}
+  [[clang::annotate(1)]] int y2; // expected-error {{'annotate' attribute requires a string}}
   __attribute__((annotate("bar", 1))) int z; // expected-error {{'annotate' attribute takes one argument}}
+  [[clang::annotate("bar", 1)]] int z2; // expected-error {{'annotate' attribute takes one argument}}
+
   int u = __builtin_annotation(z, (char*) 0); // expected-error {{second argument to __builtin_annotation must be a non-wide string constant}}
   int v = __builtin_annotation(z, (char*) L"bar"); // expected-error {{second argument to __builtin_annotation must be a non-wide string constant}}
   int w = __builtin_annotation(z, "foo");
Index: utils/TableGen/ClangAttrEmitter.cpp
===================================================================
--- utils/TableGen/ClangAttrEmitter.cpp
+++ utils/TableGen/ClangAttrEmitter.cpp
@@ -87,6 +87,8 @@
     } else if (Variety == "Clang") {
       Ret.emplace_back("GNU", Name, "", false);
       Ret.emplace_back("CXX11", Name, "clang", false);
+      if (Spelling->getValueAsBit("IncludeC"))
+        Ret.emplace_back("C2x", Name, "clang", false);
     } else
       Ret.push_back(FlattenedSpelling(*Spelling));
   }