Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -723,6 +723,7 @@
              .Case("macos_app_extension", "macOS (App Extension)")
              .Case("tvos_app_extension", "tvOS (App Extension)")
              .Case("watchos_app_extension", "watchOS (App Extension)")
+             .Case("swift", "Swift")
              .Default(llvm::StringRef());
 }
 static llvm::StringRef getPlatformNameSourceSpelling(llvm::StringRef Platform) {
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -2993,6 +2993,9 @@
   InGroup<Availability>;
 def note_overridden_method : Note<
   "overridden method is here">;
+def warn_availability_swift_unavailable_deprecated_only : Warning<
+  "only 'unavailable' and 'deprecated' are supported for Swift availability">,
+  InGroup<Availability>;
 def note_protocol_method : Note<
   "protocol method is here">;
 
Index: include/clang/Basic/Features.def
===================================================================
--- include/clang/Basic/Features.def
+++ include/clang/Basic/Features.def
@@ -51,6 +51,7 @@
 FEATURE(attribute_availability_with_strict, true)
 FEATURE(attribute_availability_with_replacement, true)
 FEATURE(attribute_availability_in_templates, true)
+FEATURE(attribute_availability_swift, true)
 FEATURE(attribute_cf_returns_not_retained, true)
 FEATURE(attribute_cf_returns_retained, true)
 FEATURE(attribute_cf_returns_on_parameters, true)
Index: lib/Parse/ParseDecl.cpp
===================================================================
--- lib/Parse/ParseDecl.cpp
+++ lib/Parse/ParseDecl.cpp
@@ -1001,6 +1001,21 @@
       continue;
     }
 
+    if (Keyword == Ident_deprecated && Platform->Ident &&
+        Platform->Ident->isStr("swift")) {
+      // For swift, we deprecate for all versions.
+      if (Changes[Deprecated].KeywordLoc.isValid()) {
+        Diag(KeywordLoc, diag::err_availability_redundant)
+          << Keyword
+          << SourceRange(Changes[Deprecated].KeywordLoc);
+      }
+
+      Changes[Deprecated].KeywordLoc = KeywordLoc;
+      // Use a fake version here.
+      Changes[Deprecated].Version = VersionTuple(1);
+      continue;
+    }
+
     if (Tok.isNot(tok::equal)) {
       Diag(Tok, diag::err_expected_after) << Keyword << tok::equal;
       SkipUntil(tok::r_paren, StopAtSemi);
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -2410,6 +2410,15 @@
   if (const auto *SE = dyn_cast_or_null<StringLiteral>(AL.getReplacementExpr()))
     Replacement = SE->getString();
 
+  if (II->isStr("swift")) {
+    if (Introduced.isValid() || Obsoleted.isValid() ||
+        (!IsUnavailable && !Deprecated.isValid())) {
+      S.Diag(AL.getLoc(),
+             diag::warn_availability_swift_unavailable_deprecated_only);
+      return;
+    }
+  }
+
   AvailabilityAttr *NewAttr = S.mergeAvailabilityAttr(ND, AL.getRange(), II,
                                                       false/*Implicit*/,
                                                       Introduced.Version,
Index: test/Index/availability.c
===================================================================
--- test/Index/availability.c
+++ test/Index/availability.c
@@ -14,9 +14,14 @@
 
 void bar2(void) __attribute__((availability(macosx,introduced=10.4,deprecated=10.5,obsoleted=10.7))) __attribute__((availability(ios,introduced=3.2,deprecated=10.0))) __attribute__((availability(macosx,introduced=10.4,deprecated=10.5,obsoleted=10.7))) __attribute__((availability(ios,introduced=3.2,deprecated=10.0)));
 
+void foo2(void) __attribute__((availability(swift,unavailable)));
+void foo3(void) __attribute__((availability(swift,deprecated)));
+
 // RUN: c-index-test -test-load-source all %s | FileCheck %s
 // CHECK: FunctionDecl=foo:3:6{{.*}}(ios, introduced=3.2, deprecated=4.1) (macos, introduced=10.4, deprecated=10.5, obsoleted=10.7)
 // CHECK: EnumConstantDecl=old_enum:6:3 (Definition) (deprecated)
 // CHECK: EnumConstantDecl=old_enum_plat:10:3 {{.*}} (macos, introduced=10.4, deprecated=10.5, obsoleted=10.7)
 // CHECK: FunctionDecl=bar:13:6{{.*}}(ios, introduced=3.2) (macos, introduced=10.4, deprecated=10.5, obsoleted=10.6, message="use foobar")
 // CHECK: FunctionDecl=bar2:15:6{{.*}}(ios, introduced=3.2, deprecated=10.0) (macos, introduced=10.4, deprecated=10.5, obsoleted=10.7)
+// CHECK: FunctionDecl=foo2:17:6{{.*}}(swift, unavailable)
+// CHECK: FunctionDecl=foo3:18:6{{.*}}(swift, deprecated=1)
Index: test/Sema/attr-availability-swift.c
===================================================================
--- test/Sema/attr-availability-swift.c
+++ test/Sema/attr-availability-swift.c
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin9 -fsyntax-only -fblocks -verify %s
+// RUN: %clang_cc1 -triple x86_64-apple-darwin9 -fsyntax-only -ast-dump %s | FileCheck %s
+//
+
+#if !__has_feature(attribute_availability_with_message)
+# error "Missing __has_feature"
+#endif
+
+#if __has_feature(attribute_availability_swift)
+# warning "okay"
+// expected-warning@-1{{okay}}
+#else
+# error "Missing __has_feature"
+#endif
+
+extern int noSwiftGlobal1 __attribute__((availability(swift, unavailable)));
+// CHECK: AvailabilityAttr {{.*}}swift 0 0 0 Unavailable "" ""
+extern int noSwiftGlobal1 __attribute__((availability(macosx, introduced=10.1))); // okay
+// CHECK: AvailabilityAttr {{.*}}Inherited swift 0 0 0 Unavailable "" ""
+// CHECK: AvailabilityAttr {{.*}}macos 10.1 0 0 "" ""
+extern int noSwiftGlobal1 __attribute__((availability(swift, unavailable, message="and this one has a message"))); // okay
+// CHECK: AvailabilityAttr {{.*}}Inherited macos 10.1 0 0 "" ""
+// CHECK: AvailabilityAttr {{.*}}swift 0 0 0 Unavailable "and this one has a message" ""
+extern int noSwiftGlobal2 __attribute__((availability(swift, introduced=5))); // expected-warning{{only 'unavailable' and 'deprecated' are supported for Swift availability}}
+// CHECK: VarDecl
+// CHECK-NOT: AvailabilityAttr
+extern int noSwiftGlobal3 __attribute__((availability(swift, deprecated, message="t")));
+// CHECK: VarDecl
+// CHECK: AvailabilityAttr {{.*}}swift 0 1 0 "t" ""