diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -2177,6 +2177,11 @@
   let HasCustomParsing = 1;
 }
 
+def SwiftPrivate : InheritableAttr {
+  let Spellings = [GNU<"swift_private">];
+  let Documentation = [SwiftPrivateDocs];
+}
+
 def NoDeref : TypeAttr {
   let Spellings = [Clang<"noderef">];
   let Documentation = [NoDerefDocs];
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -3713,6 +3713,19 @@
   }];
 }
 
+def SwiftPrivateDocs : Documentation {
+  let Category = SwiftDocs;
+  let Heading = "swift_private";
+  let Content = [{
+Declarations marked with the ``swift_private`` attribute are hidden from the
+framework client but are still made available for use within the framework or
+Swift SDK overlay.
+
+The purpose of this attribute is to permit a more idomatic implementation of
+declarations in Swift while hiding the non-idiomatic one.
+  }];
+}
+
 def OMPDeclareSimdDocs : Documentation {
   let Category = DocCatFunction;
   let Heading = "#pragma omp declare simd";
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -7899,6 +7899,9 @@
   case ParsedAttr::AT_SwiftObjCMembers:
     handleSimpleAttribute<SwiftObjCMembersAttr>(S, D, AL);
     break;
+  case ParsedAttr::AT_SwiftPrivate:
+    handleSimpleAttribute<SwiftPrivateAttr>(S, D, AL);
+    break;
 
   // XRay attributes.
   case ParsedAttr::AT_XRayLogArgs:
diff --git a/clang/test/AST/attr-swift_private.m b/clang/test/AST/attr-swift_private.m
new file mode 100644
--- /dev/null
+++ b/clang/test/AST/attr-swift_private.m
@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -ast-dump %s | FileCheck %s
+
+@interface I
+- (void)method __attribute__((__swift_private__));
+@end
+
+// CHECK: ObjCInterfaceDecl {{.*}} I
+// CHECK: ObjCMethodDecl {{.*}} method 'void'
+// CHECK: SwiftPrivateAttr
+
+@interface J : I
+- (void)method;
+@end
+
+// CHECK: ObjCInterfaceDecl {{.*}} J
+// CHECK: ObjCMethodDecl {{.*}} method 'void'
+// CHECK: SwiftPrivateAttr {{.*}} Inherited
+
+void f(void) __attribute__((__swift_private__));
+// CHECK: FunctionDecl {{.*}} f 'void (void)'
+// CHECK: SwiftPrivateAttr
+
+void f(void) {
+}
+// CHECK: FunctionDecl {{.*}} f 'void (void)'
+// CHECK: SwiftPrivateAttr {{.*}} Inherited
diff --git a/clang/test/SemaObjC/attr-swift_private.m b/clang/test/SemaObjC/attr-swift_private.m
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaObjC/attr-swift_private.m
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -verify -fsyntax-only -fobjc-arc %s
+
+__attribute__((__swift_private__))
+@protocol P
+@end
+
+__attribute__((__swift_private__))
+@interface I
+@end
+
+@interface J
+@property id property __attribute__((__swift_private__));
+- (void)instanceMethod __attribute__((__swift_private__));
++ (void)classMethod __attribute__((__swift_private__));
+@end
+
+void f(void) __attribute__((__swift_private__));
+
+struct __attribute__((__swift_private__)) S {};
+
+enum __attribute__((__swift_private__)) E {
+  one,
+  two,
+};
+
+typedef struct { } T __attribute__((__swift_private__));
+
+void g(void) __attribute__((__swift_private__("private")));
+// expected-error@-1 {{'__swift_private__' attribute takes no arguments}}