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
@@ -2183,6 +2183,15 @@
   let Documentation = [SwiftNewTypeDocs];
 }
 
+def SwiftPrivate : InheritableAttr {
+  let Spellings = [GNU<"swift_private">];
+  let Subjects =
+      SubjectList<[Enum, Function, Struct, TypedefName,
+                   ObjCClassMethod, ObjCInstanceMethod, ObjCInterface, ObjCProperty, ObjCProtocol],
+                  ErrorDiag>;
+  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
@@ -3585,6 +3585,19 @@
   }];
 }
 
+def SwiftPrivateDocs : Documentation {
+  let Category = SwiftDocs;
+  let Heading = "swift_private";
+  let Content = [{
+Objective-C 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.
+  }];
+}
+
 def OMPDeclareSimdDocs : Documentation {
   let Category = DocCatFunction;
   let Heading = "#pragma omp declare simd";
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2610,6 +2610,8 @@
   else if (const auto *SNA = dyn_cast<SwiftNameAttr>(Attr))
     NewAttr = S.mergeSwiftNameAttr(D, *SNA,
                                    SNA->getName(), AMK == Sema::AMK_Override);
+  else if (isa<SwiftPrivateAttr>(Attr) && AMK == Sema::AMK_Override)
+    NewAttr = nullptr;
   else if (const auto *OA = dyn_cast<OptimizeNoneAttr>(Attr))
     NewAttr = S.mergeOptimizeNoneAttr(D, *OA);
   else if (const auto *InternalLinkageA = dyn_cast<InternalLinkageAttr>(Attr))
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
@@ -7853,6 +7853,9 @@
   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/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 -fblocks %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}}