Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -2130,6 +2130,12 @@
   let ASTNode = 0;
 }
 
+def SwiftBridgedTypedef : Attr {
+  let Spellings = [GNU<"swift_bridged_typedef">];
+  let Subjects = SubjectList<[TypedefName], ErrorDiag>;
+  let Documentation = [SwiftBridgedTypedefDocs];
+}
+
 def SwiftObjCMembers : Attr {
   let Spellings = [GNU<"swift_objc_members">];
   let Subjects = SubjectList<[ObjCInterface], ErrorDiag>;
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -3476,6 +3476,27 @@
   }];
 }
 
+def SwiftBridgedTypedefDocs : Documentation {
+  let Category = SwiftDocs;
+  let Heading = "swift_bridged";
+  let Content = [{
+The ``swift_bridged_typedef`` attribute indicates that when the typedef to which
+the attribute appertains is imported into Swift, it should refer to the bridged
+Swift type (e.g. Swift's ``String``) rather than the Objective-C type as written
+(e.g. ``NSString``).
+
+  .. code-block:: c
+
+    @interface NSString;
+    typedef NSString *AliasedString __attribute__((__swift_bridged_typedef__));
+
+    extern void acceptsAliasedString(AliasedString _Nonnull parameter);
+
+In this case, the function ``acceptsAliasedString`` will be imported into Swift
+as a function which accepts a ``String`` type parameter.
+  }];
+}
+
 def SwiftObjCMembersDocs : Documentation {
   let Category = SwiftDocs;
   let Heading = "swift_objc_members";
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -7533,6 +7533,9 @@
     break;
 
   // Swift attributes.
+  case ParsedAttr::AT_SwiftBridgedTypedef:
+    handleSimpleAttribute<SwiftBridgedTypedefAttr>(S, D, AL);
+    break;
   case ParsedAttr::AT_SwiftError:
     handleSwiftError(S, D, AL);
     break;
Index: clang/test/Misc/pragma-attribute-supported-attributes-list.test
===================================================================
--- clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -146,6 +146,7 @@
 // CHECK-NEXT: Section (SubjectMatchRule_function, SubjectMatchRule_variable_is_global, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property)
 // CHECK-NEXT: SetTypestate (SubjectMatchRule_function_is_member)
 // CHECK-NEXT: SpeculativeLoadHardening (SubjectMatchRule_function, SubjectMatchRule_objc_method)
+// CHECK-NEXT: SwiftBridgedTypedef (SubjectMatchRule_type_alias)
 // CHECK-NEXT: SwiftContext (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: SwiftError (SubjectMatchRule_function, SubjectMatchRule_objc_method)
 // CHECK-NEXT: SwiftErrorResult (SubjectMatchRule_variable_is_parameter)
Index: clang/test/SemaObjC/attr-swift_bridged_typedef.m
===================================================================
--- /dev/null
+++ clang/test/SemaObjC/attr-swift_bridged_typedef.m
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -verify -fsyntax-only %s
+
+@interface NSString
+@end
+
+typedef NSString *NSStringAlias __attribute__((__swift_bridged_typedef__));
+
+typedef int IntAlias __attribute__((__swift_bridged_typedef__));
+
+struct __attribute__((swift_bridged_typedef)) S {};
+// expected-error@-1 {{'swift_bridged_typedef' attribute only applies to typedefs}}
+
+// expected-error@+1 {{'__swift_bridged_typedef__' attribute takes no arguments}}
+typedef unsigned char UnsignedChar __attribute__((__swift_bridged_typedef__("UnsignedChar")));