Index: lib/CodeGen/MicrosoftCXXABI.cpp
===================================================================
--- lib/CodeGen/MicrosoftCXXABI.cpp
+++ lib/CodeGen/MicrosoftCXXABI.cpp
@@ -827,6 +827,7 @@
     return RAA_Default;
 
   case llvm::Triple::x86_64:
+  case llvm::Triple::aarch64:
     return !canCopyArgument(RD) ? RAA_Indirect : RAA_Default;
   }
 
Index: test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp
===================================================================
--- test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp
+++ test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp
@@ -2,6 +2,7 @@
 // RUN: %clang_cc1 -std=c++11 -emit-llvm %s -o - -triple=i386-pc-win32 -mconstructor-aliases -fno-rtti | FileCheck -check-prefix WIN32 %s
 // RUN: %clang_cc1 -std=c++11 -emit-llvm %s -o - -triple=thumb-pc-win32 -mconstructor-aliases -fno-rtti | FileCheck -check-prefix WOA %s
 // RUN: %clang_cc1 -std=c++11 -emit-llvm %s -o - -triple=x86_64-pc-win32 -mconstructor-aliases -fno-rtti | FileCheck -check-prefix WIN64 %s
+// RUN: %clang_cc1 -std=c++11 -emit-llvm %s -o - -triple=aarch64-windows-msvc -mconstructor-aliases -fno-rtti | FileCheck -check-prefix WOA64 %s
 
 struct Empty {};
 
@@ -227,12 +228,14 @@
 // LINUX-LABEL: define void @_Z22small_arg_with_vftable16SmallWithVftable(%struct.SmallWithVftable* %s)
 // WIN32: define dso_local void @"?small_arg_with_vftable@@YAXUSmallWithVftable@@@Z"(<{ %struct.SmallWithVftable }>* inalloca)
 // WIN64: define dso_local void @"?small_arg_with_vftable@@YAXUSmallWithVftable@@@Z"(%struct.SmallWithVftable* %s)
+// WOA64: define dso_local void @"?small_arg_with_vftable@@YAXUSmallWithVftable@@@Z"(%struct.SmallWithVftable* %s)
 
 void medium_arg_with_copy_ctor(MediumWithCopyCtor s) {}
 // LINUX-LABEL: define void @_Z25medium_arg_with_copy_ctor18MediumWithCopyCtor(%struct.MediumWithCopyCtor* %s)
 // WIN32: define dso_local void @"?medium_arg_with_copy_ctor@@YAXUMediumWithCopyCtor@@@Z"(<{ %struct.MediumWithCopyCtor }>* inalloca)
 // WIN64: define dso_local void @"?medium_arg_with_copy_ctor@@YAXUMediumWithCopyCtor@@@Z"(%struct.MediumWithCopyCtor* %s)
 // WOA: define dso_local arm_aapcs_vfpcc void @"?medium_arg_with_copy_ctor@@YAXUMediumWithCopyCtor@@@Z"(%struct.MediumWithCopyCtor* %s)
+// WOA64: define dso_local void @"?medium_arg_with_copy_ctor@@YAXUMediumWithCopyCtor@@@Z"(%struct.MediumWithCopyCtor* %s)
 
 void big_arg(Big s) {}
 // LINUX-LABEL: define void @_Z7big_arg3Big(%struct.Big* byval align 4 %s)