Index: libcxx/CMakeLists.txt
===================================================================
--- libcxx/CMakeLists.txt
+++ libcxx/CMakeLists.txt
@@ -120,6 +120,7 @@
 option(LIBCXX_ABI_UNSTABLE "Unstable ABI of libc++." OFF)
 option(LIBCXX_ABI_FORCE_ITANIUM "Ignore auto-detection and force use of the Itanium ABI.")
 option(LIBCXX_ABI_FORCE_MICROSOFT "Ignore auto-detection and force use of the Microsoft ABI.")
+option(LIBCXX_ABI_HIDDEN_USE_INTERNAL_LINKAGE "Give internal linkage to symbols that are not part of the ABI" OFF)
 set(LIBCXX_ABI_DEFINES "" CACHE STRING "A semicolon separated list of ABI macros to define in the site config header.")
 option(LIBCXX_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)
 
@@ -662,6 +663,7 @@
 config_define_if(LIBCXX_ABI_UNSTABLE _LIBCPP_ABI_UNSTABLE)
 config_define_if(LIBCXX_ABI_FORCE_ITANIUM _LIBCPP_ABI_FORCE_ITANIUM)
 config_define_if(LIBCXX_ABI_FORCE_MICROSOFT _LIBCPP_ABI_FORCE_MICROSOFT)
+config_define_if(LIBCXX_ABI_HIDDEN_USE_INTERNAL_LINKAGE _LIBCPP_ABI_HIDDEN_USE_INTERNAL_LINKAGE)
 
 config_define_if_not(LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE)
 config_define_if_not(LIBCXX_ENABLE_STDIN _LIBCPP_HAS_NO_STDIN)
Index: libcxx/docs/BuildingLibcxx.rst
===================================================================
--- libcxx/docs/BuildingLibcxx.rst
+++ libcxx/docs/BuildingLibcxx.rst
@@ -351,6 +351,15 @@
   Build the "unstable" ABI version of libc++. Includes all ABI changing features
   on top of the current stable version.
 
+.. option:: LIBCXX_ABI_HIDDEN_USE_INTERNAL_LINKAGE:BOOL
+
+  **Default**: ``OFF``
+
+  Give internal linkage to all symbols that are not part of the ABI. This
+  allows linking translation units built with different versions of libc++
+  together, at the cost of code bloat (because non exported functions are
+  duplicated in each TU).
+
 .. option:: LIBCXX_ABI_DEFINES:STRING
 
   **Default**: ``""``
Index: libcxx/docs/DesignDocs/VisibilityMacros.rst
===================================================================
--- libcxx/docs/DesignDocs/VisibilityMacros.rst
+++ libcxx/docs/DesignDocs/VisibilityMacros.rst
@@ -42,9 +42,7 @@
 
 **_LIBCPP_HIDE_FROM_ABI**
   Mark a function as not being part of the ABI of any final linked image that
-  uses it, and also as being internal to each TU that uses that function. In
-  other words, the address of a function marked with this attribute is not
-  guaranteed to be the same across translation units.
+  uses it.
 
 **_LIBCPP_HIDE_FROM_ABI_AFTER_V1**
   Mark a function as being hidden from the ABI (per `_LIBCPP_HIDE_FROM_ABI`)
@@ -61,6 +59,21 @@
   ABI, we should create a new _LIBCPP_HIDE_FROM_ABI_AFTER_XXX macro, and we can
   use it to start removing symbols from the ABI after that stable version.
 
+**_LIBCPP_ABI_HIDDEN_USE_INTERNAL_LINKAGE**
+  This macro controls whether symbols hidden from the ABI with `_LIBCPP_HIDE_FROM_ABI`
+  are local to each translation unit in addition to being local to each final
+  linked image. When enabled, this means that translation units compiled
+  with different versions of libc++ can be linked together, since all non
+  ABI-facing functions are local to each translation unit. This allows static
+  archives built with different versions of libc++ to be linked together. This
+  also means that functions marked with `_LIBCPP_HIDE_FROM_ABI` are not guaranteed
+  to have the same address across translation unit boundaries.
+
+  When the macro is not defined (the default), there is no guarantee that
+  translation units compiled with different versions of libc++ can interoperate.
+  However, this leads to code size improvements, since non ABI-facing functions
+  can be deduplicated across translation unit boundaries.
+
 **_LIBCPP_TYPE_VIS**
   Mark a type's typeinfo, vtable and members as having default visibility.
   This attribute cannot be used on class templates.
Index: libcxx/include/__config
===================================================================
--- libcxx/include/__config
+++ libcxx/include/__config
@@ -796,7 +796,11 @@
 #endif
 
 #ifndef _LIBCPP_HIDE_FROM_ABI
-#  define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_INTERNAL_LINKAGE
+#  ifdef _LIBCPP_ABI_HIDDEN_USE_INTERNAL_LINKAGE
+#    define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_INTERNAL_LINKAGE
+#  else
+#    define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_ALWAYS_INLINE
+#  endif
 #endif
 
 #ifdef _LIBCPP_BUILDING_LIBRARY
Index: libcxx/include/__config_site.in
===================================================================
--- libcxx/include/__config_site.in
+++ libcxx/include/__config_site.in
@@ -14,6 +14,7 @@
 #cmakedefine _LIBCPP_ABI_UNSTABLE
 #cmakedefine _LIBCPP_ABI_FORCE_ITANIUM
 #cmakedefine _LIBCPP_ABI_FORCE_MICROSOFT
+#cmakedefine _LIBCPP_ABI_HIDDEN_USE_INTERNAL_LINKAGE
 #cmakedefine _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 #cmakedefine _LIBCPP_HAS_NO_STDIN
 #cmakedefine _LIBCPP_HAS_NO_STDOUT