Simplify stack-allocated Lisp objects, and make them more portable.

The build_local_string macro was used in two ways: (1) string
literals for which scoped allocation suffices, and (2) file name
components, where it's not safe in general to assume bounded-size
ASCII data.  Simplify by defining a new macro SCOPED_STRING that
allocates a block-scope string, and by using SCOPED_STRING for (1)
and build_string for (2).  Furthermore, actually use stack
allocation only for objects known to have sufficient alignment.
This simpler implementation means Emacs can make
USE_STACK_LISP_OBJECTS the default unless GC_MARK_STACK !=
GC_MAKE_GCPROS_NOOPS.
* lisp.h (GCALIGNED): Align even if !USE_STACK_LISP_OBJECTS,
for fewer differences among implementations.
(struct Lisp_String): Now GCALIGNED.
(USE_STACK_LISP_OBJECTS): Default to true, since the
implementation no longer insists on a nonempty GCALIGNED.
But make it false if GC_MARK_STACK != GC_MAKE_GCPROS_NOOPS.
(SCOPED_CONS_INITIALIZER): Remove, since it's no longer needed
separately.  Move definiens to scoped_cons.  The old definition
was incorrect when GCALIGNED was defined to be empty.
(union Aligned_String): New type.
(USE_STACK_CONS, USE_STACK_STRING): New constants, so that the
implementation ports to compilers that don't align strictly enough.
Don't worry about the union sizes; it's not worth bothering about.
(scoped_cons, scoped_list1, scoped_list3, scoped_list4):
Rewrite using USE_STACK_CONS.
(scoped_cons): Assume the use of union Aligned_Cons.
(lisp_string_size, make_local_string, build_local_string): Remove.
Unless otherwise specified, all callers of build_local_string
changed to use SCOPED_STRING.
(SCOPED_STRING): New macro.
* data.c (wrong_choice):
* menu.c (single_menu_item):
* process.c (Fformat_network_address):
Hoist use of SCOPED_STRING out of a scope, so that its returned
object lives long enough.
* fileio.c (Fexpand_file_name): Use build_string, not SCOPED_STRING,
as the string might be long or might not be ASCII.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/xselect.c b/src/xselect.c
index 0bc7fbc204a..d90d056e960 100644
--- a/src/xselect.c
+++ b/src/xselect.c
@@ -2160,7 +2160,7 @@ static Lisp_Object
 x_clipboard_manager_error_1 (Lisp_Object err)
 {
   Fmessage (2, ((Lisp_Object [])
-    { build_local_string ("X clipboard manager error: %s\n\
+    { SCOPED_STRING ("X clipboard manager error: %s\n\
 If the problem persists, set `x-select-enable-clipboard-manager' to nil."),
       CAR (CDR (err)) }));
   return Qnil;
@@ -2230,7 +2230,7 @@ x_clipboard_manager_save_all (void)
       if (FRAME_LIVE_P (XFRAME (local_frame)))
         {
           Fmessage (1, ((Lisp_Object [])
-            { build_local_string
+            { SCOPED_STRING
                 ("Saving clipboard to X clipboard manager...") }));
           internal_condition_case_1 (x_clipboard_manager_save, local_frame,
                                      Qt, x_clipboard_manager_error_2);