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, 4 insertions, 6 deletions

diff --git a/src/xfns.c b/src/xfns.c
index 3b094554577..f474e88ba7e 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -1570,11 +1570,9 @@ x_default_scroll_bar_color_parameter (struct frame *f,
       /* See if an X resource for the scroll bar color has been
          specified.  */
       tem = display_x_get_resource
-        (dpyinfo, build_local_string (foreground_p
-                                      ? "foreground"
-                                      : "background"),
+        (dpyinfo, SCOPED_STRING (foreground_p ? "foreground" : "background"),
          empty_unibyte_string,
-         build_local_string ("verticalScrollBar"),
+         SCOPED_STRING ("verticalScrollBar"),
          empty_unibyte_string);
       if (!STRINGP (tem))
         {
@@ -4275,8 +4273,8 @@ select_visual (struct x_display_info *dpyinfo)
 
   /* See if a visual is specified.  */
   Lisp_Object value = display_x_get_resource
-    (dpyinfo, build_local_string ("visualClass"),
-     build_local_string ("VisualClass"), Qnil, Qnil);
+    (dpyinfo, SCOPED_STRING ("visualClass"),
+     SCOPED_STRING ("VisualClass"), Qnil, Qnil);
 
   if (STRINGP (value))
     {