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, 3 insertions, 3 deletions

diff --git a/src/keymap.c b/src/keymap.c
index ed572a5a8c1..368903db5e6 100644
--- a/src/keymap.c
+++ b/src/keymap.c
@@ -1338,7 +1338,7 @@ silly_event_symbol_error (Lisp_Object c)
       *p = 0;
 
       c = reorder_modifiers (c);
-      keystring = concat2 (build_local_string (new_mods), XCDR (assoc));
+      keystring = concat2 (SCOPED_STRING (new_mods), XCDR (assoc));
 
       error ("To bind the key %s, use [?%s], not [%s]",
              SDATA (SYMBOL_NAME (c)), SDATA (keystring),
@@ -2243,7 +2243,7 @@ around function keys and event symbols.  */)
   if (CONSP (key) && INTEGERP (XCAR (key)) && INTEGERP (XCDR (key)))
     /* An interval from a map-char-table.  */
     return concat3 (Fsingle_key_description (XCAR (key), no_angles),
-                    build_local_string (".."),
+                    SCOPED_STRING (".."),
                     Fsingle_key_description (XCDR (key), no_angles));
 
   key = EVENT_HEAD (key);
@@ -3441,7 +3441,7 @@ describe_vector (Lisp_Object vector, Lisp_Object prefix, Lisp_Object args,
         {
           Lisp_Object tem;
           tem = Fkey_description (prefix, Qnil);
-          elt_prefix = concat2 (tem, build_local_string (" "));
+          elt_prefix = concat2 (tem, SCOPED_STRING (" "));
         }
       prefix = Qnil;
     }