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, 7 insertions, 7 deletions

diff --git a/src/fileio.c b/src/fileio.c
index 13e2c889020..2590942d42e 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -1111,7 +1111,7 @@ filesystem tree, not (expand-file-name ".."  dirname).  */)
 
               name = make_specified_string (nm, -1, p - nm, multibyte);
               temp[0] = DRIVE_LETTER (drive);
-              name = concat2 (build_local_string (temp), name);
+              name = concat2 (SCOPED_STRING (temp), name);
             }
 #ifdef WINDOWSNT
           if (!NILP (Vw32_downcase_file_names))
@@ -1162,11 +1162,11 @@ filesystem tree, not (expand-file-name ".."  dirname).  */)
               char newdir_utf8[MAX_UTF8_PATH];
 
               filename_from_ansi (newdir, newdir_utf8);
-              tem = build_local_string (newdir_utf8);
+              tem = build_string (newdir_utf8);
             }
           else
 #endif
-            tem = build_local_string (newdir);
+            tem = build_string (newdir);
           newdirlim = newdir + SBYTES (tem);
           if (multibyte && !STRING_MULTIBYTE (tem))
             {
@@ -1198,7 +1198,7 @@ filesystem tree, not (expand-file-name ".."  dirname).  */)
               /* `getpwnam' may return a unibyte string, which will
                  bite us since we expect the directory to be
                  multibyte.  */
-              tem = build_local_string (newdir);
+              tem = build_string (newdir);
               newdirlim = newdir + SBYTES (tem);
               if (multibyte && !STRING_MULTIBYTE (tem))
                 {
@@ -1231,7 +1231,7 @@ filesystem tree, not (expand-file-name ".."  dirname).  */)
             adir = NULL;
           else if (multibyte)
             {
-              Lisp_Object tem = build_local_string (adir);
+              Lisp_Object tem = build_string (adir);
 
               tem = DECODE_FILE (tem);
               newdirlim = adir + SBYTES (tem);
@@ -1334,7 +1334,7 @@ filesystem tree, not (expand-file-name ".."  dirname).  */)
             getcwd (adir, adir_size);
           if (multibyte)
             {
-              Lisp_Object tem = build_local_string (adir);
+              Lisp_Object tem = build_string (adir);
 
               tem = DECODE_FILE (tem);
               newdirlim = adir + SBYTES (tem);
@@ -5420,7 +5420,7 @@ auto_save_error (Lisp_Object error_val)
   ring_bell (XFRAME (selected_frame));
 
   msg = Fformat (3, ((Lisp_Object [])
-    { build_local_string ("Auto-saving %s: %s"),
+    { SCOPED_STRING ("Auto-saving %s: %s"),
       BVAR (current_buffer, name),
       Ferror_message_string (error_val) }));
   GCPRO1 (msg);