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, 6 insertions, 6 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 39d08950bf8..9d376346a0a 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1552,10 +1552,10 @@ exists, return the buffer `*scratch*' (creating it if necessary).  */)
     return notsogood;
   else
     {
-      buf = Fget_buffer (build_local_string ("*scratch*"));
+      buf = Fget_buffer (SCOPED_STRING ("*scratch*"));
       if (NILP (buf))
         {
-          buf = Fget_buffer_create (build_local_string ("*scratch*"));
+          buf = Fget_buffer_create (SCOPED_STRING ("*scratch*"));
           Fset_buffer_major_mode (buf);
         }
       return buf;
@@ -1575,10 +1575,10 @@ other_buffer_safely (Lisp_Object buffer)
     if (candidate_buffer (buf, buffer))
       return buf;
 
-  buf = Fget_buffer (build_local_string ("*scratch*"));
+  buf = Fget_buffer (SCOPED_STRING ("*scratch*"));
   if (NILP (buf))
     {
-      buf = Fget_buffer_create (build_local_string ("*scratch*"));
+      buf = Fget_buffer_create (SCOPED_STRING ("*scratch*"));
       Fset_buffer_major_mode (buf);
     }
 
@@ -5289,7 +5289,7 @@ init_buffer (int initialized)
   (void) initialized;
 #endif /* USE_MMAP_FOR_BUFFERS */
 
-  Fset_buffer (Fget_buffer_create (build_local_string ("*scratch*")));
+  Fset_buffer (Fget_buffer_create (SCOPED_STRING ("*scratch*")));
   if (NILP (BVAR (&buffer_defaults, enable_multibyte_characters)))
     Fset_buffer_multibyte (Qnil);
 
@@ -5328,7 +5328,7 @@ init_buffer (int initialized)
       && strcmp ("/", SSDATA (BVAR (current_buffer, directory))))
     bset_directory
       (current_buffer,
-       concat2 (build_local_string ("/:"), BVAR (current_buffer, directory)));
+       concat2 (SCOPED_STRING ("/:"), BVAR (current_buffer, directory)));
 
   temp = get_minibuffer (0);
   bset_directory (XBUFFER (temp), BVAR (current_buffer, directory));