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, 8 insertions, 6 deletions

diff --git a/src/data.c b/src/data.c
index 414da4cf6f7..b71d88506d0 100644
--- a/src/data.c
+++ b/src/data.c
@@ -979,18 +979,20 @@ wrong_choice (Lisp_Object choice, Lisp_Object wrong)
 {
   ptrdiff_t i = 0, len = XINT (Flength (choice));
   Lisp_Object obj, *args;
+  Lisp_Object should_be_specified = SCOPED_STRING (" should be specified");
+  Lisp_Object or = SCOPED_STRING (" or ");
+  Lisp_Object comma = SCOPED_STRING (", ");
 
   USE_SAFE_ALLOCA;
   SAFE_ALLOCA_LISP (args, len * 2 + 1);
 
-  args[i++] = build_local_string ("One of ");
+  args[i++] = SCOPED_STRING ("One of ");
 
   for (obj = choice; !NILP (obj); obj = XCDR (obj))
     {
       args[i++] = SYMBOL_NAME (XCAR (obj));
-      args[i++] = build_local_string
-        (NILP (XCDR (obj)) ? " should be specified"
-         : (NILP (XCDR (XCDR (obj))) ? " or " : ", "));
+      args[i++] = (NILP (XCDR (obj)) ? should_be_specified
+                   : NILP (XCDR (XCDR (obj))) ? or : comma);
     }
 
   obj = Fconcat (i, args);
@@ -1005,9 +1007,9 @@ static void
 wrong_range (Lisp_Object min, Lisp_Object max, Lisp_Object wrong)
 {
   xsignal2 (Qerror, Fconcat (4, ((Lisp_Object [])
-    { build_local_string ("Value should be from "),
+    { SCOPED_STRING ("Value should be from "),
       Fnumber_to_string (min),
-      build_local_string (" to "),
+      SCOPED_STRING (" to "),
       Fnumber_to_string (max) })), wrong);
 }