Avoid writing to purespace

* src/alloc.c (Fmake_string): Don't write to empty string contents.
(allocate_vector): Don't write to empty vector size.
* src/character.h (CHECK_CHARACTER_CAR, CHECK_CHARACTER_CDR):
Don't call unnecessary XSETCAR or XSETCDR.
* src/lisp.h (STRING_SET_UNIBYTE, STRING_SET_MULTIBYTE): Don't
write to empty string size_byte.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 995760a5019..477521bbf4e 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -1325,7 +1325,7 @@ STRING_MULTIBYTE (Lisp_Object str)
 /* Mark STR as a unibyte string.  */
 #define STRING_SET_UNIBYTE(STR)                         \
   do {                                                  \
-    if (EQ (STR, empty_multibyte_string))               \
+    if (XSTRING (STR)->size == 0)                       \
       (STR) = empty_unibyte_string;                     \
     else                                                \
       XSTRING (STR)->size_byte = -1;                    \
@@ -1335,7 +1335,7 @@ STRING_MULTIBYTE (Lisp_Object str)
    ASCII characters in advance.  */
 #define STRING_SET_MULTIBYTE(STR)                       \
   do {                                                  \
-    if (EQ (STR, empty_unibyte_string))                 \
+    if (XSTRING (STR)->size == 0)                       \
       (STR) = empty_multibyte_string;                   \
     else                                                \
       XSTRING (STR)->size_byte = XSTRING (STR)->size;   \