Let the OS clear new large strings of NUL

On my platform, this sped up (make-string 4000000000 0) from 2.5
to 0.015 seconds (not that people should want to do this much :-).
* src/alloc.c (allocate_string_data): New arg CLEARIT.
Callers changed.
(Fmake_string): Prefer calloc to malloc+memset when allocating a
large string of NUL bytes.
(make_clear_string): New function.
(make_uninit_string): Use it.
(make_clear_multibyte_string): New function.
(make_uninit_multibyte_string): Use it.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 36bb79d67e1..9be7bfec5c0 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3812,7 +3812,8 @@ extern void parse_str_as_multibyte (const unsigned char *, ptrdiff_t,
 /* Defined in alloc.c.  */
 extern void *my_heap_start (void);
 extern void check_pure_size (void);
-extern void allocate_string_data (struct Lisp_String *, EMACS_INT, EMACS_INT);
+extern void allocate_string_data (struct Lisp_String *, EMACS_INT, EMACS_INT,
+                                  bool);
 extern void malloc_warning (const char *);
 extern AVOID memory_full (size_t);
 extern AVOID buffer_memory_full (ptrdiff_t);