Hash-cons pure data.

* alloc.c (Fpurecopy): Hash-cons if requested.
(syms_of_alloc): Update purify-flag docstring.
* loadup.el: Setup hash-cons for pure data.

1 files changed, 8 insertions, 3 deletions

diff --git a/lisp/loadup.el b/lisp/loadup.el
index 85222ce7d9e..95af8cdb47e 100644
--- a/lisp/loadup.el
+++ b/lisp/loadup.el
@@ -64,6 +64,10 @@
 			    (expand-file-name "international" dir)
 			    (expand-file-name "textmodes" dir)))))
 
+(if (eq t purify-flag)
+    ;; Hash consing saved around 11% of pure space in my tests.
+    (setq purify-flag (make-hash-table :test 'equal)))
+
 (message "Using load-path %s" load-path)
 
 (if (or (member (nth 3 command-line-args) '("dump" "bootstrap"))
@@ -345,6 +349,10 @@
 ;; At this point, we're ready to resume undo recording for scratch.
 (buffer-enable-undo "*scratch*")
 
+;; Avoid error if user loads some more libraries now and make sure the
+;; hash-consing hash table is GC'd.
+(setq purify-flag nil)
+
 (if (null (garbage-collect))
     (setq pure-space-overflow t))
 
@@ -378,9 +386,6 @@
 	    (add-name-to-file "emacs" name t)))
       (kill-emacs)))
 
-;; Avoid error if user loads some more libraries now.
-(setq purify-flag nil)
-
 ;; For machines with CANNOT_DUMP defined in config.h,
 ;; this file must be loaded each time Emacs is run.
 ;; So run the startup code now.  First, remove `-l loadup' from args.