[COMMIT] Update a comment with a better understanding of the optimizer, bytecomp.el

APPROVE COMMIT NOTE: This patch has been committed. # HG changeset patch # User Aidan Kehoe <kehoea(a)parhasard.net&gt; # Date 1317715334 -3600 # Node ID 0b6e7ae1e78f6d81a1aab4a45315f53c894d81a6 # Parent 071b810ceb18d441cef3e92b141882ab42bc62e3 Update a comment with a better understanding of the optimizer, bytecomp.el lisp/ChangeLog addition: 2011-10-04 Aidan Kehoe <kehoea(a)parhasard.net&gt; * bytecomp.el (byte-compile-funcall): Correct a comment here, explaining why the optimizer doesn't expand (funcall #'(lambda ...)) in some contexts with inline labels, and why it's reasonable to do it here. diff -r 071b810ceb18 -r 0b6e7ae1e78f lisp/ChangeLog --- a/lisp/ChangeLog Mon Oct 03 20:16:14 2011 +0100 +++ b/lisp/ChangeLog Tue Oct 04 09:02:14 2011 +0100 ＠＠ -1,3 +1,10 ＠＠ +2011-10-04 Aidan Kehoe <kehoea(a)parhasard.net&gt; + + * bytecomp.el (byte-compile-funcall): + Correct a comment here, explaining why the optimizer doesn't + expand (funcall #'(lambda ...)) in some contexts with inline + labels, and why it's reasonable to do it here. + 2011-10-03 Aidan Kehoe <kehoea(a)parhasard.net&gt; * simple.el (handle-pre-motion-command-current-command-is-motion): diff -r 071b810ceb18 -r 0b6e7ae1e78f lisp/bytecomp.el --- a/lisp/bytecomp.el Mon Oct 03 20:16:14 2011 +0100 +++ b/lisp/bytecomp.el Tue Oct 04 09:02:14 2011 +0100 ＠＠ -4164,9 +4164,23 ＠＠ (not (eq (setq form (cons (cadadr form) (cddr form))) (setq form (byte-compile-unfold-lambda form)))) (prog1 nil (setq form `(funcall #',(car form) ,＠(cdr form)))))) - ;; Sometimes the optimizer fails to unfold well-formed calls of the - ;; form (funcall #'(lambda ...)); since we need it to do this for - ;; (declare (inline ...)) to work properly with labels, force that here. + ;; The byte-compile part of the #'labels implementation, above, + ;; happens after macroexpansion and after the source optimizer has + ;; done its thing. When labels are to be made inline we can have code + ;; that looks like (funcall #'(lambda ...) ...), when the code that + ;; the optimizer saw looked like (funcall #<compiled-function ...> + ;; ...). + ;; + ;; So, the optimizer doesn't have the opportunity to transform the + ;; former to (let (...) ...), and it's reasonable to do that here (since + ;; the labels implementation doesn't change other code that would need + ;; running through the optimizer; the lambda itself has already been + ;; through the optimizer). + ;; + ;; Equally reasonable, and conceptually a bit clearer, would be to do + ;; the transformation to (funcall #'(lambda ...) ...) in the + ;; byte-optimizer, breaking most of the #'sublis calls out of the + ;; byte-compile method. (byte-compile-form form) (mapc 'byte-compile-form (cdr form)) (byte-compile-out 'byte-call (length (cdr (cdr form)))))) -- ‘Iodine deficiency was endemic in parts of the UK until, through what has been described as “an unplanned and accidental public health triumph”, iodine was added to cattle feed to improve milk production in the 1930s.’ (EN Pearce, Lancet, June 2011) _______________________________________________ XEmacs-Patches mailing list XEmacs-Patches(a)xemacs.org http://lists.xemacs.org/mailman/listinfo/xemacs-patches