From: Mattias Engdegård <mattiase@acm.org>
Date: Fri, 15 Jul 2022 19:28:30 +0000 (+0200)
Subject: Transform (list) -> nil in source optimiser
X-Git-Tag: emacs-29.0.90~1447^2~904
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=eb0e93478e423974fe6c7c7e4d183ea8d9f0e742;p=emacs.git

Transform (list) -> nil in source optimiser

This optimisation is already done in the code generator but performing
it at this earlier stage is a useful normalising step that uncovers
more opportunities.

* lisp/emacs-lisp/byte-opt.el (byte-optimize-list): New.
---

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index a24a5044562..5a138e9fee5 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -1287,6 +1287,11 @@ See Info node `(elisp) Integer Basics'."
       `(list ,(nth 1 form))
     form))
 
+(put 'list 'byte-optimizer #'byte-optimize-list)
+(defun byte-optimize-list (form)
+  ;; (list) -> nil
+  (and (cdr form) form))
+
 ;; Fixme: delete-char -> delete-region (byte-coded)
 
 (put 'set 'byte-optimizer #'byte-optimize-set)