From: Mattias Engdegård <mattiase@acm.org>
Date: Tue, 20 Jul 2021 13:46:32 +0000 (+0200)
Subject: Strength-reduce (eq X nil) to (not X)
X-Git-Tag: emacs-28.0.90~1780
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=46d7d44894843bf30e9bc84473195c6ab892b752;p=emacs.git

Strength-reduce (eq X nil) to (not X)

* lisp/emacs-lisp/byte-opt.el (byte-optimize-eq): New optimisation,
which results in better test and branch code generation where it
applies.
---

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index 2fff0bd4a5f..7ed04b32e97 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -969,6 +969,12 @@ See Info node `(elisp) Integer Basics'."
      ;; Arity errors reported elsewhere.
      form)))
 
+(defun byte-optimize-eq (form)
+  (byte-optimize-binary-predicate
+   (pcase (cdr form)
+     ((or `(,x nil) `(nil ,x)) `(not ,x))
+     (_ form))))
+
 (defun byte-optimize-member (form)
   ;; Replace `member' or `memql' with `memq' if the first arg is a symbol,
   ;; or the second arg is a list of symbols.  Same with fixnums.
@@ -1056,7 +1062,7 @@ See Info node `(elisp) Integer Basics'."
 (put 'min 'byte-optimizer #'byte-optimize-min-max)
 
 (put '=   'byte-optimizer #'byte-optimize-binary-predicate)
-(put 'eq  'byte-optimizer #'byte-optimize-binary-predicate)
+(put 'eq  'byte-optimizer #'byte-optimize-eq)
 (put 'eql   'byte-optimizer #'byte-optimize-equal)
 (put 'equal 'byte-optimizer #'byte-optimize-equal)
 (put 'string= 'byte-optimizer #'byte-optimize-binary-predicate)