From: Mattias Engdegård <mattiase@acm.org>
Date: Fri, 16 Dec 2022 14:56:04 +0000 (+0100)
Subject: Elide broken but unnecessary `if` optimisations
X-Git-Tag: emacs-29.0.90~1122
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=13aa376e93564a8cf2ddbbcf0968c6666620db89;p=emacs.git

Elide broken but unnecessary `if` optimisations

* lisp/emacs-lisp/byte-opt.el (byte-optimize-if):
Remove explicit clauses purposing to simplify

    (if X nil t) -> (not X)
    (if X t nil) -> (not (not X))

but never did so because of a coding mistake (eq instead of equal),
found by a recently added warning.  They weren't actually needed
thanks to the optimiser's fixpoint iteration: we eventually get the
same results through

    (if X nil t) -> (if (not X) t nil) -> (if (not X) t) -> (not X)
    (if X t nil) -> (if X t) -> (not (not X))
---

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index a7e1df3622d..0da2a9b882d 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -1297,11 +1297,8 @@ See Info node `(elisp) Integer Basics'."
       (if else
           `(progn ,condition ,@else)
         condition))
-     ;; (if X nil t) -> (not X)
-     ((and (eq then nil) (eq else '(t)))
-      `(not ,condition))
-     ;; (if X t [nil]) -> (not (not X))
-     ((and (eq then t) (or (null else) (eq else '(nil))))
+     ;; (if X t) -> (not (not X))
+     ((and (eq then t) (null else))
       `(not ,(byte-opt--negate condition)))
      ;; (if VAR VAR X...) -> (or VAR (progn X...))
      ((and (symbolp condition) (eq condition then))