Subject: bug#36139: [PATCH] Make better use of the switch op in cond forms

From: Stefan Monnier <[email-masked]>
Date: Tue, 18 Jun 2019 14:48:44 -0400

> * lisp/emacs-lisp/bytecomp.el (byte-compile-cond-jump-table-info):
> Expand `memq', `memql' and `member' to their corresponding
> equality tests.
> ---
>  lisp/emacs-lisp/bytecomp.el | 46 +++++++++++++++++++++++++------------
>  1 file changed, 31 insertions(+), 15 deletions(-)
>
> diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
> index 38cce14fd6..8f089119de 100644
> --- a/lisp/emacs-lisp/bytecomp.el
> +++ b/lisp/emacs-lisp/bytecomp.el
> @@ -4117,23 +4117,39 @@ byte-compile-cond-jump-table-info
>                              (byte-compile-cond-vars (cadr condition) (cl-caddr condition))))
>                      (obj1 (car-safe vars))
>                      (obj2 (cdr-safe vars))
> -                    (body (cdr-safe clause)))
> +                    (body (cdr-safe clause))
> +                    equality)
>                 (unless prev-var
>                   (setq prev-var obj1))
> -               (unless prev-test
> -                 (setq prev-test test))
> -               (if (and obj1 (memq test '(eq eql equal))
> -                        (eq test prev-test)
> -                        (eq obj1 prev-var))
> -                   ;; discard duplicate clauses
> -                   (unless (assoc obj2 cases test)
> -                     (push (list obj2 body) cases))
> -                 (if (and (macroexp-const-p condition) condition)
> -		     (progn (push (list byte-compile--default-val
> -					(or body `(,condition)))
> -				  cases)
> -                            (throw 'break t))
> -                   (setq ok nil)
> +               (cond
> +                ((and obj1 (memq test '(eq eql equal))
> +                      (eq obj1 prev-var)
> +                      (or (not prev-test) (eq test prev-test)))
> +                 (setq prev-test test)
> +                 ;; discard duplicate clauses
> +                 (unless (assoc obj2 cases test)
> +                   (push (list obj2 body) cases)))
> +
> +                ((and obj1 (memq test '(memq memql member))
> +                      (eq obj1 prev-var)
> +                      (listp obj2)
> +                      (setq equality (cdr (assq test '((memq   . eq)
> +                                                       (memql  . eql)
> +                                                       (member . equal)))))
> +                      (or (not prev-test) (eq equality prev-test)))
> +                 (setq prev-test equality)
> +                 ;; Expand to individual equality tests.
> +                 (dolist (elem obj2)
> +                   (unless (assoc elem cases equality)
> +                     (push (list elem (or body `(',(funcall test elem obj2))))
> +                           cases))))
> +
> +                ((and (macroexp-const-p condition) condition)
> +		 (push (list byte-compile--default-val
> +                             (or body `(,condition)))
> +		       cases)
> +                 (throw 'break t))
> +                (t (setq ok nil)
>                     (throw 'break nil))))))
>           (list (cons prev-test prev-var) (nreverse cases)))))

This patch on its own is problematic because of the code-increase it
can introduce.  So I'd suggest merging it with the other one.

        Stefan