bug#14769: 24.3.50; [PATCH] optimize `concat's literals

[Lars Ingebrigtsen]

Shigeru Fukaya <shigeru.fukaya@gmail.com> writes:

> Current bytecode optimizer works only when all arguments are
> constants.
>
> With the attached small patch, adjacent successive literal arguments
> of `concat' will become optimized to a string respectively.
>
>       Make successive literals of `concat' optimized to a string.
>       * byte-opt.el (byte-optimize-form-code-walker): call
>       byte-optimize-concat-args for `concat'.
>       (byte-optimize-concat-args): New function.

I think the patch below looks sensible, but the bytecode optimiser is
not something I'm familiar with.  Does this look OK to all y'all?

>
> Regards,
> Shigeru
>
> *** byte-opt.el       Fri Jun 14 19:32:39 2013
> --- byte-opt.new.el   Wed Jul  3 01:48:29 2013
> ***************
> *** 562,568 ****
>            (if (and (get fn 'pure)
>                     (byte-optimize-all-constp args))
>                  (list 'quote (apply fn (mapcar #'eval args)))
> !            (cons fn args)))))))
>   
>   (defun byte-optimize-all-constp (list)
>     "Non-nil if all elements of LIST satisfy `macroexp-const-p"
> --- 562,572 ----
>            (if (and (get fn 'pure)
>                     (byte-optimize-all-constp args))
>                  (list 'quote (apply fn (mapcar #'eval args)))
> !            (if (eq fn 'concat)
> !                ;; Not all arguments are literals.
> !                (cons fn (byte-optimize-concat-args args))
> !              ;; Other than `concat'.
> !              (cons fn args))))))))
>   
>   (defun byte-optimize-all-constp (list)
>     "Non-nil if all elements of LIST satisfy `macroexp-const-p"
> ***************
> *** 573,578 ****
> --- 577,605 ----
>         (setq list (cdr list)))
>       constant))
>   
> + (defun byte-optimize-concat-args (args)
> +   ;;
> +   ;; Convert arguments of `concat' such that adjacent successive
> +   ;; literal arguments to one string, and remove null strings.
> +   ;;
> +   (let (newargs)
> +     (while args
> +       ;; loop for literals
> +       (let (l)
> +     (while (and args (macroexp-const-p (car args)))
> +       (push (car args) l)
> +       (setq args (cdr args)))
> +     (when l
> +       (let ((s (apply #'concat (mapcar #'eval (nreverse l)))))
> +         ;; keep non-null string
> +         (unless (equal s "")
> +           (push s newargs)))))
> +       ;; non-literal argument
> +       (when args
> +     (push (car args) newargs)
> +     (setq args (cdr args))))
> +     (nreverse newargs)))
> + 
>   (defun byte-optimize-form (form &optional for-effect)
>     "The source-level pass of the optimizer."
>     ;;
>

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