Re: [PATCH]: Add new bytecode op `switch' for implementing branch tables.

[Vibhav Pant <vibhavp@gmail.com>]

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On Tue, Feb 7, 2017 at 12:00 AM, Stefan Monnier
<monnier@iro.umontreal.ca> wrote:
>> The following patch adds support for a new op `switch` to the Emacs
>> bytecode VM and compiler.
>
> I guess the motivation is to speed up some code.
> Did you make any measurements to see what kind of effect it has?

The attached benchmark code took 9.409541956 seconds when compiled
without switch,
and 0.20807168799999998 seconds (97% speedup) when compiled with switch. It
generates a cond clause with a thousand clauses comparing a variable
with random integer values, with the last clause containing the actual
value. However,
since it's a synthetic benchmark, real world code should be better indicator of
performance improvement.

-- 
Vibhav Pant
vibhavp@gmail.com

[-- Attachment #2: switch-benchmark.el --]
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(require 'cl-lib)
(require 'benchmark)

(defmacro random-cases (cases var actual-value)
  `(cond ,@(cl-loop for i from 0 to cases
		    collect `((eq ,var ,(random)) ,i))
	 ((eq ,var ,actual-value) t)))

(message "%s"
	 (benchmark-run-compiled 100000 (let ((v 2)) (random-cases 3000 v 2))))