Re: [Emacs-diffs] emacs-24 r116836: Fix keyword argument parsing. Please bootstrap.

[Daniel Colascione <dancol@dancol.org>]

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On 03/23/2014 06:43 PM, Stefan wrote:
>> +	* emacs-lisp/cl-macs.el (cl--do-arglist): Use a little `cl-loop'
>> +	list to look for keyword arguments instead of `memq', fixing
>> +	(Bug#3647) --- unfortunately, only for freshly-compiled code.
>> +	Please make bootstrap.
> 
> Have you checked the performance and code-size impact of this change?
> Maybe it's OK to try it on trunk, but it seems much too risky
> performancewise for 24.4.  There is no hurry to fix this: the bug has
> been with us forever (IIRC it was even documented in CL's texinfo).

The new code ranges from about a half to a third of the speed of the old
code, measured by byte-compiled, lexically-bound functions that just
return lists of their arguments. Code size increases as well: with the
old code, the 7-old keyword noop function requires 99 bytecode
instructions, while the new code generates 371 instructions.

IMHO, that's fine, since keyword argument parsing isn't particularly
fast to begin with and shouldn't be on any hot path.

If we really care about performance here, we can add a subr that works
like assq (`assq-plist' ?), but that skips every other list element.
This approach should will yield correct semantics and shouldn't be any
slower (or larger) than the existing code. If you want to do it that
way, I'll back out my change from the emacs-24 branch and write
something better for trunk.


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