From: David Laight <David.Laight@ACULAB.COM>
To: 'Linus Torvalds' <torvalds@linux-foundation.org>,
Tom Tromey <tom@tromey.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>,
Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Sparse Mailing-list <linux-sparse@vger.kernel.org>
Subject: RE: [PATCH 00/11] pragma once: treewide conversion
Date: Thu, 4 Mar 2021 13:55:12 +0000 [thread overview]
Message-ID: <4835ec1d2ecc40b285596288a0df4f47@AcuMS.aculab.com> (raw)
In-Reply-To: <CAHk-=wi13+FLcRo4zmnRUmmY=AAns-Yd5NR_mVdcAd6ZrPq2fA@mail.gmail.com>
> (a) the traditional include guard optimization HAS NO HIDDEN SEMANTIC
> MEANING. It's a pure optimization that doesn't actually change
> anything else. If you don't do the optimization, absolutely nothing
> changes.
And if the parser is well written the optimisation is probably
irrelevant compared to the compile time.
OTOH that probably requires using mmap(), memchr('\n') to look
for line starts, a fast search for '[ ]*#' followed by else/endif
and a final horrid backwards check for a continuation line.
That optimisation will generally speed up header file processing.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-03-04 13:57 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <YDvLYzsGu+l1pQ2y@localhost.localdomain>
2021-02-28 17:46 ` [PATCH 00/11] pragma once: treewide conversion Linus Torvalds
2021-02-28 19:34 ` Alexey Dobriyan
2021-02-28 20:00 ` Linus Torvalds
[not found] ` <877dmo10m3.fsf@tromey.com>
2021-03-03 20:17 ` Linus Torvalds
2021-03-04 13:55 ` David Laight [this message]
2021-03-04 20:16 ` Linus Torvalds
2021-03-05 9:19 ` David Laight
2021-03-05 21:23 ` Linus Torvalds
2021-03-06 13:07 ` Miguel Ojeda
2021-03-06 21:33 ` Linus Torvalds
2021-03-23 10:03 ` Pavel Machek
2021-03-01 0:29 ` Luc Van Oostenryck
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