From: Pavel Machek <pavel@ucw.cz>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Laight <David.Laight@aculab.com>,
Tom Tromey <tom@tromey.com>,
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: Tue, 23 Mar 2021 11:03:56 +0100 [thread overview]
Message-ID: <20210323100356.GA20449@amd> (raw)
In-Reply-To: <CAHk-=wh8PptzH-=ak1D7C5Zp6EJ8eurYqVqGdQauupAFaNuG4g@mail.gmail.com>
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Hi!
> > > (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.
>
> That's actually surprisingly not even remotely true.
>
> People always think that the optimization phases of a compiler are the
> expensive ones. And yes, there are certain optimizations that can be
> *really* expensive, and people just don't even do them because they
> are _so_ expensive and are exponential in time.
Well, linux kernel can be compiled in two _seconds_ if you take
compiler optimized for fast parsing... and quick code generation.
See "SUSE Labs Conference 2018 - Compiling the Linux kernel in a
second (give or take)" on youtube.
So yes, gcc's frontend may be slow, but that does not mean job can not
be done quickly by suitable compiler.
Best regards,
Pavel
--
http://www.livejournal.com/~pavelmachek
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next prev parent reply other threads:[~2021-03-23 10:04 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
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 [this message]
2021-03-01 0:29 ` Luc Van Oostenryck
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