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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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  parent reply	other threads:[~2021-03-23 10:04 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-28 16:57 [PATCH 00/11] pragma once: treewide conversion Alexey Dobriyan
2021-02-28 16:58 ` [PATCH 01/11] pragma once: delete include/linux/atm_suni.h Alexey Dobriyan
2021-02-28 19:05   ` Jakub Kicinski
2021-02-28 16:59 ` [PATCH 02/11] pragma once: convert arch/arm/tools/gen-mach-types Alexey Dobriyan
2021-02-28 16:59   ` Alexey Dobriyan
2021-03-01 10:19   ` Russell King - ARM Linux admin
2021-03-01 10:19     ` Russell King - ARM Linux admin
2021-03-02 15:15     ` Alexey Dobriyan
2021-03-02 15:15       ` Alexey Dobriyan
2021-02-28 16:59 ` [PATCH 03/11] pragma once: convert arch/s390/tools/gen_facilities.c Alexey Dobriyan
2021-02-28 17:00 ` [PATCH 04/11] pragma once: convert drivers/gpu/drm/pl111/pl111_nomadik.h Alexey Dobriyan
2021-03-01 14:41   ` Linus Walleij
2021-02-28 17:01 ` [PATCH 05/11] pragma once: convert drivers/scsi/qla2xxx/qla_target.h Alexey Dobriyan
2021-02-28 22:07   ` Bart Van Assche
2021-02-28 17:02 ` [PATCH 06/11] pragma once: convert include/linux/cb710.h Alexey Dobriyan
2021-03-03 23:13   ` Michał Mirosław
2021-02-28 17:02 ` [PATCH 07/11] pragma once: convert kernel/time/timeconst.bc Alexey Dobriyan
2021-02-28 17:03 ` [PATCH 08/11] pragma once: convert scripts/atomic/ Alexey Dobriyan
2021-03-01  7:55   ` Peter Zijlstra
2021-02-28 17:04 ` [PATCH 09/11] pragma once: convert scripts/selinux/genheaders/genheaders.c Alexey Dobriyan
2021-02-28 18:37   ` Paul Moore
2021-02-28 18:57     ` Alexey Dobriyan
2021-02-28 17:05 ` [PATCH 10/11] pragma once: delete few backslashes Alexey Dobriyan
2021-02-28 17:05   ` Alexey Dobriyan
2021-03-01  8:54   ` Ido Schimmel
2021-03-01  8:54     ` Ido Schimmel
2021-03-02 19:00   ` Vineet Gupta
2021-03-02 19:00     ` Vineet Gupta
2021-03-04 14:22   ` Edward Cree
2021-03-04 14:22     ` Edward Cree
2021-03-23 10:09     ` Pavel Machek
2021-03-23 10:09       ` Pavel Machek
2021-02-28 17:05 ` [PATCH 11/11] pragma once: conversion script (in Python 2) Alexey Dobriyan
2021-02-28 17:11 ` [PATCH 12/11] pragma once: scripted treewide conversion Alexey Dobriyan
2021-02-28 17:11   ` Alexey Dobriyan
2021-03-01 17:35   ` Darrick J. Wong
2021-02-28 17:46 ` [PATCH 00/11] pragma once: " 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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