From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [PATCH][2.6.8-rc1-mm1] drivers/scsi/sg.c gcc341 inlining fix Date: Thu, 15 Jul 2004 09:09:38 -0400 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <40F68212.2020405@pobox.com> References: <200407150946.i6F9kqXn010635@harpo.it.uu.se> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from parcelfarce.linux.theplanet.co.uk ([195.92.249.252]:25991 "EHLO www.linux.org.uk") by vger.kernel.org with ESMTP id S266193AbUGONJ4 (ORCPT ); Thu, 15 Jul 2004 09:09:56 -0400 In-Reply-To: <200407150946.i6F9kqXn010635@harpo.it.uu.se> List-Id: linux-scsi@vger.kernel.org To: Mikael Pettersson Cc: axboe@suse.de, wli@holomorphy.com, B.Zolnierkiewicz@elka.pw.edu.pl, akpm@osdl.org, dgilbert@interlog.com, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org Mikael Pettersson wrote: > On Wed, 14 Jul 2004 23:12:54 -0700, William Lee Irwin III wrote: > >>Jeff Garzik wrote: >> >>>>>Or you could just call it "gcc is dumb" rather than a compiler bug. >> >>On Wed, Jul 14 2004, Andrew Morton wrote: >>[... code snippet ...] >> >>>>is pretty dumb too. I don't see any harm if this compiler feature/problem >>>>pushes us to fix the above in the obvious way. >> >>On Thu, Jul 15, 2004 at 07:56:56AM +0200, Jens Axboe wrote: >> >>>Excuse my ignorance, but why on earth would that be dumb? Looks >>>perfectly legit to me, and I have to agree with Jeff that the compiler >>>is exceedingly dumb if it fails to inline that case. >> >>Enter gcc... >> >>Maybe "the obvious way" is sending a someone off to whip gcc into shape, >>or possibly reporting it as a gcc problem. > > > It shows you guys aren't compiler writers. Actually, I have written most of a [simple] compiler backend. > Compilers for top-down (define-before-use) languages like C > have traditionally also worked in a top-down fashion, processing > one top-level declaration at a time. Forward references are > either errors, or are (when a proper declaration is in scope) > left to the linker to resolve. > > Processing an entire compilation-unit (e.g. whole C file) > as a single unit is typically _only_ done when either the > language semantics requires it (not C, but e.g. Haskell), > or when very high optimisation levels are requested. Or in the case where you parse the entire file, then generate code for the entire file in a separate pass. Which does NOT imply unit-at-a-time, for the readers at home. It just implies generation of the AST. > In the case of gcc-3.4.1 failing to inline, you are asking > gcc to do something (peeking forward) which it never has > promised to do. And with the kernel using -fno-unit-at-a-time > for stack conservation reasons, gcc is actually being _told_ > not to do global compilation. > > This is not a gcc bug, nor is it being "exceedingly dumb". Actually, yes it is. Jeff