linux-kernel - Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load

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Message-ID: <yw1xfvh9532k.fsf@unicorn.mansr.com>
Date:	Wed, 06 Aug 2014 11:23:47 +0100
From:	Måns Rullgård <mans@...sr.com>
To:	Jakub Jelinek <jakub@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Josh Boyer <jwboyer@...oraproject.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>,
	Michel Dänzer <michel@...nzer.net>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Josh Stone <jistone@...hat.com>
Subject: Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

Jakub Jelinek <jakub@...hat.com> writes:

> There have been several man-years of work to get from the 25% var coverage
> to 67%, several DWARF extensions (most of them to be available in DWARF5 or
> work in progress on that) and with -fno-var-tracking-assignments that is
> just returned to the old state.

This is a typical "but look at all the work we've put in, it *has* to
work" argument.  As always, it is completely without merit.

>> In other words, anybody who relies on it has already learnt to work
>> around it. Or, more likely, there just isn't anybody who relies on it.
>> 
>> I don't understand how you guys can be so cavalier about a compiler
>> bug that has already resulted in actual real problems. You bring up
>
> I have no problem with a -fno-var-tracking-assignments workaround for
> compilers that have the PR61801 wrong-code bug.

Are there any that with reasonable confidence do not?

-- 
Måns Rullgård
mans@...sr.com
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