linux-kernel - Re: Fedora's latest gcc produces unbootable kernels

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Message-ID: <20071203115112.GT16835@devserv.devel.redhat.com>
Date:	Mon, 3 Dec 2007 06:51:12 -0500
From:	Jakub Jelinek <jakub@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Thomas Gleixner <tglx@....tglx.de>,
	Pierre Ossman <drzeus-list@...eus.cx>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Fedora's latest gcc produces unbootable kernels

On Mon, Dec 03, 2007 at 12:34:17PM +0100, Thomas Gleixner wrote:
> Of course just to annoy you :)

It doesn't matter whether I'm annoyed about this or not, but whether gcc is
able to generate decent code with it or not.  And especially with union it
is not, at least through all the tree ssa passes.  You already have a lot of
the details hidden in ktime.h accessor inlines, so I don't think it would be
hard to add further one or two.

Anyway, even just using typedef struct ktime { s64 tv64; } ktime_t; could
make things better in case you have just one field.  Unlike unions, structs
can be (and in this case most likely will be) scalarized by SRA, so
half of tree SSA passes will see it as integral var and will be able to
perform optimizations on it.

	Jakub
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