From: Jeff Garzik <jeff@garzik.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kamil Dudka <kdudka@redhat.com>,
Sparse Mailing-list <linux-sparse@vger.kernel.org>,
Pekka J Enberg <penberg@cs.helsinki.fi>
Subject: Re: linearize bug?
Date: Sat, 27 Aug 2011 11:37:06 -0400 [thread overview]
Message-ID: <4E590F22.6030800@garzik.org> (raw)
In-Reply-To: <CA+55aFzGViNgNO8rkv1kT8TZBXNWoJ8kMDHFormT_EzK3LGvZQ@mail.gmail.com>
On 08/27/2011 11:29 AM, Linus Torvalds wrote:
> On Sat, Aug 27, 2011 at 4:34 AM, Kamil Dudka<kdudka@redhat.com> wrote:
>>
>> Two years ago I proposed a patch that I believe would solve your problem:
>>
>> https://patchwork.kernel.org/patch/40307/
>
> Ack.
>
> The sparse output still looks like sh*t, because when linearizing
> loops sparse doesn't treat the first conditional specially, so instead
> of noticing that "0< 10" and getting rid of the first jump, it will
> generate the loop with the (general) conditional at the end, which
> will then result in lots of phi-nodes etc.
>
> I guess some trivial loop optimizations might be a good idea. But
> Kamil's patch looks correct, and the PHI-node cross-bb optimization
> does look bogus.
On our point of view, we probably prefer to simply turn off as many
transformations as possible. They just waste time, when an optimizing
LLVM backend is going to perform the same transformations anyway.
Jeff
next prev parent reply other threads:[~2011-08-27 15:37 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-27 6:29 linearize bug? Jeff Garzik
2011-08-27 11:34 ` Kamil Dudka
2011-08-27 15:29 ` Linus Torvalds
2011-08-27 15:37 ` Jeff Garzik [this message]
2011-08-27 15:53 ` Linus Torvalds
2011-08-27 16:54 ` Kamil Dudka
2011-08-27 17:13 ` Linus Torvalds
2011-08-27 17:27 ` Linus Torvalds
2011-08-27 19:26 ` Linus Torvalds
2011-08-27 20:03 ` Jeff Garzik
2011-08-28 6:26 ` Pekka Enberg
2011-08-27 23:39 ` [PATCH] cse: update PHI users when throwing away an instruction Kamil Dudka
2011-08-28 0:34 ` Linus Torvalds
2011-08-28 6:32 ` Christopher Li
2011-08-28 6:33 ` Pekka Enberg
2011-08-28 8:53 ` Jeff Garzik
2011-08-27 22:07 ` linearize bug? Jeff Garzik
-- strict thread matches above, loose matches on Subject: below --
2006-11-12 4:09 Jeff Garzik
2006-11-13 4:43 ` Linus Torvalds
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