From: Alan Lawrence <alan.lawrence@arm.com>
To: Bill Schmidt <wschmidt@linux.vnet.ibm.com>
Cc: "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH 10/11][RS6000] Migrate reduction optabs to reduc_..._scal
Date: Fri, 07 Nov 2014 10:09:00 -0000 [thread overview]
Message-ID: <545C9A4E.2010903@arm.com> (raw)
In-Reply-To: <1415300196.18771.32.camel@gnopaine>
Ah I see now! Thank you for explaining that bit, I was a bit puzzled when I saw
it, but it makes sense now!
Cheers, Alan
Bill Schmidt wrote:
> On Thu, 2014-11-06 at 16:44 +0000, Alan Lawrence wrote:
>> Hmmm. I am a little surprised by your mention of "saturation points" as I would
>> not expect any variety of reduc_plus to be a saturating operation???
>
> I wouldn't either, but the underlying vsum4ubs and vsum4sbs instructions
> used in these patterns do both a reduction and an add to another value.
> If that other value is large enough this can trigger a saturation event.
> However, the patterns use vzero for this other value, so it's not
> possible to approach the saturation cutoff for either instruction since
> the reductions are being done on byte values. (Each word in the vector
> result is the sum of the corresponding four byte values in the vector
> source, added to the other value, which here is zero.)
>
> Thanks,
> Bill
next prev parent reply other threads:[~2014-11-07 10:09 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-24 11:57 [PATCH v2 0-6/11] Fix PR/61114, make direct vector reductions endianness-neutral Alan Lawrence
2014-10-24 11:58 ` [PATCH 7/11][ARM] Migrate to new reduc_plus_scal_optab Alan Lawrence
2014-11-03 17:32 ` Ramana Radhakrishnan
2014-10-24 12:01 ` [PATCH v2 0-6/11] Fix PR/61114, make direct vector reductions endianness-neutral Richard Biener
2014-10-24 12:05 ` [PATCH 8/11][ARM] Migrate to new reduc_[us](min|max)_scal_optab Alan Lawrence
2014-11-04 11:08 ` Ramana Radhakrishnan
2014-10-24 12:06 ` [PATCH 9/11][i386] Migrate reduction optabs to reduc_..._scal Alan Lawrence
2014-10-24 12:07 ` [PATCH 10/11][RS6000] " Alan Lawrence
2014-10-24 12:14 ` Alan Lawrence
2014-10-25 0:08 ` David Edelsohn
2014-11-03 17:51 ` Bill Schmidt
2014-11-06 16:44 ` Alan Lawrence
2014-11-06 18:57 ` Bill Schmidt
2014-11-07 10:09 ` Alan Lawrence [this message]
2014-11-10 22:39 ` Michael Meissner
2014-11-11 7:10 ` Segher Boessenkool
2014-11-12 1:54 ` Michael Meissner
2014-11-12 9:26 ` Segher Boessenkool
2014-11-12 19:20 ` Michael Meissner
2014-11-12 12:32 ` Alan Lawrence
2014-11-12 18:53 ` Alan Lawrence
2014-12-11 15:59 ` Ping: " Alan Lawrence
2014-12-11 18:37 ` Alan Lawrence
2014-10-24 12:12 ` [Protopatch 11/11][IA64] Migrate to reduc_(plus|min|max)_scal_v2df optab Alan Lawrence
2014-10-24 12:50 ` Alan Lawrence
2014-10-24 15:19 ` [PATCH v2 0-6/11] Fix PR/61114, make direct vector reductions endianness-neutral Matthew Fortune
2014-10-27 11:48 ` Richard Biener
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