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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/102494] Failure to optimize vector reduction properly especially when using OpenMP
Date: Mon, 27 Sep 2021 08:47:09 +0000	[thread overview]
Message-ID: <bug-102494-4-9YXB6HawK3@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-102494-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102494

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
The vectorizer looks for a way to "shift" the whole vector by either vec_shr
or a corresponding vec_perm with constant shuffle operands.  When the target
provides none of those you get element extracts and scalar adds.

So yes, the vectorizer does the work for you but only if you hand it the
pieces.

It could possibly use a larger vector, doing only the "tail" of its final
reduction, so try with v8hi instead of v4hi, but it's not really clear if
such strategy would be good in general.

  parent reply	other threads:[~2021-09-27  8:47 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-27  0:52 [Bug tree-optimization/102494] New: Failure to optimize out " gabravier at gmail dot com
2021-09-27  1:45 ` [Bug tree-optimization/102494] " pinskia at gcc dot gnu.org
2021-09-27  3:01 ` crazylht at gmail dot com
2021-09-27  5:08 ` [Bug tree-optimization/102494] Failure to optimize " crazylht at gmail dot com
2021-09-27  5:13 ` crazylht at gmail dot com
2021-09-27  5:55 ` crazylht at gmail dot com
2021-09-27  8:47 ` rguenth at gcc dot gnu.org [this message]
2021-09-28  6:57 ` crazylht at gmail dot com
2021-09-28  7:09 ` rguenther at suse dot de
2021-10-08  2:10 ` cvs-commit at gcc dot gnu.org
2021-10-25 21:44 ` peter at cordes dot ca
2021-10-25 22:00 ` peter at cordes dot ca
2021-10-26  8:13 ` crazylht at gmail dot com

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