From: Segher Boessenkool <segher@kernel.crashing.org>
To: HAO CHEN GUI <guihaoc@linux.ibm.com>
Cc: gcc-patches <gcc-patches@gcc.gnu.org>, David <dje.gcc@gmail.com>,
"Kewen.Lin" <linkw@linux.ibm.com>,
Peter Bergner <bergner@linux.ibm.com>,
xionghuluo@tencent.com
Subject: Re: [PATCH-2, rs6000] Reverse V8HI on Power8 by vector rotation [PR100866]
Date: Mon, 24 Oct 2022 16:40:46 -0500 [thread overview]
Message-ID: <20221024214046.GC25951@gate.crashing.org> (raw)
In-Reply-To: <a4b84496-105a-200f-3a88-2b0a33ce638d@linux.ibm.com>
Hi!
On Mon, Oct 24, 2022 at 11:14:20AM +0800, HAO CHEN GUI wrote:
> This patch implements V8HI byte reverse on Power8 by vector rotation.
Please put *byte* reverse as the commit subject as well?
> It should be effecient than orignial vector permute. The patch comes from
> Xionghu's comments in PR. I just added a test case for it.
Yeah, on all existing CPUs such a rotate is as fast or faster than a
permute insn. And for bigger modes, we need more insns two dependent
rotates for V4SI, and that is unlikely to be faster than a single
permutation, certainly not if code can be unrolled.
Okay for trunk. Thanks!
Segher
prev parent reply other threads:[~2022-10-24 21:41 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-24 3:14 HAO CHEN GUI
2022-10-24 21:40 ` Segher Boessenkool [this message]
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