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Date: Fri, 15 Nov 2013 19:25:00 -0000
From: Richard Earnshaw <rearnsha@arm.com>
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To: Cong Hou <congh@google.com>
CC: GCC Patches <gcc-patches@gcc.gnu.org>,  Richard Biener <rguenther@suse.de>
Subject: Re: [PATCH] Support addsub/subadd as non-isomorphic operations for SLP vectorizer.
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On 15/11/13 02:06, Cong Hou wrote:
> Hi
>=20
> This patch adds the support to two non-isomorphic operations addsub
> and subadd for SLP vectorizer. More non-isomorphic operations can be
> added later, but the limitation is that operations on even/odd
> elements should still be isomorphic. Once such an operation is
> detected, the code of the operation used in vectorized code is stored
> and later will be used during statement transformation. Two new GIMPLE
> opeartions VEC_ADDSUB_EXPR and VEC_SUBADD_EXPR are defined. And also
> new optabs for them. They are also documented.
>=20

Not withstanding what Richi has already said on this subject, you
certainly don't need both VEC_ADDSUB_EXPR and VEC_SUBADD_EXPR.  The
latter can always be formed by vec-negating the second operand and
passing it to VEC_ADDSUB_EXPR.

R.