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From: "jskumari at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/106770] powerpc64le: Unnecessary xxpermdi before mfvsrd
Date: Thu, 02 Mar 2023 12:42:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106770

--- Comment #10 from Surya Kumari Jangala <jskumari at gcc dot gnu.org> ---
The swap pass analyzes vector computations and removes unnecessary doublewo=
rd
swaps (xxswapdi instructions). The swap pass first constructs webs and remo=
ves
swap instructions if possible. If the web contains operations that are
sensitive to element order, such as an extract, then such instructions shou=
ld
be modified. For example, the lane is changed on an extract operation.

As we saw in comment 9, the swap pass has incorrectly changed the lane of t=
he
vec_extract. The swap pass modifies the extract operation even though there=
 are
no swap instructions in the web. This is a bug in the swap pass. It should
modify only those operations which are present in webs having swap
instructions.=