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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109011] missed optimization in presence of
 __builtin_ctz
Date: Mon, 06 Mar 2023 05:26:35 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109011

--- Comment #11 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Jakub Jelinek from comment #3)
> Seems they are vectorizing __builtin_ctz (x) as bitsize - .CLZ ((x - 1) &
> ~x) for CLZ_DEFINED_VALUE_AT_ZERO 2 with value bitsize.
> Perhaps we should pattern match it in tree-vect-patterns.cc that way if c=
lz
> is vectorizable (it is with -mavx512cd) and ctz is not.

Yes, I'm going to add a pattern match named vect_recog_ctz_as_clz_or_popcnt.

BTW, It looks like only x86 have vector clz but not ctz, for other targets,
they either have both or neither.=