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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/97770] [ICELAKE]suboptimal vectorization for
 vpopcntw/b/q
Date: Thu, 10 Jun 2021 06:48:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97770

--- Comment #18 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 10 Jun 2021, crazylht at gmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97770
>=20
> --- Comment #17 from Hongtao.liu <crazylht at gmail dot com> ---
> (In reply to Richard Biener from comment #16)
> > Changing the signature will not help given we don't want to regress oth=
er
> > cases.
> > Instead we have to somehow remove the pro- and demotions with the help =
of
> > patterns.  I think using .POPCOUNT should work there.
>=20
> I'm thinking of reimplementing _mm_popcnt_u64 with a backend builtin like
> __builtin_ia32_popcountll which is defined as ULONGLONG_FTYPE_ULONGLONG, =
and
> handle that in TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION.

That's going to work I guess but it will pessimize general optimization
which no longer know this is computing popcount (not sure if the old
version exposed that fact).=