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From: "unlvsur at live dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/107563] __builtin_shufflevector fails to pshufd
 instructions under default x86_64 compilation toggle which is the sse2 one
Date: Tue, 08 Nov 2022 00:11:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107563

--- Comment #3 from cqwrteur <unlvsur at live dot com> ---
(In reply to cqwrteur from comment #2)
> (In reply to cqwrteur from comment #0)
> > #if defined(__SSE2__)
> >=20
> > using temp_vec_type [[__gnu__::__vector_size__ (16)]] =3D char;
> > void foo(temp_vec_type& v) noexcept
> > {
> > 	v=3D__builtin_shufflevector(v,v,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0);
> > }
> >=20
> > #endif
> >=20
> > g++ -S pq.cc -Ofast
> > proves sse2 is enabled by default, but it does not call
> > https://www.felixcloutier.com/x86/pshufb
> > neither
> > https://www.felixcloutier.com/x86/pshufd
> >=20
> > while g++ -S pq.cc -Ofast -msse4.2 will generate them correctly. Which =
is
> > buggy
>=20
> pshufb is sse3 sorry. but pshufd is sse2. It can be used for generating t=
he
> right instruction.

https://godbolt.org/z/6baWWoE4e
BTW. -msse3 does not use pshufb either. i do not know why=