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Subject: [Bug target/99881] Regression compare -O2 -ftree-vectorize with -O2
 on SKX/CLX
Date: Fri, 02 Apr 2021 14:29:27 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99881

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-04-02
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Hongtao.liu from comment #0)
> testcase is extracted from 557.xz_r
>=20
> void
> foo (int* __restrict a, int n, int c)
> {
>     a[0] =3D n;
>     a[1] =3D c;
> }
>=20
> gcc -O2 -ftree-vectorize -fvect-cost-model=3Dvery-cheap
>=20
> foo(int*, int, int):
>         movd    xmm0, esi
>         movd    xmm1, edx
>         punpckldq       xmm0, xmm1
>         movq    QWORD PTR [rdi], xmm0
>         ret
>=20
> without vectorization
>=20
> foo(int*, int, int):
>         mov     DWORD PTR [rdi], esi
>         mov     DWORD PTR [rdi+4], edx
>         ret
>=20
> cost model:
> scalar: 2 times scalar_store costs 24,
> vector: 1 times unaligned_store costs 12, vec_contruct 8

How is vec_contruct cost computed today?=