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From: "rsandifo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110449] Vect: use a small step to calculate
 the loop induction if the loop is unrolled during loop vectorization
Date: Wed, 28 Jun 2023 20:11:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110449

rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org,
                   |                            |rsandifo at gcc dot gnu.org

--- Comment #1 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.or=
g> ---
Interesting idea!  But I think the ideal thing here would be
to do the 8*step after the store:

.L2:
        add     v29.4s, v31.4s, v28.4s  # +=3D 4*step
        stp     q31, q29, [x0]
        add     v31.4s, v31.4s, v27.4s  # +=3D 8*step
        add     x0, x0, 32
        cmp     x1, x0
        bne     .L2

This has the advantage that the loop-carried dependency
is only one ADD instruction deep, rather than 2 ADDs deep.

I haven't looked how easy it would be to do though=E2=80=A6=