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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/77579] Missed multiple add (int) for CSEd case
Date: Tue, 16 May 2023 20:06:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D77579

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
           Assignee|pinskia at gcc dot gnu.org         |unassigned at gcc d=
ot gnu.org

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Thinking about this some more, doing the multiply multiple times is actually
slower on most cores.
So this is not something you want to do normally but with a constant multip=
ly
you do for small power of 2 constant.

E.g.:
```
void f(int x, int y, int z, int *s)
{
   int t =3D y * 2;
   s[0] =3D t + x;
   s[1] =3D x - t;
}
```
You should get:

        add     w2, w0, w1 lsl 1
        sub     w0, w0, w1 lsl 1
        stp     w2, w0, [x3]

And no seperate lsl instruction as the cost to do the lsl is free in this c=
ase.

Anyways I am not working on this any more.=