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Date: Wed, 11 Nov 2009 16:41:04 +0100
Message-ID: <761ea48b0911110741u20343771of659340b837c5a05@mail.gmail.com>
Subject: Re: [Qemu-devel] load-store experiment...
From: Laurent Desnogues <laurent.desnogues@gmail.com>
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To: Chad <chad.page@gmail.com>
Cc: qemu-devel@nongnu.org

On Wed, Nov 11, 2009 at 8:51 AM, Chad <chad.page@gmail.com> wrote:
> (this is mostly to get some ideas going rather than trying to get anythin=
g
> upstream... yet!)
>
> This version of tcg_out_mov for i386's tcg-target.c filters out the
>
> mov %ebx, %edx
> mov %ebx, [some index]
> mov %edx, %ebx

The question is:  what TCG sequence produces this kind of code?


Laurent

> I don't have benchmarks, but it does remove a few mov's and qemu can stil=
l
> load and run a linux kernel ;)
>
> It'd be easier to do more optimizations if qemu recorded output at the
> assembly instruction level.
>
> ---
>
> static uint8_t *lmovloc =3D 0;
> static int lmovret =3D -1, lmovarg =3D -1;
> static inline void tcg_out_mov(TCGContext *s, int ret, int arg)
> {
> =A0=A0=A0 int ldiff, nowrite =3D 0;
>
> =A0=A0=A0 if (arg !=3D ret) {
> =A0=A0=A0=A0=A0=A0=A0 /* Check for a mov, mov->x, mov pattern */
> =A0=A0=A0=A0=A0=A0=A0 ldiff =3D s->code_ptr - lmovloc;
> =A0=A0=A0=A0=A0=A0=A0 if (((ldiff =3D=3D 8) || (ldiff =3D=3D 5)) &&
> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 (*(lmovloc + 2) =
=3D=3D 0x89) &&
> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 ((lmovret =3D=3D r=
et) && (lmovarg =3D=3D arg))) nowrite =3D 1;
> =A0=A0=A0=A0=A0=A0=A0 /* Write */
> =A0=A0=A0=A0=A0=A0=A0 lmovloc =3D s->code_ptr;
> =A0=A0=A0=A0=A0=A0=A0 if (!nowrite) {
> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 tcg_out_modrm(s, 0x8b, ret,=
 arg);
> =A0=A0=A0=A0=A0=A0=A0 } else {
> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 qemu_log("removed\n");
> =A0=A0=A0=A0=A0=A0=A0 }
> =A0=A0=A0=A0=A0=A0=A0 lmovret =3D arg; lmovarg =3D ret;
> =A0=A0=A0 }
> }
>