* [Qemu-devel] load-store experiment...
@ 2009-11-11 7:51 Chad
2009-11-11 15:41 ` Laurent Desnogues
0 siblings, 1 reply; 3+ messages in thread
From: Chad @ 2009-11-11 7:51 UTC (permalink / raw)
To: qemu-devel
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(this is mostly to get some ideas going rather than trying to get anything
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
I don't have benchmarks, but it does remove a few mov's and qemu can still
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 = 0;
static int lmovret = -1, lmovarg = -1;
static inline void tcg_out_mov(TCGContext *s, int ret, int arg)
{
int ldiff, nowrite = 0;
if (arg != ret) {
/* Check for a mov, mov->x, mov pattern */
ldiff = s->code_ptr - lmovloc;
if (((ldiff == 8) || (ldiff == 5)) &&
(*(lmovloc + 2) == 0x89) &&
((lmovret == ret) && (lmovarg == arg))) nowrite = 1;
/* Write */
lmovloc = s->code_ptr;
if (!nowrite) {
tcg_out_modrm(s, 0x8b, ret, arg);
} else {
qemu_log("removed\n");
}
lmovret = arg; lmovarg = ret;
}
}
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] load-store experiment...
2009-11-11 7:51 [Qemu-devel] load-store experiment Chad
@ 2009-11-11 15:41 ` Laurent Desnogues
2009-11-12 6:01 ` Chad
0 siblings, 1 reply; 3+ messages in thread
From: Laurent Desnogues @ 2009-11-11 15:41 UTC (permalink / raw)
To: Chad; +Cc: qemu-devel
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 anything
> 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 still
> 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 = 0;
> static int lmovret = -1, lmovarg = -1;
> static inline void tcg_out_mov(TCGContext *s, int ret, int arg)
> {
> int ldiff, nowrite = 0;
>
> if (arg != ret) {
> /* Check for a mov, mov->x, mov pattern */
> ldiff = s->code_ptr - lmovloc;
> if (((ldiff == 8) || (ldiff == 5)) &&
> (*(lmovloc + 2) == 0x89) &&
> ((lmovret == ret) && (lmovarg == arg))) nowrite = 1;
> /* Write */
> lmovloc = s->code_ptr;
> if (!nowrite) {
> tcg_out_modrm(s, 0x8b, ret, arg);
> } else {
> qemu_log("removed\n");
> }
> lmovret = arg; lmovarg = ret;
> }
> }
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] load-store experiment...
2009-11-11 15:41 ` Laurent Desnogues
@ 2009-11-12 6:01 ` Chad
0 siblings, 0 replies; 3+ messages in thread
From: Chad @ 2009-11-12 6:01 UTC (permalink / raw)
To: Laurent Desnogues; +Cc: qemu-devel
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On Wed, Nov 11, 2009 at 7:41 AM, Laurent Desnogues <
laurent.desnogues@gmail.com> wrote:
>
> > 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?
>
> I added register and instruction dumps - every case is related to
qemu_[ld/st], which makes sense since it's output is outside of tcg's
regular register tracking...
- Chad
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