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* Change x86 prefix order
@ 2006-12-06  7:00 H. J. Lu
  2006-12-06 16:43 ` Randy Dunlap
  0 siblings, 1 reply; 5+ messages in thread
From: H. J. Lu @ 2006-12-06  7:00 UTC (permalink / raw)
  To: gcc, GNU C Library, linux kernel

On x86, the order of prefix SEG_PREFIX, ADDR_PREFIX, DATA_PREFIX and
LOCKREP_PREFIX isn't fixed. Currently, gas generates

LOCKREP_PREFIX ADDR_PREFIX DATA_PREFIX SEG_PREFIX

I will check in a patch:

http://sourceware.org/ml/binutils/2006-12/msg00054.html

tomorrow and change gas to generate

SEG_PREFIX ADDR_PREFIX DATA_PREFIX LOCKREP_PREFIX


H.J.

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: Change x86 prefix order
  2006-12-06  7:00 Change x86 prefix order H. J. Lu
@ 2006-12-06 16:43 ` Randy Dunlap
  2006-12-06 17:00   ` H. J. Lu
  0 siblings, 1 reply; 5+ messages in thread
From: Randy Dunlap @ 2006-12-06 16:43 UTC (permalink / raw)
  To: H. J. Lu; +Cc: gcc, GNU C Library, linux kernel

On Tue, 5 Dec 2006 23:00:14 -0800 H. J. Lu wrote:

> On x86, the order of prefix SEG_PREFIX, ADDR_PREFIX, DATA_PREFIX and
> LOCKREP_PREFIX isn't fixed. Currently, gas generates
> 
> LOCKREP_PREFIX ADDR_PREFIX DATA_PREFIX SEG_PREFIX
> 
> I will check in a patch:
> 
> http://sourceware.org/ml/binutils/2006-12/msg00054.html
> 
> tomorrow and change gas to generate
> 
> SEG_PREFIX ADDR_PREFIX DATA_PREFIX LOCKREP_PREFIX

Hi,
Could you provide a "why" for this in addition to the
"what", please?

---
~Randy

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: Change x86 prefix order
  2006-12-06 16:43 ` Randy Dunlap
@ 2006-12-06 17:00   ` H. J. Lu
  0 siblings, 0 replies; 5+ messages in thread
From: H. J. Lu @ 2006-12-06 17:00 UTC (permalink / raw)
  To: Randy Dunlap; +Cc: gcc, GNU C Library, linux kernel

On Wed, Dec 06, 2006 at 08:43:17AM -0800, Randy Dunlap wrote:
> On Tue, 5 Dec 2006 23:00:14 -0800 H. J. Lu wrote:
> 
> > On x86, the order of prefix SEG_PREFIX, ADDR_PREFIX, DATA_PREFIX and
> > LOCKREP_PREFIX isn't fixed. Currently, gas generates
> > 
> > LOCKREP_PREFIX ADDR_PREFIX DATA_PREFIX SEG_PREFIX
> > 
> > I will check in a patch:
> > 
> > http://sourceware.org/ml/binutils/2006-12/msg00054.html
> > 
> > tomorrow and change gas to generate
> > 
> > SEG_PREFIX ADDR_PREFIX DATA_PREFIX LOCKREP_PREFIX
> 
> Hi,
> Could you provide a "why" for this in addition to the
> "what", please?

LOCKREP_PREFIX is also used as SIMD prefix. DATA_PREFIX can be used as
either SIMD prefix or data size prefix for SIMD instructions. The new
order

SEG_PREFIX ADDR_PREFIX DATA_PREFIX LOCKREP_PREFIX

will make SIMD prefixes close to SIMD opcode.


H.J.

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: Change x86 prefix order
  2006-12-06 17:52 Mikael Pettersson
@ 2006-12-06 18:00 ` H. J. Lu
  0 siblings, 0 replies; 5+ messages in thread
From: H. J. Lu @ 2006-12-06 18:00 UTC (permalink / raw)
  To: Mikael Pettersson; +Cc: rdunlap, gcc, libc-alpha, linux-kernel

On Wed, Dec 06, 2006 at 06:52:39PM +0100, Mikael Pettersson wrote:
> 
> If hardware x86 decoders (i.e., Intel or AMD processors)
> get measurably faster with the new order, that would be
> a good reason to change it.

I was told that AMD processors had no preferences and Intel processors
preferred the proposed order.


H.J.

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: Change x86 prefix order
@ 2006-12-06 17:52 Mikael Pettersson
  2006-12-06 18:00 ` H. J. Lu
  0 siblings, 1 reply; 5+ messages in thread
From: Mikael Pettersson @ 2006-12-06 17:52 UTC (permalink / raw)
  To: hjl, rdunlap; +Cc: gcc, libc-alpha, linux-kernel

On Wed, 6 Dec 2006 09:00:30 -0800, H. J. Lu wrote:
>On Wed, Dec 06, 2006 at 08:43:17AM -0800, Randy Dunlap wrote:
>> On Tue, 5 Dec 2006 23:00:14 -0800 H. J. Lu wrote:
>> 
>> > On x86, the order of prefix SEG_PREFIX, ADDR_PREFIX, DATA_PREFIX and
>> > LOCKREP_PREFIX isn't fixed. Currently, gas generates
>> > 
>> > LOCKREP_PREFIX ADDR_PREFIX DATA_PREFIX SEG_PREFIX
>> > 
>> > I will check in a patch:
>> > 
>> > http://sourceware.org/ml/binutils/2006-12/msg00054.html
>> > 
>> > tomorrow and change gas to generate
>> > 
>> > SEG_PREFIX ADDR_PREFIX DATA_PREFIX LOCKREP_PREFIX
>> 
>> Hi,
>> Could you provide a "why" for this in addition to the
>> "what", please?
>
>LOCKREP_PREFIX is also used as SIMD prefix. DATA_PREFIX can be used as
>either SIMD prefix or data size prefix for SIMD instructions. The new
>order
>
>SEG_PREFIX ADDR_PREFIX DATA_PREFIX LOCKREP_PREFIX
>
>will make SIMD prefixes close to SIMD opcode.

That's still just "what" and doesn't explain why
this change is desirable.

Software x86 decoders clearly must handle any valid
prefix order, so they shouldn't care. (I've written one
recently. It's tedious but not rocket science.)

If hardware x86 decoders (i.e., Intel or AMD processors)
get measurably faster with the new order, that would be
a good reason to change it.

/Mikael

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2006-12-06 18:00 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2006-12-06  7:00 Change x86 prefix order H. J. Lu
2006-12-06 16:43 ` Randy Dunlap
2006-12-06 17:00   ` H. J. Lu
2006-12-06 17:52 Mikael Pettersson
2006-12-06 18:00 ` H. J. Lu

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