Re: [PATCH] don't generate long nops on i686 (only when -march=[intel])

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Aug 6, 2010 at 12:46 PM, Quentin Neill
<quentin.neill.gnu@gmail.com> wrote:
> On Fri, Aug 6, 2010 at 12:58 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Fri, Aug 6, 2010 at 9:59 AM, Quentin Neill
>> <quentin.neill.gnu@gmail.com> wrote:
>>> On Fri, Aug 6, 2010 at 11:35 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>
>>>> I was wondering if it is necessary and possible to add the negative option
>>>> to all ISAs?
>>>
>>> It is feasible, I looked into this.
>>>
>>> One problem with the current setup, there is no way to disambiguate
>>> between ".nop" and ".nonop" and ".nononop" (etc) because we're using a
>>> pair of entries in the init table, and then detecting the "no" prefix.
>>>
>> [snip]
>>
>> One problem is .nosse turns off ALL SSE/SSE2/..., not just
>> SSE. So what should ".arch .nosse3" disable? Should it also
>> disable SSSE3, SSE4, AVX, ....
>
> Okay, now I see that ".nosse" is one of several outliers:
>
> .no87 means &= ?~(8087|287|387|687|FISTTP)
> .nosse means &= ~(sse|sse2|sse2|ssse3|sse4_1|sse4_2|sse4a|avx)
> .noavx means &= ~(avx)
>
> .87 [is not defined]
> .sse means |= (mmx|sse)
> .avx means |= (mmx|sse|sse2|sse3|ssse3|sse4_1|sse4_2|avx)
>
> If we normalize all entries so that ".noXXX" would means exactly the
> opposite of ".XXX" in all cases (answering your question about
> .nosse3), we'd have to clean these up and/or change their meanings..
>
> If not, then I guess we have to go and define what all the ".noXXX"
> flags mean, which in my opinion means just adding them to the existing
> infrastructure.
>
> Note I'm not really answering your question "if it is necessary". ?Do
> we have an idea how many people are using these directives?
>

I have no idea. I don't think we need to do anything for now. We will
see if anyone asks for them.  Then we can get some ideas on exactly
what should be done.

Thanks.


-- 
H.J.