Re: [PATCH 1/2] x86: eliminate TS_XSAVE

H. Peter Anvin
2010-05-05T12:10:04Z

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Your code is functionally equivalent to the immediate values patch; neither uses a direct branch which would be more efficient.

"Avi Kivity" <avi@redhat.com> wrote:

>On 05/04/2010 09:24 PM, H. Peter Anvin wrote:
>>
>> I would like to request one change, however. I would like to see the
>> alternatives code to be:
>>
>> movb $0,reg
>> movb $1,reg
>>
>> ... instead of using xor (which has to be padded with NOPs, which is of
>> course pointless since the slot is a fixed size.)
>
>Right.
>
>> I would suggest using
>> a byte-sized variable instead of a dword-size variable to save a few
>> bytes, too.
>>
>
>I used a bool, and the code already compiles to a byte mov. Though it
>could be argued that a word instruction is better since it avoids a
>false dependency, and allows a preceding instruction that modifies %reg
>to be executed after the mov instruction.
>
>> Once the jump label framework is integrated and has matured, I think we
>> should consider using it to save the mov/test/jump.
>>
>
>IIRC that has an implied unlikely() which isn't suitable here?
>
>Perhaps the immediate values patches.
>
>--
>error compiling committee.c: too many arguments to function
>

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