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SubjectRe: [patch 13/17] Immediate Values - x86 Optimization
Mathieu Desnoyers wrote:
> * H. Peter Anvin (hpa@zytor.com) wrote:
>> Mathieu Desnoyers wrote:
>>> Ok, so the most flexible solution that I see, that should fit for both
>>> x86 and x86_64 would be :
>>> 1 byte : "=q" : "a", "b", "c", or "d" register for the i386. For
>>> x86-64 it is equivalent to "r" class (for 8-bit
>>> instructions that do not use upper halves).
>>> 2, 4, 8 bytes : "=r" : A register operand is allowed provided that it is
>>> in a
>>> general register.
>> Any reason to keep carrying this completely misleading comment chunk still?
>>
>> -hpa
>
> This comment explains why I use the =q constraint for the 1 bytes
> immediate value. It makes sure we use an instruction with 1-byte opcode,
> without REX.R prefix, on x86_64.

No, it doesn't. That would be "=Q".

-hpa


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