Re: [patch 5/8] Immediate Values - x86 Optimization

H. Peter Anvin
2007-11-13T19:39:55Z

Mathieu Desnoyers wrote:
>> - Use "=g" constraint for char immediate value inline assembly.
>>
>> "=g" is the same as "=rmi" which is inherently bogus. In your actual code
>> you use "=r", the correct constraint is "=q".
>
> q
> Any register accessible as rl. In 32-bit mode, a, b, c, and d; in 64-bit mode, any integer register.
>
>
> I am worried that "=q" might exclude the si and di registers in 32-bit mode.
>
> What exactly is wrong with "=r" ?
>

For "char" (8-bit) values, sp/bp/si/di are illegal in 32-bit mode.

Hence "=q".

-hpa