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

["H. Peter Anvin" <hpa@zytor.com>]

Mathieu Desnoyers wrote:
> * H. Peter Anvin (hpa@zytor.com) wrote:
> > 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".
>
> Ah! yep, I see, so we say:
>
> 1 byte : "=q"
> 2 bytes : "=r"
> 4 bytes : "=r"
> 8 bytes : "=r"
>
> ? (si and di appear to be legal for 2 and 4 bytes in 32-bit mode)

That's right.

	-hpa
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