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