[cfe-commits] [PATCH] Asm multiple alternative constraints revisited

[Eli Friedman]

On Thu, Aug 5, 2010 at 6:24 PM, John Thompson
<john.thompson.jtsoftware at gmail.com> wrote:
> Eli,
>
> One thing
> I also noticed is that the back-end doesn't consider multiple constraints in
> parallel, as ChooseConstraintTuple does, but it seems like it should be
> okay, as long as the backend can find suitable instrustions.

That's precisely the issue; multiple-alternative constraints require
examining all the constraints at once.  From the gcc docs: "For
example, on the 68000, a logical-or instruction can combine register
or an immediate value into memory, or it can combine any kind of
operand into a register; but it cannot combine one memory location
into another. "

-Eli