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SubjectRe: [PATCH] 2.1.131: i386 tweak to switch_to()
On Tue, Dec 15, 1998 at 05:06:15PM +0100, Andrea Arcangeli wrote:
> On Tue, 15 Dec 1998, Geert Uytterhoeven wrote:
> >cc == condition codes
>
> Ah, but does gcc have a way to save/restore the condition code register
> on i386? (and btw the condition code register is eflags? right?)

gcc does not save/restore the condition codes, but it does compute which
instructions set them, which use them, and when they're stable in
between. (E.g., subtract instructions set condition codes, which can
optimise away a following compare instruction if they're related).

Actually, I don't think "cc" as a clobber makes any difference for GCC &
x86 at the moment, because I think cc setters always precede the
instructions that use them (on x86). But I wouldn't rely on it, and I
saw some discussion of relaxing this in the x86 machine description.

-- Jamie


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