Re: [PATCH] 2.1.131: i386 tweak to switch_to()

Marc Lehmann (pcg@goof.com)
Fri, 18 Dec 1998 00:36:19 +0100


On Wed, Dec 16, 1998 at 12:29:46AM +0000, Jamie Lokier wrote:
>
> gcc does not save/restore the condition codes, but it does compute which
> instructions set them,

No.

> which use them, and when they're stable in between.

No.

> (E.g., subtract instructions set condition codes, which can optimise away a
> following compare instruction if they're related).

No.

> 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

Yes.

> 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.

Yes. Uh-oh, millions of asms breaking, AGAIN :)

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