[discuss] When is RBX used for base pointer?

[H.J. Lu]

On Feb 13, 2008 2:49 PM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Wed, 13 Feb 2008, H.J. Lu wrote:
>
> > Our proposal is at
> >
> > http://gcc.gnu.org/ml/gcc/2007-12/msg00567.html
> >
> > For most cases, we can align stack with RBP/RSP. But
> > we need an extra register when there is dynamic stack
> > allocation or nested functions. It has to be callee-saved
> > to work with setjmp/longjmp.
>
> I'm probably missing something, but why does it have to be a fixed
> register at all?  Why not simply saying "a free callee-saved register"?
>

We allocate this register when expanding prologue. Joey, Xuepeng,
will "a free callee-saved register" work here?

H.J.