Porting libsanitizer to aarch64

[Jakub Jelinek]

On Thu, May 23, 2013 at 05:28:29PM +0100, Richard Earnshaw wrote:
> >FWIW, I would actually recommend against conditionalizing FRAME_GROWS_DOWNWARD
> >for a new port.  Just make it _always_ grow down and save yourself the
> >additional code bloat in the backend.
> 
> Doing that would add significantly to the cost of setting up the frame.

Why?

> FRAME_GROWS_DOWNWARD
> Define this macro to nonzero value if the addresses of local
> variable slots are at negative offsets from the frame pointer.

Yes, but this usually talks about the eliminable soft frame pointer,
something that can be eliminated later on to hard frame pointer or stack
pointer.  So, if right now say you are eliminating soft frame pointer
to hard frame pointer with offset zero, you could eliminate it to
hard frame pointer minus frame size instead or vice versa (haven't looked
what aarch64 does now).

	Jakub