Prologue analysis interface

[Jim Blandy]

On 11/22/05, Joel Brobecker <brobecker@adacore.com> wrote:
> > The frame pointer bits do involve some target heuristics.  I think we
> > could do away with that, if we had reason to (i.e. an interesting
> > target which didn't use a fixed register for this).  But I'm not
> > suggesting it until we have such a target, hopefully not for a long
> > time.
>
> Not sure if this is relevant, but the HPPA ABI says that when there
> is a frame pointer, it is either in r3 or r4, depending on the frame
> size (IIRC). GCC doesn't follow the ABI, and always uses r3, but I am
> pretty sure that the HP C compiler does follow that convention...

The MIPS (if I recall, the first architecture to give us real
headaches in prologue analysis, before it became popular, things were
pretty simple and the current approach worked pretty well) doesn't
designate a particular register for use as a frame pointer, either.

I think all we really need to know is how to find the original SP (for
use as the CFA).  Having a designated frame pointer narrows the set of
places we need to look, but we could search all the registers for
something with the right value.