[PATCH]: Stack alignment

[Geoff Keating]

"John David Anglin" <dave@hiauly1.hia.nrc.ca> writes:

> > > When STACK_BOUNDARY is set to 64, there is one fill word in the frame
> > > as a result of the starting frame offset and the need to align it to a
> > > STACK_BOUNDARY.  If STACK_BOUNDARY were set to 512, we would have 15
> > > fill words.
> > 
> > Eh?  Is the stack pointer aligned or not?
> 
> This turned out to be totally wrong.  Here is the actual problem.
> 
> Reload aligns the stack in each iteration.  It uses a default alignment
> value of BIGGEST_ALIGNMENT.  If STARTING_FRAME_OFFSET % BIGGEST_ALIGNMENT
> is not zero, the rounding in assign_stack_temp_for_type will cause the
> frame size to be non-zero.  As a result, you will never have a non-empty
> frame and code for doing the stack adjustments needs to be emitted in
> the prologue and epilogue.

Right.  This is because you need to keep the stack aligned, so you can
never have an empty frame.  Which brings us back to a variant of the
previous poster's question: is the stack pointer supposed to be
aligned, or not?

-- 
- Geoffrey Keating <geoffk@geoffk.org>