[PATCH 1/4] rs6000_stack_info changes for -fsplit-stack

[Alan Modra]

On Mon, May 18, 2015 at 02:05:59PM -0400, David Edelsohn wrote:
> On Sun, May 17, 2015 at 10:54 PM, Alan Modra <amodra@gmail.com> wrote:
> > This patch changes rs6000_stack_info to keep save areas offsets even
> > when not used.  I need lr_save_offset valid for split-stack, and it
> > seemed reasonable to treat the other offsets the same.  Not zeroing
> > the offsets requires just one change in code that uses them, the
> > use_backchain_to_restore_sp expression in rs6000_emit_epilogue, not
> > counting the debug_stack_info changes.
> >
> >         * config/rs6000/rs6000.c (rs6000_stack_info): Don't zero offsets
> >         when not saving registers.
> >         (debug_stack_info): Adjust to omit printing unused offsets,
> >         as before.
> >         (rs6000_emit_epilogue): Adjust use_backchain_to_restore_sp
> >         expression.
> 
> I think that the vrsave_save_offset change may break saving of
> callee-saved VRs.  See PR 55276.

I checked.  It doesn't break that testcase.  PR 55276 was really
caused by using vrsave_mask for two purposes, firstly to track which
altivec registers have been saved, and secondly to control use of the
vrsave stack slot and whether mfvrsave/mtvrsave insns are generated.
Patch 2/4 removes this conflation.

-- 
Alan Modra
Australia Development Lab, IBM