Altivec + 16 byte alignment

[John David Anglin]

> If yes, then STACK_ALIGNMENT is set too low.  You should
> advertise what you have.  If no, then calling between two
> functions compiled with different compilers will not 
> preserve the 256 bit alignment you claim.

You mean STACK_BOUNDARY?

> There are passes in gcc, particularly combine, that look
> at the advertised alignment for a pointer and know that
> the low bits are zero, and perform optimizations based on
> this.  If the alignment doesn't exist, the optimizations
> produce incorrect results.

I assume that it's actually the value specified by
PREFERRED_STACK_BOUNDARY stack boundary that is used for
the above.

Currently on the PA 32-bit ports, STACK_BOUNDARY
is 64 (same as BIGGEST_ALIGNMENT and PARM_BOUNDARY) but
PREFERRED_STACK_BOUNDARY is 512.  In part, this is because
we must define a non-zero STARTING_FRAME_OFFSET and the
start of the locals must lie on a STACK_BOUNDARY.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6605)