Altivec + 16 byte alignment

[Richard Henderson]

On Wed, Feb 12, 2003 at 10:07:54PM +0100, Franz Sirl wrote:
> ... and the stack pointer is kept aligned (to 256 bits) by 
> independent code as well

Is this 256 bits ABI mandated?  I.e. will a non-gcc ppc
compiler maintain this alignment as well?

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.

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.


r~