Altivec + 16 byte alignment

[Mike Stump]

On Tuesday, February 11, 2003, at 11:59 AM, John David Anglin wrote:
>>       /* Ignore alignment we can't do with expected alignment of the
>>          boundary.  */
>>       if (alignment * BITS_PER_UNIT > PREFERRED_STACK_BOUNDARY)
>> 	alignment = PREFERRED_STACK_BOUNDARY / BITS_PER_UNIT;
>> 			
>>     but really that's wrong, and at a minimum it should warn the user
>>     that their requested alignment isn't going to happen (better 
>> would be
>>     to just ensure the requested alignment).  We occasionally get bug
>>     reports about this, but so far no-one has invested the effort to
>>     implement arbitrary stack alignment.
>>
>> Now we have *yet another* macro involved in alignment!
>
> Another issue is GCC's alignment attribute is silently ignored for 
> stack
> locals and the documentation doesn't say that.

Let us agree that this is just a bug, or at least a bug for CPUs that 
have hard requirements of say 16 bytes (Altivec, SSE) and the user asks 
for 16 byte alignment and we silently only do 8 byte alignment.