Vector alignment tracking

[Jakub Jelinek]

On Thu, Oct 13, 2011 at 06:57:47PM +0200, Andi Kleen wrote:
> > Or I am missing someting?
> 
> I often see the x86 vectorizer with -mtune=generic generate a lot of
> complicated code just to adjust for potential misalignment.
> 
> My thought was just if the alias oracle knows what the original
> declaration is, and it's available for changes (e.g. LTO), it would be 
> likely be better to just add an __attribute__((aligned()))
> there.
> 
> In the general case it's probably harder, you would need some 
> cost model to decide when it's worth it.

GCC already does that on certain targets, see
increase_alignment in tree-vectorizer.c.  Plus, various backends attempt
to align larger arrays more than they have to be aligned.

	Jakub