Re: [AArch64][PR65375] Fix RTX cost for vector SET

[James Greenhalgh <james.greenhalgh@arm.com>]

On Wed, Apr 15, 2015 at 11:45:36AM +0100, Kugan wrote:
> > There are two ways I see that we could clean things up, both of which
> > require some reworking of your patch.
> > 
> > Either we remove my check above and teach the RTX costs how to properly
> > cost vector operations, or we fix my check to catch all vector RTX
> > and add the special cases for the small subset of things we understand
> > up there.
> > 
> > The correct approach in the long term is to fix the RTX costs to correctly
> > understand vector operations, so I'd much prefer to see a patch along
> > these lines, though I appreciate that is a substantially more invasive
> > piece of work.
> > 
> 
> 
> I agree that rtx cost for vector is not handled right now. We might not
> be able to completely separate as Kyrill suggested.  We still need the
> vector SET with VOIDmode to be handled inline. This patch is that part.
> We can work on the others as a separate function, if you prefer that. I
> am happy to look this as a separate patch.

My point is that adding your patch while keeping the logic at the top
which claims to catch ALL vector operations makes for less readable
code.

At the very least you'll need to update this comment:

  /* TODO: The cost infrastructure currently does not handle
     vector operations.  Assume that all vector operations
     are equally expensive.  */

to make it clear that this doesn't catch vector set operations.

But fixing the comment doesn't improve the messy code so I'd certainly
prefer to see one of the other approaches which have been discussed.

Thanks,
James