Re: [RFC][Scalar masks 1/x] Introduce GEN_MASK_EXPR.

[Jeff Law <law at redhat dot com>]

On 08/21/2015 10:30 AM, Ilya Enkovich wrote:
> > If we're checking an optab to drive an optimization, then we're probably on
> > the wrong track.
>
> That's totally similar to VEC_COND_EXPR which we generate comparison into.
It is.  The vectorizer is riddled with this stuff.  Sigh.  So I won't 
consider this a negative for the scalar  mask support.

> > I think this ties into the overall discussion about
> > whether or not to represent these masks in gimple or try to handle them
> > later during gimple->rtl expansion.
>
> Currently we don't have any abstraction for masks, it is supported
> using vector of integers. When I expand it I have no idea whether it
> is just a vector of integers to be stored or a mask to be used for
> MASK_LOAD. Actually it may be used in both cases at the same time.
>
> Handling it in RTL means we have to undo bool->int transformation made
> in GIMPLE. For trivial cases it may be easy but in generic it can be
> challenging.  I want to avoid it from the beginning.
I wasn't suggesting handling them in RTL, but at the border between 
gimple and RTL.

But if we can't reliably determine how a particular mask is going to be 
used at that point, then doing things at the gimple/RTL border may be a 
spectacularly bad idea ;-)

jeff