Re: [Scalar masks 2/x] Use bool masks in if-conversion

[Jeff Law <law@redhat.com>]

On 08/21/2015 04:49 AM, Ilya Enkovich wrote:
>
> I want a work with bitmasks to be expressed in a natural way using
> regular integer operations. Currently all masks manipulations are
> emulated via vector statements (mostly using a bunch of vec_cond). For
> complex predicates it may be nontrivial to transform it back to scalar
> masks and get an efficient code. Also the same vector may be used as
> both a mask and an integer vector. Things become more complex if you
> additionally have broadcasts and vector pack/unpack code. It also
> should be transformed into a scalar masks manipulations somehow.
Or why not model the conversion at the gimple level using a 
CONVERT_EXPR?   In fact, the more I think about it, that seems to make 
more sense to me.

We pick a canonical form for the mask, whatever it may be.  We use that 
canonical form and model conversions between it and the other form via 
CONVERT_EXPR.  We then let DOM/PRE find/eliminate the redundant 
conversions.  If it's not up to the task, we should really look into why 
and resolve.

Yes, that does mean we have two forms which I'm not terribly happy about 
and it means some target dependencies on what the masked vector 
operation looks like (ie, does it accept a simple integer or vector 
mask), but I'm starting to wonder if, as distasteful as I find it, it's 
the right thing to do.

>>
>> But I don't like changing our IL so much as to allow 'integer' masks everywhere.
I'm warming up to that idea...

jeff