On 08/18/2011 02:23 AM, Richard Guenther wrote:
>>> >> The first one (inefficient) is vec0 > vec1 ? {-1,...} : {0,...}
>>> >> The second is vec0 > vec1. expand_vec_cond_expr is stupid, which is
>>> >> fine, but it means that we need to construct it carefully.
>> >
>> > This is still important.
> Yes. I think the backends need to handle optimizing this case,
> esp. considering targets that do not have instructions to produce
> a {-1,...}/{0,...} bitmask from a comparison but produce a vector
> of condition codes. With using vec0 > vec1 ? {-1...} : {0,...} for
> mask = vec0 > vec1; we avoid exposing the result kind of
> vector comparisons.
>
> It should be easily possible for x86 for example to recognize
> the -1 : 0 case.
>
I think you've been glossing over the hard part with "..." up there.
I challenge you to actually fill that in with something meaningful
in rtl.
I suspect that you simply have to add another named pattern that
will Do What You Want on mips and suchlike that produce a CCmode.
r~
