Vector subregs

[Daniel Berlin]

On Friday, December 14, 2001, at 01:59  PM, Alexandre Oliva wrote:

> On Dec 14, 2001, Dale Johannesen <dalej@apple.com> wrote:
>
>> Subreg's of vectors don't have a register implementation on any
>> hardware AFAIK, so there is no reason to support them.
>
> Hmm...  The SH4 can use 4 FP registers as a V4SF unit for some
> operations, as well as 4 of these sets as a 4x4 SF matrix.  I suppose
> it would be reasonable to be able to use subregs to refer to
> individual registers that compose such vectors and matrices, wouldn't
> it?
>
Vectors maybe, matrices, no.
I'd rather see a vec_slice rtl or something.
Yes, I know you probably *could* use subregs for vectors.
But remember that one of the most annoying things right now about RTL 
that we don't represent subscripting of arrays, etc. It's way too low 
level.
Why should we do the same thing to vectors and matrices, by using 
subregs , when we have a chance to do it right at the start, and just 
say what we mean (which is a slice of a vector/matrix)?
Also think of trying to allocate vector subregs in a reasonable way, or 
matrix subregs in a reasonable way.
We have vec_merge, vec_sel, etc. Just add a vec_slice.

--Dan