Re: RFC: PR14880 vec_duplicate or vec_select?

[Aldy Hernandez <aldyh at redhat dot com>]

> 	The Altivec vspltM (vec_splat) instruction sets each element of
> the result to the specified element of the input vector.  One could
> describe it as selecting the same source vector sub part into each element
> of the result (vec_select) or duplicating the 1-element sub-vector into
> all elements (vec_duplicate).  I am not sure how this should be
> canonicalized in GCC or if there already is a preferred form.

Precisely my question.  Anyone?  Dorit?  Once we decide what is the
preferred form, we should update the documentation (which is severely
lacking for vec_* rtl).

BTW, if we should use vec_duplicate, how would you express getting the
1-element sub-vector out?  It looks to me like vec_select is appropriate.

BTW2, perhaps I'm not looking hard enough, but I don't see anywhere in
GCC where we're using vec_select or vec_duplicate.  Mind you, we must
get away from the unspec's eventually...

Aldy