[Bug target/91103] AVX512 vector element extract uses more than 1 shuffle instruction; VALIGND can grab any element

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91103

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-07-09
     Ever confirmed|0                           |1

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Thanks for the detailed analysis - currently the vectorizer makes N explicit
element extracts and N explicit scalar stores.  That's not very friendly for
the targets to generate the kind of mixed code from.  I'm thinking of
somehow generalizing how we represent strided stores similar to scatters
but in a way making the index vector implicitely specified by an affine
combination (constant * reg).  It probably needs another set of expanders
for that though.