[Bug target/71921] missed vectorization optimization

[arjan at linux dot intel.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71921

Arjan van de Ven <arjan at linux dot intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|6.1.1                       |6.3.0

--- Comment #6 from Arjan van de Ven <arjan at linux dot intel.com> ---
Having poked at this a bunch, I now have a proposed patch (well I know it needs
work, but it's there to show the idea) and a set of "evidence" and an improved
test case. I'll be attaching the raw files to this bug and then make a summary
post as well.