[X86] Add support for -mvzeroupper and -mno-vzeroupper to match gcc

Authored by craig.topper on Nov 4 2019, 10:20 AM.


[X86] Add support for -mvzeroupper and -mno-vzeroupper to match gcc

-mvzeroupper will force the vzeroupper insertion pass to run on
CPUs that normally wouldn't. -mno-vzeroupper disables it on CPUs
where it normally runs.

To support this with the default feature handling in clang, we
need a vzeroupper feature flag in X86.td. Since this flag has
the opposite polarity of the fast-partial-ymm-or-zmm-write we
used to use to disable the pass, we now need to add this new
flag to every CPU except KNL/KNM and BTVER2 to keep identical

Remove -fast-partial-ymm-or-zmm-write which is no longer used.

Differential Revision: https://reviews.llvm.org/D69786