[Bug target/101456] Unnecessary vzeroupper when upper bits of YMM registers already zero

[hjl.tools at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101456

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
         Resolution|FIXED                       |---
             Status|RESOLVED                    |REOPENED
   Last reconfirmed|                            |2022-02-15

--- Comment #8 from H.J. Lu <hjl.tools at gmail dot com> ---
It turns out that reading YMM registers with all zero bits needs VZEROUPPER
on Sandy Bride, Ivy Bridge, Haswell, Broadwell and Alder Lake to avoid
SSE <-> AVX transition penalty.