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

[hjl.tools at gmail dot com]

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

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
We need to verify that LOADING the zero YMM register won't trigger
SSE<->AVX transition penalty.