found out the avx instruction vzeroall will. in fact. not zero all the xmm/ymm/zmm registers, but will do the modest task of only zeroing the first sixteen of them.
pretty cool to see something with "all" in the name be followed up with a description beginning with:
zeroes some of ...
i understand why that's the case—it's not really necessary anymore, on top of a few other reasons—but it's another thing to add to the "ah, x86 Thing™, gotcha" pile
