FYI: A while back, I needed to test if a vector register contained all zeroes, but could not figure out how without loading another register via VZERO and then using VCEQGS but I didn't like that since it is really comparing two 64-bit elements. Finally, I found I could use VTM against another register loaded via VONE, and test for CC=0. Today I realized I can just issue a VTM with the same register as source and mask, and check for CC=0. No extra register required.
Testing vector registers is hard, since most vector instructions do not set condition codes (including the [non decimal] arithmetic and bitwise operations). Robert Ngan DXC Luxoft
