vpclmulqdq with avx-512f adds evex-encoded 512-bit version of pclmulqdq instruction. with avx-512vl, it adds evex-encoded 256- and 128-bit versions. vpclmulqdq alone (that is, on non-avx512 cpus) adds only vex-encoded 256-bit version. (availability of the vex-encoded 128-bit version is indicated by different cpuid bits: pclmulqdq and avx.) the wider than 128-bit variations of the instruction perform the same operation on each 128-bit portion of input registers, but they do not extend it to select quadwords from different 128-bit fields (the meaning of imm8 operand is the same: either low or high quadword of the 128-bit field is selected).