[PATCH] PR gas/16489: GAS doesn't complain about same register used for destination and index in AVX512 gather insn

[Michael Zolotukhin]

> If the patch doesn't change anything in testsuite, it means it
> isn't necessary.
It is not necessary, but the assert allowing zmm-register is weaker
than it should be for AVX2 case, which doesn't allow zmm registers by
definition.  The change just makes the assert correct, the way it
should've been before.  But anyway, I could omit this change if
needed.

Michael