Some other architectures like PDP-11 and 680x0 had a dedicated "clear register" instruction.
It could have been added to x86, even as a group of single-byte opcodes with the register encoded in three bits (as with PUSH, POP, and INC/DEC outside of long mode). But the XOR idiom was already established on the 8080 by that point.
It could have been added to x86, even as a group of single-byte opcodes with the register encoded in three bits (as with PUSH, POP, and INC/DEC outside of long mode). But the XOR idiom was already established on the 8080 by that point.