AFAIR there always was a dedicated command for comparing with zero - for all flavors of "comparison" - because it's quite easy to implement and happens sufficiently often (e.g. when decrementing down).

And this command would also be shorter in length, since it doesn't need to read a constant from memory to compare with. And shorter length will also add up to the speed gain.

Now even if you used the longer command to compare with 0, a good assembler could try to optimize (think constant folding) a "comparison to a constant 0" to the shorter and faster "zero-compare"

I learned several assemblers, mainly MOS 6502 and Motorola 68000, but that was too long ago to tell you now where I've experienced this and give the correct mnemonics.

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