alt Hacker NewsYep. The XOR trick - relying on special use of opcode rather than special register - is probably related to limited number of (general purpose) registers in typical '70 era CPU design (8080, 6502, Z80, 8086).
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wongarsu • today at 1:21 PM
And [as mentioned in the article] even modern x86 implementations have a zero register. So you have this weird special opcode that (when called with identical source and destination) only triggers register renaming
bonzini • today at 1:03 PM
A move on SPARC is technically an OR of the source with the zero register. "move %l0, %l1" is assembled as "or %g0, %l0, %l1". So if you want to zero a register you OR %g0 with itself.
Unfortunately, 6502 can't XOR the accumulator with itself. I don't recall if the Z80 can, and loading an immediate 0 would be most efficient on those anyway.