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I don't think that'll work. Consider the positive integer 0b01: the shift yields 0b10, then the and yields 0.

I've actually tried to come up with a simpler example. It's tougher than you'd think, and you pretty much have to do weird stuff with flags. The superoptimiser trick is pretty neat.

Do you mean (r0 << 1) & 1? That would always yield zero.

Faster code for same end result is:

xor r0, r0