ARM is a big target, there could be cpus where lsl is 1 cycle and add is 2+. Wit... | Hacker News

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		DullPointer 22 days ago \| parent \| context \| favorite \| on: You can't fool the optimizer ARM is a big target, there could be cpus where lsl is 1 cycle and add is 2+. Without knowing about specific compiler targets/settings this looks reasonable. Dumb in the majority case? Absolutely, but smart on the lowest common denominator.

adwn 22 days ago [–]

> Without knowing about specific compiler targets/settings this looks reasonable.

But we do, armv8-a clang 21.1.0 with O3, and it doesn't.

> […] but smart on the lowest common denominator.

No, that would be the single add instruction.

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