Hopefully someone with a deeper understanding can verify or discredit this here. I'm curious to see the fix for this (I assume it will generate a fix).
At least (at a high level) in LLVM, branches and cmovs are represented with the exact same construct, and one of the codegen passes looks at the condition and the two sides and heuristically determines whether to emit a branch or a cmov.
I don't know how Go codegen works, but I assume they do something similar.
Would you mind expanding? If the conditional move isn't needed, and given that it's costly in terms of perfs, how is that “totally sensible” to have one here?
My best guess is that it's because of the added cost to the other branch: printing is expensive, so the compiler really doesn't want to do that, and would prefer to incorrectly predict not-printing than to incorrectly predict printing.
If that tradeoff is what causes the difference in behaviour here, then I understand. But I don't like it, because it's ridiculous and we shouldn't have to con the compiler into doing what's right. If we're going to have to do this, I'd rather have the language provide a way for us to make explicit what we expect here.
if a > b
b = a
continue
else
continue