[fmstephe]

Yeah, after reading the blog post I felt reasonably confident that this is a compiler bug (in terms of perf).

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).

[tylerhou]

I don't know if I would classify it as a bug, but definitely a heuristic that could use tuning.

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.

[dataflow]

Confused, why do you think this is a compiler bug? You should definitely expect a predictable branch to be faster than a conditional move, and the insertion of a conditional move in the original is totally sensible (albeit not intuitive if you haven't seen it).

[littlestymaar]

> and the insertion of a conditional move in the original is totally sensible (albeit not intuitive if you haven't seen it).

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?