I don't see an issue with the gotos, those are direct jumps so there is no cost there.
The real question is the if branching vs cmov. I do not now the impact of Meltdown, Spectre and L1TF mitigation on Haswell branch predictors though as one of the main goal was fixing speculative execution and much of Haswell performance came from its very impressive predictors. Here is a benchmark suite for branch vs branchless: [https://github.com/xiadz/cmov](https://github.com/xiadz/cmov). On past architecture (circa 2010) if/else was faster than cmov for predictable branches (like testing if nil), seems like it changed for Skylake (security patch might change that again). Also ARM, MIPS arch, and even AMD processors might have a completely different behaviour. Finally cmov only make sense for assignment like this: let foo = if bool_a: 10 else: 20
