That would be great, if only it worked as intended! From the perspective of an optimizing compiler, `a == b ? a : b` is worse than `b` regardless of the probability you assign to `a == b`.

ETA: someone on Lobsters (https://lobste.rs/s/1an425/quadrupling_code_performance_with...) noticed that `[[unlikely]]` actually works on LLVM (not on GCC, and with worse codegen on LLVM, but it's still good to know) -- updated the post.