[pjmlp]

That is also covered by new C++ attributes, namely [[assume(expr)]].

However better not give data to the function that contradicts the condition if you don't want to figth nasal daemons.

[JonChesterfield]

Glad assume(expr) is available, if it maps onto builtin-expect but confused by the UB reference. Why would taking the less likely path be undefined behaviour?

Edit. It's because assume does not map to expect, it maps to builtin_assume. So that's just another way to write undefined c++.

[pjmlp]

Ah, I thought it was the same, I spend most of my C++ coding time on VC++ anyway.