How to use C++20's likely/unlikely attribute in if-else statement

Question

This question is about C++20\'s [[likely]]/[[unlikely]] feature, not compiler-defined macros.

This documents (cppreference) only gave an ex

Answer 1

Based on example from Jacksonville’18 ISO C++ Report the syntax is correct, but it seems that it is not implemented yet:

if (a>b) [[likely]] {

10.6.6 Likelihood attributes [dcl.attr.likelihood] draft