I wasn't aware of __builtin_unpredictable until yesterday. I was aware of __builtin_expect_with_probability. Unfortunately I've found both of them to be essentially useless with today's compilers.
Mmm, it looks like LLVM even has a pass to actively convert generated cmovs into branches if one of the operands touches memory [^1], and that only supported way to force things to be brancheless is inline assembly [^2].
