Not really.. in part 1 of a hypothetical spectre attack, you’d have to figure out how to time a branch hit/miss, and the presence of likely may change the times

Not really.. in part 1 of a hypothetical spectre attack, you’d have to figure out how to time a branch hit/miss, and the presence of likely may change the times/inputs you’d need to use to do that. These attributes are just hints to move hot/slow code near/far away and to maybe to the right thing if there’s no branch prediction. They cannot prevent speculative execution.