That belief is surprising, because I remember an at least 10 year old optimization advice from Intel to put ud2 after a ret or jmp to avoid speculation. Also s

That belief is surprising, because I remember an at least 10 year old optimization advice from Intel to put ud2 after a ret or jmp to avoid speculation. Also some amount of speculation even for untaken branches is unavoidable: the fetch stage need to know whether to fetch the next instruction or not before the unconditional jump is decoded, which is multiple pipeline stages downstream.