[orthoxerox]

> This is intriguing; could you elaborate on the latter? Would tiered JIT perhaps have more runtime information which would be more useful when optimising frequently-accessed code paths or tight loops?

Exactly. In addition to that, it's hard for the compiler to guess which branch is the frequent one in code. Or if it's the only one, if, for example, you link against implementations of some interface but only use one at runtime.