[Tuna-Fish]

JIT has strictly more information than an ahead-of-time compiler running without good profiling data (that should be based on the real workload, not a dev test). JITs can notice things like paths never taken and compile the code into a set of sanity checks and a single completely inlined tight codepath for the common case, and when sanity checks fail, fall back to normal code.

JIT does, however, use cycles at runtime to do the actual compile. While I have seen benchmarks where JIT wins over AoT, I'd still bet that the balance favors traditional compilers.

[j_baker]

Right, but those extra cycles tend to be a one-time thing. In a program that runs in a short amount of time, then the amount of time it takes to compile this might negate any speed gains. In a longer-lived application (like a web app), this can make a bigger difference.

[xtho]

The jit has more information about runtime behaviour. The question is though whether haskell's or similar slightly more advanced type systems aren't able to compensate for that.