alt Hacker NewsI'd have to take a contrary view on that. It'll take some time for the technologies to be developed, but ultimately managed JIT compilation has the potential to exceed native compiled speeds. It'll be a fun journey getting there though.
The initial order-of-magnitude jump in perf that JITs provided took us from the 5-2x overhead for managed runtimes down to some (1 + delta)x. That was driven by runtime type inference combined with a type-aware JIT compiler.
I expect that there's another significant, but smaller perf jump that we haven't really plumbed out - mostly to be gained from dynamic _value_ inference that's sensitive to _transient_ meta-stability in values flowing through the program.
Basically you can gather actual values flowing through code at runtime, look for patterns, and then inline / type-specialize those by deriving runtime types that are _tighter_ than the annotated types.
I think there's a reasonable amount of juice left in combining those techniques with partial specialization and JIT compilation, and that should get us over the hump from "slightly slower than native" to "slightly faster than native".
I get it's an outlier viewpoint though. Whenever I hear "managed jitcode will never be as fast as native", I interpret that as a friendly bet :)
Replies
Any optimizations discovered at runtime by a JIT can also be applied to precompiled code. The precompiled code is then not spending runtime cycles looking for patterns, or only doing so in the minimally necessary way. So for projects which are maximally sensitive to performance, native will always be capable of outperforming JIT.
It's then just a matter of how your team values runtime performance vs other considerations such as workflow, binary portability, etc. Virtually all projects have an acceptable range of these competing values, which is where JIT shines, in giving you almost all of the performance with much better dev economics.
> JIT compilation has the potential to exceed native compiled speeds
The battlecry of Java developers riding their tortoises.
Don’t we have decades of real-world experience showing native code almost always performs better?
For most things it doesn’t matter, but it always rubs me the wrong way when people mention this about JIT since it almost never works that way in the real world (you can look at web framework benchmarks as an easy example)