Slower than Python

[Walter Bright]

On 3/3/2013 12:03 AM, Russel Winder wrote:
> Yes because the C/C++/D/etc. compilers are attempting to predict the
> control flow of the program in execution and optimize all cases for all
> possibilities. JIT's are just focussing on the runtime bottlenecks with
> the actual data as being used. This allows for more focussed code
> generation in the actual context. I would suspect that in many cases the
> generated code is effectively the same but JITs can often do unexpected
> and faster codes because they have more data to optimize with and less
> optimization to do.

I've heard this was the advantage of JITs for the last 15 years. I haven't seen 
any data to justify it, and I have trouble thinking of any significant 
improvements to code gen that could be made with runtime data.

That is for JITting statically typed languages. The situation is a bit better 
for dynamic ones, because the JIT can do a better job than a compiler because 
most of the time, only one type is used in a particular spot, and the JIT can 
pick that up and "statically" type it, as opposed to a compiler which cannot.