I would say the profiler output is the best source of information. Lithium is not using black magic at all. Actually on large framework like lithium, performance problems come more from obvious errors that get hiden in the quantity of code than in code that you did not crazy optimize.
Only the profiler will tell you if there is a hidden malloc that is slowing down all the rest, or a inefficient datastructure, or ...
There is probably lot of non optimized code in lithium, it just has no impact (or if it has I still has to find it).
That said, for other kind of software (usually more CPU bound), going down to assembly or using SIMD can be the only way to get good perfs.
Only the profiler will tell you if there is a hidden malloc that is slowing down all the rest, or a inefficient datastructure, or ...
There is probably lot of non optimized code in lithium, it just has no impact (or if it has I still has to find it).
That said, for other kind of software (usually more CPU bound), going down to assembly or using SIMD can be the only way to get good perfs.