Should it not be precompiled already?
Yes and no! Julia consist of multiple compilation stages:
parsing -> lowering -> type inference -> LLVM IR -> native code.
The first 2 (maybe partly 3 if all types are fixed) are done during what we call precompilation.
The last three only happen when you call a function.
using StaticArrays # precompiled
m = @SMatrix rand(3, 3)
@profiler inv(m) # lots of calls to type inference