Julia High Performance - Second Edition

Default inlining

The Julia compiler automatically inlines functions that it considers inline-worthy. The compiler implements a set of heuristics to determine what to inline. Essentially, this boils down to small functions with deterministic types.

While inlining usually results in an increase in code speed, it also simultaneously increases the size of the generated code. Hence, a balance needs to be maintained. The heuristics are, therefore, tuned to maximize the performance of a typical Julia code without causing excessive bloating of the compiled code.

As an example, let's take a look at a simple set of functions, f and g: 

function f(x)    a=x*5    b=a+3endg(x) = f(2*x)

We can then look at the processed Abstract Syntax Tree (AST) after ...