Julia High Performance - Second Edition

Constant propagation

One very useful optimization that the Julia compiler implements when calling functions is called constant propagation. When a function is called with an argument that is known at compile time, the invocation can happen once at compile time, and the call is then replaced with a constant value at runtime. While we have seen some constant values being combined within a single function (with inlining), constant propagation occurs across a function call boundary – which means that this is a more complex, and powerful, optimization.

As a simple example to demonstrate constant propagation, we define a sqr function that takes one argument and then returns the square of that value. A second function, sqr2, calls the first function ...