Why is inlining so important in C++? Clearly, it reduces function call overhead: if a function is inlined, there is no need to spend time setting up its arguments, jumping to it, creating a stack frame, and then undoing all that upon returning. More interestingly, though, inlining enables other compiler optimizations. In this article, I will show examples of constant propagation and loop-invariant code motion (LICM). Then, I will explain how inlining enables these optimizations to apply more widely and show an example of the consequences when that doesn’t happen.