[Feature Request] compiler V2 optimization: code sinking

[junxzm1990]

🚀 Feature Request

Given the following code (brought up by @georgemitenkov ):

t1 = expensive();
if c {
  use(t1); // t1 is only used here
}

use(t1) is not always executed. Thus, by moving t1 = expensive() under if will optimize the execution when c is false. This is a typical case of code sinking.

Comment by @vineethk:

For this to be safe, either:

• expensive() has to be pure
• or all code following it has to be pure until the point of usage

For this code motion to be advantageous:

• we need a stack-machine cost model to show us that code motion does not cause increase in code size (what if there were multiple uses in multiple branches, etc)