PSA: Compiler optimisation remarks

[Michael_Gottesman]

@ahti

@Saklad5

Add this to the list of things that is undocumented for no clear reason.

I'm gonna take a stab and guess that this was probably developed as a tool for folks working on the optimizer, not for developers to use for guidance on rearranging their code to be more optimizer friendly.

As such, I would expect the decisions and factors that are laid bare by this attribute to be able to change with any dot release, and certainly not base any critical decisions on the info gleamed from this.

E.g. some code is too slow to ship without optimization, but if we just move this line here a little, the cost and benefit shift slightly and it gets optimized, then some dot release comes along at a random point in the future, and suddenly the critical section is slow again without any code changes.

This is not true. I just wanted to improve it further before I really shouted about it. If it is useful to you... use it! That being said, you are correct that it doesn't provide guarantees per say, but it /can/ help you to understand your code (which is the point).