By knowing the instruction set and execution units of a particular CPU you are targeting you can also avoid those instructions. What you need is already publicly available in documentation. Not to mention that you can find out a lot just by measuring code performance.
Developers really do not need so much architectural details, and it is a nonsense to expect that any sane CPU manufacturer would release such details which could be used by their competitors. Research and development is an expensive business, and technological advances are not something you want to give to your competitors for free. But I digress, you should have known all that before you asked the question.
