There is the observable behaviour, and the machine code instructions that actually get generated in every single case for the same kind of text input.

Which for example, unless you can exactly replicate the world every single time a PGO data gathering session is done, there are no guarantees that the compiler will generate exactly the same machine code pattern, when given various PGO files generated at different occurrences.

Thanks, yes. To get back to the "We do still read Assembly code in the world of compilers" analogy, in the case of LLM usage, the observable behaviour is...