If you can’t understand the difference between a bug that will rarely cause a compiler encountering an edge case to generate a wrong instruction and an LLM that will generate 2 completely different programs with zero overlap because you added a single word to your prompt, then I don’t know what to tell you.
The point is that expert humans (the GCC developers) writing code (C++) that generates code (ASM) does not appear to be as deterministic as you seem to think it is.