Your “analogy” doesn’t hold up. The scrutiny applied to compilers are done by the compiler developers. Eventually if requirements don’t change the full test suite becomes the oracle. Not because of an attestation from a ghost in the machine but because of scrutiny done, let’s say over two years on a compiler that was reaching feature parity.
This obviously holds for compilers generating correct code since it is so well defined.
And this also holds for the efficiency of the generated code, since that is also obviously scrutinized by compiler developers.
Granted, the venerable LLM and the compiler do meet in a sort of functional intersection where all you can concievably care about is some thing that has a well-defined test for functionality or fitness. In the compiler’s case that’s the benchmark (good enough to not look at the assembly). But then one should go to that example directly and not to compilers in general.