> The simplest programs might generate the same hash, but don't expect all code to generate the same-hash binary by default

Debian and others have put quite a lot of work into reproducible software builds:

https://wiki.debian.org/ReproducibleBuilds#Even_more

This of course only works if the compiler cooperates.

The bug linked earlier is a regression in Clang 10. Clang 9 was deterministic for the same file, flags, etc.