I always thought that big compilers (clang/gcc/msvc) have some degree of non-determinism due to myriad of optimization passes in combination with heuristics deciding when and where to use certain kind of optimization. Is that true or not?

And certainly if you define deterministic compilation as always producing the same binary, this is already broken by compiler macros like "__DATE__" and randomly generated names during link-time optimization. [1]

[1] https://blog.conan.io/2019/09/02/Deterministic-builds-with-C...