When does a compiler produce randomness? I think non reproducible builds are usually due to environmental inputs (for example: build a date macro) or an undeesp

When does a compiler produce randomness? I think non reproducible builds are usually due to environmental inputs (for example: build a date macro) or an undeespecified build process (such as: what compiler version, what build optimizations are used, etc). All of that can be constrained / defined, it's just work that people often don't do.