Most compilers are nondeterministic in small ways. For example, it's common to use hash tables that are keyed by pointer address and then iterate over the entri

Most compilers are nondeterministic in small ways. For example, it's common to use hash tables that are keyed by pointer address and then iterate over the entries in storage order, so the order in which certain things are emitted will change from run to run. This is why "deterministic builds" are such a big deal, and not just an obvious thing that you get for free. I don't know what the chances are that such a thing could ever translate into good assembly being emitted in one run and bad assembly being emitted in the next.