This varies from trivial to very hard to mostly data dependent with different architectures. llvm-mca might be of interest. One should be able to do a best-cas

This varies from trivial to very hard to mostly data dependent with different architectures. llvm-mca might be of interest. One should be able to do a best-case calculation, mostly assuming caches hit and branch prediction gets the answer right. Register renaming manages to stay out of the way. Getting more dubious, there is a statistical representation of program performance on unknown (or partially known) data. One might be able to estimate that usefully, though I haven't seen it done.