Multiple functions can be assigned the same integer key about byfl

[spakin]

Chris,

Please confirm that 5330f9a really does fix the problem you're observing. Your bug report nearly drove me and Rob Aulwes (who wrote the Byfl function-hashing code) mad because function names are mapped to random numbers; we couldn't figure out how filenames could play a role in that. We had forgotten that the seed for the random-number generator is a hash of llvm::Module::getModuleIdentifier(), which is normally the filename. 5330f9a uses a more complicated seed function including time and process ID in hopes of eliminating key clashes (at least with very high probability).

I consider key collision worthy of a fatal error. Even though it implies only that data will get jumbled across functions—and not even that if neither -bf-by-func not -bf-call-stack is used—I'd think it would be baffling to users to suddenly get garbled performance results. With the improved seed function, my hope is that key collisions should never happen in our lifetime.

As always, thanks for the bug report,
— Scott

[cdaley]

Hello Scott,

5330f9a fixes the problem, thanks!

Chris

[spakin]

Chris,

Great! Thanks for the re-testing.

— Scott