mozilla/rust — pull request #12635 by alexcrichton (2014-03-01 00:40:05+00:00)
Title: rustc: Move to FNV hashing for node/def ids

This leverages the new hashing framework and hashmap implementation to provide a
much speedier hashing algorithm for node ids and def ids. The hash algorithm
used is currentl FNV hashing, but it's quite easy to swap out.

I originally implemented hashing as the identity function, but this actually
ended up in slowing down rustc compiling libstd from 8s to 13s. I would suspect
that this is a result of a large number of collisions.

With FNV hashing, we get these timings (compiling with --no-trans, in seconds):

| | before | after |
|-----------|---------:|--------:|
| libstd | 8.324 | 6.703 |
| stdtest | 47.674 | 46.857 |
| libsyntax | 9.918 | 8.400 |