Initial compile time benchmarks

[Ömer Sinan Ağacan]

Hi all,

Using Ben's timing patch [^1], Cabal, and a Haskell program to parse generated
logs [^2], I generated some tables that show compile times of modules in hxt,
haskell-src-exts, lens, and all of their dependencies:

https://gist.githubusercontent.com/osa1/fd82335181a584679c9f3200b7b0a8a5/raw/5d46b0e7006c7ef9fae913f7d6932b74c83835f1/gistfile1.txt

Some notes:

- Modules and passes in modules are sorted.

- At the end of the file you can see the cumulative numbers for the passes. In
  fact, that's a small table so I'm just going to paste it here:

    ======================Total======================
    CodeGen                                    41.32%
    Simplifier                                 34.83%
    Renamer/typechecker                        12.22%
    Desugar                                     2.11%
    CorePrep                                    1.90%
    Demand analysis                             1.44%
    CoreTidy                                    1.35%
    Called arity analysis                       1.10%
    Float inwards                               0.96%
    Common sub-expression                       0.87%
    Parser                                      0.75%
    SpecConstr                                  0.57%
    Specialise                                  0.30%
    Worker Wrapper binds                        0.17%
    Liberate case                               0.12%
    ByteCodeGen                                 0.00%
    Simplify                                    0.00%

I don't know how to make use of this yet, but I thought ghc-devs may find it
useful.

As a next thing I'm hoping to add some more `withTiming` calls. The analyze
program can handle nested `withTiming` calls and renders passes as a tree (GHC
HEAD doesn't have nested `withTiming`s so we don't see it in the file above),
so we can benchmark things in more details. I also want to experiment a little
bit with different `force` parameters to `withTiming`. If anyone has any other
ideas I can also try those.

---

[^1]: https://phabricator.haskell.org/D1959
[^2]: https://github.com/osa1/analyze-ghc-timings