Allow building benchmarks with rustbuild

[bluss]

Rustbuild should allow building / testing / running benchmarks

I imagine rustbuild's approach will be a lot better for benchmark development and running compared to the old makefiles.

Optional parts:

• Allow testing different optimization / compiler flags

[alexcrichton]

To clarify, by benchmarks, do you mean the one in libraries? (like src/libstd and such).

If that's true then I could totally see this being something like:

./x.py bench src/libstd
./x.py bench src/libcore
# ...

[bluss]

Yes, for example src/libcollectionstest/ contains benchmarks that I want to add to & run.

[alexcrichton]

Cool! In that case this should be relatively easy to do I think. The steps for this would be:

• Add a new Bench subcommand along with all necessary flag parsing for it
• Add a new Bench kind for generating build steps
• Add a convenience method for generating bench rules
• Add a rule for each crate to run benchmarks. Here everything depend on libtest
• Add a method to actually run benchmarks in check.rs. Probably just modify the existing krate method to just call cargo bench instead of cargo test.

And I think that's it! After that ./x.py bench should run all the benchmarks we've got for all crates, and specific crates could be selected like ./x.py bench src/libcollections.