Commits on May 12, 2016

1. Improve derived implementations for enums with lots of fieldless vari… …

   …ants
   
   A number of trait methods like PartialEq::eq or Hash::hash don't
   actually need a distinct arm for each variant, because the code within
   the arm only depends on the number and types of the fields in the
   variants. We can easily exploit this fact to create less and better
   code for enums with multiple variants that have no fields at all, the
   extreme case being C-like enums.
   
   For nickel.rs and its by now infamous 800 variant enum, this reduces
   optimized compile times by 25% and non-optimized compile times by 40%.
   Also peak memory usage is down by almost 40% (310MB down to 190MB).
   
   To be fair, most other crates don't benefit nearly as much, because
   they don't have as huge enums. The crates in the Rust distribution that
   I measured saw basically no change in compile times (I only tried
   optimized builds) and only 1-2% reduction in peak memory usage.

   

   dotdash committed May 12, 2016
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