Commits on May 11, 2016

1. [MIR trans] Optimize trans for biased switches …

   Currently, all switches in MIR are exhausitive, meaning that we can have
   a lot of arms that all go to the same basic block, the extreme case
   being an if-let expression which results in just 2 possible cases, be
   might end up with hundreds of arms for large enums.
   
   To improve this situation and give LLVM less code to chew on, we can
   detect whether there's a pre-dominant target basic block in a switch
   and then promote this to be the default target, not translating the
   corresponding arms at all.
   
   In combination with rust-lang#33544 this makes unoptimized MIR trans of
   nickel.rs as fast as using old trans and greatly improves the times for
   optimized builds, which are only 30-40% slower instead of ~300%.
   
   cc rust-lang#33111

   

   dotdash committed May 11, 2016
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