[PATCH] LowerSwitch: replace unreachable default with popular case destination

[Hans Wennborg]

Hi resistor, kariddi,

SimplifyCFG currently does this transformation, but I'm planning to remove that (see [1]) in order to be able to exploit unreachable defaults in lowering. By moving it here, we make sure that we don't lose functionality for IR going through SImplifyCFG -> LowerSwitch.

It seems LowerSwitch already has some code to exploit unreachable defaults for reducing the number of comparisons, so this will only replace an unreachable default if there is a destination shared by two or more cases.

Please take a look.

1. http://reviews.llvm.org/D6471

http://reviews.llvm.org/D6697

Files:
  lib/Transforms/Utils/LowerSwitch.cpp
  test/Transforms/LowerSwitch/fold-popular-case-to-unreachable-default.ll

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