[PATCH] Add an instcombine rule to optimize max(~a, ~b) to ~min(a, b) when profitable

[Sanjoy Das]

Hi majnemer, hfinkel,

This case is interesting because ScalarEvolutionExpander lowers min(a, b) as ~max(~a,~b).  I think the profitability heuristics can be made more clever/aggressive, but this is a start.

A clang bootstrapped with this change passes `make check`.  The rule fires 159 times.

http://reviews.llvm.org/D7821

Files:
  lib/Transforms/InstCombine/InstCombineSelect.cpp
  test/Transforms/InstCombine/max-of-nots.ll

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