[PATCH] D142803: [AggressiveInstCombine] Implement a general way to simplify complex logical operations.

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This patch involves boolean ring to simplify logical operations. We can treat `&` as ring multiplication and `^` as ring addition.
So we need to canonicalize all other operations to `*` `+`. Like:

  a & b -> a * b
  a ^ b -> a + b
  ~a -> a + 1
  a | b -> a * b + a + b
  c ? a : b -> c * a + (c + 1) * b

In the code, we use a mask set to represent an expression. Every value that is not comes from logical operations could be a bit in the mask.
The mask itself is a multiplication chain. The mask set is an addiction chain.
We can calculate two expressions based on boolean algebras.

For now, the initial patch only enabled on and/or/xor, and only optimized for branch condition. 
Later we can enhance the code step by step.

Reference: https://en.wikipedia.org/wiki/Boolean_ring


https://reviews.llvm.org/D142803

Files:
  llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
  llvm/test/Transforms/AggressiveInstCombine/complex-logic-ops.ll

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