[LogicCombine 1/?] Implement a general way to simplify logical operations.
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, Later we can enhance the code step by step. Reference: https://en.wikipedia.org/wiki/Boolean_ring Reviewed By: spatel Differential Revision: https://reviews.llvm.org/D142803
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