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55591e689c
This implements support for isKnownNonZero, computeKnownBits when freeze is involved. ``` br (x != 0), BB1, BB2 BB1: y = freeze x ``` In the above program, we can say that y is non-zero. The reason is as follows: (1) If x was poison, `br (x != 0)` raised UB (2) If x was fully undef, the branch again raised UB (3) If x was non-zero partially undef, say `undef | 1`, `freeze x` will return a nondeterministic value which is also non-zero. (4) If x was just a concrete value, it is trivial Reviewed By: nikic Differential Revision: https://reviews.llvm.org/D75808