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For the 'inverse shift', we currently always perform a subtraction of the original (masked) shift amount. But for the case where we are handling power-of-2 type widths, we can replace: (sub bw-1, (and amt, bw-1) ) -> (and (xor amt, bw-1), bw-1) -> (and ~amt, bw-1) This allows x86 shifts to fold away the and-mask. Followup to D77301 + D80466. http://volta.cs.utah.edu:8080/z/Nod0Gr Differential Revision: https://reviews.llvm.org/D80489