For the following case:
t8: i32 = or t7, t4
t10: i32 = ORRWrs t8, t8, TargetConstant:i32<73>
Current code wrongly returns (t8 >> shiftConstant) as the
UsefulBits of t8, which in fact is (t8 | (t8 >> shiftConstant)).
Reviewed by: sdesmalen, mdchen
Differential Revision: https://reviews.llvm.org/D102759