(BitRev16   x) => (SRLconst [48] (RBIT <typ.UInt64> x))
(BitRev8    x) => (SRLconst [56] (RBIT <typ.UInt64> x))

// In fact, UMOD will be translated into UREM instruction, and UREM is originally translated into
// UDIV and MSUB instructions. But if there is already an identical UDIV instruction just before or
// after UREM (case like quo, rem := z/y, z%y), then the second UDIV instruction becomes redundant.