=> (SET(B|AE)store  [off] {sym} ptr (BTQconst [int8(log32(c))] x) mem)
(SET(NE|EQ)store [off] {sym} ptr (TESTQ (MOVQconst [c]) x) mem) && isUint64PowerOfTwo(c)
    => (SET(B|AE)store  [off] {sym} ptr (BTQconst [int8(log64(c))] x) mem)

// Handle bit-testing in the form (a>>b)&1 != 0 by building the above rules
// and further combining shifts.
(BT(Q|L)const [c] (SHRQconst [d] x)) && (c+d)<64 => (BTQconst [c+d] x)