((NE|EQ) (TESTQconst [c] x)) && isUint64PowerOfTwo(int64(c))
    => ((ULT|UGE) (BTQconst [int8(log32(c))] x))
((NE|EQ) (TESTQ (MOVQconst [c]) x)) && isUint64PowerOfTwo(c)
    => ((ULT|UGE) (BTQconst [int8(log64(c))] x))
(SET(NE|EQ) (TESTL (SHLL (MOVLconst [1]) x) y)) => (SET(B|AE)  (BTL x y))
(SET(NE|EQ) (TESTQ (SHLQ (MOVQconst [1]) x) y)) => (SET(B|AE)  (BTQ x y))
(SET(NE|EQ) (TESTLconst [c] x)) && isUint32PowerOfTwo(int64(c))

	return int64(bits.Len8(uint8(n))) - 1
}
func log16(n int16) int64 {
	return int64(bits.Len16(uint16(n))) - 1
}
func log32(n int32) int64 {
	return int64(bits.Len32(uint32(n))) - 1
}
func log64(n int64) int64 {
	return int64(bits.Len64(uint64(n))) - 1
}

// log2uint32 returns logarithm in base 2 of uint32(n), with log2(0) = -1.
// Rounds down.
func log2uint32(n int64) int64 {