(Lsh64x(64|32|16|8)  x y) && shiftIsBounded(v) => (SLD x y)
(Lsh32x(64|32|16|8)  x y) && shiftIsBounded(v) => (SLW x y)
(Lsh16x(64|32|16|8)  x y) && shiftIsBounded(v) => (SLD x y)
(Lsh8x(64|32|16|8)   x y) && shiftIsBounded(v) => (SLD x y)
(Rsh64Ux(64|32|16|8) x y) && shiftIsBounded(v) => (SRD x y)
(Rsh32Ux(64|32|16|8) x y) && shiftIsBounded(v) => (SRW x y)

// b2i32 translates a boolean value to 0 or 1.
func b2i32(b bool) int32 {
	if b {
		return 1
	}
	return 0
}

// shiftIsBounded reports whether (left/right) shift Value v is known to be bounded.
// A shift is bounded if it is shifting by less than the width of the shifted value.
func shiftIsBounded(v *Value) bool {
	return v.AuxInt != 0
}

// canonLessThan returns whether x is "ordered" less than y, for purposes of normalizing