public final int getSlot(Varnode vn) {
		int n = input.length;
		int i;
		for (i = 0; i < n; ++i) {
			if (input[i] == vn) {
				break;
			}
		}
		return i;
	}
Assuming vn is an input to this op, return its input slot number
@param vn is the input varnode
@return the slot number
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/pcode/PcodeOp.java