private void buildVnUp(Varnode vn) {		// Follow def edge
		PcodeOp op;
		for (;;) {
			PcodeOp tmpop = vn.getDef();
			if (tmpop == null) {
				return;
			}
			op = tmpop;
			if (transtable[op.getOpcode()] != 0) {
				break;	// Do not ignore this operation
			}
			vn = op.getInput(0);
		}
		opedge.add(new ToOpEdge(op, -1));
	}
Encode a particular PcodeOp and slot
@param op is the PcodeOp to preserve
@param slot is the slot to preserve (-1 for output, >=0 for input)
@param method is the method to use for encoding (4, 5, or 6)
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/pcode/DynamicHash.java