@Override
	protected void decodeHeader(Decoder decoder) throws DecoderException {
		super.decodeHeader(decoder);
		altindex = (int) decoder.readSignedInteger(AttributeId.ATTRIB_ALTINDEX);
	}
@return the alternative index, used as an id for the original basic block Object
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/pcode/BlockCopy.java