presto-main/src/main/java/io/prestosql/operator/project/PageFieldsToInputParametersRewriter.java/Visitor/getParameterForField
class Visitor:        private Integer getParameterForField(InputReferenceExpression reference)
        {
            return fieldToParameter.computeIfAbsent(reference.getField(), field -> {
                inputChannels.add(field);
                return nextParameter++;
            });
        }