presto-main/src/main/java/io/prestosql/operator/project/DictionaryAwarePageProjection.java/DictionaryAwarePageProjectionWork/setupDictionaryBlockProjection
class DictionaryAwarePageProjectionWork:        private void setupDictionaryBlockProjection()
        {
            block = block.getLoadedBlock();

            Optional<Block> dictionary = Optional.empty();
            if (block instanceof RunLengthEncodedBlock) {
                dictionary = Optional.of(((RunLengthEncodedBlock) block).getValue());
            }
            else if (block instanceof DictionaryBlock) {
                dictionary = Optional.of(((DictionaryBlock) block).getDictionary());
            }

            // Try use dictionary processing first; if it fails, fall back to the generic case
            dictionaryProcessingProjectionWork = createDictionaryBlockProjection(dictionary);
        }