presto-main/src/main/java/io/prestosql/sql/planner/EffectivePredicateExtractor.java/EffectivePredicateExtractor/visitExchange
class EffectivePredicateExtractor:        @Override
        public Expression visitExchange(ExchangeNode node, Void context)
        {
            return deriveCommonPredicates(node, source -> {
                Map<Symbol, SymbolReference> mappings = new HashMap<>();
                for (int i = 0; i < node.getInputs().get(source).size(); i++) {
                    mappings.put(
                            node.getOutputSymbols().get(i),
                            node.getInputs().get(source).get(i).toSymbolReference());
                }
                return mappings.entrySet();
            });
        }