presto-main/src/main/java/io/prestosql/sql/gen/RowExpressionCompiler.java/Visitor/visitVariableReference
class Visitor:        @Override
        public BytecodeNode visitVariableReference(VariableReferenceExpression reference, Context context)
        {
            if (reference.getName().startsWith(TEMP_PREFIX)) {
                return context.getScope().getTempVariable(reference.getName().substring(TEMP_PREFIX.length()));
            }
            return fieldReferenceCompiler.visitVariableReference(reference, context.getScope());
        }