presto-main/src/main/java/io/prestosql/sql/gen/PageFunctionCompiler.java/PageFunctionCompiler/fieldReferenceCompiler
class PageFunctionCompiler:    private static RowExpressionVisitor<BytecodeNode, Scope> fieldReferenceCompiler(CallSiteBinder callSiteBinder)
    {
        return new InputReferenceCompiler(
                (scope, field) -> scope.getVariable("block_" + field),
                (scope, field) -> scope.getVariable("position"),
                callSiteBinder);
    }