Non-simple variables are forbidden in PHP 7
-----
<?php
global $$foo->bar;
-----
!!php7
Syntax error, unexpected T_OBJECT_OPERATOR, expecting ';' from 2:13 to 2:14
array(
    0: Stmt_Global(
        vars: array(
            0: Expr_Variable(
                name: Expr_Variable(
                    name: foo
                )
            )
        )
    )
    1: Expr_ConstFetch(
        name: Name(
            parts: array(
                0: bar
            )
        )
    )
)