FunC does not respect error code 5 in left shift and right shift operators

[jeshecdom]

In the following contract that uses right and left shifts:

contract Test() {

    receive(){}
    
    get fun getBool1(x: Int): Bool {
        return (-1 >> x) <= 1;
    }

    get fun getBool2(x: Int): Bool {
        return (-1 << x) <= 1;
    }
}

Getters getBool1 and getBool2 will return true for any assignment of parameter x outside the interval [0..256]. However, the expected behavior is to produce error code 5 when calling such getters outside the allowed interval [0..256]. The interpreter does report an error; for example, interpreting (-1 >> x) <= 1 when x = -2 produces the error: Cannot evaluate expression to a constant: the number of bits shifted ('-2') must be within [0..256] range.

The FunC code of the above getters is:

(tuple, int) $Test$_fun_getBool1(tuple $self, int $x) impure inline_ref {
    var ($self) = $self;
    var $fresh$ret_0 = ((-1 >> $x) <= 1);
    return ($self, $fresh$ret_0);
}

(tuple, int) $Test$_fun_getBool2(tuple $self, int $x) impure inline_ref {
    var ($self) = $self;
    var $fresh$ret_1 = ((-1 << $x) <= 1);
    return ($self, $fresh$ret_1);
}

While the Fift code of the above getters is:

$Test$_fun_getBool1 PROCREF:<{
    DROP
    TRUE
}>
$Test$_fun_getBool2 PROCREF:<{
    DROP
    TRUE
}>

Notice that FunC replaced the expressions (-1 >> $x) <= 1 and (-1 << $x) <= 1 with TRUE in the Fift code.

The above means that it is not safe to rely on catching error code 5 in try/catch statements in order to execute important business logic, similar to issue #2832 for integer overflows.

[i582]

ton-blockchain/ton#1651