Constant folding enters unreachable code

[LucasSte]

While testing one of the contracts of #744 , I found out that constant folding enters unreachable code with the following error:

thread 'main' panicked at 'internal error: entered unreachable code', src/codegen/constant_folding.rs:763:42

/**
 *Submitted for verification at BscScan.com on 2021-07-28
 */

// ----------------------------------------------------------------------------

// ERC Token Standard #20 Interface

//

// ----------------------------------------------------------------------------

abstract contract ERC20Interface {
    function totalSupply() public view virtual returns (uint256);

    function balanceOf(address tokenOwner)
        public
        view
        virtual
        returns (uint256 balance);

    function allowance(address tokenOwner, address spender)
        public
        view
        virtual
        returns (uint256 remaining);

    function transfer(address to, uint256 tokens)
        public
        virtual
        returns (bool success);

    function approve(address spender, uint256 tokens)
        public
        virtual
        returns (bool success);

    function transferFrom(
        address from,
        address to,
        uint256 tokens
    ) public virtual returns (bool success);

    event Transfer(address indexed from, address indexed to, uint256 tokens);
    event Approval(
        address indexed tokenOwner,
        address indexed spender,
        uint256 tokens
    );
}

// ----------------------------------------------------------------------------

// Safe Math Library

// ----------------------------------------------------------------------------

contract SafeMath {
    function safeAdd(uint256 a, uint256 b) public pure returns (uint256 c) {
        c = a + b;
        require(c >= a);
    }

    function safeSub(uint256 a, uint256 b) public pure returns (uint256 c) {
        require(b <= a);
        c = a - b;
    }

    function safeMul(uint256 a, uint256 b) public pure returns (uint256 c) {
        c = a * b;
        require(a == 0 || c / a == b);
    }

    function safeDiv(uint256 a, uint256 b) public pure returns (uint256 c) {
        require(b > 0);
        c = a / b;
    }
}

contract CodeWithJD is ERC20Interface, SafeMath {
    string public name;

    string public symbol;
    uint8 public decimals;
    // 18 decimals is the strongly suggested default, avoid changing it

    uint256 public _totalSupply;
    mapping(address => uint256) balances;
    mapping(address => mapping(address => uint256)) allowed;

    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */

    constructor() public {
        name = "STOPBUYINGSHITE";
        symbol = "SHITE";
        decimals = 18;
        _totalSupply = 1000000000000000000000000;
        balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }

    function totalSupply() public view override returns (uint256) {
        return _totalSupply - balances[address(0)];
    }

    function balanceOf(address tokenOwner)
        public
        view
        override
        returns (uint256 balance)
    {
        return balances[tokenOwner];
    }

    function allowance(address tokenOwner, address spender)
        public
        view
        override
        returns (uint256 remaining)
    {
        return allowed[tokenOwner][spender];
    }

    function approve(address spender, uint256 tokens)
        public
        override
        returns (bool success)
    {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        return true;
    }

    function transfer(address to, uint256 tokens)
        public
        override
        returns (bool success)
    {
        balances[msg.sender] = safeSub(balances[msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(msg.sender, to, tokens);
        return true;
    }

    function transferFrom(
        address from,
        address to,
        uint256 tokens
    ) public override returns (bool success) {
        balances[from] = safeSub(balances[from], tokens);
        allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(from, to, tokens);
        return true;
    }
}

[LucasSte]

The simplest failing contract I could find was this one:

contract CodeWithJD {
    mapping(address => uint256) balances;
    function totalSupply() public view returns (uint256) {
        return balances[address(0)];
    }
}

[LucasSte]

Fixed with #796.