Incorrect SSA for indirect call to function modifying global state

[aaronyoo]

SSA doesn't track global state modification through indirect call. Consider the following two test cases, one performs the correct behavior but the other doesn't. I have attached screenshots of the resulting SSA IR in graph form

Correct:

pragma solidity >=0.4.16 <0.7.0;
contract Contract {
    int public a;
    function f() public {
        e();
        a += 1;
    }

    function e() public {
        a -= 1;
    }
}

Incorrect:

pragma solidity >=0.4.16 <0.7.0;
pragma solidity >=0.4.16 <0.7.0;
contract Contract {
    int public a;
    function f() public {
        g();
        a += 1;
    }

    function e() public {
        a -= 1;
    }

    function g() public {
        e();
    }
}

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The correct version uses a phi node to track the alteration to global state through the function call. However, when we add one more layer of indirection, it no longer tracks that alteration.