fix: Make IR set type of reference to popped element correctly

[kevinclancy]

Notes

The IR generated for calls to pop (for dynamic array types and bytes) would obtain a reference to the last element of the array and then delete it. But the type of this reference was always uint256 even though it should have been the type of the array element.

Now, we set the reference's type to the array element type. For bytes, we set the reference's type to bytes1.

Trail o' Bits developed a fix for this, but I think they used the wrong element type for bytes. It should be bytes1 but they use bytes. I will file an issue with them about this.

Testing

• Run make test and verify all tests succeed.
• Run ./evaluate.sh run 100 in tool-eval and verify all projects succeed
• Run pipenv run slither test.sol --print slithir, where test.sol contains the following:

pragma solidity ^0.8.13;

contract Poptest {
    struct S {
        int x;
        int y;
    }
    S[] a;
    function poptest() internal {
        a.pop();
    }
}

Examine the IR and verify that the deleted reference variable has the correct type. Also, try changing the array a's type to bytes.

Related Issue

https://github.com/CertiKProject/slither-task/issues/501)

Additional Comments

I will file an issue in the Slither repo about handling bytes incorrectly.