Want query to detect mutual assignment

[ryao]

Description of the issue

Here is a minimal test case showing mutual assignment where we do b = a; followed by a = b;:

int main(void) {
        int a = 0;
        int b = a;
        int c = 1;
        a = b;
        return a*b*c;
}

The statement a = b; is redundant. Unless the variables are marked volatile, there should be no legitimate reason for code to do this. We just found an instance of this in OpenZFS:

https://github.com/openzfs/zfs/pull/14565/files#r1124115812

A quick search revealed that PVS Studio has a check for this:

https://pvs-studio.com/en/docs/warnings/v587/

[tausbn]

Thank you for your suggestion! I will forward it to the C/C++ team.

I will note, however, that as we are currently focusing on improving our security queries (and since this seems to be more of a "code correctness" query with no immediate security consequences), it may be a while before your suggestion gets addressed.

[jketema]

The C/C++ team discussed this, and as this is not security related we will indeed not schedule this any time soon. Do note that we accept external contributions. Hence, I'd like to encourage you to develop a query yourself.