C++: CWE-190 Tests.

[geoffw0]

New tests for CWE-190:

• the first commit (test6.cpp) is one I had lying around from a previous investigation that never got put in a PR. We currently pass it.
• the second commit (test2.cpp) diagnoses the latest SAMATE-cpp regression (at least one of the new failures; it's theoretically possible there could be multiple new issues, but this is unlikely as they look superficially similar).

@MathiasVP - I'm interested in whether you might have an idea what's going on here, and how widely it's likely to cause problems in real-world scenarios. The SAMATE regression itself is quite small.

[MathiasVP]

@MathiasVP - I'm interested in whether you might have an idea what's going on here, and how widely it's likely to cause problems in real-world scenarios. The SAMATE regression itself is quite small.

Interestingly, the result comes back if we add another member to the single-field struct MyStruct. So I suspect this has something to do with the missing implementation of getPreUpdateNode for store steps without a ChiInstruction. I don't know why it's only a problem for pass-by-value, though.

[geoffw0]

I forgot to simplify this. The type doesn't matter, I get the same results with int.

[MathiasVP]

LGTM! I've found the underlying issue for the missing result and I'll have a fix for it very soon.