GCC Compatibility

[fabianbs96]

Make phasar compile with gcc (g++-11 and g++-13) and uncover (and fix) two bugs related to json ser/de with LLVMAliasSet and LLVMBasedICFG that were not detected until now, because of nlohmann's implicit conversions feature.

[vulder]

What's the underlying reason to have a lambda here instead of a normal static member?

[fabianbs96]

The original reason was to make it easier to pass this as callback to other functions, such as in here or here.

Not sure whether it is worth it in the end though.

[vulder]

Hmm, not 100% sure here (github code review might hide things), but would this not just work in the same way with a static function?

struct Foo {
    static int foobar(int val) {
        return val * 2;
    }
};

template <typename Fn>
int call(Fn&& f) {
    return f(21);
}

int main() {
    return call(Foo::foobar);
}

If I missed something pls let me know. Then we could try to find a way to express this better.

[fabianbs96]

It would work, but then foobar would implicitly decay into a function-pointer, whereas a lambda has its own type.
This has two implications: (1) A function-pointer requires storage space when captured by a flow/edge function -- the captureless lambda plays well with [[no_unique_address]] and empty-base optimization. (2) The function-pointer is less likely to be inlined.

[fabianbs96]

I just noticed that we can simplify the lambda using our recently-added fn template:

-  static constexpr auto isLLVMZeroValue = [](const llvm::Value *V) noexcept {
-    return isZeroValueHelper(V);
-  };
+  static constexpr auto isLLVMZeroValue = fn<isZeroValueHelper>;

[vulder]

I'm not sure if the lambda gets completely removed in this usage context but I also don't have strong opinion on the usage here, my primary goal was just to get rid of the gcc hackaround.

If the fn fixes it, fine for me.

[vulder]

What's the problem here for gcc?

[fabianbs96]

For gcc, the type LLVMZeroValue is incomplete in the lambda, so it cannot perform the implicit conversion to pointer-to-base for the comparison V == getInstance()