Any way to generate warnings for function-pointer comparisons?

Question

It took me forever to track down that there was a bug in my code being triggered by /OPT:ICF:

Because /OPT:ICF can cause the same add

Answer 1

Is there any compiler option or tool (whether part of Visual C++, GCC, Clang, or other) that can analyze my code and tell me where I'm comparing function pointers with each other, like in the code above?

I'm not sure if there exists such a compiler option.

However, there is such a tool. clang-tidy. You can write your own checks for clang-tidy, it's actually remarkably easy if you follow this blog. Specifically, the AST comes with a bunch of matchers already, which should handle the use-case you want.

Something like this seems to work:

binaryOperator(
    anyOf(hasOperatorName("=="), hasOperatorName("!=")),
    hasLHS(ignoringImpCasts(declRefExpr(hasType(functionType())))),
    hasRHS(ignoringImpCasts(declRefExpr(hasType(functionType())))))

Which flags the example in the OP:

fp.cxx:3:25: note: "root" binds here
int main(void) { return test1 == test2; }
                        ^~~~~~~~~~~~~~

---

That works specifically for the OP case, but you actually have to be more explicit to match all the other likely cases:

const auto AnyFunc = ignoringImpCasts(declRefExpr(hasType(anyOf(
    functionType(),
    pointsTo(functionType()),
    references(functionType())))));

Finder->AddMatcher(binaryOperator(
    anyOf(hasOperatorName("=="), hasOperatorName("!=")),
    hasLHS(AnyFunc),
    hasRHS(AnyFunc)).bind("op"), this);

Or something close to that effect.