[PATCH] D61816: [CFG] [analyzer] pr41300: Add a branch to skip virtual base initializers when they are handled by the superclass.

[Kristóf Umann via Phabricator via cfe-commits]

Szelethus added inline comments.


================
Comment at: clang/lib/Analysis/CFG.cpp:1434-1438
+  // For C++ constructor add initializers to CFG. Virtual base classes may have
+  // already been initialized by the superclass. Make a branch so that it was
+  // possible to jump straight to non-virtual bases and fields, skipping
+  // virtual bases. We only need to do this once because all virtual base
+  // initializers go all together before all other initializers.
----------------
Szelethus wrote:
> I find this a little too vague. The standard states:
> 
> > First, and only for the constructor of the most derived class (4.5) , virtual base classes are initialized in the order they appear on a depth-first left-to-right traversal of the directed acyclic graph of base classes, where “left-to-right” is the order of appearance of the base classes in the derived class base-specifier-list.
> >
> > Then, direct base classes are initialized in declaration order as they appear in the (regardless of the order of the mem-initializer s).
> >
> > Then, non-static data members are initialized in the order they were declared in the class definition (again regardless of the order of the mem-initializer s).
> >
> > Finally, the base-specifier-list compound-statement of the constructor body is executed.
> 
> This would be an overkill here, but how does this sound like:
> 
> > Constructor delegations are ignored to virtual bases unless the object is of the most derived class.
> >
> >  class VBase { VBase() = default; VBase(int) {} };
> >  class A : virtual public VBase { A() : VBase(0) {} };
> >  class B : public A {};
> >
> >  B b; // Constructor calls in order: VBase(), A(), B().
> >       // VBase(int) is ignored, B isn't the most derived class that
> >       // delegates to the virtual base.
> >
> > This may result in the virtual base(s) being already initialized at this point, in which case we should jump right onto non-virtual bases and fields. To handle this, make a CFG branch. We only need to do this once, since the standard states that all virtual bases shall be initialized before non-virtual bases and direct data members.
> 
> Also, the comment of mine complementing this inline raises a concern about "doing this only once", can you specify?
Mind you, this is the order of initialization for non-delegating constructors!


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D61816/new/

https://reviews.llvm.org/D61816