When can the compiler statically bind a call to a virtual function?

Question

I expected the compiler to be able to statically resolve a function call to a virtual function if the type of the class is known at compile time (e.g. if the class instance is not being used through a reference or a pointer as illustrated in Case 1) below).

However, I have observed a strange behavior with Visual Studio 2010's C++ compiler and I would like to know if there is any reason for the compiler not to statically bind the calls to the "right" virtual function when the instances of the classes with the virtual functions are members in a structure that is being accessed by reference.

Should I expect the compiler to statically bind the calls to f() in Case 2) below? Is the "reference"ness of cr somehow propagating to cr.a even though a is an A and not an A&?

struct A
{
    virtual void f() ;
    virtual ~A() ;
};

struct B : A
{
    virtual void f() ;
    virtual ~B() ;
};

struct C {
    A a ;
    B b ;
};

C & GetACRef() ;

void test()
{
    // Case 1) The following calls to f() are statically bound i.e.
    // f() is called without looking up the virtual function ptr.
    C c ;  
    c.a.f() ;
    c.b.f() ;
    A a ;
    a.f() ;

    // Case 2) The following calls to f() go through the dynamic dispatching
    // virtual function lookup code. You can check if you generate the .asm
    // for this file.
    C & cr = GetACRef() ; // Note that C is not polymorphic
    cr.a.f() ; // visual C++ 2010 generates call to f using virtual dispatching
    cr.b.f() ; // visual C++ 2010 generates call to f using virtual dispatching  
}

Answer 1

Obviously the compiler writers have not bothered to solve this case. Perhaps it is not common enough in real code to be worth their attention.

If GetACRef is defined elsewhere, it is also possible that C is polymorphic there, which could affect the optimizations.

Note that a compiler isn't solving every possible case where a small test program is "obvious" to a human. The compilers' focus is cases that happen often in large real programs.