Is there any penalty/cost of virtual inheritance in C++, when calling non-virtual base method?

Question

Does using virtual inheritance in C++ have a runtime penalty in compiled code, when we call a regular function member from its base class? Sample code:

Answer 1

There has to be a cost to virtual-inheritance.

The proof is that virtually inherited classes occupy more than the sum of the parts.

Typical case:

struct A{double a;};

struct B1 : virtual A{double b1;};
struct B2 : virtual A{double b2;};

struct C : virtual B1, virtual B2{double c;}; // I think these virtuals are not strictly necessary

static_assert( sizeof(A) == sizeof(double) ); // as expected

static_assert( sizeof(B1) > sizeof(A) + sizeof(double) ); // the equality holds for non-virtual inheritance
static_assert( sizeof(B2) > sizeof(A) + sizeof(double) );  // the equality holds for non-virtual inheritance

static_assert( sizeof(C) > sizeof(A) + sizeof(double) + sizeof(double) + sizeof(double) );
static_assert( sizeof(C) > sizeof(A) + sizeof(double) + sizeof(double) + sizeof(double) + sizeof(double));

(https://godbolt.org/z/zTcfoY)

What is stored additionally? I don't exactly understand. I think it is something like a virtual table but for accessing individual members.