用于进行gcc测试

				// { dg-do run  }				// Test that conversion from D* to B*& works properly.								extern "C" int printf (const char *, ...);								struct V {				  int a;				};								struct B: virtual V {				  int b;				};								struct D: B {				  int c;				};								V* gp = 0;								void foo(V * const &r) {				  gp = r;				}								int bar(V *r) {				  return (r != gp);				}								int main() {				  D *p = new D;				  foo(p);				  return bar(p);				}