用于进行gcc测试

				// { dg-do run }								// Copyright (C) 2002 Free Software Foundation, Inc.				// Contributed by Nathan Sidwell 27 Nov 2002 								// covariant returns. Fixed offset.								struct B1;				struct B2;				struct D;								struct B1				{				  virtual B1 *foo1 () {return this;}				  virtual B2 *foo2 (D *);				};				struct B2				{				  virtual B2 *baz1 () {return this;}				  virtual B1 *baz2 (D *);				};								struct D : B1, B2				{				  virtual D *foo1 () {return this;}				  virtual D *foo2 (D *d) {return d;}				  virtual D *baz1 () {return this;}				  virtual D *baz2 (D *d) {return d;}				};								B2 *B1::foo2 (D *d) {return d;}				B1 *B2::baz2 (D *d) {return d;}								int test (B1 *b1, B2 *b2, D *d)				{				  if (b1->foo1 () != b1)				    return 1;				  if (b2->baz1 () != b2)				    return 2;				  if (b1->foo2 (d) != b2)				    return 3;				  if (b2->baz2 (d) != b1)				    return 4;				  return 0;				}								int test (D *d)				{				  if (d->foo2 (d) != d)				    return 11;				  if (d->baz2 (d) != d)				    return 12;				  if (d->foo1 () != d)				    return 13;				  if (d->baz1 () != d)				    return 14;				  return 0;				}								int main ()				{				  D d;				  int r;				  				  if ((r = test (&d, &d, &d)))				    return r;				  if ((r = test (&d)))				    return r;				  return 0;				}