用于进行gcc测试

				/* PR tree-optimization/20913				   COPY-PROP did not fold COND_EXPR, blocking some copy propagation				   opportunities.  */								/* { dg-do link } */				/* { dg-options "-O2 -fno-tree-dominator-opts" } */								int				foo (int a, int b, int c, int d)				{				  int x, y;								  b = a;				  if (a == b)				    x = c;				  else				    {				      link_error ();				      x = d;				    }								  if (x == c)				    return a;				  else				    {				      link_error ();				      return b;				    }				}								main()				{				  foo (1, 2, 3, 4);				}