gcc/testsuite/gcc.c-torture/execute/builtins/20010124-1-lib.c

/* Verify that structure return doesn't invoke memcpy on 
   overlapping objects.  */

extern void abort (void);
extern int inside_main;
typedef __SIZE_TYPE__ size_t;

struct S {
  char stuff[1024];
};

union U {
  struct {
    int space;
    struct S s;
  } a;
  struct {
    struct S s;
    int space;
  } b;
};
  
struct S f(struct S *p)
{
  return *p;
}

void g(union U *p)
{
}

void *memcpy(void *a, const void *b, size_t len)
{
  if (inside_main)
    {
      if (a < b && a+len > b)
        abort ();
      if (b < a && b+len > a)
        abort ();
      return a;
    }
  else
    {
      char *dst = (char *) a;
      const char *src = (const char *) b;
      while (len--)
        *dst++ = *src++;
      return a;
    }
}