// Force a full GC and sweep.
	GC()

	// Process specials.
	for i, s := range specials {
		if !s.done {
			printlock()
			println("runtime: object", i, "was not swept")
			throw("IsReachable failed")
		}
		if s.reachable {
			mask |= 1 << i
		}
		lock(&mheap_.speciallock)
		mheap_.specialReachableAlloc.free(unsafe.Pointer(s))
		unlock(&mheap_.speciallock)
	}

	return mask