newC := buildTypeAssertCache(oldC, t, tab)

	// Update cache. Use compare-and-swap so if multiple threads
	// are fighting to update the cache, at least one of their
	// updates will stick.
	atomic_casPointer((*unsafe.Pointer)(unsafe.Pointer(&s.Cache)), unsafe.Pointer(oldC), unsafe.Pointer(newC))

	return tab
}

func buildTypeAssertCache(oldC *abi.TypeAssertCache, typ *_type, tab *itab) *abi.TypeAssertCache {