// Allocate black during GC.
	// All slots hold nil so no scanning is needed.
	// This may be racing with GC so do it atomically if there can be
	// a race marking the bit.
	if gcphase != _GCoff {
		gcmarknewobject(span, span.base())
	}

	if raceenabled {
		// TODO(mknyszek): Track individual objects.
		racemalloc(unsafe.Pointer(span.base()), span.elemsize)
	}

	if msanenabled {