// since we're not holding the heap lock.
		s.spanclass = spanclass
		if sizeclass := spanclass.sizeclass(); sizeclass == 0 {
			s.elemsize = nbytes
			s.nelems = 1
			s.divMul = 0
		} else {
			s.elemsize = uintptr(class_to_size[sizeclass])
			if !s.spanclass.noscan() && heapBitsInSpan(s.elemsize) {
				// Reserve space for the pointer/scan bitmap at the end.

			if hasHeader {
				size += mallocHeaderSize
			}
			var sizeclass uint8
			if size <= smallSizeMax-8 {
				sizeclass = size_to_class8[divRoundUp(size, smallSizeDiv)]
			} else {
				sizeclass = size_to_class128[divRoundUp(size-smallSizeMax, largeSizeDiv)]
			}
			size = uintptr(class_to_size[sizeclass])
			spc := makeSpanClass(sizeclass, noscan)
			span = c.alloc[spc]
			v := nextFreeFast(span)

		// Handle header-less objects.
		return typePointers{elem: addr, addr: addr, mask: span.heapBitsSmallForAddr(addr)}
	}

	// All of these objects have a header.
	var typ *_type
	if spc.sizeclass() != 0 {
		// Pull the allocation header from the first word of the object.
		typ = *(**_type)(unsafe.Pointer(addr))
		addr += mallocHeaderSize
	} else {
		typ = span.largeType
		if typ == nil {