// or after s.freeindex.
// There are hardware instructions that can be used to make this
// faster if profiling warrants it.
func (s *mspan) nextFreeIndex() uint16 {
	sfreeindex := s.freeindex
	snelems := s.nelems
	if sfreeindex == snelems {
		return sfreeindex
	}
	if sfreeindex > snelems {
		throw("s.freeindex > s.nelems")
	}

	aCache := s.allocCache

			}
			if s, ok := sl.tryAcquire(s); ok {
				// We got ownership of the span, so let's sweep it.
				s.sweep(true)
				// Check if there's any free space.
				freeIndex := s.nextFreeIndex()
				if freeIndex != s.nelems {
					s.freeindex = freeIndex
					sweep.active.end(sl)
					goto havespan
				}
				// Add it to the swept list, because sweeping didn't give us any free space.
				c.fullSwept(sg).push(s.mspan)

			}
			mbits.advance()
			abits.advance()
		}
	}

	// Check for zombie objects.
	if s.freeindex < s.nelems {
		// Everything < freeindex is allocated and hence
		// cannot be zombies.
		//
		// Check the first bitmap byte, where we have to be
		// careful with freeindex.
		obj := uintptr(s.freeindex)
		if (*s.gcmarkBits.bytep(obj / 8)&^*s.allocBits.bytep(obj / 8))>>(obj%8) != 0 {
			s.reportZombies()
		}

		n := (s.npages << _PageShift) / size
		if n > uintptr(len(freemark)) {
			throw("freemark array doesn't have enough entries")
		}

		for freeIndex := uint16(0); freeIndex < s.nelems; freeIndex++ {
			if s.isFree(uintptr(freeIndex)) {
				freemark[freeIndex] = true
			}
		}

		for j := uintptr(0); j < n; j, p = j+1, p+size {
			if freemark[j] {
				freemark[j] = false
				continue
			}

	s = c.alloc[spc]
	shouldhelpgc = false
	freeIndex := s.nextFreeIndex()
	if freeIndex == s.nelems {
		// The span is full.
		if s.allocCount != s.nelems {
			println("runtime: s.allocCount=", s.allocCount, "s.nelems=", s.nelems)
			throw("s.allocCount != s.nelems && freeIndex == s.nelems")
		}
		c.refill(spc)
		shouldhelpgc = true
		s = c.alloc[spc]

		freeIndex = s.nextFreeIndex()
	}

	frMLIndex         ID = 319
	frMQIndex         ID = 320
	frMRIndex         ID = 321
	frMUIndex         ID = 322
	frNCIndex         ID = 323
	frNEIndex         ID = 324
	frPFIndex         ID = 325
	frPMIndex         ID = 326
	frREIndex         ID = 327
	frRWIndex         ID = 328
	frSCIndex         ID = 329
	frSNIndex         ID = 330
	frSYIndex         ID = 331
	frTDIndex         ID = 332

	// freeindex is the slot index between 0 and nelems at which to begin scanning
	// for the next free object in this span.
	// Each allocation scans allocBits starting at freeindex until it encounters a 0
	// indicating a free object. freeindex is then adjusted so that subsequent scans begin
	// just past the newly discovered free object.
	//
	// If freeindex == nelem, this span has no free objects.
	//

		if s.state.get() != mSpanInUse {
			continue
		}

		// Find all allocated objects.
		abits := s.allocBitsForIndex(0)
		for i := uintptr(0); i < uintptr(s.nelems); i++ {
			if abits.index < uintptr(s.freeindex) || abits.isMarked() {
				x := s.base() + i*s.elemsize
				trace.HeapObjectExists(x, s.typePointersOfUnchecked(x).typ)
			}
			abits.advance()
		}
	}

	// Write out all the goroutine stacks.

	spc := makeSpanClass(0, false)
	h.initSpan(s, spanAllocHeap, spc, base, userArenaChunkPages)
	s.isUserArenaChunk = true
	s.elemsize -= userArenaChunkReserveBytes()
	s.limit = s.base() + s.elemsize
	s.freeindex = 1
	s.allocCount = 1

	// Account for this new arena chunk memory.
	gcController.heapInUse.add(int64(userArenaChunkBytes))
	gcController.heapReleased.add(-int64(userArenaChunkBytes))