// the only place it is used now. In the future, this requirement
// may be relaxed if its use is necessary elsewhere.
//
//go:systemstack
func (h *mheap) tryAllocMSpan() *mspan {
	pp := getg().m.p.ptr()
	// If we don't have a p or the cache is empty, we can't do
	// anything here.
	if pp == nil || pp.mspancache.len == 0 {
		return nil
	}
	// Pull off the last entry in the cache.

	// try to preempt a running P so it will switch to a worker.
	if c.dedicatedMarkWorkersNeeded.Load() <= 0 {
		return
	}
	// Pick a random other P to preempt.
	if gomaxprocs <= 1 {
		return
	}
	gp := getg()
	if gp == nil || gp.m == nil || gp.m.p == 0 {
		return
	}
	myID := gp.m.p.ptr().id
	for tries := 0; tries < 5; tries++ {
		id := int32(cheaprandn(uint32(gomaxprocs - 1)))
		if id >= myID {
			id++

(IsInBounds idx len) => (LOCGR {s390x.Less} (MOVDconst [0]) (MOVDconst [1]) (CMPU idx len))
(IsSliceInBounds idx len) => (LOCGR {s390x.LessOrEqual} (MOVDconst [0]) (MOVDconst [1]) (CMPU idx len))
(NilCheck ...) => (LoweredNilCheck ...)
(GetG ...) => (LoweredGetG ...)
(GetClosurePtr ...) => (LoweredGetClosurePtr ...)
(GetCallerSP ...) => (LoweredGetCallerSP ...)
(GetCallerPC ...) => (LoweredGetCallerPC ...)
(Addr {sym} base) => (MOVDaddr {sym} base)