// whether the span has been zeroed. Note that it may not be.
func (h *mheap) alloc(npages uintptr, spanclass spanClass) *mspan {
	// Don't do any operations that lock the heap on the G stack.
	// It might trigger stack growth, and the stack growth code needs
	// to be able to allocate heap.
	var s *mspan
	systemstack(func() {
		// To prevent excessive heap growth, before allocating n pages

// Called when backing up on a branch.
func (ft *factsTable) restore() {
	if ft.unsatDepth > 0 {
		ft.unsatDepth--
	} else {
		ft.unsat = false
	}
	for {
		old := ft.stack[len(ft.stack)-1]
		ft.stack = ft.stack[:len(ft.stack)-1]
		if old == checkpointFact {
			break
		}
		if old.r == lt|eq|gt {
			delete(ft.facts, old.p)
		} else {
			ft.facts[old.p] = old.r
		}
	}
	for {

		// Do not include local development, so that people working in the
		// main branch for day-to-day work on the Go toolchain itself can
		// still have full paths for stack traces for compiler crashes and the like.
		env = append(env, "GOFLAGS=-trimpath -ldflags=-w -gcflags=cmd/...=-dwarf=false")
	}
	return env
}

	// max(maxID, numLMS/2). This level of the recursion needs maxID,
	// and all deeper levels of the recursion will need no more than numLMS/2,
	// so this one allocation is guaranteed to suffice for the entire stack
	// of recursive calls.
	tmp := oldTmp
	if len(tmp) < len(saTmp) {
		tmp = saTmp
	}
	if len(tmp) < numLMS {
		// TestSAIS/forcealloc reaches this code.
		n := maxID
		if n < numLMS/2 {

// minIovec is the size of the small initial allocation used by
// Readv, Writev, etc.
//
// This small allocation gets stack allocated, which lets the
// common use case of len(iovs) <= minIovs avoid more expensive
// heap allocations.
const minIovec = 8

// appendBytes converts bs to Iovecs and appends them to vecs.

//
// There are 3 cases today (as paraphrased from the ELFv2 document):
//
//  1. R2 holds the TOC pointer on entry. The call stub must save R2 into the ELFv2 TOC stack save slot.
//
//  2. R2 holds the TOC pointer on entry. The caller has already saved R2 to the TOC stack save slot.
//
//  3. R2 does not hold the TOC pointer on entry. The caller has no expectations of R2.
//

		re1 := p.stack[n-1]
		re3 := p.stack[n-3]
		// Make re3 the more complex of the two.
		if re1.Op > re3.Op {
			re1, re3 = re3, re1
			p.stack[n-3] = re3
		}
		mergeCharClass(re3, re1)
		p.reuse(re1)
		p.stack = p.stack[:n-1]
		return true
	}

	if n >= 2 {
		re1 := p.stack[n-1]
		re2 := p.stack[n-2]
		if re2.Op == opVerticalBar {
			if n >= 3 {

		// assignments, so it won't use much stack space, so
		// it's OK to not split the stack. Splitting the stack
		// can run into a bug in clang (as of 2018-11-09):
		// this is a leaf function, and when clang sees a leaf
		// function it won't emit the split stack prologue for
		// the function. However, if this function refers to a
		// non-split-stack function, which will happen if the

	// lastStackScan is the number of bytes of stack that were scanned
	// last GC cycle.
	lastStackScan atomic.Uint64

	// maxStackScan is the amount of allocated goroutine stack space in
	// use by goroutines.
	//
	// This number tracks allocated goroutine stack space rather than used
	// goroutine stack space (i.e. what is actually scanned) because used
	// goroutine stack space is much harder to measure cheaply. By using

			alignedValue := p.From.Offset
			v := pcAlignPadLength(pc, alignedValue)
			pc += int64(v)
		}
	}
	return pc
}

// stackOffset updates Addr offsets based on the current stack size.
//
// The stack looks like:
// -------------------
// |                 |
// |      PARAMs     |
// |                 |
// |                 |
// -------------------
// |    Parent RA    |   SP on function entry