before they become visible as GC roots. Otherwise, the GC may
   observe stale heap pointers. See "Zero-initialization versus
   zeroing".

Zero-initialization versus zeroing
==================================

There are two types of zeroing in the runtime, depending on whether
the memory is already initialized to a type-safe state.

If memory is not in a type-safe state, meaning it potentially contains

	var to unsafe.Pointer
	if !et.Pointers() {
		to = mallocgc(tomem, nil, false)
		if copymem < tomem {
			memclrNoHeapPointers(add(to, copymem), tomem-copymem)
		}
	} else {
		// Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.
		to = mallocgc(tomem, et, true)
		if copymem > 0 && writeBarrier.enabled {
			// Only shade the pointers in old.array since we know the destination slice to

	if goexperiment.CgoCheck2 {
		cgoCheckMemmove2(typ, dst, src, 0, typ.Size_)
	}
}

// wbZero performs the write barrier operations necessary before
// zeroing a region of memory at address dst of type typ.
// Does not actually do the zeroing.
//
//go:nowritebarrierrec
//go:nosplit
func wbZero(typ *_type, dst unsafe.Pointer) {
	// This always copies a full value of type typ so it's safe

	} else {
		n.(*ir.AssignStmt).X = left
	}
	as := n.(*ir.AssignStmt)

	if oaslit(as, init) {
		return ir.NewBlockStmt(as.Pos(), nil)
	}

	if as.Y == nil {
		// TODO(austin): Check all "implicit zeroing"
		return as
	}

	if !base.Flag.Cfg.Instrumenting && ir.IsZero(as.Y) {
		return as
	}

	switch as.Y.Op() {
	default:
		as.Y = walkExpr(as.Y, init)

	case ir.ORECV:

	// Sort pointer-typed before non-pointer types.
	// Keeps the stack's GC bitmap compact.
	ap := a.Type().HasPointers()
	bp := b.Type().HasPointers()
	if ap != bp {
		return ap
	}

	// Group variables that need zeroing, so we can efficiently zero
	// them altogether.
	ap = a.Needzero()
	bp = b.Needzero()
	if ap != bp {
		return ap
	}

	// Sort variables in descending alignment order, so we can optimally

				(MOVDstore ptr (MOVDconst [0]) mem))))

// Medium 8-aligned zeroing uses a Duff's device
// 8 and 128 are magic constants, see runtime/mkduff.go
(Zero [s] {t} ptr mem)
	&& s%8 == 0 && s <= 8*128
	&& t.Alignment()%8 == 0 && !config.noDuffDevice =>
	(DUFFZERO [8 * (128 - s/8)] ptr mem)

// Generic zeroing uses a loop
(Zero [s] {t} ptr mem) =>
	(LoweredZero [t.Alignment()]
		ptr

	// not Linux decides to back this memory with transparent huge
	// pages. There's latency involved in this zeroing, but the hugepage
	// gains are almost always worth it. Note: it's important that we
	// clear even if it's freshly mapped and we know there's no point
	// to zeroing as *that* is the critical signal to use huge pages.
	memclrNoHeapPointers(unsafe.Pointer(s.base()), s.elemsize)
	s.needzero = 0

	b.Kind = kind
	b.ResetControls()
	b.Aux = nil
	b.AuxInt = 0
	b.Controls[0] = v
	b.Controls[1] = w
	v.Uses++
	w.Uses++
}

// truncateValues truncates b.Values at the ith element, zeroing subsequent elements.
// The values in b.Values after i must already have had their args reset,
// to maintain correct value uses counts.
func (b *Block) truncateValues(i int) {
	tail := b.Values[i:]

             * corresponds to the least significant nonzero byte in lw ^ rw, since lw and rw are
             * little-endian. Long.numberOfTrailingZeros(diff) tells us the least significant
             * nonzero bit, and zeroing out the first three bits of L.nTZ gives us the shift to get
             * that least significant nonzero byte.
             */
            int n = Long.numberOfTrailingZeros(lw ^ rw) & ~0x7;

             * corresponds to the least significant nonzero byte in lw ^ rw, since lw and rw are
             * little-endian. Long.numberOfTrailingZeros(diff) tells us the least significant
             * nonzero bit, and zeroing out the first three bits of L.nTZ gives us the shift to get
             * that least significant nonzero byte.
             */
            int n = Long.numberOfTrailingZeros(lw ^ rw) & ~0x7;