// In terms of 32-bit halves, this is:
	// 	x1:x0 := r.Uint64()
	// 	0:hi, lo1:lo0 := bits.Mul64(x1:x0, 0:n)
	// Writing out the multiplication in terms of bits.Mul32 allows
	// using direct hardware instructions and avoiding
	// the computations involving these zeros.
	x := r.Uint64()
	lo1a, lo0 := bits.Mul32(uint32(x), n)
	hi, lo1b := bits.Mul32(uint32(x>>32), n)
	lo1, c := bits.Add32(lo1a, lo1b, 0)
	hi += c

	r := pr.newReader(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)
	pkg := r.pkg()
	r.Bool() // TODO(mdempsky): Remove; was "has init"

	for i, n := 0, r.Len(); i < n; i++ {
		// As if r.obj(), but avoiding the Scope.Lookup call,
		// to avoid eager loading of imports.
		r.Sync(pkgbits.SyncObject)
		assert(!r.Bool())
		r.p.objIdx(r.Reloc(pkgbits.RelocObj))
		assert(r.Len() == 0)
	}

	r.Sync(pkgbits.SyncEOF)

	}
}

func TestGcZombieReporting(t *testing.T) {
	// This test is somewhat sensitive to how the allocator works.
	// Pointers in zombies slice may cross-span, thus we
	// add invalidptr=0 for avoiding the badPointer check.
	// See issue https://golang.org/issues/49613/
	got := runTestProg(t, "testprog", "GCZombie", "GODEBUG=invalidptr=0")
	want := "found pointer to free object"
	if !strings.Contains(got, want) {

	// Only pass the expanding context to the new instance if their packages
	// match. Since type reference cycles are only possible within a single
	// package, this is sufficient for the purposes of short-circuiting cycles.
	// Avoiding passing the context in other cases prevents unnecessary coupling
	// of types across packages.
	if expanding != nil && expanding.Obj().pkg == obj.pkg {
		inst.ctxt = expanding.inst.ctxt
	}

The build cache works by storing (locally or remotely) build outputs and allowing builds to fetch these outputs from the cache when it is determined that inputs have not changed, avoiding the expensive work of regenerating them.

A first feature using the build cache is _task output caching_.

	// Only pass the expanding context to the new instance if their packages
	// match. Since type reference cycles are only possible within a single
	// package, this is sufficient for the purposes of short-circuiting cycles.
	// Avoiding passing the context in other cases prevents unnecessary coupling
	// of types across packages.
	if expanding != nil && expanding.Obj().pkg == obj.pkg {
		inst.ctxt = expanding.inst.ctxt
	}

      Multiset<E> multisetToModify, Multiset<?> occurrencesToRetain) {
    checkNotNull(multisetToModify);
    checkNotNull(occurrencesToRetain);
    // Avoiding ConcurrentModificationExceptions is tricky.
    Iterator<Entry<E>> entryIterator = multisetToModify.entrySet().iterator();
    boolean changed = false;
    while (entryIterator.hasNext()) {

// is smaller. Above maxCapacity decisions about allocation are left
// to the Go runtime on append. This allows a caller to make an
// educated guess about the potential size of the total list while
// still avoiding overly aggressive initial allocation. If sizes
// is empty maxCapacity will be used as the size to grow.
func growSlice(v reflect.Value, maxCapacity int, sizes ...int) {
	cap := v.Cap()
	max := cap

Just avoiding the copy of files doesn't necessarily improve things too much, but because it used the cache for that step, it can **use the cache for the next step**. For example, it could use the cache for the instruction that installs dependencies with:

	// dispatchEvent() call. That may prevent Go GC from freeing items
	// from previous phases that are sitting behind the current length
	// of the slice, but there is only a limited number of those and the
	// gain from avoiding memory allocations is much bigger.
	c.watchersBuffer = c.watchersBuffer[:0]

	if event.Type == watch.Bookmark {
		c.startDispatchingBookmarkEventsLocked()