src/runtime/gc_test.go - go - Git at Google

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package runtime_test

 import (
 	"fmt"
 	"internal/asan"
 	"math/bits"
 	"math/rand"
 	"os"
 	"reflect"
 	"runtime"
 	"runtime/debug"
 	"slices"
 	"strings"
 	"sync"
 	"sync/atomic"
 	"testing"
 	"time"
 	"unsafe"
 )

 func TestGcSys(t *testing.T) {
 	t.Skip("skipping known-flaky test; golang.org/issue/37331")
 	if os.Getenv("GOGC") == "off" {
 		t.Skip("skipping test; GOGC=off in environment")
 	}
 	got := runTestProg(t, "testprog", "GCSys")
 	want := "OK\n"
 	if got != want {
 		t.Fatalf("expected %q, but got %q", want, got)
 	}
 }

 func TestGcDeepNesting(t *testing.T) {
 	type T [2][2][2][2][2][2][2][2][2][2]*int
 	a := new(T)

 	// Prevent the compiler from applying escape analysis.
 	// This makes sure new(T) is allocated on heap, not on the stack.
 	t.Logf("%p", a)

 	a[0][0][0][0][0][0][0][0][0][0] = new(int)
 	*a[0][0][0][0][0][0][0][0][0][0] = 13
 	runtime.GC()
 	if *a[0][0][0][0][0][0][0][0][0][0] != 13 {
 		t.Fail()
 	}
 }

 func TestGcMapIndirection(t *testing.T) {
 	defer debug.SetGCPercent(debug.SetGCPercent(1))
 	runtime.GC()
 	type T struct {
 		a [256]int
 	}
 	m := make(map[T]T)
 	for i := 0; i < 2000; i++ {
 		var a T
 		a.a[0] = i
 		m[a] = T{}
 	}
 }

 func TestGcArraySlice(t *testing.T) {
 	type X struct {
 		buf     [1]byte
 		nextbuf []byte
 		next    *X
 	}
 	var head *X
 	for i := 0; i < 10; i++ {
 		p := &X{}
 		p.buf[0] = 42
 		p.next = head
 		if head != nil {
 			p.nextbuf = head.buf[:]
 		}
 		head = p
 		runtime.GC()
 	}
 	for p := head; p != nil; p = p.next {
 		if p.buf[0] != 42 {
 			t.Fatal("corrupted heap")
 		}
 	}
 }

 func TestGcRescan(t *testing.T) {
 	type X struct {
 		c     chan error
 		nextx *X
 	}
 	type Y struct {
 		X
 		nexty *Y
 		p     *int
 	}
 	var head *Y
 	for i := 0; i < 10; i++ {
 		p := &Y{}
 		p.c = make(chan error)
 		if head != nil {
 			p.nextx = &head.X
 		}
 		p.nexty = head
 		p.p = new(int)
 		*p.p = 42
 		head = p
 		runtime.GC()
 	}
 	for p := head; p != nil; p = p.nexty {
 		if *p.p != 42 {
 			t.Fatal("corrupted heap")
 		}
 	}
 }

 func TestGcLastTime(t *testing.T) {
 	ms := new(runtime.MemStats)
 	t0 := time.Now().UnixNano()
 	runtime.GC()
 	t1 := time.Now().UnixNano()
 	runtime.ReadMemStats(ms)
 	last := int64(ms.LastGC)
 	if t0 > last || last > t1 {
 		t.Fatalf("bad last GC time: got %v, want [%v, %v]", last, t0, t1)
 	}
 	pause := ms.PauseNs[(ms.NumGC+255)%256]
 	// Due to timer granularity, pause can actually be 0 on windows
 	// or on virtualized environments.
 	if pause == 0 {
 		t.Logf("last GC pause was 0")
 	} else if pause > 10e9 {
 		t.Logf("bad last GC pause: got %v, want [0, 10e9]", pause)
 	}
 }

 var hugeSink any

 func TestHugeGCInfo(t *testing.T) {
 	// The test ensures that compiler can chew these huge types even on weakest machines.
 	// The types are not allocated at runtime.
 	if hugeSink != nil {
 		// 400MB on 32 bots, 4TB on 64-bits.
 		const n = (400 << 20) + (unsafe.Sizeof(uintptr(0))-4)<<40
 		hugeSink = new([n]*byte)
 		hugeSink = new([n]uintptr)
 		hugeSink = new(struct {
 			x float64
 			y [n]*byte
 			z []string
 		})
 		hugeSink = new(struct {
 			x float64
 			y [n]uintptr
 			z []string
 		})
 	}
 }

 func TestPeriodicGC(t *testing.T) {
 	if runtime.GOARCH == "wasm" {
 		t.Skip("no sysmon on wasm yet")
 	}

 	// Make sure we're not in the middle of a GC.
 	runtime.GC()

 	var ms1, ms2 runtime.MemStats
 	runtime.ReadMemStats(&ms1)

 	// Make periodic GC run continuously.
 	orig := *runtime.ForceGCPeriod
 	*runtime.ForceGCPeriod = 0

 	// Let some periodic GCs happen. In a heavily loaded system,
 	// it's possible these will be delayed, so this is designed to
 	// succeed quickly if things are working, but to give it some
 	// slack if things are slow.
 	var numGCs uint32
 	const want = 2
 	for i := 0; i < 200 && numGCs < want; i++ {
 		time.Sleep(5 * time.Millisecond)

 		// Test that periodic GC actually happened.
 		runtime.ReadMemStats(&ms2)
 		numGCs = ms2.NumGC - ms1.NumGC
 	}
 	*runtime.ForceGCPeriod = orig

 	if numGCs < want {
 		t.Fatalf("no periodic GC: got %v GCs, want >= 2", numGCs)
 	}
 }

 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) {
 		t.Fatalf("expected %q in output, but got %q", want, got)
 	}
 }

 func TestGCTestMoveStackOnNextCall(t *testing.T) {
 	if asan.Enabled {
 		t.Skip("extra allocations with -asan causes this to fail; see #70079")
 	}
 	t.Parallel()
 	var onStack int
 	// GCTestMoveStackOnNextCall can fail in rare cases if there's
 	// a preemption. This won't happen many times in quick
 	// succession, so just retry a few times.
 	for retry := 0; retry < 5; retry++ {
 		runtime.GCTestMoveStackOnNextCall()
 		if moveStackCheck(t, &onStack, uintptr(unsafe.Pointer(&onStack))) {
 			// Passed.
 			return
 		}
 	}
 	t.Fatal("stack did not move")
 }

 // This must not be inlined because the point is to force a stack
 // growth check and move the stack.
 //
 //go:noinline
 func moveStackCheck(t *testing.T, new *int, old uintptr) bool {
 	// new should have been updated by the stack move;
 	// old should not have.

 	// Capture new's value before doing anything that could
 	// further move the stack.
 	new2 := uintptr(unsafe.Pointer(new))

 	t.Logf("old stack pointer %x, new stack pointer %x", old, new2)
 	if new2 == old {
 		// Check that we didn't screw up the test's escape analysis.
 		if cls := runtime.GCTestPointerClass(unsafe.Pointer(new)); cls != "stack" {
 			t.Fatalf("test bug: new (%#x) should be a stack pointer, not %s", new2, cls)
 		}
 		// This was a real failure.
 		return false
 	}
 	return true
 }

 func TestGCTestMoveStackRepeatedly(t *testing.T) {
 	// Move the stack repeatedly to make sure we're not doubling
 	// it each time.
 	for i := 0; i < 100; i++ {
 		runtime.GCTestMoveStackOnNextCall()
 		moveStack1(false)
 	}
 }

 //go:noinline
 func moveStack1(x bool) {
 	// Make sure this function doesn't get auto-nosplit.
 	if x {
 		println("x")
 	}
 }

 func TestGCTestIsReachable(t *testing.T) {
 	var all, half []unsafe.Pointer
 	var want uint64
 	for i := 0; i < 16; i++ {
 		// The tiny allocator muddies things, so we use a
 		// scannable type.
 		p := unsafe.Pointer(new(*int))
 		all = append(all, p)
 		if i%2 == 0 {
 			half = append(half, p)
 			want |= 1 << i
 		}
 	}

 	got := runtime.GCTestIsReachable(all...)
 	if got&want != want {
 		// This is a serious bug - an object is live (due to the KeepAlive
 		// call below), but isn't reported as such.
 		t.Fatalf("live object not in reachable set; want %b, got %b", want, got)
 	}
 	if bits.OnesCount64(got&^want) > 1 {
 		// Note: we can occasionally have a value that is retained even though
 		// it isn't live, due to conservative scanning of stack frames.
 		// See issue 67204. For now, we allow a "slop" of 1 unintentionally
 		// retained object.
 		t.Fatalf("dead object in reachable set; want %b, got %b", want, got)
 	}
 	runtime.KeepAlive(half)
 }

 var pointerClassBSS *int
 var pointerClassData = 42

 func TestGCTestPointerClass(t *testing.T) {
 	if asan.Enabled {
 		t.Skip("extra allocations cause this test to fail; see #70079")
 	}
 	t.Parallel()
 	check := func(p unsafe.Pointer, want string) {
 		t.Helper()
 		got := runtime.GCTestPointerClass(p)
 		if got != want {
 			// Convert the pointer to a uintptr to avoid
 			// escaping it.
 			t.Errorf("for %#x, want class %s, got %s", uintptr(p), want, got)
 		}
 	}
 	var onStack int
 	var notOnStack int
 	check(unsafe.Pointer(&onStack), "stack")
 	check(unsafe.Pointer(runtime.Escape(&notOnStack)), "heap")
 	check(unsafe.Pointer(&pointerClassBSS), "bss")
 	check(unsafe.Pointer(&pointerClassData), "data")
 	check(nil, "other")
 }

 func BenchmarkAllocation(b *testing.B) {
 	type T struct {
 		x, y *byte
 	}
 	ngo := runtime.GOMAXPROCS(0)
 	work := make(chan bool, b.N+ngo)
 	result := make(chan *T)
 	for i := 0; i < b.N; i++ {
 		work <- true
 	}
 	for i := 0; i < ngo; i++ {
 		work <- false
 	}
 	for i := 0; i < ngo; i++ {
 		go func() {
 			var x *T
 			for <-work {
 				for i := 0; i < 1000; i++ {
 					x = &T{}
 				}
 			}
 			result <- x
 		}()
 	}
 	for i := 0; i < ngo; i++ {
 		<-result
 	}
 }

 func TestPrintGC(t *testing.T) {
 	if testing.Short() {
 		t.Skip("Skipping in short mode")
 	}
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
 	done := make(chan bool)
 	go func() {
 		for {
 			select {
 			case <-done:
 				return
 			default:
 				runtime.GC()
 			}
 		}
 	}()
 	for i := 0; i < 1e4; i++ {
 		func() {
 			defer print("")
 		}()
 	}
 	close(done)
 }

 func testTypeSwitch(x any) error {
 	switch y := x.(type) {
 	case nil:
 		// ok
 	case error:
 		return y
 	}
 	return nil
 }

 func testAssert(x any) error {
 	if y, ok := x.(error); ok {
 		return y
 	}
 	return nil
 }

 func testAssertVar(x any) error {
 	var y, ok = x.(error)
 	if ok {
 		return y
 	}
 	return nil
 }

 var a bool

 //go:noinline
 func testIfaceEqual(x any) {
 	if x == "abc" {
 		a = true
 	}
 }

 func TestPageAccounting(t *testing.T) {
 	// Grow the heap in small increments. This used to drop the
 	// pages-in-use count below zero because of a rounding
 	// mismatch (golang.org/issue/15022).
 	const blockSize = 64 << 10
 	blocks := make([]*[blockSize]byte, (64<<20)/blockSize)
 	for i := range blocks {
 		blocks[i] = new([blockSize]byte)
 	}

 	// Check that the running page count matches reality.
 	pagesInUse, counted := runtime.CountPagesInUse()
 	if pagesInUse != counted {
 		t.Fatalf("mheap_.pagesInUse is %d, but direct count is %d", pagesInUse, counted)
 	}
 }

 func init() {
 	// Enable ReadMemStats' double-check mode.
 	*runtime.DoubleCheckReadMemStats = true
 }

 func TestReadMemStats(t *testing.T) {
 	base, slow := runtime.ReadMemStatsSlow()
 	if base != slow {
 		logDiff(t, "MemStats", reflect.ValueOf(base), reflect.ValueOf(slow))
 		t.Fatal("memstats mismatch")
 	}
 }

 func logDiff(t *testing.T, prefix string, got, want reflect.Value) {
 	typ := got.Type()
 	switch typ.Kind() {
 	case reflect.Array, reflect.Slice:
 		if got.Len() != want.Len() {
 			t.Logf("len(%s): got %v, want %v", prefix, got, want)
 			return
 		}
 		for i := 0; i < got.Len(); i++ {
 			logDiff(t, fmt.Sprintf("%s[%d]", prefix, i), got.Index(i), want.Index(i))
 		}
 	case reflect.Struct:
 		for i := 0; i < typ.NumField(); i++ {
 			gf, wf := got.Field(i), want.Field(i)
 			logDiff(t, prefix+"."+typ.Field(i).Name, gf, wf)
 		}
 	case reflect.Map:
 		t.Fatal("not implemented: logDiff for map")
 	default:
 		if got.Interface() != want.Interface() {
 			t.Logf("%s: got %v, want %v", prefix, got, want)
 		}
 	}
 }

 func BenchmarkReadMemStats(b *testing.B) {
 	var ms runtime.MemStats
 	const heapSize = 100 << 20
 	x := make([]*[1024]byte, heapSize/1024)
 	for i := range x {
 		x[i] = new([1024]byte)
 	}

 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		runtime.ReadMemStats(&ms)
 	}

 	runtime.KeepAlive(x)
 }

 func applyGCLoad(b *testing.B) func() {
 	// We’ll apply load to the runtime with maxProcs-1 goroutines
 	// and use one more to actually benchmark. It doesn't make sense
 	// to try to run this test with only 1 P (that's what
 	// BenchmarkReadMemStats is for).
 	maxProcs := runtime.GOMAXPROCS(-1)
 	if maxProcs == 1 {
 		b.Skip("This benchmark can only be run with GOMAXPROCS > 1")
 	}

 	// Code to build a big tree with lots of pointers.
 	type node struct {
 		children [16]*node
 	}
 	var buildTree func(depth int) *node
 	buildTree = func(depth int) *node {
 		tree := new(node)
 		if depth != 0 {
 			for i := range tree.children {
 				tree.children[i] = buildTree(depth - 1)
 			}
 		}
 		return tree
 	}

 	// Keep the GC busy by continuously generating large trees.
 	done := make(chan struct{})
 	var wg sync.WaitGroup
 	for i := 0; i < maxProcs-1; i++ {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
 			var hold *node
 		loop:
 			for {
 				hold = buildTree(5)
 				select {
 				case <-done:
 					break loop
 				default:
 				}
 			}
 			runtime.KeepAlive(hold)
 		}()
 	}
 	return func() {
 		close(done)
 		wg.Wait()
 	}
 }

 func BenchmarkReadMemStatsLatency(b *testing.B) {
 	stop := applyGCLoad(b)

 	// Spend this much time measuring latencies.
 	latencies := make([]time.Duration, 0, 1024)

 	// Run for timeToBench hitting ReadMemStats continuously
 	// and measuring the latency.
 	b.ResetTimer()
 	var ms runtime.MemStats
 	for i := 0; i < b.N; i++ {
 		// Sleep for a bit, otherwise we're just going to keep
 		// stopping the world and no one will get to do anything.
 		time.Sleep(100 * time.Millisecond)
 		start := time.Now()
 		runtime.ReadMemStats(&ms)
 		latencies = append(latencies, time.Since(start))
 	}
 	// Make sure to stop the timer before we wait! The load created above
 	// is very heavy-weight and not easy to stop, so we could end up
 	// confusing the benchmarking framework for small b.N.
 	b.StopTimer()
 	stop()

 	// Disable the default */op metrics.
 	// ns/op doesn't mean anything because it's an average, but we
 	// have a sleep in our b.N loop above which skews this significantly.
 	b.ReportMetric(0, "ns/op")
 	b.ReportMetric(0, "B/op")
 	b.ReportMetric(0, "allocs/op")

 	// Sort latencies then report percentiles.
 	slices.Sort(latencies)
 	b.ReportMetric(float64(latencies[len(latencies)*50/100]), "p50-ns")
 	b.ReportMetric(float64(latencies[len(latencies)*90/100]), "p90-ns")
 	b.ReportMetric(float64(latencies[len(latencies)*99/100]), "p99-ns")
 }

 func TestUserForcedGC(t *testing.T) {
 	// Test that runtime.GC() triggers a GC even if GOGC=off.
 	defer debug.SetGCPercent(debug.SetGCPercent(-1))

 	var ms1, ms2 runtime.MemStats
 	runtime.ReadMemStats(&ms1)
 	runtime.GC()
 	runtime.ReadMemStats(&ms2)
 	if ms1.NumGC == ms2.NumGC {
 		t.Fatalf("runtime.GC() did not trigger GC")
 	}
 	if ms1.NumForcedGC == ms2.NumForcedGC {
 		t.Fatalf("runtime.GC() was not accounted in NumForcedGC")
 	}
 }

 func writeBarrierBenchmark(b *testing.B, f func()) {
 	runtime.GC()
 	var ms runtime.MemStats
 	runtime.ReadMemStats(&ms)
 	//b.Logf("heap size: %d MB", ms.HeapAlloc>>20)

 	// Keep GC running continuously during the benchmark, which in
 	// turn keeps the write barrier on continuously.
 	var stop uint32
 	done := make(chan bool)
 	go func() {
 		for atomic.LoadUint32(&stop) == 0 {
 			runtime.GC()
 		}
 		close(done)
 	}()
 	defer func() {
 		atomic.StoreUint32(&stop, 1)
 		<-done
 	}()

 	b.ResetTimer()
 	f()
 	b.StopTimer()
 }

 func BenchmarkWriteBarrier(b *testing.B) {
 	if runtime.GOMAXPROCS(-1) < 2 {
 		// We don't want GC to take our time.
 		b.Skip("need GOMAXPROCS >= 2")
 	}

 	// Construct a large tree both so the GC runs for a while and
 	// so we have a data structure to manipulate the pointers of.
 	type node struct {
 		l, r *node
 	}
 	var wbRoots []*node
 	var mkTree func(level int) *node
 	mkTree = func(level int) *node {
 		if level == 0 {
 			return nil
 		}
 		n := &node{mkTree(level - 1), mkTree(level - 1)}
 		if level == 10 {
 			// Seed GC with enough early pointers so it
 			// doesn't start termination barriers when it
 			// only has the top of the tree.
 			wbRoots = append(wbRoots, n)
 		}
 		return n
 	}
 	const depth = 22 // 64 MB
 	root := mkTree(22)

 	writeBarrierBenchmark(b, func() {
 		var stack [depth]*node
 		tos := -1

 		// There are two write barriers per iteration, so i+=2.
 		for i := 0; i < b.N; i += 2 {
 			if tos == -1 {
 				stack[0] = root
 				tos = 0
 			}

 			// Perform one step of reversing the tree.
 			n := stack[tos]
 			if n.l == nil {
 				tos--
 			} else {
 				n.l, n.r = n.r, n.l
 				stack[tos] = n.l
 				stack[tos+1] = n.r
 				tos++
 			}

 			if i%(1<<12) == 0 {
 				// Avoid non-preemptible loops (see issue #10958).
 				runtime.Gosched()
 			}
 		}
 	})

 	runtime.KeepAlive(wbRoots)
 }

 func BenchmarkBulkWriteBarrier(b *testing.B) {
 	if runtime.GOMAXPROCS(-1) < 2 {
 		// We don't want GC to take our time.
 		b.Skip("need GOMAXPROCS >= 2")
 	}

 	// Construct a large set of objects we can copy around.
 	const heapSize = 64 << 20
 	type obj [16]*byte
 	ptrs := make([]*obj, heapSize/unsafe.Sizeof(obj{}))
 	for i := range ptrs {
 		ptrs[i] = new(obj)
 	}

 	writeBarrierBenchmark(b, func() {
 		const blockSize = 1024
 		var pos int
 		for i := 0; i < b.N; i += blockSize {
 			// Rotate block.
 			block := ptrs[pos : pos+blockSize]
 			first := block[0]
 			copy(block, block[1:])
 			block[blockSize-1] = first

 			pos += blockSize
 			if pos+blockSize > len(ptrs) {
 				pos = 0
 			}

 			runtime.Gosched()
 		}
 	})

 	runtime.KeepAlive(ptrs)
 }

 func BenchmarkScanStackNoLocals(b *testing.B) {
 	var ready sync.WaitGroup
 	teardown := make(chan bool)
 	for j := 0; j < 10; j++ {
 		ready.Add(1)
 		go func() {
 			x := 100000
 			countpwg(&x, &ready, teardown)
 		}()
 	}
 	ready.Wait()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		b.StartTimer()
 		runtime.GC()
 		runtime.GC()
 		b.StopTimer()
 	}
 	close(teardown)
 }

 func BenchmarkMSpanCountAlloc(b *testing.B) {
 	// Allocate one dummy mspan for the whole benchmark.
 	s := runtime.AllocMSpan()
 	defer runtime.FreeMSpan(s)

 	// n is the number of bytes to benchmark against.
 	// n must always be a multiple of 8, since gcBits is
 	// always rounded up 8 bytes.
 	for _, n := range []int{8, 16, 32, 64, 128} {
 		b.Run(fmt.Sprintf("bits=%d", n*8), func(b *testing.B) {
 			// Initialize a new byte slice with pseudo-random data.
 			bits := make([]byte, n)
 			rand.Read(bits)

 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {
 				runtime.MSpanCountAlloc(s, bits)
 			}
 		})
 	}
 }

 func countpwg(n *int, ready *sync.WaitGroup, teardown chan bool) {
 	if *n == 0 {
 		ready.Done()
 		<-teardown
 		return
 	}
 	*n--
 	countpwg(n, ready, teardown)
 }

 func TestMemoryLimit(t *testing.T) {
 	if testing.Short() {
 		t.Skip("stress test that takes time to run")
 	}
 	if runtime.NumCPU() < 4 {
 		t.Skip("want at least 4 CPUs for this test")
 	}
 	got := runTestProg(t, "testprog", "GCMemoryLimit")
 	want := "OK\n"
 	if got != want {
 		t.Fatalf("expected %q, but got %q", want, got)
 	}
 }

 func TestMemoryLimitNoGCPercent(t *testing.T) {
 	if testing.Short() {
 		t.Skip("stress test that takes time to run")
 	}
 	if runtime.NumCPU() < 4 {
 		t.Skip("want at least 4 CPUs for this test")
 	}
 	got := runTestProg(t, "testprog", "GCMemoryLimitNoGCPercent")
 	want := "OK\n"
 	if got != want {
 		t.Fatalf("expected %q, but got %q", want, got)
 	}
 }

 func TestMyGenericFunc(t *testing.T) {
 	runtime.MyGenericFunc[int]()
 }
	// Copyright 2011 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package runtime_test

	import (
	"fmt"
	"internal/asan"
	"math/bits"
	"math/rand"
	"os"
	"reflect"
	"runtime"
	"runtime/debug"
	"slices"
	"strings"
	"sync"
	"sync/atomic"
	"testing"
	"time"
	"unsafe"
	)

	func TestGcSys(t *testing.T) {
	t.Skip("skipping known-flaky test; golang.org/issue/37331")
	if os.Getenv("GOGC") == "off" {
	t.Skip("skipping test; GOGC=off in environment")
	}
	got := runTestProg(t, "testprog", "GCSys")
	want := "OK\n"
	if got != want {
	t.Fatalf("expected %q, but got %q", want, got)
	}
	}

	func TestGcDeepNesting(t *testing.T) {
	type T [2][2][2][2][2][2][2][2][2][2]*int
	a := new(T)

	// Prevent the compiler from applying escape analysis.
	// This makes sure new(T) is allocated on heap, not on the stack.
	t.Logf("%p", a)

	a[0][0][0][0][0][0][0][0][0][0] = new(int)
	*a[0][0][0][0][0][0][0][0][0][0] = 13
	runtime.GC()
	if *a[0][0][0][0][0][0][0][0][0][0] != 13 {
	t.Fail()
	}
	}

	func TestGcMapIndirection(t *testing.T) {
	defer debug.SetGCPercent(debug.SetGCPercent(1))
	runtime.GC()
	type T struct {
	a [256]int
	}
	m := make(map[T]T)
	for i := 0; i < 2000; i++ {
	var a T
	a.a[0] = i
	m[a] = T{}
	}
	}

	func TestGcArraySlice(t *testing.T) {
	type X struct {
	buf [1]byte
	nextbuf []byte
	next *X
	}
	var head *X
	for i := 0; i < 10; i++ {
	p := &X{}
	p.buf[0] = 42
	p.next = head
	if head != nil {
	p.nextbuf = head.buf[:]
	}
	head = p
	runtime.GC()
	}
	for p := head; p != nil; p = p.next {
	if p.buf[0] != 42 {
	t.Fatal("corrupted heap")
	}
	}
	}

	func TestGcRescan(t *testing.T) {
	type X struct {
	c chan error
	nextx *X
	}
	type Y struct {
	X
	nexty *Y
	p *int
	}
	var head *Y
	for i := 0; i < 10; i++ {
	p := &Y{}
	p.c = make(chan error)
	if head != nil {
	p.nextx = &head.X
	}
	p.nexty = head
	p.p = new(int)
	*p.p = 42
	head = p
	runtime.GC()
	}
	for p := head; p != nil; p = p.nexty {
	if *p.p != 42 {
	t.Fatal("corrupted heap")
	}
	}
	}

	func TestGcLastTime(t *testing.T) {
	ms := new(runtime.MemStats)
	t0 := time.Now().UnixNano()
	runtime.GC()
	t1 := time.Now().UnixNano()
	runtime.ReadMemStats(ms)
	last := int64(ms.LastGC)
	if t0 > last \|\| last > t1 {
	t.Fatalf("bad last GC time: got %v, want [%v, %v]", last, t0, t1)
	}
	pause := ms.PauseNs[(ms.NumGC+255)%256]
	// Due to timer granularity, pause can actually be 0 on windows
	// or on virtualized environments.
	if pause == 0 {
	t.Logf("last GC pause was 0")
	} else if pause > 10e9 {
	t.Logf("bad last GC pause: got %v, want [0, 10e9]", pause)
	}
	}

	var hugeSink any

	func TestHugeGCInfo(t *testing.T) {
	// The test ensures that compiler can chew these huge types even on weakest machines.
	// The types are not allocated at runtime.
	if hugeSink != nil {
	// 400MB on 32 bots, 4TB on 64-bits.
	const n = (400 << 20) + (unsafe.Sizeof(uintptr(0))-4)<<40
	hugeSink = new([n]*byte)
	hugeSink = new([n]uintptr)
	hugeSink = new(struct {
	x float64
	y [n]*byte
	z []string
	})
	hugeSink = new(struct {
	x float64
	y [n]uintptr
	z []string
	})
	}
	}

	func TestPeriodicGC(t *testing.T) {
	if runtime.GOARCH == "wasm" {
	t.Skip("no sysmon on wasm yet")
	}

	// Make sure we're not in the middle of a GC.
	runtime.GC()

	var ms1, ms2 runtime.MemStats
	runtime.ReadMemStats(&ms1)

	// Make periodic GC run continuously.
	orig := *runtime.ForceGCPeriod
	*runtime.ForceGCPeriod = 0

	// Let some periodic GCs happen. In a heavily loaded system,
	// it's possible these will be delayed, so this is designed to
	// succeed quickly if things are working, but to give it some
	// slack if things are slow.
	var numGCs uint32
	const want = 2
	for i := 0; i < 200 && numGCs < want; i++ {
	time.Sleep(5 * time.Millisecond)

	// Test that periodic GC actually happened.
	runtime.ReadMemStats(&ms2)
	numGCs = ms2.NumGC - ms1.NumGC
	}
	*runtime.ForceGCPeriod = orig

	if numGCs < want {
	t.Fatalf("no periodic GC: got %v GCs, want >= 2", numGCs)
	}
	}

	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) {
	t.Fatalf("expected %q in output, but got %q", want, got)
	}
	}

	func TestGCTestMoveStackOnNextCall(t *testing.T) {
	if asan.Enabled {
	t.Skip("extra allocations with -asan causes this to fail; see #70079")
	}
	t.Parallel()
	var onStack int
	// GCTestMoveStackOnNextCall can fail in rare cases if there's
	// a preemption. This won't happen many times in quick
	// succession, so just retry a few times.
	for retry := 0; retry < 5; retry++ {
	runtime.GCTestMoveStackOnNextCall()
	if moveStackCheck(t, &onStack, uintptr(unsafe.Pointer(&onStack))) {
	// Passed.
	return
	}
	}
	t.Fatal("stack did not move")
	}

	// This must not be inlined because the point is to force a stack
	// growth check and move the stack.
	//
	//go:noinline
	func moveStackCheck(t testing.T, new int, old uintptr) bool {
	// new should have been updated by the stack move;
	// old should not have.

	// Capture new's value before doing anything that could
	// further move the stack.
	new2 := uintptr(unsafe.Pointer(new))

	t.Logf("old stack pointer %x, new stack pointer %x", old, new2)
	if new2 == old {
	// Check that we didn't screw up the test's escape analysis.
	if cls := runtime.GCTestPointerClass(unsafe.Pointer(new)); cls != "stack" {
	t.Fatalf("test bug: new (%#x) should be a stack pointer, not %s", new2, cls)
	}
	// This was a real failure.
	return false
	}
	return true
	}

	func TestGCTestMoveStackRepeatedly(t *testing.T) {
	// Move the stack repeatedly to make sure we're not doubling
	// it each time.
	for i := 0; i < 100; i++ {
	runtime.GCTestMoveStackOnNextCall()
	moveStack1(false)
	}
	}

	//go:noinline
	func moveStack1(x bool) {
	// Make sure this function doesn't get auto-nosplit.
	if x {
	println("x")
	}
	}

	func TestGCTestIsReachable(t *testing.T) {
	var all, half []unsafe.Pointer
	var want uint64
	for i := 0; i < 16; i++ {
	// The tiny allocator muddies things, so we use a
	// scannable type.
	p := unsafe.Pointer(new(*int))
	all = append(all, p)
	if i%2 == 0 {
	half = append(half, p)
	want \|= 1 << i
	}
	}

	got := runtime.GCTestIsReachable(all...)
	if got&want != want {
	// This is a serious bug - an object is live (due to the KeepAlive
	// call below), but isn't reported as such.
	t.Fatalf("live object not in reachable set; want %b, got %b", want, got)
	}
	if bits.OnesCount64(got&^want) > 1 {
	// Note: we can occasionally have a value that is retained even though
	// it isn't live, due to conservative scanning of stack frames.
	// See issue 67204. For now, we allow a "slop" of 1 unintentionally
	// retained object.
	t.Fatalf("dead object in reachable set; want %b, got %b", want, got)
	}
	runtime.KeepAlive(half)
	}

	var pointerClassBSS *int
	var pointerClassData = 42

	func TestGCTestPointerClass(t *testing.T) {
	if asan.Enabled {
	t.Skip("extra allocations cause this test to fail; see #70079")
	}
	t.Parallel()
	check := func(p unsafe.Pointer, want string) {
	t.Helper()
	got := runtime.GCTestPointerClass(p)
	if got != want {
	// Convert the pointer to a uintptr to avoid
	// escaping it.
	t.Errorf("for %#x, want class %s, got %s", uintptr(p), want, got)
	}
	}
	var onStack int
	var notOnStack int
	check(unsafe.Pointer(&onStack), "stack")
	check(unsafe.Pointer(runtime.Escape(&notOnStack)), "heap")
	check(unsafe.Pointer(&pointerClassBSS), "bss")
	check(unsafe.Pointer(&pointerClassData), "data")
	check(nil, "other")
	}

	func BenchmarkAllocation(b *testing.B) {
	type T struct {
	x, y *byte
	}
	ngo := runtime.GOMAXPROCS(0)
	work := make(chan bool, b.N+ngo)
	result := make(chan *T)
	for i := 0; i < b.N; i++ {
	work <- true
	}
	for i := 0; i < ngo; i++ {
	work <- false
	}
	for i := 0; i < ngo; i++ {
	go func() {
	var x *T
	for <-work {
	for i := 0; i < 1000; i++ {
	x = &T{}
	}
	}
	result <- x
	}()
	}
	for i := 0; i < ngo; i++ {
	<-result
	}
	}

	func TestPrintGC(t *testing.T) {
	if testing.Short() {
	t.Skip("Skipping in short mode")
	}
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
	done := make(chan bool)
	go func() {
	for {
	select {
	case <-done:
	return
	default:
	runtime.GC()
	}
	}
	}()
	for i := 0; i < 1e4; i++ {
	func() {
	defer print("")
	}()
	}
	close(done)
	}

	func testTypeSwitch(x any) error {
	switch y := x.(type) {
	case nil:
	// ok
	case error:
	return y
	}
	return nil
	}

	func testAssert(x any) error {
	if y, ok := x.(error); ok {
	return y
	}
	return nil
	}

	func testAssertVar(x any) error {
	var y, ok = x.(error)
	if ok {
	return y
	}
	return nil
	}

	var a bool

	//go:noinline
	func testIfaceEqual(x any) {
	if x == "abc" {
	a = true
	}
	}

	func TestPageAccounting(t *testing.T) {
	// Grow the heap in small increments. This used to drop the
	// pages-in-use count below zero because of a rounding
	// mismatch (golang.org/issue/15022).
	const blockSize = 64 << 10
	blocks := make([]*[blockSize]byte, (64<<20)/blockSize)
	for i := range blocks {
	blocks[i] = new([blockSize]byte)
	}

	// Check that the running page count matches reality.
	pagesInUse, counted := runtime.CountPagesInUse()
	if pagesInUse != counted {
	t.Fatalf("mheap_.pagesInUse is %d, but direct count is %d", pagesInUse, counted)
	}
	}

	func init() {
	// Enable ReadMemStats' double-check mode.
	*runtime.DoubleCheckReadMemStats = true
	}

	func TestReadMemStats(t *testing.T) {
	base, slow := runtime.ReadMemStatsSlow()
	if base != slow {
	logDiff(t, "MemStats", reflect.ValueOf(base), reflect.ValueOf(slow))
	t.Fatal("memstats mismatch")
	}
	}

	func logDiff(t *testing.T, prefix string, got, want reflect.Value) {
	typ := got.Type()
	switch typ.Kind() {
	case reflect.Array, reflect.Slice:
	if got.Len() != want.Len() {
	t.Logf("len(%s): got %v, want %v", prefix, got, want)
	return
	}
	for i := 0; i < got.Len(); i++ {
	logDiff(t, fmt.Sprintf("%s[%d]", prefix, i), got.Index(i), want.Index(i))
	}
	case reflect.Struct:
	for i := 0; i < typ.NumField(); i++ {
	gf, wf := got.Field(i), want.Field(i)
	logDiff(t, prefix+"."+typ.Field(i).Name, gf, wf)
	}
	case reflect.Map:
	t.Fatal("not implemented: logDiff for map")
	default:
	if got.Interface() != want.Interface() {
	t.Logf("%s: got %v, want %v", prefix, got, want)
	}
	}
	}

	func BenchmarkReadMemStats(b *testing.B) {
	var ms runtime.MemStats
	const heapSize = 100 << 20
	x := make([]*[1024]byte, heapSize/1024)
	for i := range x {
	x[i] = new([1024]byte)
	}

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	runtime.ReadMemStats(&ms)
	}

	runtime.KeepAlive(x)
	}

	func applyGCLoad(b *testing.B) func() {
	// We’ll apply load to the runtime with maxProcs-1 goroutines
	// and use one more to actually benchmark. It doesn't make sense
	// to try to run this test with only 1 P (that's what
	// BenchmarkReadMemStats is for).
	maxProcs := runtime.GOMAXPROCS(-1)
	if maxProcs == 1 {
	b.Skip("This benchmark can only be run with GOMAXPROCS > 1")
	}

	// Code to build a big tree with lots of pointers.
	type node struct {
	children [16]*node
	}
	var buildTree func(depth int) *node
	buildTree = func(depth int) *node {
	tree := new(node)
	if depth != 0 {
	for i := range tree.children {
	tree.children[i] = buildTree(depth - 1)
	}
	}
	return tree
	}

	// Keep the GC busy by continuously generating large trees.
	done := make(chan struct{})
	var wg sync.WaitGroup
	for i := 0; i < maxProcs-1; i++ {
	wg.Add(1)
	go func() {
	defer wg.Done()
	var hold *node
	loop:
	for {
	hold = buildTree(5)
	select {
	case <-done:
	break loop
	default:
	}
	}
	runtime.KeepAlive(hold)
	}()
	}
	return func() {
	close(done)
	wg.Wait()
	}
	}

	func BenchmarkReadMemStatsLatency(b *testing.B) {
	stop := applyGCLoad(b)

	// Spend this much time measuring latencies.
	latencies := make([]time.Duration, 0, 1024)

	// Run for timeToBench hitting ReadMemStats continuously
	// and measuring the latency.
	b.ResetTimer()
	var ms runtime.MemStats
	for i := 0; i < b.N; i++ {
	// Sleep for a bit, otherwise we're just going to keep
	// stopping the world and no one will get to do anything.
	time.Sleep(100 * time.Millisecond)
	start := time.Now()
	runtime.ReadMemStats(&ms)
	latencies = append(latencies, time.Since(start))
	}
	// Make sure to stop the timer before we wait! The load created above
	// is very heavy-weight and not easy to stop, so we could end up
	// confusing the benchmarking framework for small b.N.
	b.StopTimer()
	stop()

	// Disable the default */op metrics.
	// ns/op doesn't mean anything because it's an average, but we
	// have a sleep in our b.N loop above which skews this significantly.
	b.ReportMetric(0, "ns/op")
	b.ReportMetric(0, "B/op")
	b.ReportMetric(0, "allocs/op")

	// Sort latencies then report percentiles.
	slices.Sort(latencies)
	b.ReportMetric(float64(latencies[len(latencies)*50/100]), "p50-ns")
	b.ReportMetric(float64(latencies[len(latencies)*90/100]), "p90-ns")
	b.ReportMetric(float64(latencies[len(latencies)*99/100]), "p99-ns")
	}

	func TestUserForcedGC(t *testing.T) {
	// Test that runtime.GC() triggers a GC even if GOGC=off.
	defer debug.SetGCPercent(debug.SetGCPercent(-1))

	var ms1, ms2 runtime.MemStats
	runtime.ReadMemStats(&ms1)
	runtime.GC()
	runtime.ReadMemStats(&ms2)
	if ms1.NumGC == ms2.NumGC {
	t.Fatalf("runtime.GC() did not trigger GC")
	}
	if ms1.NumForcedGC == ms2.NumForcedGC {
	t.Fatalf("runtime.GC() was not accounted in NumForcedGC")
	}
	}

	func writeBarrierBenchmark(b *testing.B, f func()) {
	runtime.GC()
	var ms runtime.MemStats
	runtime.ReadMemStats(&ms)
	//b.Logf("heap size: %d MB", ms.HeapAlloc>>20)

	// Keep GC running continuously during the benchmark, which in
	// turn keeps the write barrier on continuously.
	var stop uint32
	done := make(chan bool)
	go func() {
	for atomic.LoadUint32(&stop) == 0 {
	runtime.GC()
	}
	close(done)
	}()
	defer func() {
	atomic.StoreUint32(&stop, 1)
	<-done
	}()

	b.ResetTimer()
	f()
	b.StopTimer()
	}

	func BenchmarkWriteBarrier(b *testing.B) {
	if runtime.GOMAXPROCS(-1) < 2 {
	// We don't want GC to take our time.
	b.Skip("need GOMAXPROCS >= 2")
	}

	// Construct a large tree both so the GC runs for a while and
	// so we have a data structure to manipulate the pointers of.
	type node struct {
	l, r *node
	}
	var wbRoots []*node
	var mkTree func(level int) *node
	mkTree = func(level int) *node {
	if level == 0 {
	return nil
	}
	n := &node{mkTree(level - 1), mkTree(level - 1)}
	if level == 10 {
	// Seed GC with enough early pointers so it
	// doesn't start termination barriers when it
	// only has the top of the tree.
	wbRoots = append(wbRoots, n)
	}
	return n
	}
	const depth = 22 // 64 MB
	root := mkTree(22)

	writeBarrierBenchmark(b, func() {
	var stack [depth]*node
	tos := -1

	// There are two write barriers per iteration, so i+=2.
	for i := 0; i < b.N; i += 2 {
	if tos == -1 {
	stack[0] = root
	tos = 0
	}

	// Perform one step of reversing the tree.
	n := stack[tos]
	if n.l == nil {
	tos--
	} else {
	n.l, n.r = n.r, n.l
	stack[tos] = n.l
	stack[tos+1] = n.r
	tos++
	}

	if i%(1<<12) == 0 {
	// Avoid non-preemptible loops (see issue #10958).
	runtime.Gosched()
	}
	}
	})

	runtime.KeepAlive(wbRoots)
	}

	func BenchmarkBulkWriteBarrier(b *testing.B) {
	if runtime.GOMAXPROCS(-1) < 2 {
	// We don't want GC to take our time.
	b.Skip("need GOMAXPROCS >= 2")
	}

	// Construct a large set of objects we can copy around.
	const heapSize = 64 << 20
	type obj [16]*byte
	ptrs := make([]*obj, heapSize/unsafe.Sizeof(obj{}))
	for i := range ptrs {
	ptrs[i] = new(obj)
	}

	writeBarrierBenchmark(b, func() {
	const blockSize = 1024
	var pos int
	for i := 0; i < b.N; i += blockSize {
	// Rotate block.
	block := ptrs[pos : pos+blockSize]
	first := block[0]
	copy(block, block[1:])
	block[blockSize-1] = first

	pos += blockSize
	if pos+blockSize > len(ptrs) {
	pos = 0
	}

	runtime.Gosched()
	}
	})

	runtime.KeepAlive(ptrs)
	}

	func BenchmarkScanStackNoLocals(b *testing.B) {
	var ready sync.WaitGroup
	teardown := make(chan bool)
	for j := 0; j < 10; j++ {
	ready.Add(1)
	go func() {
	x := 100000
	countpwg(&x, &ready, teardown)
	}()
	}
	ready.Wait()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	b.StartTimer()
	runtime.GC()
	runtime.GC()
	b.StopTimer()
	}
	close(teardown)
	}

	func BenchmarkMSpanCountAlloc(b *testing.B) {
	// Allocate one dummy mspan for the whole benchmark.
	s := runtime.AllocMSpan()
	defer runtime.FreeMSpan(s)

	// n is the number of bytes to benchmark against.
	// n must always be a multiple of 8, since gcBits is
	// always rounded up 8 bytes.
	for _, n := range []int{8, 16, 32, 64, 128} {
	b.Run(fmt.Sprintf("bits=%d", n8), func(b testing.B) {
	// Initialize a new byte slice with pseudo-random data.
	bits := make([]byte, n)
	rand.Read(bits)

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	runtime.MSpanCountAlloc(s, bits)
	}
	})
	}
	}

	func countpwg(n int, ready sync.WaitGroup, teardown chan bool) {
	if *n == 0 {
	ready.Done()
	<-teardown
	return
	}
	*n--
	countpwg(n, ready, teardown)
	}

	func TestMemoryLimit(t *testing.T) {
	if testing.Short() {
	t.Skip("stress test that takes time to run")
	}
	if runtime.NumCPU() < 4 {
	t.Skip("want at least 4 CPUs for this test")
	}
	got := runTestProg(t, "testprog", "GCMemoryLimit")
	want := "OK\n"
	if got != want {
	t.Fatalf("expected %q, but got %q", want, got)
	}
	}

	func TestMemoryLimitNoGCPercent(t *testing.T) {
	if testing.Short() {
	t.Skip("stress test that takes time to run")
	}
	if runtime.NumCPU() < 4 {
	t.Skip("want at least 4 CPUs for this test")
	}
	got := runTestProg(t, "testprog", "GCMemoryLimitNoGCPercent")
	want := "OK\n"
	if got != want {
	t.Fatalf("expected %q, but got %q", want, got)
	}
	}

	func TestMyGenericFunc(t *testing.T) {
	runtime.MyGenericFunc[int]()
	}