"unsafe"
)

// Go uses a hybrid barrier that combines a Yuasa-style deletion
// barrier—which shades the object whose reference is being
// overwritten—with Dijkstra insertion barrier—which shades the object
// whose reference is being written. The insertion part of the barrier
// is necessary while the calling goroutine's stack is grey. In
// pseudocode, the barrier is:
//
//     writePointer(slot, ptr):

// This implements the write barrier buffer. The write barrier itself
// is gcWriteBarrier and is implemented in assembly.
//
// See mbarrier.go for algorithmic details on the write barrier. This
// file deals only with the buffer.
//
// The write barrier has a fast path and a slow path. The fast path
// simply enqueues to a per-P write barrier buffer. It's written in

	z := *y // no barrier
	*x = z  // ERROR "write barrier"
}

func f2(x *interface{}, y interface{}) {
	*x = y // no barrier (dead store)

	z := y // no barrier
	*x = z // ERROR "write barrier"
}

func f2a(x *interface{}, y *interface{}) {
	*x = *y // no barrier (dead store)

	z := y // no barrier
	*x = z // ERROR "write barrier"
}

func f3(x *string, y string) {

			runtime.Goexit()
		}()

		// Generate some garbage.
		x[i] = make([]byte, 1024*1024)

		// Give GC some time to install stack barriers in the G.
		time.Sleep(50 * time.Microsecond)
		atomic.StoreInt32(&done, 1)
		for atomic.LoadInt32(&done) == 1 {
			runtime.Gosched()
		}
	}

		// value of makeT() is not copied out of the args area of
		// stack frame in a timely fashion. So when write barriers
		// are enabled, the marshaling of the args for the write
		// barrier call clobbers the result of makeT() before it is
		// read by the write barrier code.
		g = makeT()
		sink = make([]byte, 1000) // force write barriers to eventually happen
	}
}
func TestIssue15854b(t *testing.T) {
	const N = 10000
	a := make([]T, N)

	sigCtxt sigContext
}

func (h *debugCallHandler) inject(info *siginfo, ctxt *sigctxt, gp2 *g) bool {
	// TODO(49370): This code is riddled with write barriers, but called from
	// a signal handler. Add the go:nowritebarrierrec annotation and restructure
	// this to avoid write barriers.

	switch h.gp.atomicstatus.Load() {
	case _Grunning:
		if getg().m != h.mp {
			println("trap on wrong M", getg().m, h.mp)
			return false

// - Maps and channels contains no-in-heap types are disallowed.
//
// 4. Write barriers on pointers to not-in-heap types can be omitted.
//
// The last point is the real benefit of NotInHeap. The runtime uses
// it for low-level internal structures to avoid memory barriers in the
// scheduler and the memory allocator where they are illegal or simply

// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Make sure dead write barriers are handled correctly.

package main

func f(p **int) {
	// The trick here is to eliminate the block containing the write barrier,
	// but only after the write barrier branches are inserted.
	// This requires some delicate code.
	i := 0
	var b []bool
	var s string
	for true {
		if b[i] {

//go:noinline
func f() {
	// The compiler optimizes this to direct copying
	// the call result to both globals, with write
	// barriers. The first write barrier call clobbers
	// the result of g on stack.
	X = g()
	Y = X
}

var X, Y T

const N = 1000

func main() {
	// Keep GC running so the write barrier is on.
	go func() {
		for {
			runtime.GC()
		}
	}()

	for i := 0; i < N; i++ {
		runtime.Gosched()

`go:nowritebarrier` directs the compiler to emit an error if the
following function contains any write barriers. (It *does not*
suppress the generation of write barriers; it is simply an assertion.)

Usually you want `go:nowritebarrierrec`. `go:nowritebarrier` is
primarily useful in situations where it's "nice" not to have write
barriers, but not required for correctness.

go:nowritebarrierrec and go:yeswritebarrierrec