test: add write barrier test

Update #80196

Change-Id: If121610638034f782aed14c9dc054eba42662d4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/795360
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

test/fixedbugs/issue80196.go

diff --git a/test/fixedbugs/issue80196.go b/test/fixedbugs/issue80196.go
new file mode 100644
index 0000000..3063280
--- /dev/null
+++ b/test/fixedbugs/issue80196.go
@@ -0,0 +1,33 @@
+// run
+
+// Copyright 2026 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 main
+
+type S [5]*byte
+
+//go:noinline
+func f() S {
+	return S{}
+}
+
+var sink *S
+
+//go:noinline
+func g() (s S) {
+	sink = &s
+	s = f()
+	return
+}
+
+func main() {
+	for i := range 1000000 {
+		s := g()
+		if s != (S{}) {
+			println(s[0], s[1], s[2], s[3], s[4])
+			panic(i)
+		}
+	}
+}