cmd/compile: fix OASWB rewriting in racewalk

Special case for rewriting OAS inits omitted OASWB, added
that and OAS2FUNC.  The special case cannot be default case,
that causes racewalk to fail in horrible ways.

Fixes #16008.

Change-Id: Ie0d2f5735fe9d8255a109597b36d196d4f86703a
Reviewed-on: https://go-review.googlesource.com/23954Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/internal/gc/racewalk.go

@@ -164,7 +164,7 @@ func instrumentnode(np **Node, init *Nodes, wr int, skip int) {
 				var outn Nodes
 				outn.Set(out)
 				instrumentnode(&ls[i], &outn, 0, 0)
-				if ls[i].Op != OAS || ls[i].Ninit.Len() == 0 {
+				if ls[i].Op != OAS && ls[i].Op != OASWB && ls[i].Op != OAS2FUNC || ls[i].Ninit.Len() == 0 {
 					out = append(outn.Slice(), ls[i])
 				} else {
 					// Splice outn onto end of ls[i].Ninit

test/fixedbugs/issue16008.go

+// errorcheck -0 -race
+
+package foo
+
+const benchmarkNumNodes = 10000
+
+func BenchmarkUpdateNodeTransaction(b B) {
+	s, nodeIDs := setupNodes(benchmarkNumNodes)
+	b.ResetTimer()
+	for i := 0; i < b.N(); i++ {
+		_ = s.Update(func(tx1 Tx) error {
+			_ = UpdateNode(tx1, &Node{
+				ID: nodeIDs[i%benchmarkNumNodes],
+			})
+			return nil
+		})
+	}
+}
+
+type B interface {
+	ResetTimer()
+	N() int
+}
+
+type Tx interface {
+}
+
+type Node struct {
+	ID string
+}
+
+type MemoryStore struct {
+}
+
+// go:noinline
+func setupNodes(n int) (s *MemoryStore, nodeIDs []string) {
+	return
+}
+
+//go:noinline
+func (s *MemoryStore) Update(cb func(Tx) error) error {
+	return nil
+}
+
+var sink interface{}
+
+//go:noinline
+func UpdateNode(tx Tx, n *Node) error {
+	sink = tx
+	sink = n
+	return nil
+}