cmd/compile: fix race detector handling of OBLOCK nodes

Fixes #7561 correctly.
Fixes #9137.

Change-Id: I7f27e199d7101b785a7645f789e8fe41a405a86f
Reviewed-on: https://go-review.googlesource.com/11713Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

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

@@ -434,6 +434,12 @@ func ordermapassign(n *Node, order *Order) {
 				a = Nod(OAS, m, l.N)
 				typecheck(&a, Etop)
 				post = list(post, a)
+			} else if flag_race != 0 && n.Op == OAS2FUNC && !isblank(l.N) {
+				m = l.N
+				l.N = ordertemp(m.Type, order, false)
+				a = Nod(OAS, m, l.N)
+				typecheck(&a, Etop)
+				post = list(post, a)
 			}
 		}
 

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

@@ -147,27 +147,27 @@ func racewalknode(np **Node, init **NodeList, wr int, skip int) {
 		goto ret
 
 	case OBLOCK:
-		if n.List == nil {
-			goto ret
-		}
-
-		switch n.List.N.Op {
-		// Blocks are used for multiple return function calls.
-		// x, y := f() becomes BLOCK{CALL f, AS x [SP+0], AS y [SP+n]}
-		// We don't want to instrument between the statements because it will
-		// smash the results.
-		case OCALLFUNC, OCALLMETH, OCALLINTER:
-			racewalknode(&n.List.N, &n.List.N.Ninit, 0, 0)
-
-			var fini *NodeList
-			racewalklist(n.List.Next, &fini)
-			n.List = concat(n.List, fini)
-
-			// Ordinary block, for loop initialization or inlined bodies.
-		default:
-			racewalklist(n.List, nil)
+		var out *NodeList
+		for l := n.List; l != nil; l = l.Next {
+			switch l.N.Op {
+			case OCALLFUNC, OCALLMETH, OCALLINTER:
+				racewalknode(&l.N, &out, 0, 0)
+				out = list(out, l.N)
+				// Scan past OAS nodes copying results off stack.
+				// Those must not be instrumented, because the
+				// instrumentation calls will smash the results.
+				// The assignments are to temporaries, so they cannot
+				// be involved in races and need not be instrumented.
+				for l.Next != nil && l.Next.N.Op == OAS && iscallret(l.Next.N.Right) {
+					l = l.Next
+					out = list(out, l.N)
+				}
+			default:
+				racewalknode(&l.N, &out, 0, 0)
+				out = list(out, l.N)
+			}
 		}
-
+		n.List = out
 		goto ret
 
 	case ODEFER:

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

@@ -2127,6 +2127,11 @@ func callnew(t *Type) *Node {
 	return mkcall1(fn, Ptrto(t), nil, typename(t))
 }
 
+func iscallret(n *Node) bool {
+	n = outervalue(n)
+	return n.Op == OINDREG && n.Reg == int16(Thearch.REGSP)
+}
+
 func isstack(n *Node) bool {
 	n = outervalue(n)
 

src/runtime/race/race_test.go

@@ -173,3 +173,12 @@ func TestIssue8102(t *testing.T) {
 		}
 	}
 }
+
+func TestIssue9137(t *testing.T) {
+	a := []string{"a"}
+	i := 0
+	a[i], a[len(a)-1], a = a[len(a)-1], "", a[:len(a)-1]
+	if len(a) != 0 || a[:1][0] != "" {
+		t.Errorf("mangled a: %q %q", a, a[:1])
+	}
+}

src/runtime/race/testdata/mop_test.go

@@ -1587,6 +1587,110 @@ func TestRaceBlockAs(t *testing.T) {
 	<-c
 }
 
+func TestRaceBlockCall1(t *testing.T) {
+	done := make(chan bool)
+	x, y := 0, 0
+	go func() {
+		f := func() (int, int) {
+			return 42, 43
+		}
+		x, y = f()
+		done <- true
+	}()
+	_ = x
+	<-done
+	if x != 42 || y != 43 {
+		panic("corrupted data")
+	}
+}
+func TestRaceBlockCall2(t *testing.T) {
+	done := make(chan bool)
+	x, y := 0, 0
+	go func() {
+		f := func() (int, int) {
+			return 42, 43
+		}
+		x, y = f()
+		done <- true
+	}()
+	_ = y
+	<-done
+	if x != 42 || y != 43 {
+		panic("corrupted data")
+	}
+}
+func TestRaceBlockCall3(t *testing.T) {
+	done := make(chan bool)
+	var x *int
+	y := 0
+	go func() {
+		f := func() (*int, int) {
+			i := 42
+			return &i, 43
+		}
+		x, y = f()
+		done <- true
+	}()
+	_ = x
+	<-done
+	if *x != 42 || y != 43 {
+		panic("corrupted data")
+	}
+}
+func TestRaceBlockCall4(t *testing.T) {
+	done := make(chan bool)
+	x := 0
+	var y *int
+	go func() {
+		f := func() (int, *int) {
+			i := 43
+			return 42, &i
+		}
+		x, y = f()
+		done <- true
+	}()
+	_ = y
+	<-done
+	if x != 42 || *y != 43 {
+		panic("corrupted data")
+	}
+}
+func TestRaceBlockCall5(t *testing.T) {
+	done := make(chan bool)
+	var x *int
+	y := 0
+	go func() {
+		f := func() (*int, int) {
+			i := 42
+			return &i, 43
+		}
+		x, y = f()
+		done <- true
+	}()
+	_ = y
+	<-done
+	if *x != 42 || y != 43 {
+		panic("corrupted data")
+	}
+}
+func TestRaceBlockCall6(t *testing.T) {
+	done := make(chan bool)
+	x := 0
+	var y *int
+	go func() {
+		f := func() (int, *int) {
+			i := 43
+			return 42, &i
+		}
+		x, y = f()
+		done <- true
+	}()
+	_ = x
+	<-done
+	if x != 42 || *y != 43 {
+		panic("corrupted data")
+	}
+}
 func TestRaceSliceSlice(t *testing.T) {
 	c := make(chan bool, 1)
 	x := make([]int, 10)