cmd/compile: add instrumentation of OKEY

Instrument operands of OKEY.
Also instrument OSLICESTR. Previously it was not needed
because of preceeding bounds checks (which were instrumented).
But the preceeding bounds checks have disappeared.

Change-Id: I3b0de213e23cbcf5b8ef800abeded5eeeb3f8287
Reviewed-on: https://go-review.googlesource.com/11417Reviewed-by: Russ Cox <rsc@golang.org>

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

@@ -299,8 +299,14 @@ func racewalknode(np **Node, init **NodeList, wr int, skip int) {
 		}
 		goto ret
 
-	case OSLICE, OSLICEARR, OSLICE3, OSLICE3ARR:
+	case OSLICE, OSLICEARR, OSLICE3, OSLICE3ARR, OSLICESTR:
 		racewalknode(&n.Left, init, 0, 0)
+		racewalknode(&n.Right, init, 0, 0)
+		goto ret
+
+	case OKEY:
+		racewalknode(&n.Left, init, 0, 0)
+		racewalknode(&n.Right, init, 0, 0)
 		goto ret
 
 	case OADDR:
@@ -413,7 +419,6 @@ func racewalknode(np **Node, init **NodeList, wr int, skip int) {
 		OTYPE,
 		ONONAME,
 		OLITERAL,
-		OSLICESTR, // always preceded by bounds checking, avoid double instrumentation.
 		OTYPESW: // ignored by code generation, do not instrument.
 		goto ret
 	}

src/runtime/race/testdata/slice_test.go

@@ -578,3 +578,15 @@ func TestRaceCompareString(t *testing.T) {
 	s1 = s2
 	<-c
 }
+
+func TestRaceSlice3(t *testing.T) {
+	done := make(chan bool)
+	x := make([]int, 10)
+	i := 2
+	go func() {
+		i = 3
+		done <- true
+	}()
+	_ = x[:1:i]
+	<-done
+}