[turbofan] Optimize store to typed arrays only if the value is plain primitive.

test/mjsunit/compiler/regress-v8-5756.js

Index: test/mjsunit/compiler/regress-v8-5756.js
diff --git a/test/mjsunit/compiler/regress-v8-5756.js b/test/mjsunit/compiler/regress-v8-5756.js
new file mode 100644
index 0000000000000000000000000000000000000000..b7bfcda52bb43c8105bd86df507547abffab6933
--- /dev/null
+++ b/test/mjsunit/compiler/regress-v8-5756.js
@@ -0,0 +1,31 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+z = {};
+t = new Uint8Array(3);
+var m = 0;
+var x = 10;
+
+function k() {
+  ++m;
+  if (m % 10 != 9) {
+    if (m > 20) // This if is to just force it to deoptimize.
+      x = '1';  // this deoptimizes during the second invocation of k.
+                // This causes two deopts, one eager at x = 1 and the
+                // other lazy at t[2] = z.
+     t[2] = z; // since we are assigning to Uint8Array, ToNumber
+              // is called which calls this funciton again.
+  }
+}
+
+function f1() {
+  z.toString = k;
+  z.toString();
+  z.toString();
+  %OptimizeFunctionOnNextCall(k);
+  z.toString();
+}
+f1();