[turbofan] Simply context specialization and fix for OSR.

test/mjsunit/compiler/osr-for-let.js

+// Copyright 2015 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 --use-osr --turbo-osr
+
+"use strict";
+
+function test(expected, func) {
+  assertEquals(expected, func());
+  assertEquals(expected, func());
+  assertEquals(expected, func());
+}
+
+function bar() {
+  var result;
+  {
+    let sum = 0;
+    for (let i = 0; i < 90; i++) {
+      sum += i;
+      if (i == 45) %OptimizeOsr();
+    }
+    result = sum;
+  }
+  return result;
+}
+
+test(4005, bar);
+
+function baz() {
+  let sum = 0;
+  for (let i = 0; i < 2; i++) {
+    sum = 2;
+    %OptimizeOsr();
+  }
+  return sum;
+}
+
+test(2, baz);
+
+function qux() {
+  var result = 0;
+  for (let i = 0; i < 2; i++) {
+    result = i;
+    %OptimizeOsr();
+  }
+  return result;
+}
+
+test(1, qux);
+
+function nux() {
+  var result = 0;
+  for (let i = 0; i < 2; i++) {
+    {
+      let sum = i;
+      %OptimizeOsr();
+      result = sum;
+    }
+  }
+  return result;
+}
+
+test(1, nux);
+
+function blo() {
+  var result;
+  {
+    let sum = 0;
+    for (let i = 0; i < 90; i++) {
+      sum += i;
+      if (i == 45) %OptimizeOsr();
+    }
+    result = ret;
+    function ret() {
+      return sum;
+    }
+  }
+  return result;
+}
+
+test(4005, blo());