[turbofan] Introduce ChangeTaggedToTaggedSigned operator.

test/mjsunit/regress/regress-crbug-687029.js

Index: test/mjsunit/regress/regress-crbug-687029.js
diff --git a/test/mjsunit/regress/regress-crbug-687029.js b/test/mjsunit/regress/regress-crbug-687029.js
new file mode 100644
index 0000000000000000000000000000000000000000..c3ca01fad17a9618ce8d2b614ec7ea7b76dcf7cd
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-687029.js
@@ -0,0 +1,14 @@
+// Copyright 2017 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
+
+function foo(x) {
+  x = Math.clz32(x);
+  return "a".indexOf("a", x);
+}
+foo(1);
+foo(1);
+%OptimizeFunctionOnNextCall(foo);
+foo();