v8/test/mjsunit/regress/regress-7014-2.js

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// 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 --turbofan --no-always-turbofan
function foo(s) {
return s[5];
}
%PrepareFunctionForOptimization(foo);
assertEquals("f", foo("abcdef"));
assertEquals(undefined, foo("a"));
%OptimizeFunctionOnNextCall(foo);
assertEquals("f", foo("abcdef"));
assertEquals(undefined, foo("a"));
assertOptimized(foo);
// Now mess with the String.prototype.
String.prototype.__proto__ = new Proxy(String.prototype.__proto__, {
get(target, property) {
return "5";
}
});
assertEquals("f", foo("abcdef"));
%PrepareFunctionForOptimization(foo);
assertEquals("5", foo("a"));
%OptimizeFunctionOnNextCall(foo);
assertEquals("f", foo("abcdef"));
assertEquals("5", foo("a"));
assertOptimized(foo);