v8/test/mjsunit/keyed-load-hole-to-undefined.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 --turbofan --no-always-turbofan

// is specified because the test corrupts the "pristine"
// array prototype chain by storing an element, and this is tracked
// per-isolate. A subsequent stress run would send the load generic,
// and no more deoptimizations of foo would occur.

function foo(a, i) { return a[i]; }

%PrepareFunctionForOptimization(foo);
var a = ['one', , 'three'];
foo(a, 0);
foo(a, 0);
foo(a, 0);
%OptimizeFunctionOnNextCall(foo);
assertEquals(undefined, foo(a, 1));
assertOptimized(foo);

// Whereas if we disrupt the prototype chain...
Array.prototype[1] = 'cow';
assertEquals('cow', foo(a, 1));
assertUnoptimized(foo);