v8/test/mjsunit/regress/regress-760790.js
Jakob Gruber 2859dba713 [csa] Canonicalize empty elements in AllocateJSArray
Prior to this, AllocateJSArray would go ahead and allocate an empty
FixedArray as elements if passed any capacity that is not a compile-time
constant 0.

Things break later on since we rely on the fact that empty fixed arrays
are always canonicalize, and we use

  obj.elements == empty_fixed_array_constant

interchangeably with

  obj.elements.length == 0.

This CL introduces two new branches in AllocateJSArray: one if the
capacity is known to be non-zero; and another that explicitly
distinguishes between 0 and non-zero capacities.

Bug: chromium:760790
Change-Id: I7c22b19ce9ce15a46f91b0f75e6b4a1ff3a29a0f
Reviewed-on: https://chromium-review.googlesource.com/645959
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47776}
2017-09-01 16:56:53 +00:00

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JavaScript

// 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.
function g() {
var a = Array(0);
a[0]++;
}
g();
g();
g();