0f88153075
In general, deleting a property from a fast-properties object
requires transitioning the object to dictionary mode. However,
when the most-recently-added property is deleted, we can simply
roll back the last map transition that the object went through.
This is a performance experiment: it should make things faster,
but if it turns out to have more negative than positive impact,
we will have to revert it.
TBR=bmeurer@chromium.org (just adding a comment)
Previously reviewed at https://codereview.chromium.org/2830093002
Previously landed as 98acfb36e1 / r44799
Review-Url: https://codereview.chromium.org/2840583002
Cr-Commit-Position: refs/heads/master@{#44808}
57 lines
1.4 KiB
JavaScript
57 lines
1.4 KiB
JavaScript
// Copyright 2014 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Flags: --allow-natives-syntax
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// Test loading existent and nonexistent properties from dictionary
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// mode objects.
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function SlowObject() {
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this.foo = 1;
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this.bar = 2;
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this.qux = 3;
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this.z = 4;
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delete this.qux;
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assertFalse(%HasFastProperties(this));
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}
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function SlowObjectWithBaz() {
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var o = new SlowObject();
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o.baz = 4;
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return o;
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}
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function Load(o) {
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return o.baz;
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}
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for (var i = 0; i < 10; i++) {
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var o1 = new SlowObject();
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var o2 = SlowObjectWithBaz();
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assertEquals(undefined, Load(o1));
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assertEquals(4, Load(o2));
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}
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// Test objects getting optimized as fast prototypes.
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function SlowPrototype() {
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this.foo = 1;
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}
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SlowPrototype.prototype.bar = 2;
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SlowPrototype.prototype.baz = 3;
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SlowPrototype.prototype.z = 4;
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delete SlowPrototype.prototype.baz;
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assertFalse(%HasFastProperties(SlowPrototype.prototype));
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var slow_proto = new SlowPrototype;
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// ICs make prototypes fast.
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function ic() { return slow_proto.bar; }
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ic();
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ic();
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assertTrue(%HasFastProperties(slow_proto.__proto__));
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// Prototypes stay fast even after deleting properties.
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assertTrue(%HasFastProperties(SlowPrototype.prototype));
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var fast_proto = new SlowPrototype();
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assertTrue(%HasFastProperties(SlowPrototype.prototype));
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assertTrue(%HasFastProperties(fast_proto.__proto__));
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