2d889aa9a4
https://github.com/tc39/ecma262/pull/988 gained concensus during the september 2017 TC39 meetings. This moves the load of the "next" method to the very beginning of the iteration protocol, rather than during each iteration step. This impacts: - yield* - for-of loops - spread arguments - array spreads In the v8 implementation, this also affects async iteration versions of these things (the sole exception being the Async-From-Sync iterator, which requires a few more changes to work with this, likely done in a followup patch). This change introduces a new AST node, ResolvedProperty, which can be used as a callee by Call nodes to produce the same bytecode as Property calls, without observably re-loading the property. This is used in several AST-desugarings involving the iteration protocol. BUG=v8:6861, v8:5699 R=rmcilroy@chromium.org TBR=neis@chromium.org, adamk@chromium.org Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng Change-Id: I9685db6e85315ba8a2df87a4537c2bf491e1e35b Reviewed-on: https://chromium-review.googlesource.com/857593 Commit-Queue: Caitlin Potter <caitp@igalia.com> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org> Cr-Commit-Position: refs/heads/master@{#50518}
45 lines
950 B
JavaScript
45 lines
950 B
JavaScript
// Copyright 2017 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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(function modifyNext() {
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'use strict';
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var a = [];
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var ai = a[Symbol.iterator]();
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var original_next = ai.__proto__['next'];
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function maxWithZero(...args) {
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return Math.max(0, ...args);
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}
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function testMax(x, y) {
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return maxWithZero(x, y);
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}
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testMax(1, 2);
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testMax(1, 2);
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%OptimizeFunctionOnNextCall(testMax);
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var r = testMax(1, 2);
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assertEquals(2, r);
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var called = 0;
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Object.defineProperty(ai.__proto__, 'next', {
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get: function() {
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called++;
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return original_next;
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}
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});
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var r2 = testMax(1, 2);
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// .next() is only loaded once during the iteration prologue (see
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// https://github.com/tc39/ecma262/pull/988/ and v8:6861)
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assertEquals(1, called);
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assertEquals(2, r2);
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})();
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