Leszek Swirski
ca4fd87385
Drop the FixedArray allocation in ArrayDestructure, and write registers
directly when performing the ArrayDestructure.
This is needed not (just) for performance, but for correctness. The
two-phase approach of reading the iterator into a FixedArray and then
setting registers meant that throwing an exception in `next()` would
cause either all or none of the target registers to be set, rather
than setting them one-by-one as they are returned by the iterator.
This is done differently depending on the tier:
* In Ignition and Sparkplug, the ArrayDestructure builtin now writes
directly to the register frame, receiving its address as an
argument.
* In Maglev, the ArrayDestructure builtin is effectively eagerly
inlined, desugared into the appropriate iteration protocol
execution, where the abstract interpreter register values are
updated one-by one to be exception safe, and lazy continuations
handle finishing the writes to the remaining register in case
there's a deopt
* In Turbofan, I ain't doin' all that, so it's UNREACHABLE. Please
write your local Turbolev representative to get the Maglev
implementation working in the 4th tier.
TAG=agy
Conversation-Id: 7fc7c031-68c6-4ddc-bdff-6ce4e63adc59
Change-Id: Ie1d21dc20f845e8d04aea8a177cd632b155dbd32
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/8035120
Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#108498}
75 lines
1.8 KiB
JavaScript
75 lines
1.8 KiB
JavaScript
// Copyright 2026 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 --maglev --turbolev --array-destructure-bytecode
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(function TestDestructuringAsValueExpression() {
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let a, b;
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let arr = [10, 20];
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let res = ([a, b] = arr);
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assertEquals(arr, res);
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assertEquals(10, a);
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assertEquals(20, b);
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})();
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(function TestDestructuringInReturnStatement() {
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function f(arr) {
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let x, y;
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return ([x, y] = arr);
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}
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%PrepareFunctionForOptimization(f);
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let arr = [30, 40];
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assertEquals(arr, f(arr));
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assertEquals(arr, f(arr));
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%OptimizeFunctionOnNextCall(f);
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assertEquals(arr, f(arr));
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assertOptimized(f);
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})();
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(function TestChainedDestructuringAssignments() {
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function f(arr) {
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let a, b, c, d;
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let res = ([a, b] = ([c, d] = arr));
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assertEquals(arr, res);
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return a + b + c + d;
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}
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%PrepareFunctionForOptimization(f);
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assertEquals(220, f([50, 60]));
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assertEquals(220, f([50, 60]));
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%OptimizeFunctionOnNextCall(f);
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assertEquals(220, f([50, 60]));
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assertOptimized(f);
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})();
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(function TestDestructuringWithDefaultValuesInExpression() {
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function f(arr) {
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let x, y;
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return ([x = 100, y = 200] = arr);
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}
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%PrepareFunctionForOptimization(f);
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let arr1 = [5, undefined];
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assertEquals(arr1, f(arr1));
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%OptimizeFunctionOnNextCall(f);
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assertEquals(arr1, f(arr1));
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assertOptimized(f);
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})();
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(function TestDestructuringWithHoles() {
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function f(arr) {
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let x, z;
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return ([x, , z] = arr);
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}
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%PrepareFunctionForOptimization(f);
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let arr = [10, 20, 30];
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assertEquals(arr, f(arr));
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assertEquals(arr, f(arr));
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%OptimizeFunctionOnNextCall(f);
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assertEquals(arr, f(arr));
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assertOptimized(f);
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})();
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