Riya Amemiya
3eed742a70
Add a fast path for Array.prototype.flat in Torque/CSA that uses a 2-pass approach: first compute the output length, then preallocate and write directly. This avoids runtime call overhead and is modeled after JSC's implementation but adapted for V8's elements/protector model. The implementation uses a stack-based iterative traversal to support arbitrary depth without recursion overhead. The fast path is only taken when: - Input is a FastJSArray with fast elements - NoElements and ArraySpecies protectors are intact - No proxies, accessors, or custom elements in the chain - Nested arrays (when depth > 0) are also FastJSArrays If any precondition fails, we fall back to the existing slow path. Performance improvement for large arrays(20M) is 3x~16x (in a single-run benchmark). Change-Id: I2eea8c149b5c6a522fef086f36df108ca7a0a2e2 Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/7526287 Reviewed-by: Olivier Flückiger <olivf@chromium.org> Reviewed-by: Leszek Swirski <leszeks@chromium.org> Commit-Queue: Olivier Flückiger <olivf@chromium.org> Commit-Queue: Leszek Swirski <leszeks@chromium.org> Cr-Commit-Position: refs/heads/main@{#105498}
49 lines
1.5 KiB
JavaScript
49 lines
1.5 KiB
JavaScript
// Copyright 2025 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 assertSmiElementsKind(arr) {
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assertTrue(%HasSmiElements(arr),
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'Expected SMI elements kind, got: ' + JSON.stringify(arr));
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}
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function assertDoubleElementsKind(arr) {
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assertTrue(%HasDoubleElements(arr),
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'Expected DOUBLE elements kind, got: ' + JSON.stringify(arr));
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}
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function assertObjectElementsKind(arr) {
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assertTrue(%HasObjectElements(arr),
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'Expected OBJECT elements kind, got: ' + JSON.stringify(arr));
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}
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// Early return for packed numeric source.
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assertSmiElementsKind([1].flat());
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assertDoubleElementsKind([1.1].flat());
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// All sub-arrays have the same elements kind.
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assertSmiElementsKind([[1]].flat());
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assertSmiElementsKind([[1],[1]].flat());
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assertDoubleElementsKind([[1.1]].flat());
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assertDoubleElementsKind([[1.1],[2.2]].flat());
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// Mixed sub-array kinds produce DOUBLE (SMIs fit in doubles).
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assertDoubleElementsKind([[1],[1.1]].flat());
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assertObjectElementsKind([[1],[[1.1]]].flat());
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// Non-number leaf elements.
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assertObjectElementsKind([["hello"]].flat());
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assertObjectElementsKind([[1, "hello"]].flat());
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// Generic source with Smi-only contents.
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let generic = [{}];
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generic[0] = 1;
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assertSmiElementsKind(generic.flat());
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assertSmiElementsKind([generic].flat());
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// Depth > 1.
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assertSmiElementsKind([[[1]]].flat(2));
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assertDoubleElementsKind([[[1.1],[2.2]]].flat(2));
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