Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 1de12d99d9edd9ff4f5dfcc77b07f729c93267ac
https://github.com/WebKit/WebKit/commit/1de12d99d9edd9ff4f5dfcc77b07f729c93267ac
Author: Sosuke Suzuki <[email protected]>
Date: 2026-05-03 (Sun, 03 May 2026)
Changed paths:
A JSTests/microbenchmarks/new-array-constant-size-zero-fill-16.js
A JSTests/microbenchmarks/new-array-constant-size-zero-fill-4.js
A JSTests/microbenchmarks/new-array-constant-size-zero-fill-8.js
A JSTests/stress/new-array-constant-size-zero-fill.js
M Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp
Log Message:
-----------
[JSC] Unroll zero-fill for `NewButterflyWithSize` with small constant length
https://bugs.webkit.org/show_bug.cgi?id=313825
Reviewed by Yusuke Suzuki.
`NewButterflyWithSize` is inserted by DFGConstantFoldingPhase from
`new Array(N)` where N is a small Int32 constant. Even though the length
is known at compile time, `compileNewButterflyWithSize` still emitted a
runtime hole-fill loop via `emitInitializeButterfly`.
This patch reuses `emitFillStorageWithJSEmpty` /
`emitFillStorageWithDoubleEmpty` (the same helpers the recently landed
`NewTypedArray` constant-size unroll uses) when `butterflyLength` is
within the unroll budget (16 words). On ARM64 the loop body collapses
into `stp xzr, xzr` pairs.
Microbenchmark (DFG only, JSC_useFTLJIT=false):
baseline patched
new-array-constant-size-zero-fill-4 341.2569+-7.7353
328.1310+-6.3353 might be 1.0400x faster
new-array-constant-size-zero-fill-8 504.6251+-6.3335 ^
442.1297+-17.8307 ^ definitely 1.1414x faster
new-array-constant-size-zero-fill-16 844.2062+-22.6756 ^
679.9115+-17.8603 ^ definitely 1.2416x faster
<geometric> 525.7819+-3.3028 ^
461.9929+-5.6665 ^ definitely 1.1381x faster
Tests: JSTests/microbenchmarks/new-array-constant-size-zero-fill-16.js
JSTests/microbenchmarks/new-array-constant-size-zero-fill-4.js
JSTests/microbenchmarks/new-array-constant-size-zero-fill-8.js
JSTests/stress/new-array-constant-size-zero-fill.js
* JSTests/microbenchmarks/new-array-constant-size-zero-fill-16.js: Added.
(foo):
(bar):
* JSTests/microbenchmarks/new-array-constant-size-zero-fill-4.js: Added.
(foo):
(bar):
* JSTests/microbenchmarks/new-array-constant-size-zero-fill-8.js: Added.
(foo):
(bar):
* JSTests/stress/new-array-constant-size-zero-fill.js: Added.
(shouldBe):
(shouldBeArrayOfHoles):
(make0):
(make1):
(make2):
(make3):
(make7):
(make8):
(make15):
(make16):
(make17):
(make32):
(make100):
(make999):
(makeProfiled):
(freshAfterDoubleProfile):
(mutate):
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp:
Canonical link: https://commits.webkit.org/312496@main
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