Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 56dcc0037aa258bc1c52ab3742874be18768ef6e
https://github.com/WebKit/WebKit/commit/56dcc0037aa258bc1c52ab3742874be18768ef6e
Author: Chris Dumez <[email protected]>
Date: 2026-01-08 (Thu, 08 Jan 2026)
Changed paths:
M Source/WTF/wtf/text/ASCIIFastPath.h
M Source/WTF/wtf/text/StringCommon.h
M Source/WTF/wtf/text/StringImpl.cpp
Log Message:
-----------
Optimize StringImpl::create8BitIfPossible()
https://bugs.webkit.org/show_bug.cgi?id=304792
Reviewed by Darin Adler.
Optimize StringImpl::create8BitIfPossible(). Avoid allocating new string
unnecessarily in the "slow" path. Rely on highly optimized `copyElements()`
to copy characters in the fast path. I also rely on `charactersAreAllLatin1()`
to determine if we can use the fast path and found out it was a lot slower
than `std::ranges::all_of()` with larger strings containing non-Latin1.
As a result, I also optimized `charactersAreAllLatin1()` as follows:
- Included a SIMD implementation for ARM64 NEON.
- Early return when finding a non-Latin1 character to avoid scanning to
whole string unnecessarily.
With these changes, StringImpl::create8BitIfPossible() is now consisently
faster than it used to be for all kinds of input strings:
================
=== All ASCII (8-bit compatible) ===
Benchmark Version Size Avg (ns) Min (ns) Max
(ns) MB/s Result
--------------------------------------------------------------------------------------------------------------
AllASCII Old 1 21.39 0.00
12208.00 93.52 8-bit
AllASCII New 1 15.70 0.00
17916.00 127.37 8-bit
→ Speedup: 1.36x (faster by 26.58%)
AllASCII Old 8 16.56 0.00
13417.00 966.37 8-bit
AllASCII New 8 15.43 0.00
10292.00 1036.92 8-bit
→ Speedup: 1.07x (faster by 6.80%)
AllASCII Old 16 17.62 0.00
11000.00 1815.86 8-bit
AllASCII New 16 15.39 0.00
14583.00 2078.72 8-bit
→ Speedup: 1.14x (faster by 12.65%)
AllASCII Old 32 19.55 0.00
11834.00 3273.16 8-bit
AllASCII New 32 15.83 0.00
11833.00 4043.32 8-bit
→ Speedup: 1.24x (faster by 19.05%)
AllASCII Old 64 27.82 0.00
10291.00 4600.73 8-bit
AllASCII New 64 16.90 0.00
20292.00 7571.86 8-bit
→ Speedup: 1.65x (faster by 39.24%)
AllASCII Old 128 56.19 0.00
14375.00 4555.87 8-bit
AllASCII New 128 18.30 0.00
12416.00 13990.88 8-bit
→ Speedup: 3.07x (faster by 67.44%)
AllASCII Old 256 111.16 41.00
26791.00 4606.15 8-bit
AllASCII New 256 21.84 0.00
12833.00 23442.15 8-bit
→ Speedup: 5.09x (faster by 80.35%)
AllASCII Old 512 181.74 83.00
23250.00 5634.35 8-bit
AllASCII New 512 33.45 0.00
24000.00 30610.58 8-bit
→ Speedup: 5.43x (faster by 81.59%)
AllASCII Old 1024 311.10 208.00
30583.00 6583.02 8-bit
AllASCII New 1024 67.20 0.00
18750.00 30476.86 8-bit
→ Speedup: 4.63x (faster by 78.40%)
AllASCII Old 4096 1083.80 916.00
46291.00 7558.62 8-bit
AllASCII New 4096 244.86 166.00
18959.00 33455.68 8-bit
→ Speedup: 4.43x (faster by 77.41%)
AllASCII Old 16384 4171.20 3625.00
43958.00 7855.77 8-bit
AllASCII New 16384 871.47 666.00
29083.00 37600.87 8-bit
→ Speedup: 4.79x (faster by 79.11%)
AllASCII Old 65536 16447.48 14541.00
55250.00 7969.12 8-bit
AllASCII New 65536 3175.16 2750.00
27125.00 41280.49 8-bit
→ Speedup: 5.18x (faster by 80.70%)
=== All 16-bit Required ===
Benchmark Version Size Avg (ns) Min (ns) Max
(ns) MB/s Result
--------------------------------------------------------------------------------------------------------------
All16Bit Old 1 21.05 0.00
14333.00 95.02 16-bit
All16Bit New 1 14.23 0.00
10541.00 140.55 16-bit
→ Speedup: 1.48x (faster by 32.40%)
All16Bit Old 8 20.79 0.00
17125.00 769.56 16-bit
All16Bit New 8 15.76 0.00
19083.00 1015.50 16-bit
→ Speedup: 1.32x (faster by 24.22%)
All16Bit Old 16 21.53 0.00
15042.00 1486.21 16-bit
All16Bit New 16 15.31 0.00
18250.00 2089.74 16-bit
→ Speedup: 1.41x (faster by 28.88%)
All16Bit Old 32 21.63 0.00
49667.00 2958.18 16-bit
All16Bit New 32 15.66 0.00
10625.00 4087.71 16-bit
→ Speedup: 1.38x (faster by 27.63%)
All16Bit Old 64 22.93 0.00
15375.00 5583.00 16-bit
All16Bit New 64 15.99 0.00
25791.00 8003.13 16-bit
→ Speedup: 1.43x (faster by 30.24%)
All16Bit Old 128 24.44 0.00
14959.00 10474.61 16-bit
All16Bit New 128 16.76 0.00
19792.00 15278.07 16-bit
→ Speedup: 1.46x (faster by 31.44%)
All16Bit Old 256 29.16 0.00
18750.00 17559.42 16-bit
All16Bit New 256 20.34 0.00
18500.00 25171.53 16-bit
→ Speedup: 1.43x (faster by 30.24%)
All16Bit Old 512 37.72 0.00
19667.00 27143.93 16-bit
All16Bit New 512 23.07 0.00
8375.00 44382.30 16-bit
→ Speedup: 1.64x (faster by 38.84%)
All16Bit Old 1024 52.62 0.00
21584.00 38918.68 16-bit
All16Bit New 1024 33.23 0.00
10583.00 61636.57 16-bit
→ Speedup: 1.58x (faster by 36.86%)
All16Bit Old 4096 118.67 41.00
17541.00 69032.42 16-bit
All16Bit New 4096 98.49 0.00
25083.00 83177.57 16-bit
→ Speedup: 1.20x (faster by 17.01%)
All16Bit Old 16384 455.45 291.00
26208.00 71947.19 16-bit
All16Bit New 16384 297.08 208.00
30208.00 110299.11 16-bit
→ Speedup: 1.53x (faster by 34.77%)
All16Bit Old 65536 1335.24 1083.00
23208.00 98163.39 16-bit
All16Bit New 65536 1239.36 1000.00
24333.00 105757.95 16-bit
→ Speedup: 1.08x (faster by 7.18%)
=== 16-bit Character at End ===
Benchmark Version Size Avg (ns) Min (ns) Max
(ns) MB/s Result
--------------------------------------------------------------------------------------------------------------
16BitAtEnd Old 8 22.05 0.00
11875.00 725.63 16-bit
16BitAtEnd New 8 15.39 0.00
14791.00 1039.83 16-bit
→ Speedup: 1.43x (faster by 30.22%)
16BitAtEnd Old 64 39.59 0.00
12250.00 3233.51 16-bit
16BitAtEnd New 64 17.01 0.00
17375.00 7525.66 16-bit
→ Speedup: 2.33x (faster by 57.03%)
16BitAtEnd Old 512 220.28 125.00
28750.00 4648.65 16-bit
16BitAtEnd New 512 36.31 0.00
16625.00 28199.77 16-bit
→ Speedup: 6.07x (faster by 83.52%)
16BitAtEnd Old 4096 1196.95 1000.00
30958.00 6844.05 16-bit
16BitAtEnd New 4096 253.95 166.00
27458.00 32258.79 16-bit
→ Speedup: 4.71x (faster by 78.78%)
16BitAtEnd Old 65536 17901.83 15708.00
58875.00 7321.71 16-bit
16BitAtEnd New 65536 3276.21 2833.00
38125.00 40007.20 16-bit
→ Speedup: 5.46x (faster by 81.70%)
=== 16-bit Character at Start ===
Benchmark Version Size Avg (ns) Min (ns) Max
(ns) MB/s Result
--------------------------------------------------------------------------------------------------------------
16BitAtStart Old 8 20.80 0.00
21166.00 769.36 16-bit
16BitAtStart New 8 15.57 0.00
13125.00 1027.74 16-bit
→ Speedup: 1.34x (faster by 25.14%)
16BitAtStart Old 64 22.06 0.00
17083.00 5802.22 16-bit
16BitAtStart New 64 15.92 0.00
17917.00 8039.36 16-bit
→ Speedup: 1.39x (faster by 27.83%)
16BitAtStart Old 512 38.28 0.00
18916.00 26751.01 16-bit
16BitAtStart New 512 22.94 0.00
17667.00 44646.57 16-bit
→ Speedup: 1.67x (faster by 40.08%)
16BitAtStart Old 4096 116.60 41.00
18958.00 70257.22 16-bit
16BitAtStart New 4096 96.39 0.00
53875.00 84990.64 16-bit
→ Speedup: 1.21x (faster by 17.34%)
16BitAtStart Old 65536 1340.98 1083.00
28333.00 97743.33 16-bit
16BitAtStart New 65536 1247.90 1000.00
28666.00 105033.84 16-bit
→ Speedup: 1.07x (faster by 6.94%)
=== Mixed (90% 8-bit) ===
Benchmark Version Size Avg (ns) Min (ns) Max
(ns) MB/s Result
--------------------------------------------------------------------------------------------------------------
Mixed90 Old 64 24.67 0.00
15667.00 5187.81 16-bit
Mixed90 New 64 15.99 0.00
8709.00 8006.46 16-bit
→ Speedup: 1.54x (faster by 35.20%)
Mixed90 Old 512 41.39 0.00
10834.00 24741.84 16-bit
Mixed90 New 512 23.41 0.00
16750.00 43737.15 16-bit
→ Speedup: 1.77x (faster by 43.43%)
Mixed90 Old 4096 129.96 41.00
21625.00 63032.45 16-bit
Mixed90 New 4096 97.66 41.00
21834.00 83878.94 16-bit
→ Speedup: 1.33x (faster by 24.85%)
Mixed90 Old 65536 1353.72 1083.00
22250.00 96823.82 16-bit
Mixed90 New 65536 1238.73 1041.00
21125.00 105811.28 16-bit
→ Speedup: 1.09x (faster by 8.49%)
================
* Source/WTF/wtf/text/ASCIIFastPath.h:
(WTF::isLatin1):
(WTF::charactersAreAllLatin1):
* Source/WTF/wtf/text/StringCommon.h:
(WTF::isLatin1): Deleted.
* Source/WTF/wtf/text/StringImpl.cpp:
(WTF::StringImpl::create8BitIfPossible):
Canonical link: https://commits.webkit.org/305259@main
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