8355177: Speed up StringBuilder::append(char[]) via UTF16::compress & Unsafe::copyMemory

[wenshao]

In BufferedReader.readLine and other similar scenarios, we need to use StringBuilder.append(char[]) to build the string.

For these scenarios, we can use the intrinsic method StringUTF16.compress and Unsafe.copyMemory instead of the character copy of the char-by-char loop to improve the speed.

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Progress

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Issue

• JDK-8355177: Speed up StringBuilder::append(char[]) via UTF16::compress & Unsafe::copyMemory (Enhancement - P4)

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[wenshao]

Below are the performance numbers on a MacBookPro M1 Max, showing a 112% speed increase when coder = LATIN1 and a 44.19% speed increase when coder = UTF16.

shell

git remote add wenshao git@github.com:wenshao/jdk.git
git fetch wenshao

# basline
git clone ee356d3af177877e2702db08a3b55d170a7e454c
make test TEST="micro:java.lang.StringBuilders.appendWithCharArray"

# current
git clone cd5137097b4a7be370cf60df9aa5000203ea99c0
make test TEST="micro:java.lang.StringBuilders.appendWithCharArray"

Performance Numbrers

-Benchmark                                 Mode  Cnt   Score   Error  Units (baseline cd5137097b4)
-StringBuilders.appendWithCharArrayLatin1  avgt   15  33.039 ± 0.059  ns/op
-StringBuilders.appendWithCharArrayUTF16   avgt   15  19.977 ± 0.054  ns/op

+Benchmark                                 Mode  Cnt   Score   Error  Units (current ee356d3af17)
+StringBuilders.appendWithCharArrayLatin1  avgt   15  15.533 ± 0.039  ns/op +112.70%
+StringBuilders.appendWithCharArrayUTF16   avgt   15  13.868 ± 0.053  ns/op +44.19%

[mlbridge]

Webrevs

• 02: Full (db110895)
• 01: Full - Incremental (ec6482b0)
• 00: Full (ee356d3a)

[AlanBateman]

/reviewers 2

[openjdk]

@AlanBateman
The total number of required reviews for this PR (including the jcheck configuration and the last /reviewers command) is now set to 2 (with at least 1 Reviewer, 1 Author).

[liach]

This might be helpful combined with #21730.

[liach]

Should we update this.count eagerly after compression?

[wenshao]

In the StringLatin1.canEncode(c) branch of the original code, this.count is not updated either, and the behavior is the same as before.