8357289: Break down the String constructor into smaller methods

[wenshao]

Through JVM Option +PrintInlining, we found that String has a constructor codeSize of 852, which is too large. This caused failed to inline.

The following is the output information of PrintInlining:

                @ 9   java.lang.String::<init> (12 bytes)   inline (hot)
!m                 @ 1   java.nio.charset.Charset::defaultCharset (52 bytes)   inline (hot)
!                  @ 8   java.lang.String::<init> (852 bytes)   failed to inline: hot method too big

In Java code, the big method that cannot be inlined is the following constructor

String(Charset charset, byte[] bytes, int offset, int length) {}

The above String constructor is too large; break it down into smaller methods with a codeSize under 325 to allow them to be inlined by the C2.

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8357289 needs maintainer approval

Issue

• JDK-8357289: Break down the String constructor into smaller methods (Enhancement - P4 - Requested)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk25u-dev.git pull/32/head:pull/32
$ git checkout pull/32

Update a local copy of the PR:
$ git checkout pull/32
$ git pull https://git.openjdk.org/jdk25u-dev.git pull/32/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 32

View PR using the GUI difftool:
$ git pr show -t 32

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk25u-dev/pull/32.diff

Using Webrev

Link to Webrev Comment

[wenshao]

/approval 8357289 request This PR makes minimal changes, but significantly improves the performance of constructing Strings, so it requests a backport to JDK 25. The code logic remains unchanged, requiring no additional testing, and the risk is relatively low.

[bridgekeeper]

👋 Welcome back swen! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@wenshao
8357289: The approval request was already up to date.

[mlbridge]

Webrevs

• 00: Full (45b4eb7f)

[openjdk]

This backport pull request has now been updated with issue from the original commit.