RFR: 8357289: Break down the String constructor into smaller methods

[Chen Liang]

On Sun, 18 May 2025 12:48:07 GMT, Shaojin Wen <swen at openjdk.org> wrote:

> 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.

src/java.base/share/classes/java/lang/String.java line 690:

> 688:                 .onUnmappableCharacter(CodingErrorAction.REPLACE);
> 689:         char[] ca = new char[en];
> 690:         int caLen = decodeWithDecoder(cd, ca, bytes, offset, length);

Let's restore the CharacterCodingException for now. I don't think we should change the exceptions as part of the break down.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25290#discussion_r2094621982