Integrated: 8338937: Optimize the string concatenation of ClassDesc

[Shaojin Wen]

On Sun, 25 Aug 2024 13:36:34 GMT, Shaojin Wen <swen at openjdk.org> wrote:

> The string concatenation of java.base module is implemented based on StringBuilder, which will result in extra object allocation and slow performance. We can solve this problem by using String.concat method and StringConcatHelper to provide concat method.
> 
> for example, 
> 
> * use "+"
> 
> class ClassDesc {
>     default String displayName() {
>         c.displayName() + "[]".repeat(depth)
>     }
> }
> 
> 
> bytecode:
> 
> 106: new           #40                 // class java/lang/StringBuilder
> 109: dup
> 110: invokespecial #42                 // Method java/lang/StringBuilder."<init>":()V
> 113: aload_2
> 114: invokeinterface #195,  1          // InterfaceMethod displayName:()Ljava/lang/String;
> 119: invokevirtual #50                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
> 122: ldc           #198                // String []
> 124: iload_1
> 125: invokevirtual #200                // Method java/lang/String.repeat:(I)Ljava/lang/String;
> 128: invokevirtual #50                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
> 131: invokevirtual #53                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
> 134: areturn
> 
> 
> * use String#concat
> 
> c.displayName().concat("[]".repeat(depth))
> 
> 
> bytecode:
> 
> 112: ldc           #198                // String []
> 114: iload_1
> 115: invokevirtual #200                // Method java/lang/String.repeat:(I)Ljava/lang/String;
> 118: invokevirtual #86                 // Method java/lang/String.concat:(Ljava/lang/String;)Ljava/lang/String;

This pull request has now been integrated.

Changeset: 55312e15
Author:    Shaojin Wen <swen at openjdk.org>
Committer: Chen Liang <liach at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/55312e1549c36be46b0f3b3b40763a33311c3e25
Stats:     57 lines in 7 files changed: 39 ins; 4 del; 14 mod

8338937: Optimize the string concatenation of ClassDesc

Reviewed-by: liach

-------------

PR: https://git.openjdk.org/jdk/pull/20705