RFR: 8338937: Optimize the string concatenation of ClassDesc [v2]

[Chen Liang]

On Tue, 27 Aug 2024 11:52:38 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;
>
> Shaojin Wen has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - more concat
>  - Suggestions from @ExE-Boss
>  - concat Object value

Tier 1-3 tests look good.

For context, some core library developers are currently investigating if we can mark some classes and methods as used in early startup, after this problem was raised in OpenJDK committer's workshop (and encountered in the generics experiment work shown in JVMLS 2024); those methods can fail fast if they use lambdas, and we can make compiler generate regular string concat in other methods.

However, most of your changes here are on code used before string concat is ready, so this is a good improvement.

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

Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20705#pullrequestreview-2278655776
PR Comment: https://git.openjdk.org/jdk/pull/20705#issuecomment-2327592311