RFR: 8336856: Optimize String Concat [v11]

[Chen Liang]

On Wed, 24 Jul 2024 14:56:48 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/invoke/StringConcatFactory.java line 1119:
>> 
>>> 1117: 
>>> 1118:         private static MethodHandle generate(Lookup lookup, MethodType args, String[] constants) throws Exception {
>>> 1119:             lookup = MethodHandles.Lookup.IMPL_LOOKUP;
>> 
>> I think you can try moving the inline copy generation to java.lang's StringConcatHelper; this way, we don't need to expose stringSize, coder etc. through JavaLangAccess (we may update String impl detail in the future) and just access the generated MethodHandle.
>
> If you do not use TRUSTED Lookup, errors will occur when processing records.
> 
> You can see this build error https://github.com/wenshao/jdk/actions/runs/10049344961/job/27775952878
> 
> TEST: java/lang/reflect/records/RecordReflectionTest.java
> 
> 
> Caused by: java.lang.IllegalAccessException: no such method: java.lang.StringConcatHelper$$StringConcat/0xad1b77c0.concat(R1,R2,R3)String/invokeStatic
>     at java.base/java.lang.invoke.MemberName.makeAccessException(MemberName.java:906)
>     at java.base/java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:989)
>     at java.base/java.lang.invoke.MethodHandles$Lookup.resolveOrFail(MethodHandles.java:3750)
>     at java.base/java.lang.invoke.MethodHandles$Lookup.findStatic(MethodHandles.java:2648)
>     at java.base/java.lang.invoke.StringConcatFactory$SimpleStringBuilderStrategy.generate(StringConcatFactory.java:727)
>     ... 41 more
> Caused by: java.lang.LinkageError: bad method type alias: (R1,R2,R3)String not visible from class java.lang.StringConcatHelper$$StringConcat/0xad1b77c0
>     at java.base/java.lang.invoke.MemberName.ensureTypeVisible(MemberName.java:812)
>     at java.base/java.lang.invoke.MemberName$Factory.resolve(MemberName.java:961)
>     at java.base/java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:986)
>     ... 44 more
> 
> 
> 
>     record R1() {}
> 
>     record R2(int i, int j) {}
> 
>     record R3(List<String> ls) {}
> 
>    // error
>     record R4(R1 r1, R2 r2, R3 r3) {}
> 
> 
> This PR also fixes the issue with TRUSTED not working in MemberName.java after using TRUSTED Lookup.

The solution is to call `.erase()` on the input method handle, and call `viewAsType` on the result method handle.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20273#discussion_r1689992258