RFR: 8338930: StringConcatFactory hardCoded string concatenation strategy [v3]

[ExE Boss]

On Sun, 25 Aug 2024 14:29:16 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> This is a follow-up to PR #20273, which improves performance when the number of parameters exceeds 20.
>> 
>> When the number of parameters is large, the possibility of reuse will be lower, so we can use the static concat method and write the length and coder directly into the bytecode to solve the performance regression problem.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   add control flag `reuseThreshold`

As the `paramTypes` passed to `MethodType​::methodType(…)` and `MethodTypeDesc​::of(…)` are guaranteed valid and aren’t mutated afterwards, this can use `MethodType​::methodType​(…, trusted = true)` and `MethodTypeDescImpl​::ofValidated(…)`:

src/java.base/share/classes/java/lang/invoke/StringConcatFactory.java line 1202:

> 1200:                 paramTypes[i + prefixArgs] = needStringOf(cl) ? CD_String : ConstantUtils.classDesc(cl);
> 1201:             }
> 1202:             return MethodTypeDesc.of(CD_int, paramTypes);

Suggestion:

            return MethodTypeDescImpl.ofValidated(CD_int, paramTypes);

src/java.base/share/classes/java/lang/invoke/StringConcatFactory.java line 1219:

> 1217:                 }
> 1218:             }
> 1219:             return MethodTypeDesc.of(CD_int, paramTypes);

Suggestion:

            return MethodTypeDescImpl.ofValidated(CD_int, paramTypes.toArray(ConstantUtils.EMPTY_CLASSDESC));

src/java.base/share/classes/java/lang/invoke/StringConcatFactory.java line 1234:

> 1232:                 paramTypes[i + 1] = needStringOf(cl) ? CD_String : ConstantUtils.classDesc(cl);
> 1233:             }
> 1234:             return MethodTypeDesc.of(CD_int, paramTypes);

Suggestion:

            return MethodTypeDescImpl.ofValidated(CD_int, paramTypes);

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PR Review: https://git.openjdk.org/jdk/pull/20675#pullrequestreview-2259314494
PR Review Comment: https://git.openjdk.org/jdk/pull/20675#discussion_r1730377690
PR Review Comment: https://git.openjdk.org/jdk/pull/20675#discussion_r1730377709
PR Review Comment: https://git.openjdk.org/jdk/pull/20675#discussion_r1730377739