On Mon, 29 May 2023 07:25:26 GMT, Jan Lahoda <jlah...@openjdk.org> wrote:
>> The pattern matching switches are using a bootstrap method
>> `SwitchBootstrap.typeSwitch` to implement the jumps in the switch.
>> Basically, for a switch like:
>>
>> switch (obj) {
>> case String s when s.isEmpty() -> {}
>> case String s -> {}
>> case CharSequence cs -> {}
>> ...
>> }
>>
>>
>> this method will produce a MethodHandle that will be analyze the provided
>> selector value (`obj` in the example), and will return the case index to
>> which the switch should jump. This method also accepts a (re)start index for
>> the search, which is used to handle guards. For example, if the
>> `s.isEmpty()` guard in the above sample returns false, the matching is
>> restarted on the next case.
>>
>> The current implementation is fairly slow, it basically goes through the
>> labels in a loop. The proposal here is to replace that with a MethodHandle
>> structure like this:
>>
>> obj == null ? -1
>> : switch (restartIndex) {
>> case 0 -> obj instanceof String ? 0 : obj instanceof
>> CharSequence ? 2 : ... ;
>> case 1 -> obj instanceof String ? 1 : obj instanceof
>> CharSequence ? 2 : ... ;
>> case 2 -> obj instanceof CharSequence ? 2 : ... ;
>> ...
>> default -> <labels-count>;
>> }
>>
>>
>> This appear to run faster than the current implementation, using testcase
>> similar to the one used for https://github.com/openjdk/jdk/pull/9746 , these
>> are the results
>>
>> PatternsOptimizationTest.testLegacyIndyLongSwitch thrpt 25 1515989.562
>> ± 32047.918 ops/s
>> PatternsOptimizationTest.testHandleIndyLongSwitch thrpt 25 2630707.585
>> ± 37202.210 ops/s
>>
>> PatternsOptimizationTest.testLegacyIndyShortSwitch thrpt 25 6789310.900
>> ± 61921.636 ops/s
>> PatternsOptimizationTest.testHandleIndyShortSwitch thrpt 25 10771729.464
>> ± 69607.467 ops/s
>>
>>
>> The "LegacyIndy" is the current implementation, "HandleIndy" is the one
>> proposed here. The translation in javac used is the one from #9746 in all
>> cases.
>
> Jan Lahoda has updated the pull request with a new target base due to a merge
> or a rebase. The pull request now contains six commits:
>
> - Reflecting review feedback.
> - Merge branch 'master' into JDK-8291966
> - Adding comments
> - Improving performance
> - Merge branch 'master' into JDK-8291966
> - 8291966: SwitchBootstrap.typeSwitch could be faster
src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java line 340:
> 338:
> createRepeatIndexSwitch(lookup, labels),
> 339:
> MethodHandles.insertArguments(MAPPED_ENUM_LOOKUP, 1, lookup, enumClass,
> labels, new EnumMap())));
> 340: target = MethodHandles.permuteArguments(body,
> MethodType.methodType(int.class, Object.class, int.class), 1, 0);
This `guardWithTest` does the opposite to what’s described in the above comment.
src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java line 389:
> 387: }
> 388: }
> 389: return enumMap.map[value.ordinal()];
`enumMap.map` never gets set before this line.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/9779#discussion_r1550058760
PR Review Comment: https://git.openjdk.org/jdk/pull/9779#discussion_r1550057327
