Integrated: 8291966: SwitchBootstrap.typeSwitch could be faster

[Jan Lahoda]

On Fri, 5 Aug 2022 16:12:08 GMT, Jan Lahoda <jlahoda at 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.

This pull request has now been integrated.

Changeset: 9be5769a
Author:    Jan Lahoda <jlahoda at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/9be5769a68d7cc9dced732649adc4c977b8eac8d
Stats:     197 lines in 2 files changed: 110 ins; 15 del; 72 mod

8291966: SwitchBootstrap.typeSwitch could be faster

Reviewed-by: asotona

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

PR: https://git.openjdk.org/jdk/pull/9779