On Wed, 31 May 2023 14:05:56 GMT, Jan Lahoda <jlah...@openjdk.org> wrote:
>> 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
>
> This patch is intended to eliminate some consecutive unnecessary tests like
> in case like:
>
> switch (o) {
> case Runnable r when ... -> {}
> case Runnable r when ... -> {}
> case Runnable r when ... -> {}
> case Object o -> {}
> }
>
>
> If `o` is not a `Runnable`, the `instanceof` will only happen for the first
> case, and the rest will be skipped, as these tests could not pass. But (as a
> current limitation), if it is not a consecutive run, the duplicate
> `instanceof` checks will still happen.
>
> I am quite sure there are ways to improve the bootstrap further, but might be
> better to have some (more) real-world examples to know what to optimize for.
@lahodaj
> This patch is intended to eliminate some consecutive unnecessary tests like
> in case like:
>
> ```java
> switch (o) {
> case Runnable r when ... -> {}
> case Runnable r when ... -> {}
> case Runnable r when ... -> {}
> case Object o -> {}
> }
> ```
I would expect that the above code would produce bytecode equivalent to:
loop: for (int _i = 0;;) {
switch (invokedynamic typeSwitch(o, _i) { Runnable.class, Object.class
}) {
case 0 /* Runnable */ -> {
_i++;
Runnable r = (Runnable) o;
if (...) {
break loop;
} else if (...) {
break loop;
} else if (...) {
break loop;
}
continue loop;
}
case 1 /* Object */ -> {
_i++;
break loop;
}
case -1 -> throw new NullPointerException();
default -> throw new MatchException();
}
}
-------------
PR Comment: https://git.openjdk.org/jdk/pull/9779#issuecomment-1577468813
