RFR: 8300543 Compiler Implementation for Pattern Matching for switch [v2]

[Vicente Romero]

On Thu, 20 Apr 2023 14:07:01 GMT, Vicente Romero <vromero at openjdk.org> wrote:

>> The intent here is to avoid eager initialization of enums - so, until the enum is initialized, `lazyDoEnumSwitch` will be used (which, by itself, won't compute any results, except the result for `null`), which is then replaced with `doEnumSwitch` using the enum constants directly.
>> 
>> The enum switches support patterns as well, so something like:
>> 
>> enum E {A;}
>> E e = ...;
>> switch (e) {
>>      case E ee -> {}
>> }
>> 
>> is valid, and should trigger the part with Class labels.
>
> yep I found a similar test case triggering this code

could you explain a bit more the relation between `lazyDoEnumSwitch` and `doEnumSwitch` because my understanding is that `lazyDoEnumSwitch` is invoking `doEnumSwitch` so to me whenever `lazyDoEnumSwitch` is invoked there will be an immediate invocation of `doEnumSwitch` that's why I thought they could be folded together

>> `startIndex` may be non-0 when there are guards in the switch. In the case of the `enumSwitch`, something like:
>> 
>> enum E {A, B;}
>> E e = E.B;
>> switch (e) {
>>      case E ee when ee == E.A -> {}
>>      case E ee -> {}
>> }
>> 
>> 
>> the method will be called twice, one with `startIndex == 0` and once with `startIndex == 1`, after the guard fails/returns `false`.
>
> I see, thanks

and regarding checking that `startIndex` should be `>= 0`? shouldn't we check for that?

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PR Review Comment: https://git.openjdk.org/jdk/pull/13074#discussion_r1172839418
PR Review Comment: https://git.openjdk.org/jdk/pull/13074#discussion_r1172840817