RFR: 8262891: Compiler implementation for Pattern Matching for switch (Preview) [v2]

[Jan Lahoda]

On Tue, 4 May 2021 20:48:34 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Jan Lahoda has updated the pull request incrementally with three additional commits since the last revision:
>> 
>>  - Reflecting recent spec changes.
>>  - Reflecting review comments.
>>  - Reflecting review comments on SwitchBootstraps.
>
> Good work. There's a lot to take in here. I think overall, it holds up well - I like how case labels have been extended to accommodate for patterns. In the front-end, I think there are some questions over the split between Attr and Flow - maybe it is unavoidable, but I'm not sure why some control-flow analysis happens in Attr instead of Flow and I left some questions to make sure I understand what's happening.
> 
> In the backend it's mostly good work - but overall the structure of the code, both in Lower and in TransPattern is getting very difficult to follow, given there are many different kind of switches each with its own little twist attached to it. It would be nice, I think (maybe in a separate cleanup?) if the code paths serving the different switch kinds could be made more separate, so that, when reading the code we can worry only about one possible code shape. That would make the code easier to document as well.

@mcimadamore, @forax, thanks a lot for comments! I tried to apply the requested changes in recent commits (https://github.com/openjdk/jdk/pull/3863/commits/3fc2502a33cec20f39fe571eb25538ee3b459a9b https://github.com/openjdk/jdk/pull/3863/commits/aeddb85e65bf77ed62dc7fa1ad00c29646d02c99 ).

I've also tried to update the implementation for the latest spec changes here:
https://github.com/openjdk/jdk/pull/3863/commits/54ba974e1aac00bbde1c3bd2627f01caaaeda09b

The spec changes are: total patterns are nullable; pattern matching ("new") statement switches must be complete (as switch expressions).

Any further feedback is welcome!

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PR: https://git.openjdk.java.net/jdk/pull/3863