On Sat, 22 Apr 2023 01:42:41 GMT, Vladimir Ivanov <vliva...@openjdk.org> wrote:
>> Cesar Soares Lucas has updated the pull request with a new target base due
>> to a merge or a rebase. The pull request now contains 10 commits:
>>
>> - Catching up with master
>>
>> Merge remote-tracking branch 'origin/master' into
>> rematerialization-of-merges
>> - Fix tests. Remember previous reducible Phis.
>> - Address PR review 3. Some comments and be able to abort compilation.
>> - Merge with Master
>> - Addressing PR review 2: refactor & reuse MacroExpand::scalar_replacement
>> method.
>> - Address PR feeedback 1: make ObjectMergeValue subclass of ObjectValue &
>> create new IR class to represent scalarized merges.
>> - Add support for SR'ing some inputs of merges used for field loads
>> - Fix some typos and do some small refactorings.
>> - Merge master
>> - Add support for rematerializing scalar replaced objects participating in
>> allocation merges
>
> src/hotspot/share/code/debugInfo.hpp line 199:
>
>> 197: // ObjectValue describing an object that was scalar replaced.
>> 198:
>> 199: class ObjectMergeValue: public ObjectValue {
>
> I find the decision to subclass`ObjectValue` confusing and error prone: now
> `is_object()` returns true for `ObjectMergeValue`, but you have to apply the
> selector first to turn it into `ObjectValue`. And now the order of checks
> matter, so you always have to perform `is_object_merge()` first and then
> follow it with `is_object()` guard.
>
> You have 3 flavors of `ObjectValue` now:
> * good old `ObjectValue`;
> * `ObjectMergeValue`
> * merge candidates (`ObjectMergeCandidateValue`?)
>
> Does it make sense to introduce 3 different subclasses under `ObjectValue` to
> clearly distinguish the scenarios?
Hi @iwanowww . I finished implementing a version of this like the illustration
below (I didn't add a Candidate class).
ScopeValue
ObjectValue
ObjectAllocationValue
AutoBoxObjectValue
ObjectMergeValue
Here are some observations:
- I don't think ObjectMergeValue should be under ObjectValue. The two classes
only have two fields in common (_id and _visited). I think it should be a
subclass of ScopeValue.
- ObjectCandidateValue would need to go under ObjectAllocationValue because it
essentially _is_ an ObjectAllocationValue in most aspects.
- I didn't add a ObjectCandidateValue class because that class would need to go
under ObjectAllocationValue and we would still need to do an
"is_object_candidate" before all "is_object_allocation" and we would end up in
much the situation that we want to avoid - needing to do is_object_merge before
is_object.
- It seems the best place to flag an object as candidate is really in
ObjectAllocationValue.
What do you think? As I said, I already have the code, if you want I can push
it and you take a look.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/12897#discussion_r1179649780
