RFR: 8334060: Implementation of Late Barrier Expansion for G1 [v10]

[Kim Barrett]

On Wed, 28 Aug 2024 08:09:44 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Roberto Castañeda Lozano has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Rename g1XChgX to g1GetAndSetX for consistency with Ideal operation names
>
> src/hotspot/share/gc/g1/c2/g1BarrierSetC2.cpp line 166:
> 
>> 164:  * post-barrier completely, if it is possible during compile time to prove the
>> 165:  * object is newly allocated and that no safepoint exists between the allocation
>> 166:  * and the store.
> 
> It might be worth saying explicitly that this is a compile-time version of the above mentioned young
> generation filter.

We can similarly elide the post-barrier if we can prove at compile-time that the value being written
is null.  That case isn't handled here though.  Instead that's checked for in 
`refine_barrier_by_new_val_type` and in `get_store_barrier`.  I'm not sure why it's structured
that way.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19746#discussion_r1734201007