RFR: 8346194: Improve G1 pre-barrier C2 cost estimate [v2]

[Albert Mingkun Yang]

On Thu, 6 Mar 2025 10:35:07 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Hi all,
>> 
>>   please review this change that modifies pre-barrier node costs for loop-unrolling to only consider the fast path. The reasoning is similar to zgc (and the new costs as well): only the part of the barrier inlined into the main code stream, as the slow path is laid out separately and does/should not directly affect performance (particularly if there is no marking going on).
>> 
>> There are no differences/impact in performance since the post barrier cost is still very large, which fill be fixed elsewhere.
>> 
>> Testing: gha, perf testing standalone (neither micros nor actual benchmarks give any difference outside of variance), testing with JDK-8342382
>> 
>> Hth,
>>   Thomas
>
> Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update src/hotspot/share/gc/g1/c2/g1BarrierSetC2.cpp
>   
>   Co-authored-by: Roberto Castañeda Lozano <robcasloz at users.noreply.github.com>

Marked as reviewed by ayang (Reviewer).

-------------

PR Review: https://git.openjdk.org/jdk/pull/23862#pullrequestreview-2685917268