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

[Thomas Schatzl]

> 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>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23862/files
  - new: https://git.openjdk.org/jdk/pull/23862/files/429bc01b..4f8273a6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23862&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23862&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23862.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23862/head:pull/23862

PR: https://git.openjdk.org/jdk/pull/23862