JDK-8346194 : Improve G1 pre-barrier C2 cost estimate
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 24
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2024-12-13
  • Updated: 2025-03-26
  • Resolved: 2025-03-17
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JDK 25
25 b15Fixed
Related Reports
Relates :  
JDK-8342382 - Implementation of JEP G1: Improve Application Throughput with a More Efficient Write-Barrier
Description
Currently, the pre-barrier has an estimated cost of 50 nodes for the C2 compiler for code generation.

This cost assumes that all of these 50 nodes are in the regular/fast path of the generated code - however this is not the case, the large majority of these nodes are part of the seldomly executed slow path and do not matter for code layout purposes.

This is similar to ZGC, and similar to ZGC the node cost should be reduced to just 4 (cmp, bool, if, if-proj for the fast path/jmp).

Likely this will not have a lot of impact on code generation because the post-barrier's cost is still overwhelmingly large (60), but that will be fixed in JDK-8342382.
Comments
Changeset: 9f8d833f Branch: master Author: Thomas Schatzl <tschatzl@openjdk.org> Date: 2025-03-17 07:57:45 +0000 URL: https://git.openjdk.org/jdk/commit/9f8d833f8654cb4280d002ef86ce3ae9d709eddc
17-03-2025
A pull request was submitted for review. Branch: master URL: https://git.openjdk.org/jdk/pull/23862 Date: 2025-03-03 12:30:23 +0000
03-03-2025