RFR: 8345265: Minor improvements for LTO across all compilers

[Julian Waters]

On Sat, 11 Oct 2025 15:42:53 GMT, Kim Barrett <kim.barrett at oracle.com> wrote:

> The LTO vs flattening problem.

Currently that seems to be the biggest problem, I do have solutions for other smaller issues with LTO, but from what I witness the flattening problem has to be solved first before any more work can be done with LTO. While I fortunately do have time to spare to try working on the issue (I'm that "Someone else", more or less), I less fortunately don't have the knowledge required to fix that problem, as even though only G1 uses flattening, the call hierarchy is too massive to actually meaningfully discern which calls need to be flattened and which calls shouldn't be flattened. Not very sure if anyone knows which code paths shouldn't be inlined within g1ParScanThreadState.cpp, actually. If anyone knew, I could fast track the flattening issue on my end and have it solved pretty quickly.

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PR Comment: https://git.openjdk.org/jdk/pull/22464#issuecomment-3393474226