RFR: 8332082: Shenandoah: Use consistent tests to determine when pre-write barrier is active [v3]

[Aleksey Shipilev]

On Mon, 20 May 2024 16:59:25 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> This is consistent with c1 and other platforms.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix typo

Dang. So we are regressing C1 performance a little here, by changing the single load-cmp to load-and-cmp. That is unfortunate, but might be acceptable?

src/hotspot/share/gc/shenandoah/c1/shenandoahBarrierSetC1.cpp line 75:

> 73: 
> 74:   // Create a mask to test if the marking bit is set.
> 75:   // TODO: can we directly test if bit is set?

No, we cannot: C1 LIR does not have a corresponding operation.

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PR Review: https://git.openjdk.org/jdk/pull/19180#pullrequestreview-2070736549
PR Review Comment: https://git.openjdk.org/jdk/pull/19180#discussion_r1609666303