RFR: 8300148: Consider using a StoreStore barrier instead of Release barrier on ctor exit [v6]

[Joshua Cao]

On Tue, 2 Apr 2024 08:40:52 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Joshua Cao has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Add micro benchmark courtesy of @shipilev
>>  - More comprehensive IR tests based on @shipilev's suggestions
>
> test/hotspot/jtreg/compiler/c2/irTests/ConstructorBarriers.java line 244:
> 
>> 242:     @IR(failOn = IRNode.MEMBAR_RELEASE)
>> 243:     @IR(failOn = IRNode.MEMBAR_STORESTORE)
>> 244:     @IR(failOn = IRNode.MEMBAR_RELEASE)
> 
> Here and later: Looks weird to test for `MEMBAR_RELEASE` twice. Also, should it be just `failOn = IRNode.MEMBAR`?

Meant to test for `MEMBAR_VOLATILE`. We can't fail on all `MEMBAR` because there are some cases that have `MEMBAR_ACQUIRE`. Added those checks in latest commits.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18505#discussion_r1548795888