RFR: 8334431: C2 SuperWord: fix performance regression due to store-to-load-forwarding failures [v2]

[Emanuel Peter]

On Tue, 19 Nov 2024 07:53:26 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 25 commits:
>> 
>>  - manual merge
>>  - Merge branch 'master' into JDK-8334431-V-store-to-load-forwarding
>>  - Merge branch 'master' into JDK-8334431-V-store-to-load-forwarding
>>  - fix whitespace
>>  - fix tests and build
>>  - fix store-to-load forward IR rules
>>  - updates before the weekend ... who knows if they are any good
>>  - refactor to iteration threshold
>>  - use jvmArgs again, and apply same fix as 8343345
>>  - revert to jvmArgsPrepend
>>  - ... and 15 more: https://git.openjdk.org/jdk/compare/543e355b...000f9f13
>
> Why does the benchmark need to have so many methods, to make sure the different values are treated as constants?  I’m not sure, but JMH might turn @Param values into constants.  If so, then your benchmark can be greatly simplified.

@dean-long @merykitty I'm trying the `MethodHandles.constant` trick. Any chance you'd review the VM fix itself? ;)

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PR Comment: https://git.openjdk.org/jdk/pull/21521#issuecomment-2485711765