RFR: 8342692: C2: long counted loop/long range checks: don't create loop-nest for short running loops [v15]

[Roland Westrelin]

On Wed, 23 Apr 2025 09:03:48 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Roland Westrelin has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 41 commits:
>> 
>>  - merge fix
>>  - Merge branch 'master' into JDK-8342692
>>  - merge fix
>>  - Merge branch 'master' into JDK-8342692
>>  - merge
>>  - Merge branch 'master' into JDK-8342692
>>  - Merge branch 'master' into JDK-8342692
>>  - whitespace
>>  - Merge branch 'master' into JDK-8342692
>>  - TestMemorySegment test fix
>>  - ... and 31 more: https://git.openjdk.org/jdk/compare/dc5c4148...065abb29
>
> src/hotspot/share/opto/c2_globals.hpp line 824:
> 
>> 822:   product(bool, ShortRunningLongLoop, true, DIAGNOSTIC,                     \
>> 823:           "long counted loop/long range checks: don't create loop nest if"  \
>> 824:           "loop runs for small enough number of iterations")                \
> 
> Could it make sense to have `ShortLoopIter` be a flag as well? That would allow you to write a nice JMH benchmark, where we can modify the threshold :)
> 
> Wait... you mention `ShortLoopIter` in the PR description, but it only occurs once in a comment... what happened here?

See: https://github.com/openjdk/jdk/pull/21630#issuecomment-2538327199

I removed it following the discussion with @merykitty

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PR Review Comment: https://git.openjdk.org/jdk/pull/21630#discussion_r2077001856