RFR: 8361076: Add benchmark for ImageReader in preparation for Valhalla changes [v3]

[Magnus Ihse Bursie]

On Mon, 30 Jun 2025 15:08:25 GMT, David Beaumont <duke at openjdk.org> wrote:

>> Initial benchmark to capture at least some comparative measures of ImageReader performance.
>> 
>> Current results on my laptop:
>> 
>> Benchmark                                         Mode  Cnt   Score    Error  Units
>> NewImageBenchmark.warmCache_CountAllNodes         avgt    5   0.785 ±  0.140  ms/op
>> NewImageBenchmark.coldStart_CountOnly               ss    5  34.051 ± 17.662  ms/op
>> NewImageBenchmark.coldStart_InitAndCount            ss    5  31.006 ±  9.674  ms/op
>> NewImageBenchmark.coldStart_LoadJavacInitClasses    ss    5   3.752 ±  6.873  ms/op
>> 
>> The upcoming changes to ImageReader should show significant improvements to these results.
>
> David Beaumont has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Some tidying up relating to the state objects.

Build change trivially fine.

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Marked as reviewed by ihse (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26044#pullrequestreview-2973675262