RFR: 8320448: Accelerate IndexOf using AVX2 [v19]

[Scott Gibbons]

On Mon, 6 May 2024 23:19:07 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Scott Gibbons has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Rearrange; add lambdas for clarity
>
> src/hotspot/cpu/x86/stubGenerator_x86_64_string.cpp line 329:
> 
>> 327:     ////////////////////////////////////////////////////////////////////////////////////////
>> 328: 
>> 329:     __ bind(L_begin);
> 
> So far we have handled haystack <= 32 and needle_size <= 5 (?) in bytes. A high level algorithm description here is needed in comments to follow the code below.  A description of what are the various paths in terms of haystack and needle sizes and how to reason the assembly code below and make sure that all the paths are taken care of. Also the abstraction level suddenly changes here to detailed code below instead of methods for the various paths.

I added a description.  Can you please check to ensure it meets your objective?  Thanks.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16753#discussion_r1610124233