RFR: 8346954: [JMH] jdk.incubator.vector.MaskedLogicOpts fails due to IndexOutOfBoundsException [v2]

[Jatin Bhateja]

On Wed, 26 Feb 2025 07:04:58 GMT, Nicole Xu <duke at openjdk.org> wrote:

>> Suite `MaskedLogicOpts.maskedLogicOperationsLong512()` failed on both x86 and AArch64 with the following error:
>> 
>> 
>> java.lang.IndexOutOfBoundsException: Index 252 out of bounds for length 249
>> 
>> 
>> The variable `long256_arr_idx` is misused when indexing `LongVector l2`, `l3`, `l4`, `l5` in function `maskedLogicOperationsLongKernel()` resulting in the IndexOutOfBoundsException error. On the other hand, the unified index for 128-bit, 256-bit and 512-bit species might not be proper since it leaves gaps in between when accessing the data for 128-bit and 256-bit species. This will unnecessarily include the noise due to cache misses or (on some targets) prefetching additional cache lines which are not usable, thereby impacting the crispness of microbenchmark.
>> 
>> Hence, we improved the benchmark from several aspects,
>> 1. Used sufficient number of predicated operations within the vector loop while minimizing the noise due to memory operations.
>> 2. Modified the index computation logic which can now withstand any ARRAYLEN without resulting in an IOOBE.
>> 3. Removed redundant vector read/writes to instance fields, thus eliminating significant boxing penalty which translates into throughput gains.
>
> Nicole Xu has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - 8346954: [JMH] jdk.incubator.vector.MaskedLogicOpts fails due to IndexOutOfBoundsException
>    
>    Suite MaskedLogicOpts.maskedLogicOperationsLong512() failed on both x86
>    and AArch64 with the following error:
>    
>    ```
>    java.lang.IndexOutOfBoundsException: Index 252 out of bounds for length 249
>    ```
>    
>    The variable `long256_arr_idx` is misused when indexing `LongVector l2`,
>    `l3`, `l4`, `l5` in function `maskedLogicOperationsLongKernel()`
>    resulting in the IndexOutOfBoundsException error. On the other hand, the
>    unified index for 128-bit, 256-bit and 512-bit species might not be
>    proper since it leaves gaps in between when accessing the data
>    for 128-bit and 256-bit species. This will unnecessarily include the
>    noise due to cache misses or (on some targets) prefetching additional
>    cache lines which are not usable, thereby impacting the crispness of
>    microbenchmark.
>    
>    Hence, we improved the benchmark from several aspects,
>    1. Used sufficient number of predicated operations within the vector
>    loop while minimizing the noise due to memory operations.
>    2. Modified the index computation logic which can now withstand any
>    ARRAYLEN without resulting in an IOOBE.
>    3. Removed redundant vector read/writes to instance fields, thus
>    eliminating significant boxing penalty which translates into throughput
>    gains.
>    
>    Change-Id: Ie8a9d495b1ca5e36f1eae069ff70a815a2de00c0
>  - Revert "8346954: [JMH] jdk.incubator.vector.MaskedLogicOpts fails due to IndexOutOfBoundsException"
>    
>    This reverts commit 083bedec04d5ab78a420e156e74c1257ce30aee8.

LGTM

-------------

Marked as reviewed by jbhateja (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22963#pullrequestreview-2643351624