RFR: 8353686: Optimize Math.cbrt for x86 64 bit platforms [v5]

[Jatin Bhateja]

On Thu, 29 May 2025 18:56:11 GMT, Mohamed Issa <duke at openjdk.org> wrote:

>> The goal of this PR is to implement an x86_64 intrinsic for java.lang.Math.cbrt() using libm. There is a new set of micro-benchmarks are included to check the performance of specific input value ranges to help prevent regressions in the future.
>> 
>> The command to run all range specific micro-benchmarks is posted below.
>> 
>> `make test TEST="micro:CbrtPerf.CbrtPerfRanges"`
>> 
>> The results of all tests posted below were captured with an [Intel® Xeon 6761P](https://www.intel.com/content/www/us/en/products/sku/241842/intel-xeon-6761p-processor-336m-cache-2-50-ghz/specifications.html) using [OpenJDK v25-b21](https://github.com/openjdk/jdk/releases/tag/jdk-25%2B21) as the baseline version.
>> 
>> For performance data collected with the new built in range micro-benchmark, see the table below. Each result is the mean of 8 individual runs, and the input ranges used match those from the original Java implementation. Overall, the intrinsic provides a major uplift of 169% when very small inputs are used and a more modest uplift of 45% for all other inputs.
>> 
>> | Input range(s)                                  | Baseline throughput (ops/ms) | Intrinsic throughput (ops/ms) | Speedup |
>> | :-------------------------------------: | :-------------------------------: | :-------------------------------: | :---------: |
>> | [-2^(-1022), 2^(-1022)]                   | 6568                                        | 17678                                      | 2.69x       |
>> | (-INF, -2^(-1022)], [2^(-1022), INF) | 138932                                    | 200897                                    | 1.45x       |
>> 
>> Finally, the `jtreg:test/jdk/java/lang/Math/CubeRootTests.java` test passed with the changes.
>
> Mohamed Issa has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Add newline back to templateInterpreterGenerator_x86_64.cpp source file
>  - Add special case values to cbrt micro-benchmark set

LGTM,  we have already created follow up JBSs for known limiations.

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Marked as reviewed by jbhateja (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24470#pullrequestreview-2882036242