RFR: 8332587: RISC-V: secondary_super_cache does not scale well [v8]

[Gui Cao]

On Wed, 19 Jun 2024 07:45:35 GMT, Andrew Haley <aph at openjdk.org> wrote:

> Disabling `UseSecondarySupersTable` is probably not a good idea.
> 
> https://github.com/openjdk/jdk/blob/48621ae193ef70b2fae4dcb7ddc524f349beb131/src/hotspot/cpu/x86/macroAssembler_x86.cpp#L4743
> 
> is a better and easier way to handle this situation.

Hi, The same question has been raised before. Here is the implementation and test data using scalar registers. https://github.com/openjdk/jdk/pull/19320#issuecomment-2144900070
With the jmh test data, we see that there is a performance decrease from testNegative55 to testNegative64 when zbb is not available. This is because a loop is needed to count the number of 1 when Zbb is not available. Therefore, the current patch is only optimized when Zbb is available. What do you think?

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PR Review Comment: https://git.openjdk.org/jdk/pull/19320#discussion_r1645614507