RFR: 8286301: Port JEP 425 to RISC-V [v3]

[Xiaolin Zheng]

On Thu, 3 Nov 2022 02:32:00 GMT, Fei Yang <fyang at openjdk.org> wrote:

>> Hi,
>> 
>> Please review this PR porting JEP 425 (Virtual Threads) to RISC-V.
>> 
>> This is mainly adapted from the work of AArch64 port. Most of the changes lie in RISC-V scope.
>> Changes to HotSpot shared code are trivial and are always guarded by RISCV64 macro. So this won't
>> affect the rest of the world in theory.
>> 
>> There exists some differences in frame structure between AArch64 and RISC-V.
>> For AArch64, we have:
>> 
>> enum {
>>   link_offset           = 0,
>>   return_addr_offset    = 1,
>>   sender_sp_offset      = 2
>> };
>> 
>> While for RISC-V, we have:
>> 
>> enum {
>>   link_offset           = -2,
>>   return_addr_offset    = -1,
>>   sender_sp_offset      =  0
>> };
>> 
>> So we need adapations in some places where the code relies on value of sender_sp_offset to work.
>> Note that implementation for Post-call NOPs optimization is not incorporated in this PR as we plan to
>> evaluate more on its impact on performance.
>> 
>> Testing on Linux-riscv64 HiFive Unmatched board:
>>   - Minimal, Client and Server release & fastdebug build OK.
>>   - Passed tier1-tier4 tests (release build).
>>   - Passed jtreg tests under test/jdk/java/lang/Thread/virtual with extra JVM options: -XX:+VerifyContinuations -XX:+VerifyStack (fastdebug build).
>>   - Performed benchmark tests like Dacapo, SPECjvm2008, SPECjbb2015, etc. to make sure no performance regression are introduced (release build).
>
> Fei Yang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Merge branch 'master' into 8286301
>  - Fix
>  - 8286301: JEP 425 to RISC-V

Nice overall. Please let me approve this for you :-)

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Marked as reviewed by xlinzheng (no project role).

PR: https://git.openjdk.org/jdk/pull/10917