8356875: RISC-V: extension flag UseZvfh should depends on UseZfh

[Hamlin-Li]

Hi,
Can you help to review this simple patch?
If we don't enable such dependency, then there will be situation that when Zvfh is enabled but Zfh is disabled, and optimizations depending on Zvfh will be disabled (e.g. in C2) because Zfh related IR node are considered not supported.

Thanks!

By rvv spec, The Zvfh extension depends on the Zve32f and Zfhmin extensions.
But I think in logic and JVM code, we should let Zvfh depends on Zfh.

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Issue

• JDK-8356875: RISC-V: extension flag UseZvfh should depends on UseZfh (Enhancement - P4)

Reviewers

• Fei Yang (@RealFYang - Reviewer)

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8356875: RISC-V: extension flag UseZvfh should depends on UseZfh

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At the time when this comment was updated there had been 134 new commits pushed to the master branch:

• 97b0dd2: 8336906: C2: assert(bb->is_reachable()) failed: getting result from unreachable basicblock
• a989245: 8327466: ct.sym zip not reproducible across build environment timezones
• 3270b00: 8356173: Remove ThreadCritical
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[RealFYang]

For QEMU, Zvfh also means Zvfhmin and Zfhmin. So there is no Zfh if you only enable Zvfh when start QEMU.
That means hwprobe syscall will detect Zvfh and Zfhmin but no Zfh. Is there a similar issue for this case?

[Hamlin-Li]

One question: Not sure if I understand you correctly, seems to me Zfh is also detected and automatically set by hwprobe when running with qemu?

[Hamlin-Li]

For this pr, it tries to address the situation: when neither Zfh/Zvfh can not be enabled automatically (no matter what's the reason), so user could enable Zvfh manually to get some optimization, in that case it will fail to get such optimization even if with -XX:+PrintFlagsFinal it shows that UseZvfh == true, this is very confusing.
So to make this situation more understanable for user (maybe more for developer) of jdk, we'd better to automatically unset UseZvfh when UseZfh is false.

[Hamlin-Li]

Thanks for discussion.
Yes, short answer is this pr could also solve the issue you mentioned above for qemu.

[RealFYang]

Looks good. Thanks.

[Hamlin-Li]

Looks good. Thanks.

Thank you!