8368724: RISC-V: Check if unaligned_access is enabled before use

[Anjian-Wen]

we can notice that the unaligned_access.value() can only be used when the unaligned_access.enabled() is true, so we add the check here before use

Manually checked the result on platforms w/wo fast misaligned accesses by running: $java -XX:+PrintFlagsFinal -version | grep AvoidUnalignedAccess

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Issue

• JDK-8368724: RISC-V: Check if unaligned_access is enabled before use (Enhancement - P4)

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• Fei Yang (@RealFYang - Reviewer)

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8368724: RISC-V: Check if unaligned_access is enabled before use

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[Anjian-Wen]

/issue JDK-8368724

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@Anjian-Wen The primary solved issue for a PR is set through the PR title. Since the current title does not contain an issue reference, it will now be updated.

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[RealFYang]

Looks reasonable. Thanks.

[Hamlin-Li]

I think we're going to remove the AvoidUnalignedAccesses? And if unaligned_access is not enabled, then its value can not be MISALIGNED_FAST?
If both above are true, then seems this check is not necessary?

[Anjian-Wen]

I think we're going to remove the AvoidUnalignedAccesses? And if unaligned_access is not enabled, then its value can not be MISALIGNED_FAST? If both above are true, then seems this check is not necessary?

@Hamlin-Li Thanks for your review.
According to the current use of unaligned_access.value, if it is not enabled, then using value will depend on the default value -1. This change is to try to make the use of unaligned_access.value more reasonable.
Maybe we can keep this judgment and consider removing the Avoid flag latter？

[Hamlin-Li]

@Hamlin-Li Thanks for your review. According to the current use of unaligned_access.value, if it is not enabled, then using value will depend on the default value -1. This change is to try to make the use of unaligned_access.value more reasonable. Maybe we can keep this judgment and consider removing the Avoid flag latter？

If the default value is -1, then unaligned_access.value() == MISALIGNED_FAST can only be true when it's enabled, so that makes the extra check added in this pr unnecessary for UseUnalignedAccesses.
As for AvoidUnalignedAccesses, there is a discussion here to remove AvoidUnalignedAccesses: #27445 (review).
So my suggestion is to just remove AvoidUnalignedAccesses in riscv, how do you think about it?

[Hamlin-Li]

So my suggestion is to just remove AvoidUnalignedAccesses in riscv, how do you think about it?

I guess no one's already working it? Maybe you could take it if you are available. :)

[Anjian-Wen]

@Hamlin-Li Thanks for your review. According to the current use of unaligned_access.value, if it is not enabled, then using value will depend on the default value -1. This change is to try to make the use of unaligned_access.value more reasonable. Maybe we can keep this judgment and consider removing the Avoid flag latter？

If the default value is -1, then unaligned_access.value() == MISALIGNED_FAST can only be true when it's enabled, so that makes the extra check added in this pr unnecessary for UseUnalignedAccesses. As for AvoidUnalignedAccesses, there is a discussion here to remove AvoidUnalignedAccesses: #27445 (review). So my suggestion is to just remove AvoidUnalignedAccesses in riscv, how do you think about it?

@Hamlin-Li Oh, Thanks! I get it, I think it makes sence. I will try to figure out how to modify the code and remove AvoidUnalignedAccesses together