RFR: 8294468: Fix char-subscripts warnings in Hotspot [v2]

[Kim Barrett]

On Mon, 17 Oct 2022 18:08:21 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> There seem to be the only place in Hotspot where this warning fires, yet the warning is disabled wholesale for Hotspot. This is not good.
>> 
>> I can trace the addition of char-subscripts exclusion to [JDK-8211029](https://bugs.openjdk.org/browse/JDK-8211029) (Sep 2018). The only place in Hotspot where in fires is present from the initial load (2007).
>> 
>> The underlying problem that this warning tells us about is that `char` might be signed on some platforms, so we can potentially access the negative index. It is not a bug in our current code, that bounds the value of `k` under `MAXID-1`, which is `19`.
>> 
>> Additional testing:
>>  - [ ] Linux x86_64 fastdebug `tier1`
>>  - [x] The build matrix of:
>>    - GCC 10
>>    - {i686, x86_64, aarch64, powerpc64le, s390x, armhf, riscv64}
>>    - {server}
>>    - {release, fastdebug}
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
> 
>  - Merge branch 'master' into JDK-8294468-warning-char-subscripts
>  - Fix

Looks good.

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10455