RFR: 8294468: Fix char-subscripts warnings in Hotspot

[David Holmes]

On Tue, 27 Sep 2022 17:27:03 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}

Looks good. Thanks.

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Marked as reviewed by dholmes (Reviewer).

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