RFR: 8341594: Use Unsafe to coalesce reads in java.util.zip.ZipUtils [v2]

[Claes Redestad]

On Sun, 6 Oct 2024 15:11:19 GMT, Chen Liang <liach at openjdk.org> wrote:

>> It's actually not less overhead in my tests, since `checkIndex` is intrinsic and mostly disappears, while with `checkFromIndexSize` performance gets significantly worse (on par with baseline). It's on my todo to investigate this in-depth but I think `checkFromIndexSize` needs to be given similar intrinsification treatment as `checkIndex`.
>
> Actually if we trust the input index to be nonnegative, we can just check our end index for out of bounds too.

Sure, I think the JIT is pretty good at eliminating the (intrinsic) `checkIndex` calls when they are redundant though. Performance with and without these `checkIndex`es are the same in my testing, so we can eat and have the cake on this one.

FWIW I wouldn't mind giving similar treatment to `ByteArray(-LittleEndian)` and avoid the `VarHandles` dependency in those utility classes, but I have no urge to get into the sort of discussions that were spawned in #19616

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PR Review Comment: https://git.openjdk.org/jdk/pull/21377#discussion_r1789137335