RFR: 8274242: Implement fast-path for ASCII-compatible CharsetEncoders on x86 [v6]

[Tobias Hartmann]

On Wed, 29 Sep 2021 12:36:23 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> This patch extends the `ISO_8859_1.implEncodeISOArray` intrinsic on x86 to work also for ASCII encoding, which makes for example the `UTF_8$Encoder` perform on par with (or outperform) similarly getting charset encoded bytes from a String. The former took a small performance hit in JDK 9, and the latter improved greatly in the same release.
>> 
>> Extending the `EncodeIsoArray` intrinsics on other platforms should be possible, but I'm unfamiliar with the macro assembler in general and unlike the x86 intrinsic they don't use a simple vectorized mask to implement the latin-1 check. For example aarch64 seem to filter out the low bytes and then check if there's any bits set in the high bytes. Clever, but very different to the 0xFF80 2-byte mask that an ASCII test wants.
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Clean up and make TestEncodeIntrinsics fail on the particular scenario where the ISO intrinsic was used in place of the ASCII-only intrinsic

The incremental change looks good and trivial to me.

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Marked as reviewed by thartmann (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/5621