RFR: 8263038: Optimize String.format for simple specifiers [v3]

[Naoto Sato]

On Mon, 8 Mar 2021 18:52:19 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> This patch optimizes String.format expressions that uses trivial specifiers. In the JDK, the most common variation of String.format is a variation of format("foo: %s", s), which gets a significant speed-up from this.
>> 
>> Various other cleanups and minor improvements reduce overhead further and ensure we get a small gain also for more complex format strings.
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use a BOM as a sentinel for uninitialized zero

src/java.base/share/classes/java/util/Formatter.java line 1936:

> 1934:     private IOException lastException;
> 1935: 
> 1936:     // Non-unicode code point value used to mark zero as uninitialized

Sorry for being anal here, but BOM is a "noncharacter", a valid Unicode code point. So "noncharacter" over "Non-unicode code point" seems appropriate.
http://www.unicode.org/faq/private_use.html#nonchar1

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PR: https://git.openjdk.java.net/jdk/pull/2830