RFR: 8270160: Remove redundant bounds check from AbstractStringBuilder.charAt() [v4]

[Сергей Цыпанов]

> `AbstractStringBuilder.charAt(int)` does bounds check before calling `charAt()` (for non-latin Strings):
> 
> @Override
> public char charAt(int index) {
>     checkIndex(index, count);
>     if (isLatin1()) {
>         return (char)(value[index] & 0xff);
>     }
>     return StringUTF16.charAt(value, index);
> }
> 
> This can be improved by removing bounds check from ASB.charAt() in favour of one in String*.charAt(). This gives slight improvement:
> 
> before
> Benchmark                           Mode  Cnt  Score   Error  Units
> StringBuilderCharAtBenchmark.latin  avgt   50  2,827 ± 0,024  ns/op
> StringBuilderCharAtBenchmark.utf    avgt   50  2,985 ± 0,020  ns/op
> 
> after
> Benchmark                           Mode  Cnt  Score   Error  Units
> StringBuilderCharAtBenchmark.latin  avgt   50  2,434 ± 0,004  ns/op
> StringBuilderCharAtBenchmark.utf    avgt   50  2,631 ± 0,004  ns/op

Сергей Цыпанов has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' into 8270160
 - Merge branch 'master' into 8270160
   
   # Conflicts:
   #	src/java.base/share/classes/java/lang/StringLatin1.java
 - 8270160: Remove redundant bounds check from AbstractStringBuilder.charAt()

-------------

Changes: https://git.openjdk.java.net/jdk/pull/4738/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4738&range=03
  Stats: 6 lines in 2 files changed: 0 ins; 3 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4738.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4738/head:pull/4738

PR: https://git.openjdk.java.net/jdk/pull/4738