[foreign-memaccess+abi] RFR: Improve strlen performance [v4]

[Maurizio Cimadamore]

On Tue, 15 Aug 2023 10:21:41 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR suggests removing the use of native calls for strlen and instead use Java implementations.
>> 
>> The PR also suggest performance improvements for quad word strlen.
>> 
>> Here are some benchmarks that compares the performance of the new proposed methods with the performance of the JDK 21 variants (called "legacy" methods):
>> 
>> <img width="2596" alt="image" src="https://github.com/openjdk/panama-foreign/assets/7457876/c785f341-c826-4e3e-bf56-8387b1e96010">
>
> Per Minborg has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits:
> 
>  - Merge foreign-memaccess+abi and fix formatting
>  - Fix missing spaces
>  - Undo some unintended changes and clean up
>  - Merge foreign-memaccess+abi
>  - Clean up
>  - Optimize str_len variants
>  - Optimize strlen_short
>  - Fix allocation size
>  - Fix test with strcat

src/java.base/share/classes/jdk/internal/foreign/StringSupport.java line 45:

> 43:     public static String read(MemorySegment segment, long offset, Charset charset) {
> 44:         return switch (CharsetKind.of(charset)) {
> 45:             case SINGLE_BYTE -> readFast_byte(segment, offset, charset);

I believe that, in the new code, there's no more distinction between slow and fast path? So we could simplify names to just "read/write_byte".

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PR Review Comment: https://git.openjdk.org/panama-foreign/pull/862#discussion_r1294513009