[foreign-memaccess+abi] RFR: Improve strlen performance [v6]

[Maurizio Cimadamore]

On Tue, 15 Aug 2023 14:40:55 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 incrementally with one additional commit since the last revision:
> 
>   Allow heap segments of Long and Double to use chunked len calc

src/java.base/share/classes/jdk/internal/foreign/StringSupport.java line 60:

> 58: 
> 59:     private static String readByte(MemorySegment segment, long offset, Charset charset) {
> 60:         long len = segment.isNative() ||

Maybe this test should be captured into its own predicate, to avoid repetition?

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

PR Review Comment: https://git.openjdk.org/panama-foreign/pull/862#discussion_r1294727380