RFR: 8323552: AbstractMemorySegmentImpl#mismatch returns -1 when comparing distinct areas of the same instance of MemorySegment

[Maurizio Cimadamore]

On Wed, 10 Jan 2024 20:54:20 GMT, Peter Levart <plevart at openjdk.org> wrote:

> I belive there is a bug in `AbstractMemorySegmentImpl#mismatch` method. It returns `-1` (meaning that regions are equal) when passing the same instance of MemorySegment as both `srcSegment` and `dstSegment` parameters regardless of whether `srcFromOffset` and `dstFromOffset` as well as `srcToOffset` and `dstToOffset` are also equal.
> 
> Am I right?

Note there's another bug for this: https://bugs.openjdk.org/browse/JDK-8323524

src/java.base/share/classes/jdk/internal/foreign/AbstractMemorySegmentImpl.java line 684:

> 682:         srcImpl.checkAccess(srcFromOffset, srcBytes, true);
> 683:         dstImpl.checkAccess(dstFromOffset, dstBytes, true);
> 684:         if (dstImpl.equals(srcImpl) && srcFromOffset == dstFromOffset && srcBytes == dstBytes) {

I'm also ok to completely drop this check (or move it into the instance version of the mismatch method). This also needs a test.

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

PR Comment: https://git.openjdk.org/jdk/pull/17354#issuecomment-1885824510
PR Review Comment: https://git.openjdk.org/jdk/pull/17354#discussion_r1448045022