[foreign-memaccess] RFR: 8249879: Split MemorySegment and MemoryAddress [v3]

[Paul Sandoz]

On Fri, 24 Jul 2020 10:54:53 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> This patch splits, as the title suggests, the memory segment abstraction from the memory address abstraction, as
>> described in this email:
>> https://mail.openjdk.java.net/pipermail/panama-dev/2020-July/009928.html
>> 
>> Aside from the obvious updates to the two interfaces (and their implementation), this patch greatly simplifies the way
>> memory access var handles are generated; instead of spinning them on the fly (see `MemoryAccessVarHandleGenerator`,
>> which is now removed) now all var handles can be derived from a primitive from which takes a segment and a byte offset.
>> This caused the removal of several methods in the `JavaLangInvokeAccess` interface.  The new memory segment interface
>> has some more methods to perform slicing - which can basically be used to give a new base to an existing segment and
>> can therefore be used in a lot of cases as a replacement for `MemoryAddress::addOffset`.  The memory address interface
>> is simplified, and features an additional `segmentOffset` method, which returns the byte offset of an address relative
>> to the given segment (this is similar to the old `MemorySegment::rebase` method, which is now removed).  The
>> `MemoryAccess` class needed a lot of tweaks in the various signatures, to take a segment instead of a base address.  I
>> tried to update the documentation as best as I could, but it's possible I missed some references to the old
>> relationship between segment and addresses, please double check.  Of course integrating this patch is gonna cause
>> issues in foreign-abi and foreign-jextract, as these branches make (heavy) use of memory access var handles. I suspect
>> that integration will trigger a merge failure, so we can fix followup issues as part of the merge process, so that we
>> can guarantee that all the branches remain buildable.
>
> Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Address Paul's review comments.

Very nice collapsing of code.

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Marked as reviewed by psandoz (Committer).

PR: https://git.openjdk.java.net/panama-foreign/pull/260