[jdk21u-dev] RFR: 8316594: C2 SuperWord: wrong result with hand unrolled loops

[Aleksey Shipilev]

On Tue, 2 Jan 2024 17:16:18 GMT, Goetz Lindenmaier <goetz at openjdk.org> wrote:

> I backport this for parity with 21.0.3-oracle.
> 
> I had to resove SWPointer / VPointer because 8312332: C2: Refactor SWPointer out from SuperWord is not in 21.
> 
> We had previous backports that needed to be resolved because of this refactoring missing. I assume this will hit us in future repeatedly.
> 
> Thus I had a look at backporting 8312332, but that depends on three other cleanup changes:
> 8305636: Expand and clean up predicate classes and move them into separate files
> 8311691: C2: Remove legacy code related to PostLoopMultiversioning
> 8308606: C2 SuperWord: remove alignment checks when not required
> 
> All four of them can be backported clean, but 8305363 has four follow-up bugs.
> 
> So maybe we need to go the patch and accept the unclean backports right from the beginning of 21u :(

Cool. I did the similar thing in https://github.com/openjdk/jdk21u-dev/pull/21, but have not tested it deeply. In my version, I chose to pass `this` to `overlap_possible_with_any_in`, but just using `_slp` looks cleaner.

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Marked as reviewed by shade (Reviewer).

PR Review: https://git.openjdk.org/jdk21u-dev/pull/110#pullrequestreview-1801808538