RFR: 8348678: [PPC64] C2: unaligned vector load/store is ok

[Martin Doerr]

On Mon, 27 Jan 2025 16:04:33 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

> This pr changes `Matcher::misaligned_vectors_ok`  to return `true` on PPC64 for better vectorization during `SuperWord`.
> IR checking of the corresponding test `TestCastX2NotProcessedIGVN.java` is also enabled.
> 
> Tested with `TestCastX2NotProcessedIGVN.java`
> 
> The change passed our CI testing:
> Tier 1-4 of hotspot and jdk. All of langtools and jaxp. Renaissance Suite and SAP specific tests.
> Testing was done on the main platforms and also on Linux/PPC64le and AIX.

Thanks for bringing this up to date!
The old code was for Power7. ISA V2.06 specified "If EA is not word-aligned (that is, EA{62:63}g0b00),
the system alignment error handler is permitted to be invoked instead of performing the storage access."
This was updated for Power8. ISA V2.07 removed that limitation and we require Power8 for `SuperwordUseVSX`. So, arbitrary alignment is ok.

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Marked as reviewed by mdoerr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23318#pullrequestreview-2576150989