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

[Richard Reingruber]

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.

@offamitkumar [JDK-8343906](https://bugs.openjdk.org/browse/JDK-8343906) states that the test also fails on s390x.
This must have another reason then since `misaligned_vectors_ok` returns already `true` on s390x:
https://github.com/openjdk/jdk/blob/ad01dfb670215a35d4151c7129c9086888e1f9e8/src/hotspot/cpu/s390/matcher_s390.hpp#L42-L45

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PR Comment: https://git.openjdk.org/jdk/pull/23318#issuecomment-2616292433