RFR: 8310190: C2 SuperWord: AlignVector is broken, generates misaligned packs [v3]

[Emanuel Peter]

On Wed, 11 Oct 2023 16:19:23 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> `CompilerConfig::check_args_consistency()` seems to be too late. The reason is that `AlignVector` can still be changed by `VM_Version::get_processor_features` because of `UseUnalignedLoadStores`.
>> @vnkozlov do you have any other suggestion where to do this - ie when all the flags are final?
>
> You are right about. I surprise we did not have such issue before (where to put some C2 flags setting).
> I think `C2Compiler::init_c2_runtime()` could be good place for that. I don't want to do that in `Compile::Init()` or other Compile's methods which are called for each compilation.

@vnkozlov ok, this seems to work. I now disable `VerifyAlignVector` with a warning.
`Java HotSpot(TM) 64-Bit Server VM warning: VerifyAlignVector disabled because AlignVector not enabled.`

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PR Review Comment: https://git.openjdk.org/jdk/pull/14785#discussion_r1356478896