RFR: 8323582: C2 SuperWord AlignVector: misaligned vector memory access with unaligned native memory [v3]

[Emanuel Peter]

On Mon, 24 Feb 2025 12:52:42 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>>> @rwestrel I think I had tried some verifications above, but I could not even get it to work in all cases in `SuperWord`.
>>> 
>>> In `VLoop::check_preconditions_helper`, I try to find either the predicate or the multiversioning if. But I cannot always find it, and I think that one reason was that the pre-loop can be lost. At least that is what I remember from 4+ weeks ago.
>> 
>> Do you understand when that happens? It doesn't feel right that the pre loop can be lost.
>
>> @rwestrel Do you want me to find examples for the pre-loop disappearing? I suppose I can find some easily by adding an assert in SuperWord, where we bail out, as I showed above.
> 
> Yes, if not too much work.

@rwestrel I think we should just file an RFE to keep track of these assertions we would like to add once those issues are fixed.

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PR Comment: https://git.openjdk.org/jdk/pull/22016#issuecomment-2678803600