RFR: 8310190: C2 SuperWord: AlignVector is broken, generates misaligned packs [v43]

[Emanuel Peter]

On Fri, 15 Dec 2023 08:31:19 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> src/hotspot/share/opto/vectorization.cpp line 824:
>> 
>>> 822:   //   (C_const             + C_pre * pre_iter_C_const) % aw = 0                 (4c)
>>> 823:   //
>>> 824:   // We can only guarantee solutions to (4a) and (4b) if:
>> 
>> Should we also mention here that strengthening it with (4a-c) is the best we can do to prove (3) statically while we might miss some solutions for (3) where some of (4a-c) are false which, however, cannot be proven statically?
>
> Maybe we can also put (5a-b) in words:
> Suggestion:
> 
>   // We can only guarantee solutions to (4a) and (4b) if C_init and C_invar are zero or multiples of C_pre:

Ok, I added some extra comments here.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14785#discussion_r1427973108