RFR: 8326139: C2 SuperWord: split packs (match use/def packs, implemented, mutual independence) [v2]

[Vladimir Kozlov]

On Tue, 27 Feb 2024 08:20:03 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/superword.cpp line 1008:
>> 
>>> 1006: }
>>> 1007: 
>>> 1008: // Do we have pattern n1 = (iv + c) and n2 = (iv + c + 1)?
>> 
>> Why  `+1` is special case?  Does SuperWord handle case when loop's increment is not `1`?
>
> Yes, currently it only seems to handle positive `1`.
> 
> Relevant line in `SuperWord::vector_opd`, the only place where the `PopulateIndexNode` is created:
> `Node* vn = new PopulateIndexNode(iv(), igvn().intcon(1), vt);`
> 
> The verification code is at the beginning of `SuperWord::is_vector_use`:
> `offset_t->get_con() != (jint) i` -> we expect `populate_index->at(i) = (iv + i)`
> 
> That is a limitation we can surely remove in a future RFE.

I finally got what this function for :^)  Looks reasonable.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17848#discussion_r1504672303