RFR: 8320725: C2: Add "requires_strict_order" flag for floating-point add-reduction [v5]

[Emanuel Peter]

On Mon, 15 Apr 2024 06:56:06 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Bhavana Kilambi has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Revert to previous indentation
>
> src/hotspot/cpu/aarch64/aarch64_vector.ad line 2861:
> 
>> 2859:   // example, this rule can be reached from the VectorAPI (which allows for non-strictly ordered
>> 2860:   // add reduction).
>> 2861:   predicate(Matcher::vector_length(n->in(2)) == 2 && !n->as_Reduction()->requires_strict_order());
> 
> Would it make sense to change `reduce_add2F_neon` to something like `reduce_non_strict_order_add2F_neon`, just so that it is a bit clearer when one reads the opto-assembly output?

Similarly, I would put `strict_order` for the cases where that applies.

> src/hotspot/share/opto/vectorIntrinsics.cpp line 1739:
> 
>> 1737:   Node* init = ReductionNode::make_identity_con_scalar(gvn(), opc, elem_bt);
>> 1738:   Node* value = opd;
>> 1739: 
> 
> Suggestion:
> 
> 
>   assert(mask != nullptr || !is_masked_op, "Masked op needs the mask value never null");

This would restore the assert mentioned above.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18034#discussion_r1565265234
PR Review Comment: https://git.openjdk.org/jdk/pull/18034#discussion_r1565271912