RFR: 8284050: [vectorapi] Optimize masked store for non-predicated architectures [v2]

[Jatin Bhateja]

On Thu, 5 May 2022 03:17:35 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> src/hotspot/share/opto/vectorIntrinsics.cpp line 1363:
>> 
>>> 1361:       // Use the vector blend to implement the masked store. The biased elements are the original
>>> 1362:       // values in the memory.
>>> 1363:       Node* mem_val = gvn().transform(LoadVectorNode::make(0, control(), memory(addr), addr, addr_type, mem_num_elem, mem_elem_bt));
>> 
>> I'm sorry to say it, but I am pretty sure this is an invalid optimization.
>> See top-level comment for more details.
>
> Thanks for your comments! Yeah, this actually influences something due to the Java Memory Model rules which I missed to consider more. I will try the scatter ways instead. Thanks so much!

Yes, phantom store can write back stale unintended value and may create problem in multithreded applications since blending is done with an older loaded value.

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PR: https://git.openjdk.java.net/jdk/pull/8544