RFR: 8340093: C2 SuperWord: implement cost model [v4]

[Emanuel Peter]

On Thu, 6 Nov 2025 08:10:43 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> What exactly does `Matcher::vector_op_pre_select_sz_estimate` return? The number of instructions or some kind of throughput estimate?
>> 
>> Personally, I don't want to get too stuck to counting instructions, but rather getting a throughput estimate. Counting instructions is an estimate for throughput, but I don't know yet if longterm it is the best.
>> 
>> I would like to wait a little more, and start depending on the cost model for more and more cases (extract, pack, shuffle, if-conversion, ...) and then we will run into issues along the way where the cost model is not yet accurate enough. And at that point we can think again what would produce the most accurate results.
>
>> What exactly does Matcher::vector_op_pre_select_sz_estimate return? The number of instructions or some kind of throughput estimate?
> 
> I believe it tries to estimate the number of instructions generated by a node.

I'm filing an RFE now

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PR Review Comment: https://git.openjdk.org/jdk/pull/27803#discussion_r2497946170