RFR(S) 8252311: AArch64: save two words in itable lookup stub

[Andrew Dinn]

On 30/08/2020 18:18, Boris Ulasevich wrote:
> The interface method lookup stub becomes hot when interface calls
> are performed frequently. The stub assembly code can be made
> shorter (132->124 bytes) by using a pre-increment instruction variant.
> 
> http://cr.openjdk.java.net/~bulasevich/8252311/webrev.00
> http://bugs.openjdk.java.net/browse/JDK-8252311
> 
> The benchmark [1] shows [2] performance and icache loads improvement:
> performance: 6165206 -> 6307798 ops/s
> L1-icache-loads: 307.271 -> 274.604
You really need to be more careful when making claims about
improvements. The performance figures are not convincing when you look
at the associated error ranges. This could just be noise. The icache
load figure is a tad more respectable but not greatly so.

That said, this change certainly looks harmless and may well do good
because it clearly cuts down code size and executed instruction count.
There is no great need for performance figures (real or spurious) to
justify a change that is this straightforward.

I'm happy to approve it but perhaps Andrew Haley would like to comment.


regards,


Andrew Dinn
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