RFR: 8252311: AArch64: save two words in itable lookup stub

[Andrew Dinn]

On Tue, 15 Sep 2020 15:25:41 GMT, Boris Ulasevich <bulasevich at openjdk.org> wrote:

> The change was reviewed on hotspot-compiler-dev, but I missed the time to complete
> the commit to the mercural repo. Can I get it approved once again?
> 
> Issue: [JDK-8252311](https://bugs.openjdk.java.net/browse/JDK-8252311)
> 
> Description:
> 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.
> 
> Review by Andrew Dinn && Andrew Haley:
> http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2020-September/039818.html
> http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2020-September/039833.html
> 
> For the reference, benchmark scores with higher iteration number:
> Neoverse                              Cnt   Score     Error  ->    Score   Error   Units
> InvokeInterface.bench                  25  6163.804 ±  5.116 -> 6303.035 ± 5.450  ops/ms
> InvokeInterface.bench:L1-icache-loads   5   305.408 ±  1.895 ->  272.891 ± 0.750    #/op
> InvokeInterface.bench:iTLB-loads        5   221.755 ±  0.990 ->  207.635 ± 0.566    #/op
> InvokeInterface.bench:instructions      5  1035.468 ±  2.701 ->  953.466 ± 1.667    #/op

Marked as reviewed by adinn (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/189