RFR: 8374513: AArch64: Improve receiver type profiling reliability

[Andrew Haley]

On Tue, 20 Jan 2026 09:47:54 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> [JDK-8374513](https://bugs.openjdk.org/browse/JDK-8374513) is the AArch64 port of [JDK-8357258](https://bugs.openjdk.org/browse/JDK-8357258). See the bug report for more detailed information.
>> 
>> This PR executes the plan outlined in the bug:
>> - Common the receiver type profiling code in interpreter and C1
>> - Rewrite receiver type profiling code to only do atomic receiver slot installations
>> - Trim C1OptimizeVirtualCallProfiling to only claim slots when receiver is installed
>> 
>> This PR does not do atomic counter updates themselves, as it may have much wider performance implications, including regressions. This PR should be at least performance neutral.
>> 
>> Functional Testing: Linux AArch64 fastdebug Tier1-4
>> 
>> Performance Testing (to show there is no performance regression):
>> 
>> # Baseline
>> Benchmark                        (randomized)  Mode  Cnt   Score   Error  Units
>> InterfaceCalls.test1stInt2Types         false  avgt   12   1.940 ± 0.002  ns/op
>> InterfaceCalls.test1stInt2Types          true  avgt   12   7.714 ± 0.011  ns/op
>> InterfaceCalls.test1stInt3Types         false  avgt   12   6.747 ± 0.066  ns/op
>> InterfaceCalls.test1stInt3Types          true  avgt   12  18.733 ± 0.175  ns/op
>> InterfaceCalls.test1stInt5Types         false  avgt   12   6.690 ± 0.083  ns/op
>> InterfaceCalls.test1stInt5Types          true  avgt   12  21.299 ± 0.016  ns/op
>> InterfaceCalls.test2ndInt2Types         false  avgt   12   1.997 ± 0.004  ns/op
>> InterfaceCalls.test2ndInt2Types          true  avgt   12   8.027 ± 0.016  ns/op
>> InterfaceCalls.test2ndInt3Types         false  avgt   12   7.915 ± 0.114  ns/op
>> InterfaceCalls.test2ndInt3Types          true  avgt   12  16.988 ± 0.065  ns/op
>> InterfaceCalls.test2ndInt5Types         false  avgt   12   9.422 ± 0.017  ns/op
>> InterfaceCalls.test2ndInt5Types          true  avgt   12  22.736 ± 0.022  ns/op
>> InterfaceCalls.testIfaceCall            false  avgt   12   5.860 ± 0.046  ns/op
>> InterfaceCalls.testIfaceCall             true  avgt   12   5.794 ± 0.026  ns/op
>> InterfaceCalls.testIfaceExtCall         false  avgt   12   6.310 ± 0.067  ns/op
>> InterfaceCalls.testIfaceExtCall          true  avgt   12   6.239 ± 0.017  ns/op
>> InterfaceCalls.testMonomorphic          false  avgt   12   1.146 ± 0.034  ns/op
>> InterfaceCalls.testMonomorphic           true  avgt   12   1.131 ± 0.012  ns/op
>> 
>> # With PR
>> Benchmark                        (randomized)  Mode  Cnt   Score   Error  Units
>> InterfaceCalls.test1stInt2Type...
>
> src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 2275:
> 
>> 2273:   ldr(rscratch2, Address(mdp, offset));
>> 2274:   add(rscratch2, rscratch2, DataLayout::counter_increment);
>> 2275:   str(rscratch2, Address(mdp, offset));
> 
> Suggestion:
> 
>   increment(Address(mdp, offset), DataLayout::counter_increment);

... then we're good to go.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/29283#discussion_r2707581640