RFR: 8374513: AArch64: Improve receiver type profiling reliability

[Andrew Haley]

On Sat, 17 Jan 2026 01:28:40 GMT, Chad Rakoczy <duke 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.test1stInt2Types         false  avgt   12   1.941 ± 0.004  ns/op
> InterfaceCalls.test1stIn...

src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 2232:

> 2230:   mov(rscratch2, end_receiver_offset);
> 2231:   cmp(offset, rscratch2);
> 2232:   br(Assembler::NE, L_loop_search_receiver);

Suggestion:

  sub(rscratch2, offset, end_receiver_offset);
  cbz(rscratch2, L_loop_search_receiver);

src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 2239:

> 2237:     ldr(rscratch2, Address(mdp, offset));
> 2238:     cmp(rscratch2, (u1)NULL_WORD);
> 2239:     br(Assembler::EQ, L_found_empty);

Suggestion:

    cbz(rscratch2, L_found_empty);

src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 2256:

> 2254:   lea(rscratch2, Address(mdp, offset));
> 2255:   cmpxchg(/*addr*/ rscratch2, /*expected*/ zr, /*new*/ recv, Assembler::xword,
> 2256:           /*acquire*/ true, /*release*/ false, /*weak*/ false, noreg);

/*acquire*/ true, /*release*/ false, /*weak*/ false, noreg);

I'm curious about the acquire. For it to make sense here, I would have thought it must be linked with an earlier release in another thread.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/29283#discussion_r2701847302
PR Review Comment: https://git.openjdk.org/jdk/pull/29283#discussion_r2701800282
PR Review Comment: https://git.openjdk.org/jdk/pull/29283#discussion_r2701839882