[Perf] Linux/arm64: 2 Regressions on 7/2/2026 11:21:29 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | arm64
OS | azurelinux 3.0
Queue | CobaltAzureLinux
Baseline | [901aeddd1c55f5fc5a1c1450f234dd954c430ea5](https://github.com/dotnet/runtime/commit/901aeddd1c55f5fc5a1c1450f234dd954c430ea5)
Compare | [e1979b72ccb5f916649f1d9949ef663254790c25](https://github.com/dotnet/runtime/commit/e1979b72ccb5f916649f1d9949ef663254790c25)
Diff | [Diff](https://github.com/dotnet/runtime/compare/901aeddd1c55f5fc5a1c1450f234dd954c430ea5...e1979b72ccb5f916649f1d9949ef663254790c25)
Configs | CompilationMode:tiered, R2RType:r2r_interpreter, RunKind:micro

### Regressions in System.Collections.CopyTo<String>

Benchmark | Baseline | Test | Test/Base | Test Quality | Edge Detector | Baseline IR | Compare IR | IR Ratio
-- | -- | -- | -- | -- | -- | -- | -- | --
|

• [Memory - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 638.59 ns | 927.04 ns | 1.45 | 0.42 | False | | |
|

• [Array - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 811.84 ns | 966.22 ns | 1.19 | 0.45 | False | | |

![graph]()
![graph]()
[Test Report]()

### Repro
General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

```cmd
git clone https://github.com/dotnet/performance.git
py .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Collections.CopyTo*'
```

### System.Collections.CopyTo<String>.Memory(Size: 2048)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Collections.CopyTo<String>.Array(Size: 2048)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

[Profiling workflow for dotnet/runtime repository](https://github.com/dotnet/performance/blob/master/docs/profiling-workflow-dotnet-runtime.md)
[Benchmarking workflow for dotnet/runtime repository](https://github.com/dotnet/performance/blob/master/docs/benchmarking-workflow-dotnet-runtime.md)

Start with the System.Collections.CopyTo benchmark source at src/benchmarks/micro/libraries/System.Collections/CopyTo.cs and the linked regression report. Read the benchmarking and profiling workflow documents, then run the provided benchmarks_ci.py command with the stated filter. Done means the arm64 AzureLinux regression is reproduced and its responsible change is narrowed down for triage.

Written by the indexing model from the issue text.