[Perf] Linux/arm64: 2 Regressions on 9/1/2026 5:28:08 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | arm64
OS | ubuntu 22.04
Queue | AmpereUbuntu
Baseline | [ef3efe5e020e412e4f6453781d59443e975010a4](https://github.com/dotnet/runtime/commit/ef3efe5e020e412e4f6453781d59443e975010a4)
Compare | [f00a5ba2dde9f648bcd9ac77411d1a8596449303](https://github.com/dotnet/runtime/commit/f00a5ba2dde9f648bcd9ac77411d1a8596449303)
Diff | [Diff](https://github.com/dotnet/runtime/compare/ef3efe5e020e412e4f6453781d59443e975010a4...f00a5ba2dde9f648bcd9ac77411d1a8596449303)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Numerics.Tests.Perf_BigInteger

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

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

| 109.80 ns | 126.37 ns | 1.15 | 0.08 | False | | |
|

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

| 106.02 ns | 117.59 ns | 1.11 | 0.01 | 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
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Numerics.Tests.Perf_BigInteger*'
```

### System.Numerics.Tests.Perf_BigInteger.Add(arguments: 1024,1024 bits)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Numerics.Tests.Perf_BigInteger.ModPow(arguments: 16,16,16 bits)

#### 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 src/benchmarks/micro/libraries/System.Runtime.Numerics/Perf.BigInteger.cs at the cited Add and ModPow benchmarks, then run the provided benchmarks_ci.py command. Compare the baseline and test commits and inspect the linked performance report to confirm both arm64 regressions; done means the cause is identified and the performance change is addressed or explained.

Written by the indexing model from the issue text.