[Perf] Windows/x86: 1 Regression on 7/5/2026 2:44:21 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [986fba00d9f89d2dfb8ac440bf37727a18828f64](https://github.com/dotnet/runtime/commit/986fba00d9f89d2dfb8ac440bf37727a18828f64)
Compare | [8f365c934088b8ae21a4dfce8073da0d3eb22a54](https://github.com/dotnet/runtime/commit/8f365c934088b8ae21a4dfce8073da0d3eb22a54)
Diff | [Diff](https://github.com/dotnet/runtime/compare/986fba00d9f89d2dfb8ac440bf37727a18828f64...8f365c934088b8ae21a4dfce8073da0d3eb22a54)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Tests.Perf_String

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

• [Split_Csv - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config 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.Tests.Perf_String*'
```

### System.Tests.Perf_String.Split_Csv(testName: "Short Dates", lines: ["Year,Week,Start date,End date", "2006,1,1/1/2006,1/7/2006", "2006,2,1/8/2006,1/14/2006", "2006,3,1/15/2006,1/21/2006", "2006,4,1/22/2006,1/28/2006", ...])

#### 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 benchmark source in src/benchmarks/micro/libraries/System.Runtime/Perf.String.cs, then run the provided benchmarks_ci.py command for System.Tests.Perf_String on the Windows x86 configuration. Compare the baseline and test commits and use the linked report and profiling workflow to confirm and investigate the Split_Csv regression; done means the regression is explained and the result is documented or addressed.

Written by the indexing model from the issue text.