[Perf] Windows/x86: 1 Regression on 7/12/2026 10:37:49 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [c9265d78e03e96c00b7ec062f2dbf2465bbb86d6](https://github.com/dotnet/runtime/commit/c9265d78e03e96c00b7ec062f2dbf2465bbb86d6)
Compare | [010acabe079d1bd50f838de34e9815f81d977469](https://github.com/dotnet/runtime/commit/010acabe079d1bd50f838de34e9815f81d977469)
Diff | [Diff](https://github.com/dotnet/runtime/compare/c9265d78e03e96c00b7ec062f2dbf2465bbb86d6...010acabe079d1bd50f838de34e9815f81d977469)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Memory.Span<Byte>

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

• [Fill - 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.Memory.Span*'
```

### System.Memory.Span<Byte>.Fill(Size: 3000)

#### 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 at src/benchmarks/micro/libraries/System.Memory/Span.cs lines 53-54 and run the supplied benchmarks_ci.py command for System.Memory.Span. Compare the baseline and test commits and the linked report to identify why Fill(Size: 3000) regressed on Windows/x86; done means the regression is understood and the benchmark returns to baseline performance.

Written by the indexing model from the issue text.