[Perf] Windows/x86: 1 Regression on 7/24/2026 6:27:26 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [78275532612cf3b66ad46231ae08571260889264](https://github.com/dotnet/runtime/commit/78275532612cf3b66ad46231ae08571260889264)
Compare | [13cd8e344c41d55e63b2be288b1b8a1e2596b32d](https://github.com/dotnet/runtime/commit/13cd8e344c41d55e63b2be288b1b8a1e2596b32d)
Diff | [Diff](https://github.com/dotnet/runtime/compare/78275532612cf3b66ad46231ae08571260889264...13cd8e344c41d55e63b2be288b1b8a1e2596b32d)
Configs | CompilationMode:tiered, RunKind:micro

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

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

• [LastIndexOfValue - 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<Char>.LastIndexOfValue(Size: 512)

#### 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#L103-L104 and the provided benchmarking workflow. Run the benchmarks_ci.py command for System.Memory.Span, then compare the baseline and test commits using the linked report. Done means confirming the regression and identifying its responsible change or documented resolution.

Written by the indexing model from the issue text.