[Perf] Windows/x86: 4 Regressions on 7/20/2026 8:16:56 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [630a7009ba484fe96b8f0b81e2f4cc0bb6827903](https://github.com/dotnet/runtime/commit/630a7009ba484fe96b8f0b81e2f4cc0bb6827903)
Compare | [4d9d5a153993dbeb30910ece8ad346985c55d85d](https://github.com/dotnet/runtime/commit/4d9d5a153993dbeb30910ece8ad346985c55d85d)
Diff | [Diff](https://github.com/dotnet/runtime/compare/630a7009ba484fe96b8f0b81e2f4cc0bb6827903...4d9d5a153993dbeb30910ece8ad346985c55d85d)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Memory.ReadOnlySpan

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

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

| 10.92 ns | 13.55 ns | 1.24 | 0.15 | False | | |
|

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

| 7.52 ns | 9.23 ns | 1.23 | 0.26 | False | | |
|

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

| 11.13 ns | 13.52 ns | 1.21 | 0.12 | False | | |

![graph]()
![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.ReadOnlySpan*'
```

### System.Memory.ReadOnlySpan.IndexOfString(input: "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAXAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA", value: "X", comparisonType: Ordinal)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Memory.ReadOnlySpan.IndexOfString(input: "Hello WorldbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbareallyreallylongHello WorldbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbareallyreallylongHello Worldbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbareallyreallylong!xyz", value: "~", comparisonType: Ordinal)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Memory.ReadOnlySpan.IndexOfString(input: "だだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだxだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだだ", value: "x", comparisonType: Ordinal)

#### 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)

---

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [630a7009ba484fe96b8f0b81e2f4cc0bb6827903](https://github.com/dotnet/runtime/commit/630a7009ba484fe96b8f0b81e2f4cc0bb6827903)
Compare | [4d9d5a153993dbeb30910ece8ad346985c55d85d](https://github.com/dotnet/runtime/commit/4d9d5a153993dbeb30910ece8ad346985c55d85d)
Diff | [Diff](https://github.com/dotnet/runtime/compare/630a7009ba484fe96b8f0b81e2f4cc0bb6827903...4d9d5a153993dbeb30910ece8ad346985c55d85d)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Memory.Span<Int32>

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

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

| 337.96 ns | 391.51 ns | 1.16 | 0.34 | False | | |

![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<Int32>.IndexOfAnyFourValues(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 sources identified in src/benchmarks/micro/libraries/System.Memory/ReadOnlySpan.cs#L45-L65 and Span.cs#L97-L98, then run the documented benchmarks_ci.py command with the System.Memory.ReadOnlySpan filter. Compare the supplied baseline and test reports on Windows x86; done means the reported regressions are explained and the affected benchmark results no longer regress.

Written by the indexing model from the issue text.