[Perf] Windows/x64: 2 Improvements on 6/26/2026 6:28:17 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [99eb16b5420fe88e333e2d95600b8617a86d54ff](https://github.com/dotnet/runtime/commit/99eb16b5420fe88e333e2d95600b8617a86d54ff)
Compare | [207ffd155f96b38be1749584b99f3ac0a505218c](https://github.com/dotnet/runtime/commit/207ffd155f96b38be1749584b99f3ac0a505218c)
Diff | [Diff](https://github.com/dotnet/runtime/compare/99eb16b5420fe88e333e2d95600b8617a86d54ff...207ffd155f96b38be1749584b99f3ac0a505218c)
Configs | CompilationMode:tiered, RunKind:micro

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

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

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

| 29.47 ns | 25.28 ns | 0.86 | 0.02 | 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<Byte>.EndsWith(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)

---

### Run Information

Name | Value
-- | --
Architecture | x64
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [99eb16b5420fe88e333e2d95600b8617a86d54ff](https://github.com/dotnet/runtime/commit/99eb16b5420fe88e333e2d95600b8617a86d54ff)
Compare | [207ffd155f96b38be1749584b99f3ac0a505218c](https://github.com/dotnet/runtime/commit/207ffd155f96b38be1749584b99f3ac0a505218c)
Diff | [Diff](https://github.com/dotnet/runtime/compare/99eb16b5420fe88e333e2d95600b8617a86d54ff...207ffd155f96b38be1749584b99f3ac0a505218c)
Configs | CompilationMode:tiered, RunKind:micro

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

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

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

| 52.15 ns | 34.35 ns | 0.66 | 0.23 | 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<Char>.EndsWith(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 src/benchmarks/micro/libraries/System.Memory/Span.cs at lines 74-75 and the linked Windows x64 test reports for Span.EndsWith and Span.EndsWith. Run the supplied benchmarks_ci.py commands, compare the baseline and test results, and determine what runtime change accounts for the reported improvements; the issue does not define a specific fix or completion criterion.

Written by the indexing model from the issue text.