[Perf] Linux/x64: 2 Regressions on 8/14/2026 10:22:33 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [d00a0a24912957046ed2443adc0af7bbfb4c43bc](https://github.com/dotnet/runtime/commit/d00a0a24912957046ed2443adc0af7bbfb4c43bc)
Compare | [420dfbb4f584c1b0ddebec9615d1a673437050f6](https://github.com/dotnet/runtime/commit/420dfbb4f584c1b0ddebec9615d1a673437050f6)
Diff | [Diff](https://github.com/dotnet/runtime/compare/d00a0a24912957046ed2443adc0af7bbfb4c43bc...420dfbb4f584c1b0ddebec9615d1a673437050f6)
Configs | AOT:true, CompilationMode:wasm, RunKind:micro

### Regressions in Span.IndexerBench

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

• [Indexer4 - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 3.06 μs | 3.99 μs | 1.30 | 0.00 | False | | |
|

• [KnownSizeCtor2 - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 356.93 ns | 380.81 ns | 1.07 | 0.00 | False | | |

![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
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'Span.IndexerBench*'
```

### Span.IndexerBench.Indexer4(length: 1024)

#### ETL Files

#### Histogram

#### JIT Disasms

### Span.IndexerBench.KnownSizeCtor2(length: 1024)

#### 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/runtime/Span/Indexer.cs at the linked Indexer4 and KnownSizeCtor2 benchmarks, then read the benchmarking workflow and run the provided benchmarks_ci.py command with the Span.IndexerBench filter. Compare the listed baseline and compare commits and use the linked test report to verify the regression. Done means the regression is explained and benchmark results no longer show the reported slowdown.

Written by the indexing model from the issue text.