[Perf] Linux/x64: 2 Regressions on 7/31/2026 4:48:31 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [ba8afceee83540ed1d867987483f74d4ad2cfae9](https://github.com/dotnet/runtime/commit/ba8afceee83540ed1d867987483f74d4ad2cfae9)
Compare | [d5c739f99fa75a37ea863b06dd8d31a51965c8be](https://github.com/dotnet/runtime/commit/d5c739f99fa75a37ea863b06dd8d31a51965c8be)
Diff | [Diff](https://github.com/dotnet/runtime/compare/ba8afceee83540ed1d867987483f74d4ad2cfae9...d5c739f99fa75a37ea863b06dd8d31a51965c8be)
Configs | CompilationMode:wasm, RunKind:micro, RuntimeType:coreclr

### Regressions in System.Collections.Tests.Perf_BitArray

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

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

| 52.81 μs | 96.30 μs | 1.82 | 0.45 | False | | |
|

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

| 709.10 ns | 1161.19 ns | 1.64 | 0.37 | 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 'System.Collections.Tests.Perf_BitArray*'
```

### System.Collections.Tests.Perf_BitArray.BitArrayBoolArrayCtor(Size: 512)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Collections.Tests.Perf_BitArray.BitArrayBoolArrayCtor(Size: 4)

#### 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 in src/benchmarks/micro/libraries/System.Collections/Perf.BitArray.cs at lines 43-44, then run the documented benchmarks_ci.py command with the System.Collections.Tests.Perf_BitArray filter. Compare the Size 512 and Size 4 results with the linked test report and commits; done means the reported Linux/x64 WebAssembly regressions are explained and the benchmarks no longer show the regression.

Written by the indexing model from the issue text.