[Perf] Linux/x64: 3 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 | AOT:true, CompilationMode:wasm, RunKind:micro

### 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]()

| 38.25 ns | 49.43 ns | 1.29 | 0.04 | False | | |
|

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

| 24.79 ns | 31.88 ns | 1.29 | 0.08 | False | | |
|

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

| 25.39 ns | 31.64 ns | 1.25 | 0.13 | 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
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

### System.Collections.Tests.Perf_BitArray.BitArrayIntArrayCtor(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 reported System.Collections.Tests.Perf_BitArray results and the benchmark source at src/benchmarks/micro/libraries/System.Collections/Perf.BitArray.cs lines 43-44 and 55-57. Run the provided benchmarks_ci.py command, then compare the baseline and test commits and review the linked test report. Done means the cause of the three regressions is identified and the affected benchmark timings are verified after the change.

Written by the indexing model from the issue text.