[Perf] Linux/x64: 4 Regressions on 8/5/2026 1:23:13 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [2dd5330804f9d4f49599d82c90a67892d4dd8af0](https://github.com/dotnet/runtime/commit/2dd5330804f9d4f49599d82c90a67892d4dd8af0)
Compare | [c8f97975ab0d8ff84aebf176829e17f7c7052f03](https://github.com/dotnet/runtime/commit/c8f97975ab0d8ff84aebf176829e17f7c7052f03)
Diff | [Diff](https://github.com/dotnet/runtime/compare/2dd5330804f9d4f49599d82c90a67892d4dd8af0...c8f97975ab0d8ff84aebf176829e17f7c7052f03)
Configs | AOT:true, CompilationMode:wasm, RunKind:micro

### Regressions in System.Collections.CtorDefaultSize<String>

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

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

| 64.27 ns | 75.77 ns | 1.18 | 0.12 | False | | |
|

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

| 20.12 ns | 22.22 ns | 1.10 | 0.13 | 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.CtorDefaultSize*'
```

### System.Collections.CtorDefaultSize<String>.ConcurrentDictionary

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Collections.CtorDefaultSize<String>.HashSet

#### 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 | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [2dd5330804f9d4f49599d82c90a67892d4dd8af0](https://github.com/dotnet/runtime/commit/2dd5330804f9d4f49599d82c90a67892d4dd8af0)
Compare | [c8f97975ab0d8ff84aebf176829e17f7c7052f03](https://github.com/dotnet/runtime/commit/c8f97975ab0d8ff84aebf176829e17f7c7052f03)
Diff | [Diff](https://github.com/dotnet/runtime/compare/2dd5330804f9d4f49599d82c90a67892d4dd8af0...c8f97975ab0d8ff84aebf176829e17f7c7052f03)
Configs | AOT:true, CompilationMode:wasm, RunKind:micro

### Regressions in System.Buffers.Tests.ReadOnlySequenceTests<Char>

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

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

| 52.40 ns | 59.38 ns | 1.13 | 0.09 | False | | |
|

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

| 57.12 ns | 62.45 ns | 1.09 | 0.08 | 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.Buffers.Tests.ReadOnlySequenceTests*'
```

### System.Buffers.Tests.ReadOnlySequenceTests<Char>.SliceArray

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Buffers.Tests.ReadOnlySequenceTests<Char>.SliceMemory

#### 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 at src/benchmarks/micro/libraries/System.Collections/Create/CtorDefaultSize.cs lines 24-25 and 45-46, and src/benchmarks/micro/libraries/System.Buffers/ReadOnlySequenceTests.cs lines 89-90 and 104-105. Run the documented benchmarks_ci.py filters, inspect the linked test reports, and compare the baseline and test results to identify the cause of the four regressions.

Written by the indexing model from the issue text.