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[ci-scan] Known Build Error: StreamReader NegativeOneBufferSize test fails under PGO #128062

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[ci-scan] Known Build Error: StreamReader NegativeOneBufferSize test fails under PGO#128062
#129914
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EgorBo
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Known Build ErrorUse this to report build issues in the .NET Helix tabagentic-workflowsarea-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMIblocking-clean-ci-optionalBlocking optional rolling runs
Milestone
11.0.0

Description

@github-actions
github-actions
bot
opened on May 12, 2026

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Pipeline: runtime-coreclr libraries-pgo (definition 145)
Affected leg: linux-x64 Release

Error Message

{
  "ErrorMessage": ["bufferSize ('-1') must be a non-negative and non-zero value"],
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Summary

System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException fails under PGO (libraries-pgo pipeline). The test expects that new StreamReader(path, Encoding.UTF8, true, -1) does not throw, but under PGO it throws ArgumentOutOfRangeException: bufferSize ('-1') must be a non-negative and non-zero value.

The StreamReader(string, Encoding, bool, int) constructor calls ValidateArgsAndOpenPath(path, bufferSize) which skips validation for -1, then chains to the Stream-based constructor which converts -1 to DefaultBufferSize. Under normal execution this works; the PGO-compiled code path may be reordering or inlining in a way that hits validation before the -1 → default conversion.

Impact on platforms

  • runtime-coreclr libraries-pgo (def 145) · linux-x64 Release · exit code 1

Console log

System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException [FAIL]
      System.ArgumentOutOfRangeException : bufferSize ('-1') must be a non-negative and non-zero value. (Parameter 'bufferSize')
      Stack Trace:
        at System.ArgumentOutOfRangeException.ThrowNegativeOrZero[T](T value, String paramName)
        at System.IO.StreamReader..ctor(String path, Encoding encoding, Boolean detectEncodingFromByteOrderMarks, Int32 bufferSize)
        at System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException()

Console log

First build it occurred

Present in builds 1414905 (May 10) and 1414533 (May 9). ≥2 occurrences.

Recommended action

Investigate whether PGO-guided inlining/optimization is changing the evaluation order of ValidateArgsAndOpenPath and the Stream ctor's bufferSize check. The -1 sentinel value should be converted to DefaultBufferSize before ThrowIfNegativeOrZero runs.

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Note

🔒 Integrity filter blocked 4 items

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Generated by CI Outer-Loop Failure Scanner · ● 56.5M · ◷

Report

Build Definition Test Pull Request
1416672 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #126671

Summary

24-Hour Hit Count 7-Day Hit Count 1-Month Count
1 1 1

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [NegativeOneBufferSize_ShouldNotThrowException System.ArgumentOutOfRangeException]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/12/2026 11:31:36 AM UTC

Report

Build Definition Test Pull Request
1416672 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #126671
1414905 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException

Summary

24-Hour Hit Count 7-Day Hit Count 1-Month Count
0 2 2

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [NegativeOneBufferSize_ShouldNotThrowException System.ArgumentOutOfRangeException]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/12/2026 11:31:36 AM UTC

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [bufferSize ('-1') must be a non-negative and non-zero value]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/13/2026 8:12:07 AM UTC

Report

Build Repository Test Pull Request
1484392 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException
1484363 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129923
1483955 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129918
1483794 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129769
1480581 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129761
1480364 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129826
1478400 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129543
1475733 dotnet/runtime System.IO.Tests.StreamWriter_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #128702
1470142 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129561
1466621 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129466
1465227 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129398
1463187 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129379
1457883 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #126845
1455131 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129080
1452853 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #129084
1440246 dotnet/runtime System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException #128740

Summary

24-Hour Hit Count 7-Day Hit Count 1-Month Count
4 8 16

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [NegativeOneBufferSize_ShouldNotThrowException System.ArgumentOutOfRangeException]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/12/2026 11:31:36 AM UTC

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [bufferSize ('-1') must be a non-negative and non-zero value]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/13/2026 8:12:07 AM UTC

Activity

  1. github-actions
    added
    blocking-clean-ciBlocking PR or rolling runs of 'runtime' or 'runtime-extra-platforms'
    Known Build ErrorUse this to report build issues in the .NET Helix tab
    agentic-workflows
    on May 12, 2026
  2. dotnet-policy-service
    added
    untriagedNew issue has not been triaged by the area owner
    on May 12, 2026
  3. jeffschwMSFT
    added
    area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
    on May 12, 2026

  4. dotnet-policy-service commented on May 12, 2026

    @dotnet-policy-service
    dotnet-policy-serviceBot
    on May 12, 2026 – with Dotnet Policy Service
    Contributor

    Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
    See info in area-owners.md if you want to be subscribed.

  5. JulieLeeMSFT
    added
    blocking-clean-ci-optionalBlocking optional rolling runs
    and removed
    untriagedNew issue has not been triaged by the area owner
    blocking-clean-ciBlocking PR or rolling runs of 'runtime' or 'runtime-extra-platforms'
    on May 13, 2026
  6. JulieLeeMSFT
    added this to the 11.0.0 milestone on May 13, 2026
  7. JulieLeeMSFT
    assigned
    EgorBo
    on May 13, 2026

  8. kg commented on May 22, 2026

    @kg
    kg
    on May 22, 2026
    Contributor

    Failed in (1):

    Console Log: Console Log
    Source: runtime-coreclr libraries-pgo / net11.0-linux-Release-x64-jitosr_stress_random-AzureLinux.3.Amd64.Open / System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException

    Generated by ci-pipeline-monitor/scripts/update_github.py

  9. github-actions commented on Jun 18, 2026

    @github-actions
    github-actionsBot
    on Jun 18, 2026 – with GitHub Actions
    ContributorAuthor

    Workflow artifact: ci-fix
    Artifact kind: handoff
    Linked KBE: #128062

    Note

    AI/Copilot-generated triage note.

    This Known Build Error has no producible automated code change (reason: JIT/PGO miscompilation — the product code is correct and the fix requires changes to JIT optimization passes, which exceeds automated bounds), so I could not open even a best-effort PR. Looping in owners so it can be fixed forward rather than muted.

    Root cause (best analysis)

    StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException fails under PGO (runtime-coreclr libraries-pgo) because PGO-guided inlining miscompiles the -1 sentinel handling in StreamReader.

    The product code in System.Private.CoreLib/src/System/IO/StreamReader.cs is correct:

    1. StreamReader(string path, Encoding, bool, int bufferSize) (line 199) chains to:
      • ValidateArgsAndOpenPath(path, bufferSize) — which skips ThrowIfNegativeOrZero when bufferSize == -1 (line 230)
      • Then the stream-based constructor (line 138)
    2. The stream constructor (line 150-154) converts -1 to DefaultBufferSize before calling ThrowIfNegativeOrZero

    Under PGO, when both ValidateArgsAndOpenPath and the stream constructor are inlined into the string-path constructor, the JIT appears to miscompile the conditional branch that converts -1 to DefaultBufferSize. The stack trace confirms inlining:

    at System.ArgumentOutOfRangeException.ThrowNegativeOrZero[T](T value, String paramName)
at System.IO.StreamReader..ctor(String path, Encoding encoding, Boolean detectEncodingFromByteOrderMarks, Int32 bufferSize)

    The intermediate StreamReader(Stream, ...) frame is absent, confirming it was inlined. The ThrowNegativeOrZero(-1) call fires despite the guarding if (bufferSize == -1) check.

    Evidence

    Suggested reviewers / area contacts

    • Assignee: @EgorBo (already assigned, milestone 11.0.0)
    • Area owners (area-CodeGen-coreclr): @JulieLeeMSFT, @jakobbotsch

    The fix likely involves the JIT's handling of conditional branches around ThrowIfNegativeOrZero when inlining across constructor chains under PGO.

    Note

    🔒 Integrity filter blocked 1 item

    The following item was blocked because it doesn't meet the GitHub integrity level.

    To allow these resources, lower min-integrity in your GitHub frontmatter:

    tools:
  github:
    min-integrity: approved  # merged | approved | unapproved | none

    Generated by CI Outer-Loop Failure Fixer · ● 51.4M · ◷

  10. EgorBo
    added a commit that references this issue on Jun 27, 2026

    JIT: fix stale VN in redundant branch opts dominating-branch simplifi…

    8b45e69
  11. EgorBo
    closed this as completedin #129914on Jun 27, 2026
  12. eiriktsarpalis
    added a commit that references this issue on Jul 15, 2026

    JIT: fix stale VN in redundant branch opts dominating-branch simplifi…

    a1672ef
  13. github-actions
    locked and limited conversation to collaborators on Jul 28, 2026
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