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Eliminate XmlChildNodes allocations in GetXmlNodeInnerContents#13509

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JanProvaznik merged 2 commits into
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nareshjo:dev/nareshjo/GetXmlNodeInnerContents-XmlChildNodes-Allocs
Apr 13, 2026
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Eliminate XmlChildNodes allocations in GetXmlNodeInnerContents#13509
JanProvaznik merged 2 commits into
dotnet:mainfrom
nareshjo:dev/nareshjo/GetXmlNodeInnerContents-XmlChildNodes-Allocs

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@nareshjo

@nareshjo nareshjo commented Apr 9, 2026

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🤖 AI-Generated Pull Request 🤖

This pull request was generated by the VS Perf Rel AI Agent. Please review this AI-generated PR with extra care! For more information, visit our wiki. Please share feedback with TIP Insights


  • Issue:
    Utilities.GetXmlNodeInnerContents accesses node.ChildNodes twice to check Count == 1.
    In .NET Framework, XmlNode.ChildNodes calls new XmlChildNodes(this) on every access — it never caches — so each call produces 2 throwaway heap allocations.
    This method is called for every property and metadata element during evaluation, making it a significant source of GC pressure during solution load.

    Allocation sites (TypeAllocated!System.Xml.XmlChildNodes, ~86% of sampled allocations):

    GetXmlNodeInnerContents
     → XmlNode.get_ChildNodes        ← allocates new XmlChildNodes(this) every call
       → XmlChildNodes.get_Count     ← iterates all children, result used once
         → compared to == 1, wrapper discarded
    

    Callers on hot path as per Perfwatson traces:

    EvaluatePropertyElement → GetXmlNodeInnerContents        (~21%)
    ProcessMetadataElements → GetXmlNodeInnerContents      (~25%)
    DecorateItemsWithMetadata → GetXmlNodeInnerContents    (~40%)
    
  • Issue type: Avoid allocating wrapper objects when allocation-free alternatives exist on the same API surface.

  • Proposed fix: Replace node.ChildNodes.Count == 1 with node.FirstChild.NextSibling == null — a simple pointer check that answers the same question ("is there exactly one child?") with zero allocations. Cache FirstChild in a local and split the compound if into clear separate checks. This is a direct semantic equivalence (FirstChild == null!HasChildNodes, NextSibling == nullCount == 1), internal-only, and produces identical results for all edge cases.

Best practices wiki
See related failure in PRISM
ADO work item

Copilot AI review requested due to automatic review settings April 9, 2026 00:33

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Pull request overview

Reduces GC pressure in Utilities.GetXmlNodeInnerContents by avoiding repeated XmlNode.ChildNodes accesses (which allocate XmlChildNodes wrappers on .NET Framework) and using allocation-free FirstChild/NextSibling checks instead.

Changes:

  • Replaces node.ChildNodes.Count == 1 checks with firstChild.NextSibling == null to avoid per-call XmlChildNodes allocations.
  • Caches node.FirstChild and simplifies the “no children / single whitespace child / single text or CDATA child” fast paths.

Comment thread src/Build/Utilities/Utilities.cs Outdated
Comment thread src/Build/Utilities/Utilities.cs Outdated
@JanProvaznik

JanProvaznik commented Apr 10, 2026

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running experimental insertion to see impact on perf metrics

@JanProvaznik

JanProvaznik commented Apr 13, 2026

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@JanProvaznik JanProvaznik merged commit f662d33 into dotnet:main Apr 13, 2026
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This was referenced Jun 10, 2026
github-actions Bot pushed a commit to IntelliTect/Multitool that referenced this pull request Jun 29, 2026
Updated [Microsoft.Build](https://github.com/dotnet/msbuild) from 18.6.3
to 18.7.1.

<details>
<summary>Release notes</summary>

_Sourced from [Microsoft.Build's
releases](https://github.com/dotnet/msbuild/releases)._

## 18.7.1

## What's Changed
* Fix TraceEngine file contention deadlock in multithreaded mode by
@​JanProvaznik in dotnet/msbuild#13446
* Remove duplicate test cases in MultithreadableTaskAnalyzer by
@​Youssef1313 in dotnet/msbuild#13483
* Ensure ThreadSafeTaskAnalyzer.Tests is considered as a unit test
project by @​Youssef1313 in dotnet/msbuild#13481
* Fix MSBuildTask0002 analyzer warnings in already-migrated tasks by
@​JanProvaznik in dotnet/msbuild#13466
* Fix race conditions in task host path resolution by @​AR-May in
dotnet/msbuild#13485
* Migrate ToolTask and Al task to TaskEnvironment API by @​OvesN in
dotnet/msbuild#13423
* Bump main to 18.7, add vs18.6 to merge flow by @​MichalPavlik in
dotnet/msbuild#13472
* Avoid allocations in GetHashCode implementations by @​DustinCampbell
in dotnet/msbuild#13475
* Add PATs rotation to agentic workflow(s) by @​JanKrivanek in
dotnet/msbuild#13496
* Fix ASP.NET WebSite projects to copy netstandard.dll facade when
required by @​JanProvaznik in
dotnet/msbuild#13058
* Migrate AspNetCompiler to TaskEnvironment API by @​OvesN in
dotnet/msbuild#13424
* Add review workflow by @​JanKrivanek in
dotnet/msbuild#13503
* Strengthen reviewer skill: add step-back analysis dimensions by
@​JanProvaznik in dotnet/msbuild#13504
* Add 'Request Speedometer Perf Run' to VS experimental insertion build
policies by @​Copilot in dotnet/msbuild#13505
* Remove duplicate @ prefix from issueAuthor in GitOps by @​akoeplinger
in dotnet/msbuild#13492
* Improve review aw by @​JanKrivanek in
dotnet/msbuild#13510
* Migrates unit tests to use RoslynCodeTaskFactory to enable running
tests under .NET Core by @​jankratochvilcz in
dotnet/msbuild#13500
* Fix cross-AppDomain TaskItem modifier cache regression by
@​DustinCampbell in dotnet/msbuild#13493
* Discourage review agent from approving PRs by @​JanKrivanek in
dotnet/msbuild#13512
* Stop trying to deploy ValueTuple by @​rainersigwald in
dotnet/msbuild#13507
* Ad-hoc re-sign bootstrap dotnet on macOS to prevent SIGKILL by
@​jankratochvilcz in dotnet/msbuild#13513
* RoslynCodeTaskFactory: Log MSB3753 when task class does not implement
ITask by @​jankratochvilcz in
dotnet/msbuild#13517
* Update gh-aw (upon mcp policy changes) by @​JanKrivanek in
dotnet/msbuild#13526
* Eliminate XmlChildNodes allocations in GetXmlNodeInnerContents by
@​nareshjo in dotnet/msbuild#13509
* Fix telemetry allocation regression: per-engine collector ownership by
@​JanProvaznik in dotnet/msbuild#13516
* Migrate to xunit.v3 by @​Youssef1313 in
dotnet/msbuild#13482
* Fix stray brace in HandleBuildCancel trace string causing MSB1025 by
@​Copilot in dotnet/msbuild#13535
* Bumping to 10.0.4 runtime packages by @​MichalPavlik in
dotnet/msbuild#13533
* Remove early return in GetCanonicalForm, always call System.IO.Path by
@​OvesN in dotnet/msbuild#13532
* Do not overwrite GetCopyToOutputDirectoryItemsDependsOn, just add new…
by @​snechaev in dotnet/msbuild#13474
* Migrate GetReferenceAssemblyPaths task to TaskEnvironment API by
@​OvesN in dotnet/msbuild#13495
* Stabilize ToolTaskThatTimeoutAndRetry test by @​rainersigwald in
dotnet/msbuild#13489
* [automated] Merge branch 'vs18.6' => 'main' by @​github-actions[bot]
in dotnet/msbuild#13506
* Add extra test assertions around tests by @​Youssef1313 in
dotnet/msbuild#13536
* Add static eval for repo skills/agents via skill-validator by
@​JanKrivanek in dotnet/msbuild#13537
* Migrate SGen task to Task environment API by @​OvesN in
dotnet/msbuild#13457
* Fix TerminalLogger assert failure for metaproj files and cached
project eval ID by @​OvesN in
dotnet/msbuild#13480
* Filter out approving review from pr-reviewer agent by @​JanKrivanek in
dotnet/msbuild#13553
* Use a unique task name per invocation to tabilize
RoslynCodeTaskFactory_ReuseCompilation test by @​huulinhnguyen-dev in
dotnet/msbuild#13551
* Brief doc on feedback/logging/data systems by @​rainersigwald in
dotnet/msbuild#13554
* Localized file check-in by OneLocBuild Task: Build definition ID 9434:
Build ID 13881982 by @​dotnet-bot in
dotnet/msbuild#13437
* Stage 3: Forward BuildProjectFile* callbacks from OOP TaskHost to
worker node by @​JanProvaznik in
dotnet/msbuild#13350
* Enable TaskHost Callbacks by default by @​JanProvaznik in
dotnet/msbuild#13579
* Remove unactionable info from reviewer agent by @​JanKrivanek in
dotnet/msbuild#13578
* Enlighten RequiresFramework35SP1Assembly task for multithreaded mode
by @​jankratochvilcz in dotnet/msbuild#13575
* Make SdkResolver-provided environment variables take precedence over
ambient environment by @​Copilot in
dotnet/msbuild#12655
* Add dotnet/skills marketplace and enable plugins by @​Evangelink in
dotnet/msbuild#13582
* The skills/agents check filters-in only touched files by @​JanKrivanek
in dotnet/msbuild#13586
* Fix skill-validation workflow failing when agents directory is deleted
by @​JeremyKuhne in dotnet/msbuild#13592
 ... (truncated)

Commits viewable in [compare
view](dotnet/msbuild@v18.6.3...v18.7.1).
</details>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
This was referenced Jun 29, 2026
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4 participants