Compact NativeAOT dispatch cell info encoding by MichalStrehovsky · Pull Request #130824 · dotnet/runtime

MichalStrehovsky · 2026-07-15T23:40:38Z

Replaces the dispatch cell info encoding used for interface methods and generic virtual methods to use Native Layout.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

Copilot-Session: c5889318-fe12-47b1-946e-6969e02ef71d

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: c5889318-fe12-47b1-946e-6969e02ef71d

azure-pipelines · 2026-07-15T23:41:14Z

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dotnet-policy-service · 2026-07-15T23:41:53Z

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Copilot

Pull request overview

This PR changes the NativeAOT dispatch cell info sections to use a more compact encoding when multiple dispatch cells share the same descriptor (dictionary + per-cell index), and updates the runtime decoder accordingly. It also adds smoke tests intended to exercise multiple callsites sharing the same descriptor.

Changes:

Add dictionary-based encoding for interface dispatch cell info and GVM dispatch cell info (compiler-side), falling back to the existing direct encoding when it’s smaller.
Update NativeAOT runtime dispatch resolution to decode either direct or dictionary-encoded info regions.
Add/extend NativeAOT smoke tests to create multiple distinct callsites targeting the same interface/GVM descriptor.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/tests/nativeaot/SmokeTests/UnitTests/Interfaces.cs	Adds a new test to create multiple interface dispatch callsites that should share a descriptor.
src/tests/nativeaot/SmokeTests/DynamicGenerics/GenericVirtualMethods.cs	Adds multiple no-inline interface GVM call wrappers to increase shared-descriptor callsites.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/InterfaceDispatchCellInfoSectionNode.cs	Emits interface dispatch info using direct vs dictionary encoding based on size.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/GvmDispatchCellInfoSectionNode.cs	Emits GVM dispatch info using direct vs dictionary encoding based on size.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/DispatchCellNode.cs	Introduces a shared helper for dictionary size/index encoding decisions.
src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs	Updates decoding logic to understand the new direct/dictionary layouts.

MichalStrehovsky · 2026-07-17T00:11:00Z

I'm on the fence whether this is worth it at all. This adds 200 lines of complexity to get a 0.34% saving in the best case.

Size statistics

Pull request #130824

Project	Size before	Size after	Difference
TodosApi-linux	25084480	25023040	-61440
TodosApi-windows	26148352	26086912	-61440
avalonia.app-linux	19002672	18937136	-65536
avalonia.app-windows	19319296	19253248	-66048
hello-linux	1254592	1254592	0
hello-minimal-linux	1107016	1111112	4096
hello-minimal-windows	788992	789504	512
hello-windows	950784	951296	512
kestrel-minimal-linux	5392992	5388896	-4096
kestrel-minimal-windows	4921344	4913152	-8192
reflection-linux	1845416	1849512	4096
reflection-windows	1716224	1716224	0
webapiaot-linux	9882200	9857624	-24576
webapiaot-windows	10348032	10326016	-22016
winrt-component-minimal-windows	738304	738304	0

Group dispatch cells by descriptor and encode their metadata as compact NativeFormat runs backed by the existing NativeReferences table. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 99d7688e-8d4a-4dcb-a6e4-ca94fdfed0dc

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 7f337a9d-27d1-43d9-9c0c-cc6a3ea449a7

Copilot

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Replaced exceptions with assertions for cell index and slot checks, and updated external references initialization.

Copilot

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: f55b8ade-cf37-4d2c-91af-cee7b726a3ea

Copilot

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

MichalStrehovsky · 2026-07-21T11:39:51Z

Looks like this now costs next to nothing in extra complexity (the NativeArray is a general purpose data structure we can use elsewhere) and still provides a nice saving:

Size statistics

Project	Size before	Size after	Difference
TodosApi-linux	25084480	24990272	-94208
TodosApi-windows	26148352	26053120	-95232
avalonia.app-linux	19002672	18904368	-98304
avalonia.app-windows	19319296	19220992	-98304
hello-linux	1254592	1254592	0
hello-minimal-linux	1107016	1111112	4096
hello-minimal-windows	788992	790016	1024
hello-windows	950784	951808	1024
kestrel-minimal-linux	5392992	5384800	-8192
kestrel-minimal-windows	4921344	4908032	-13312
reflection-linux	1845416	1849512	4096
reflection-windows	1716224	1716736	512
webapiaot-linux	9882200	9845336	-36864
webapiaot-windows	10348032	10312704	-35328
winrt-component-minimal-windows	738304	738816	512

azure-pipelines · 2026-07-21T11:40:34Z

Azure Pipelines: Successfully started running 3 pipeline(s). 13 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

MichalStrehovsky · 2026-07-21T11:41:01Z

/azp run runtime-nativeaot-outerloop

azure-pipelines · 2026-07-21T11:41:11Z

Azure Pipelines: Successfully started running 1 pipeline(s).

Copilot

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (3)

src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs:106

GetDispatchCellInfo ignores the return value of InitializeNativeReferences. If the NativeReferences blob is missing/corrupt, subsequent GetIntPtrFromIndex calls will read from an uninitialized table and fail unpredictably. This should fail fast with BadImageFormatException (similar to other TypeLoader code paths).

            externalReferences = default;
            externalReferences.InitializeNativeReferences(typeManager);

src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs:115

The fallback loop that decrements cellIndex can underflow in release builds (cellIndex is uint) if TryGetAt never succeeds (e.g., malformed/empty info region), leading to an infinite loop. Add a defensive termination condition (and ideally a small max scan bound) that throws BadImageFormatException.

            NativeParser parser;
            while (!entries.TryGetAt(cellIndex, out parser))
            {
                Debug.Assert(cellIndex > 0);
                cellIndex--;
            }

src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs:109

GetDispatchCellInfo allocates a new NativeReader (class) on every first-time dispatch resolution. If many dispatch cells are resolved during startup, this can create avoidable GC pressure compared to the previous pointer-based indexing. Consider caching a per-module NativeReader/NativeArray (or otherwise avoiding per-call allocation) and include perf measurements showing this doesn’t regress first-call/startup time.

            NativeReader reader = new NativeReader(pInfo, checked((uint)length));
            NativeArray entries = new NativeArray(new NativeParser(reader, 0));

jkotas

(make sure to update the PR description before merging)

Compact NativeAOT dispatch cell info encoding

76963d6

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: c5889318-fe12-47b1-946e-6969e02ef71d

Copilot AI review requested due to automatic review settings July 15, 2026 23:40

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130824 MichalStrehovsky/rt-sz#239

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The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs Outdated

Use NativeArray for dispatch cell info

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Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs Outdated

Refactor dispatch methods to use assertions

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Replaced exceptions with assertions for cell index and slot checks, and updated external references initialization.

Copilot AI review requested due to automatic review settings July 17, 2026 08:21

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Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs

This was referenced Jul 17, 2026

Test failure: A COM object used through FreeThreadedStrategy is not free threaded (agile). #130961

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tracing/runtimeeventsource/nativeruntimeeventsource/nativeruntimeeventsource failing in CI #90605

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Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs Outdated

Use sparse NativeArray for dispatch cell info

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Copilot AI review requested due to automatic review settings July 21, 2026 08:56

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Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs

Comment thread src/coreclr/nativeaot/Common/src/Internal/Runtime/TypeLoader/ExternalReferencesTable.cs

MichalStrehovsky marked this pull request as ready for review July 21, 2026 11:39

This was referenced Jul 21, 2026

Assertion failed: new_time >= loop->time in Component Governance Detection dotnet/dnceng#6510

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Helix: System.IO.IOException: No space left on device #128758

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Comment thread src/coreclr/tools/Common/Compiler/DependencyAnalysis/SortableDependencyNode.cs

build-analysis Bot mentioned this pull request Jul 21, 2026

Unable to pull image from mcr.microsoft.com #117164

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Delete useless parameter

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MichalStrehovsky merged commit 756cb59 into dotnet:main Jul 23, 2026
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MichalStrehovsky deleted the compact-dispatch-cell-info branch July 23, 2026 01:32

dotnet-maestro Bot mentioned this pull request Jul 23, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#7872

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MichalStrehovsky commented Jul 15, 2026 •

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