Reduce types loaded on startup significantly #120459

davidwrighton · 2025-10-07T00:12:53Z

Reduce the number of type loads triggered by complex generic constraints. Experiments show about a 20% reduction in startup time on a proxy of the AWS lambda scenario.

The fixes are:

When a method/type has constraints, do not load the constraint types directly if they are generic interfaces. Instead, do accessibility checking and the constraint validation on the signature of the constraint instead.
When a type is loaded, enhance the special marker type optimization in the interface map to allow Interfaces which require implementation of other interfaces to use the special marker type. Notably, use the special marker type so that if a generic interface's first type parameter is used as all of the generic type parameters of a required interface we use the special marker type to indicate that the type is loaded.
- This also forces us to have a somewhat more complicated implementation of casting, since the previous model of special marker types could not experience an equivalent interface match
When resolving a default interface method, attempt to avoid loading all the interface types associated with a type. Do so by changing the iteration of interfaces to check to see if the approximate interface could possibly have an implementation
When resolving a static virtual method, attempt to avoid loading all the types of the MethodImpl records. Do so by doing a Method name check before loading the type.

In addition, fix a test so that it still throws when loading an invalid type. This required adding a path which forced the interface type to be loaded.

As part of testing this work, the lack of generic variable type safety checks was noticed in crossgen2, and the following changes were made

Add support for doing circularity checks on type and method generic parameters to the TypeValidationChecker in crossgen2
Add support for doing variance safety checks to the type loader in crossgen2

And in the runtime

Remove the circularity of type variables checks happening in generic method load, as it is redundant
Put all of the variance safety checks in the runtime under the SkipTypeValidation flag as crossgen2 can now do it reliably

Related to the work in #120407

…erly - Reduce the set of constraints that need to be loaded for Bounds and cast checking TODO: There is a path in InitTypeContext which I have #ifdef'd out as I don't understand the comment The accessibility checking needs full loading now, as we don't have a scheme to just look at all the typedefs in a signature, and instead need to do a load of the full type and work from there. This could be revisited.

This is DRAFT as we now have an unused state WhichConstraintsToLoad::TypeOrMethodVarsOnly which we never use. (It could be used for the Bounds algorithm, but that isn't actually used without doing the more expensive logic which does access validation)

davidwrighton · 2025-10-07T00:13:48Z

Should address issues in #120406

dotnet-policy-service · 2025-10-07T00:14:03Z

Tagging subscribers to this area: @mangod9
See info in area-owners.md if you want to be subscribed.

- Currently it only handles interfaces defined on valuetypes - Change it to work for interfaces that are required implementation of other interfaces - (In that case, if the interface is generic, the special instantiation type is the first type parameter of the interface, not anything else.) This change removes some safety checks that I can't find the rationale for. This may cause some entertaining failures in CI

- Tweak the logic so that it will attempt to avoid loading types if they are cannot have implementations of the method we're looking for

- This test was no longer actually forcing the type which is supposed to throw a TypeLoadException to load within the test - Tweak the test to actually force the offending type to be loaded

Copilot

Pull Request Overview

This PR reduces type loading during startup by optimizing generic constraint handling and interface map operations. It achieves approximately 20% reduction in startup time for AWS lambda scenarios by deferring unnecessary type loads and using more efficient type checking algorithms.

Key changes:

Introduces selective constraint loading to avoid loading generic interface constraints when not needed
Optimizes interface map special marker types to work with interfaces, not just value types
Implements lazy evaluation strategies for default interface method resolution and static virtual method resolution

Reviewed Changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
`src/tests/Loader/classloader/generics/ByRefLike/InvalidCSharpNegative.il`	Adds GetInterfaces() call to force interface type loading in test
`src/coreclr/vm/typehandle.cpp`	Updates constraint loading calls to use selective loading approach
`src/coreclr/vm/typedesc.h`	Defines WhichConstraintsToLoad enum and updates TypeVarTypeDesc constraint API
`src/coreclr/vm/typedesc.cpp`	Implements selective constraint loading with interface-aware logic
`src/coreclr/vm/typectxt.cpp`	Updates type context initialization to handle constraint loading changes
`src/coreclr/vm/siginfo.cpp`	Enhances special marker type handling for generic interface instantiation
`src/coreclr/vm/runtimehandles.cpp`	Updates constraint retrieval for reflection API
`src/coreclr/vm/methodtablebuilder.cpp`	Extends special marker optimization to interfaces and adds early exit optimizations
`src/coreclr/vm/methodtable.inl`	Updates interface implementation checking for new special instantiation logic
`src/coreclr/vm/methodtable.h`	Adds GetSpecialInstantiationType method and interface equivalence checking
`src/coreclr/vm/methodtable.cpp`	Implements lazy interface loading, accessibility checking, and optimized method resolution
`src/coreclr/vm/genmeth.cpp`	Updates constraint loading calls and removes unnecessary constraint loads
`src/coreclr/vm/comdelegate.cpp`	Updates delegate constraint checking to use selective loading

src/coreclr/vm/typedesc.cpp

src/coreclr/vm/methodtable.cpp

jkotas · 2025-10-09T19:56:14Z

/azp run runtime-coreclr outerloop

azure-pipelines · 2025-10-09T19:56:31Z

Azure Pipelines successfully started running 1 pipeline(s).

jkotas

The test failure looks related

src/coreclr/vm/genmeth.cpp

src/coreclr/vm/methodtable.cpp

… parameters to the TypeValidationChecker in crossgen2 - Add support for doing variance safety checks to the type loader in crossgen2 - Remove the circularity of type variables checks happening in generic method load, as it is redundant - Put all of the variance safety checks in the runtime under the SkipTypeValidation flag as crossgen2 can now do it reliably

- Add test for constraints with function pointers in them

davidwrighton · 2025-10-10T23:31:45Z

/azp run runtime-coreclr outerloop

azure-pipelines · 2025-10-10T23:31:56Z

Azure Pipelines successfully started running 1 pipeline(s).

jkotas

crossgen2 test still failing

src/coreclr/vm/methodtable.cpp

src/coreclr/vm/genmeth.cpp

src/coreclr/vm/methodtable.cpp

src/coreclr/vm/methodtablebuilder.cpp

jkotas · 2025-10-11T01:30:24Z

/azp run runtime-nativeaot-outerloop

azure-pipelines · 2025-10-11T01:30:39Z

Azure Pipelines successfully started running 1 pipeline(s).

- add SkipTypeValidation helper

jkotas · 2025-10-13T22:31:23Z

@EgorBot scenario-awslambda -arm -intel

jkotas

LGTM once the tests are passing

davidwrighton · 2025-10-14T03:14:22Z

/azp run runtime-interpreter

azure-pipelines · 2025-10-14T03:14:38Z

Azure Pipelines successfully started running 1 pipeline(s).

davidwrighton · 2025-10-14T03:16:18Z

/azp run runtime-coreclr outerloop

azure-pipelines · 2025-10-14T03:16:29Z

Azure Pipelines successfully started running 1 pipeline(s).

davidwrighton · 2025-10-14T17:01:11Z

/backport to release/10.0

github-actions · 2025-10-14T17:01:20Z

Started backporting to release/10.0: https://github.com/dotnet/runtime/actions/runs/18504146328

davidwrighton added 4 commits October 6, 2025 15:47

Clear up the issues around GetDeclaringMethodTableFromTypeVarTypeDesc

bb4a3d2

Tweak, and add comments...

db83d47

This is DRAFT as we now have an unused state WhichConstraintsToLoad::TypeOrMethodVarsOnly which we never use. (It could be used for the Bounds algorithm, but that isn't actually used without doing the more expensive logic which does access validation)

Fix build errors

c0ae70d

github-actions bot added the area-VM-coreclr label Oct 7, 2025

dotnet-policy-service bot assigned davidwrighton Oct 7, 2025

davidwrighton mentioned this pull request Oct 7, 2025

1000 more types loaded in .NET 10 vs. .NET 8 during startup in a small workload #120406

Open

build-analysis bot mentioned this pull request Oct 7, 2025

[linux-x64] [mono-aot] Test Runtime_101731.TestConvertToInt64NativeSingle(3.4028235E+38) returns exit code 22 #112557

Open

davidwrighton added 3 commits October 7, 2025 11:55

Fix bugs making it not work properly

1f742a3

Fix interface matching bug found in testing

bef91a8

build-analysis bot mentioned this pull request Oct 8, 2025

[QUIC] Sporadic long running tests #119763

Open

davidwrighton added 4 commits October 8, 2025 09:36

Optimize virtual static and default interface method resolution logic

2bdfc3c

- Tweak the logic so that it will attempt to avoid loading types if they are cannot have implementations of the method we're looking for

Update loader/classloader/generics/ByRefLike/ValidateNegative test

3b937fd

- This test was no longer actually forcing the type which is supposed to throw a TypeLoadException to load within the test - Tweak the test to actually force the offending type to be loaded

Pass around the type I want passed around

64d10ff

Remove WhichConstraintsToLoad::TypeOrMethodVarsOnly

9eef0b3

davidwrighton changed the title ~~[DRAFT] Reduce constraint load~~ Reduce types loaded on startup significantly Oct 8, 2025

davidwrighton marked this pull request as ready for review October 8, 2025 23:52

davidwrighton requested review from AaronRobinsonMSFT, Copilot and jkotas October 8, 2025 23:52

Copilot AI reviewed Oct 8, 2025

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davidwrighton added 2 commits October 8, 2025 16:56

Fix out of date comment

4a6a81c

Merge branch 'main' into reduce_constraint_load

18214f8

build-analysis bot mentioned this pull request Oct 9, 2025

Assert Interop.Sys.LSeek(this, 0, Interop.Sys.SeekWhence.SEEK_CUR) >= 0 in System.Net.XXX tests #120577

Closed

jkotas reviewed Oct 10, 2025

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src/coreclr/vm/genmeth.cpp Show resolved Hide resolved

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davidwrighton added 3 commits October 10, 2025 15:23

Code review feedback

ebca7a6

- Flesh out implementation of sig parser for constraint accessibility

9d8b167

- Add test for constraints with function pointers in them

jkotas reviewed Oct 11, 2025

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build-analysis bot mentioned this pull request Oct 11, 2025

/root/helix/work/correlation/scripts/<hash>/execute.sh: Permission denied dotnet/dnceng#3412

Open

3 tasks

davidwrighton added 2 commits October 13, 2025 13:56

- Add crossgen2 validation of interface impl variance rules

d5fad7d

- Adjust contracts as suggested

12511ff

- add SkipTypeValidation helper

EgorBot mentioned this pull request Oct 13, 2025

Benchmarks for #120459 (jkotas) EgorBot/runtime-utils#519

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jkotas approved these changes Oct 13, 2025

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build-analysis bot mentioned this pull request Oct 14, 2025

AppHost test failure: I/O failure when writing extracted files #120653

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davidwrighton merged commit 56484c9 into dotnet:main Oct 14, 2025
159 of 169 checks passed

github-actions bot mentioned this pull request Oct 14, 2025

[release/10.0] Reduce types loaded on startup significantly #120712

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4 tasks

dotnet-maestro bot mentioned this pull request Oct 15, 2025

[main] Source code updates from dotnet/runtime dotnet/dotnet#2885

Merged

Reduce types loaded on startup significantly #120459

Reduce types loaded on startup significantly #120459

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davidwrighton commented Oct 7, 2025 •

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