[release/10.0] Reduce types loaded on startup significantly by github-actions[bot] · Pull Request #120712 · dotnet/runtime

github-actions · 2025-10-14T17:03:12Z

Backport of #120459 to release/10.0

Customer Impact

Customer reported
Found internally

[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]

Regression

Yes
No

There is a regression between .NET 9 and .NET 10 where the number of types loaded on startup has increased significantly due to greater use of static virtual methods and generics. This PR addresses the issue by changing the behavior of the type loader to not require as many instantiations of interface types to be loaded by using a variety of optimization techniques. This is not a regression in the correctness of the type loader, or in its behavior, but the overall issue being addressed is a regression.

Notably

Using a technique where we load placeholder types instead of the exact needed instantiations into the interface map
Changing the constraint loading code to avoid loading the constraint instantiated over the formal generic parameters of the type/method which defines the constraint
In the default interface method and virtual static method scenarios reducing the number of types loaded while attempting to find the actual implementing method.

Testing

The positive effect of this change was validated by a new series of performance tests written specifically to address this issue. Testing has shown that this change reduces startup time of small applications by as much as 20%. The correctness of this change was validated by running the various tests available to run in CI. The issue here was missed previously as the startup numbers under our pre-existing startup testing scenario did not restrict CPU, and we had also been making other changes to the runtime which resulted in small applications have a comparable startup time to older versions when not run in a mode where the CPU time available to the application was restricted.

Risk

High. This change affects all types loaded into the process and adds new logic and failure points to all interface casting. In addition, this change adds additional failure modes into customer applications such that a TypeLoadException may be thrown at unexpected moments due to invalid metadata instead of the exception occurring at the current locations.

IMPORTANT: If this backport is for a servicing release, please verify that:

The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

…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)

…rrently 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

… 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

EgorBo · 2025-10-15T13:31:32Z

@EgorBot scenario-awslambda -arm -intel

PranavSenthilnathan · 2025-11-14T00:50:53Z

Since this PR is targeting release/10.0, this is a reminder that code complete is Monday November 17. If you want the changes in the PR in the release, please merge it on time.

JulieLeeMSFT · 2025-12-02T20:41:40Z

/ba-g Test failure is a known issue #121940.

github-actions · 2025-10-14T17:03:12Z

Backport of #120459 to release/10.0

/cc @davidwrighton

Customer Impact

Customer reported
Found internally

[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]

Regression

Yes
No

There is a regression between .NET 9 and .NET 10 where the number of types loaded on startup has increased significantly due to greater use of static virtual methods and generics. This PR addresses the issue by changing the behavior of the type loader to not require as many instantiations of interface types to be loaded by using a variety of optimization techniques. This is not a regression in the correctness of the type loader, or in its behavior, but the overall issue being addressed is a regression.

Notably

Using a technique where we load placeholder types instead of the exact needed instantiations into the interface map
Changing the constraint loading code to avoid loading the constraint instantiated over the formal generic parameters of the type/method which defines the constraint
In the default interface method and virtual static method scenarios reducing the number of types loaded while attempting to find the actual implementing method.

Testing

The positive effect of this change was validated by a new series of performance tests written specifically to address this issue. Testing has shown that this change reduces startup time of small applications by as much as 20%. The correctness of this change was validated by running the various tests available to run in CI. The issue here was missed previously as the startup numbers under our pre-existing startup testing scenario did not restrict CPU, and we had also been making other changes to the runtime which resulted in small applications have a comparable startup time to older versions when not run in a mode where the CPU time available to the application was restricted.

Risk

High. This change affects all types loaded into the process and adds new logic and failure points to all interface casting. In addition, this change adds additional failure modes into customer applications such that a TypeLoadException may be thrown at unexpected moments due to invalid metadata instead of the exception occurring at the current locations.

IMPORTANT: If this backport is for a servicing release, please verify that:

The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

…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)

…rrently 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

… 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

EgorBo · 2025-10-15T13:31:32Z

@EgorBot scenario-awslambda -arm -intel

PranavSenthilnathan · 2025-11-14T00:50:53Z

Since this PR is targeting release/10.0, this is a reminder that code complete is Monday November 17. If you want the changes in the PR in the release, please merge it on time.

JulieLeeMSFT · 2025-12-02T20:41:40Z

/ba-g Test failure is a known issue #121940.

github-actions · 2025-10-14T17:03:12Z

Backport of #120459 to release/10.0

/cc @davidwrighton

Customer Impact

Customer reported
Found internally

[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]

Regression

Yes
No

There is a regression between .NET 9 and .NET 10 where the number of types loaded on startup has increased significantly due to greater use of static virtual methods and generics. This PR addresses the issue by changing the behavior of the type loader to not require as many instantiations of interface types to be loaded by using a variety of optimization techniques. This is not a regression in the correctness of the type loader, or in its behavior, but the overall issue being addressed is a regression.

Notably

Using a technique where we load placeholder types instead of the exact needed instantiations into the interface map
Changing the constraint loading code to avoid loading the constraint instantiated over the formal generic parameters of the type/method which defines the constraint
In the default interface method and virtual static method scenarios reducing the number of types loaded while attempting to find the actual implementing method.

Testing

The positive effect of this change was validated by a new series of performance tests written specifically to address this issue. Testing has shown that this change reduces startup time of small applications by as much as 20%. The correctness of this change was validated by running the various tests available to run in CI. The issue here was missed previously as the startup numbers under our pre-existing startup testing scenario did not restrict CPU, and we had also been making other changes to the runtime which resulted in small applications have a comparable startup time to older versions when not run in a mode where the CPU time available to the application was restricted.

Risk

High. This change affects all types loaded into the process and adds new logic and failure points to all interface casting. In addition, this change adds additional failure modes into customer applications such that a TypeLoadException may be thrown at unexpected moments due to invalid metadata instead of the exception occurring at the current locations.

IMPORTANT: If this backport is for a servicing release, please verify that:

The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

…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)

…rrently 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

… 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

EgorBo · 2025-10-15T13:31:32Z

@EgorBot scenario-awslambda -arm -intel

PranavSenthilnathan · 2025-11-14T00:50:53Z

Since this PR is targeting release/10.0, this is a reminder that code complete is Monday November 17. If you want the changes in the PR in the release, please merge it on time.

JulieLeeMSFT · 2025-12-02T20:41:40Z

/ba-g Test failure is a known issue #121940.

github-actions · 2025-10-14T17:03:12Z

Backport of #120459 to release/10.0

/cc @davidwrighton

Customer Impact

Customer reported
Found internally

[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]

Regression

Yes
No

There is a regression between .NET 9 and .NET 10 where the number of types loaded on startup has increased significantly due to greater use of static virtual methods and generics. This PR addresses the issue by changing the behavior of the type loader to not require as many instantiations of interface types to be loaded by using a variety of optimization techniques. This is not a regression in the correctness of the type loader, or in its behavior, but the overall issue being addressed is a regression.

Notably

Using a technique where we load placeholder types instead of the exact needed instantiations into the interface map
Changing the constraint loading code to avoid loading the constraint instantiated over the formal generic parameters of the type/method which defines the constraint
In the default interface method and virtual static method scenarios reducing the number of types loaded while attempting to find the actual implementing method.

Testing

The positive effect of this change was validated by a new series of performance tests written specifically to address this issue. Testing has shown that this change reduces startup time of small applications by as much as 20%. The correctness of this change was validated by running the various tests available to run in CI. The issue here was missed previously as the startup numbers under our pre-existing startup testing scenario did not restrict CPU, and we had also been making other changes to the runtime which resulted in small applications have a comparable startup time to older versions when not run in a mode where the CPU time available to the application was restricted.

Risk

High. This change affects all types loaded into the process and adds new logic and failure points to all interface casting. In addition, this change adds additional failure modes into customer applications such that a TypeLoadException may be thrown at unexpected moments due to invalid metadata instead of the exception occurring at the current locations.

IMPORTANT: If this backport is for a servicing release, please verify that:

The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

…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)

…rrently 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

… 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

EgorBo · 2025-10-15T13:31:32Z

@EgorBot scenario-awslambda -arm -intel

PranavSenthilnathan · 2025-11-14T00:50:53Z

Since this PR is targeting release/10.0, this is a reminder that code complete is Monday November 17. If you want the changes in the PR in the release, please merge it on time.

JulieLeeMSFT · 2025-12-02T20:41:40Z

/ba-g Test failure is a known issue #121940.

github-actions · 2025-10-14T17:03:12Z

Backport of #120459 to release/10.0

/cc @davidwrighton

Customer Impact

Customer reported
Found internally

[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]

Regression

Yes
No

There is a regression between .NET 9 and .NET 10 where the number of types loaded on startup has increased significantly due to greater use of static virtual methods and generics. This PR addresses the issue by changing the behavior of the type loader to not require as many instantiations of interface types to be loaded by using a variety of optimization techniques. This is not a regression in the correctness of the type loader, or in its behavior, but the overall issue being addressed is a regression.

Notably

Using a technique where we load placeholder types instead of the exact needed instantiations into the interface map
Changing the constraint loading code to avoid loading the constraint instantiated over the formal generic parameters of the type/method which defines the constraint
In the default interface method and virtual static method scenarios reducing the number of types loaded while attempting to find the actual implementing method.

Testing

The positive effect of this change was validated by a new series of performance tests written specifically to address this issue. Testing has shown that this change reduces startup time of small applications by as much as 20%. The correctness of this change was validated by running the various tests available to run in CI. The issue here was missed previously as the startup numbers under our pre-existing startup testing scenario did not restrict CPU, and we had also been making other changes to the runtime which resulted in small applications have a comparable startup time to older versions when not run in a mode where the CPU time available to the application was restricted.

Risk

High. This change affects all types loaded into the process and adds new logic and failure points to all interface casting. In addition, this change adds additional failure modes into customer applications such that a TypeLoadException may be thrown at unexpected moments due to invalid metadata instead of the exception occurring at the current locations.

IMPORTANT: If this backport is for a servicing release, please verify that:

The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

…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)

…rrently 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

… 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

EgorBo · 2025-10-15T13:31:32Z

@EgorBot scenario-awslambda -arm -intel

PranavSenthilnathan · 2025-11-14T00:50:53Z

Since this PR is targeting release/10.0, this is a reminder that code complete is Monday November 17. If you want the changes in the PR in the release, please merge it on time.

JulieLeeMSFT · 2025-12-02T20:41:40Z

/ba-g Test failure is a known issue #121940.

github-actions · 2025-10-14T17:03:12Z

Backport of #120459 to release/10.0

/cc @davidwrighton

Customer Impact

Customer reported
Found internally

[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]

Regression

Yes
No

There is a regression between .NET 9 and .NET 10 where the number of types loaded on startup has increased significantly due to greater use of static virtual methods and generics. This PR addresses the issue by changing the behavior of the type loader to not require as many instantiations of interface types to be loaded by using a variety of optimization techniques. This is not a regression in the correctness of the type loader, or in its behavior, but the overall issue being addressed is a regression.

Notably

Using a technique where we load placeholder types instead of the exact needed instantiations into the interface map
Changing the constraint loading code to avoid loading the constraint instantiated over the formal generic parameters of the type/method which defines the constraint
In the default interface method and virtual static method scenarios reducing the number of types loaded while attempting to find the actual implementing method.

Testing

The positive effect of this change was validated by a new series of performance tests written specifically to address this issue. Testing has shown that this change reduces startup time of small applications by as much as 20%. The correctness of this change was validated by running the various tests available to run in CI. The issue here was missed previously as the startup numbers under our pre-existing startup testing scenario did not restrict CPU, and we had also been making other changes to the runtime which resulted in small applications have a comparable startup time to older versions when not run in a mode where the CPU time available to the application was restricted.

Risk

High. This change affects all types loaded into the process and adds new logic and failure points to all interface casting. In addition, this change adds additional failure modes into customer applications such that a TypeLoadException may be thrown at unexpected moments due to invalid metadata instead of the exception occurring at the current locations.

IMPORTANT: If this backport is for a servicing release, please verify that:

The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

…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)

…rrently 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

… 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

EgorBo · 2025-10-15T13:31:32Z

@EgorBot scenario-awslambda -arm -intel

PranavSenthilnathan · 2025-11-14T00:50:53Z

Since this PR is targeting release/10.0, this is a reminder that code complete is Monday November 17. If you want the changes in the PR in the release, please merge it on time.

JulieLeeMSFT · 2025-12-02T20:41:40Z

/ba-g Test failure is a known issue #121940.

github-actions · 2025-10-14T17:03:12Z

Backport of #120459 to release/10.0

/cc @davidwrighton

Customer Impact

Customer reported
Found internally

[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]

Regression

Yes
No

There is a regression between .NET 9 and .NET 10 where the number of types loaded on startup has increased significantly due to greater use of static virtual methods and generics. This PR addresses the issue by changing the behavior of the type loader to not require as many instantiations of interface types to be loaded by using a variety of optimization techniques. This is not a regression in the correctness of the type loader, or in its behavior, but the overall issue being addressed is a regression.

Notably

Using a technique where we load placeholder types instead of the exact needed instantiations into the interface map
Changing the constraint loading code to avoid loading the constraint instantiated over the formal generic parameters of the type/method which defines the constraint
In the default interface method and virtual static method scenarios reducing the number of types loaded while attempting to find the actual implementing method.

Testing

The positive effect of this change was validated by a new series of performance tests written specifically to address this issue. Testing has shown that this change reduces startup time of small applications by as much as 20%. The correctness of this change was validated by running the various tests available to run in CI. The issue here was missed previously as the startup numbers under our pre-existing startup testing scenario did not restrict CPU, and we had also been making other changes to the runtime which resulted in small applications have a comparable startup time to older versions when not run in a mode where the CPU time available to the application was restricted.

Risk

High. This change affects all types loaded into the process and adds new logic and failure points to all interface casting. In addition, this change adds additional failure modes into customer applications such that a TypeLoadException may be thrown at unexpected moments due to invalid metadata instead of the exception occurring at the current locations.

IMPORTANT: If this backport is for a servicing release, please verify that:

The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

…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)

…rrently 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

… 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

EgorBo · 2025-10-15T13:31:32Z

@EgorBot scenario-awslambda -arm -intel

PranavSenthilnathan · 2025-11-14T00:50:53Z

Since this PR is targeting release/10.0, this is a reminder that code complete is Monday November 17. If you want the changes in the PR in the release, please merge it on time.

JulieLeeMSFT · 2025-12-02T20:41:40Z

/ba-g Test failure is a known issue #121940.

github-actions · 2025-10-14T17:03:12Z

Backport of #120459 to release/10.0

/cc @davidwrighton

Customer Impact

Customer reported
Found internally

[Select one or both of the boxes. Describe how this issue impacts customers, citing the expected and actual behaviors and scope of the issue. If customer-reported, provide the issue number.]

Regression

Yes
No

There is a regression between .NET 9 and .NET 10 where the number of types loaded on startup has increased significantly due to greater use of static virtual methods and generics. This PR addresses the issue by changing the behavior of the type loader to not require as many instantiations of interface types to be loaded by using a variety of optimization techniques. This is not a regression in the correctness of the type loader, or in its behavior, but the overall issue being addressed is a regression.

Notably

Using a technique where we load placeholder types instead of the exact needed instantiations into the interface map
Changing the constraint loading code to avoid loading the constraint instantiated over the formal generic parameters of the type/method which defines the constraint
In the default interface method and virtual static method scenarios reducing the number of types loaded while attempting to find the actual implementing method.

Testing

The positive effect of this change was validated by a new series of performance tests written specifically to address this issue. Testing has shown that this change reduces startup time of small applications by as much as 20%. The correctness of this change was validated by running the various tests available to run in CI. The issue here was missed previously as the startup numbers under our pre-existing startup testing scenario did not restrict CPU, and we had also been making other changes to the runtime which resulted in small applications have a comparable startup time to older versions when not run in a mode where the CPU time available to the application was restricted.

Risk

High. This change affects all types loaded into the process and adds new logic and failure points to all interface casting. In addition, this change adds additional failure modes into customer applications such that a TypeLoadException may be thrown at unexpected moments due to invalid metadata instead of the exception occurring at the current locations.

IMPORTANT: If this backport is for a servicing release, please verify that:

The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

…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)

…rrently 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

… 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

EgorBo · 2025-10-15T13:31:32Z

@EgorBot scenario-awslambda -arm -intel

PranavSenthilnathan · 2025-11-14T00:50:53Z

Since this PR is targeting release/10.0, this is a reminder that code complete is Monday November 17. If you want the changes in the PR in the release, please merge it on time.

JulieLeeMSFT · 2025-12-02T20:41:40Z

/ba-g Test failure is a known issue #121940.

davidwrighton added 17 commits October 14, 2025 17:03

Clear up the issues around GetDeclaringMethodTableFromTypeVarTypeDesc
799719f

Tweak, and add comments...
82a4f0c
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
e482bb7

Fix bugs making it not work properly
1b74515

Fix interface matching bug found in testing
3de0673

Optimize virtual static and default interface method resolution logic…
9b4ccbe
… - 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 - …
87757d0
…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
e400fc7

Remove WhichConstraintsToLoad::TypeOrMethodVarsOnly
a4b1aa7

Fix out of date comment
9a3adb7

Code review feedback
f64bcac

- Flesh out implementation of sig parser for constraint accessibility…
c5a78e6
… - Add test for constraints with function pointers in them

- Add crossgen2 validation of interface impl variance rules
0f16b47

- Adjust contracts as suggested - add SkipTypeValidation helper
0ae569a

davidwrighton added the NO-MERGE The PR is not ready for merge yet (see discussion for detailed reasons) label Oct 14, 2025

build-analysisBot mentioned this pull request Oct 14, 2025
Assert Interop.Sys.LSeek(this, 0, Interop.Sys.SeekWhence.SEEK_CUR) >= 0 in System.Net.XXX tests #120577
Closed

EgorBot mentioned this pull request Oct 15, 2025
Benchmarks for #120712 (EgorBo) EgorBot/runtime-utils#524
Open

Merge branch 'release/10.0' into backport/pr-120459-to-release/10.0
82c0fb1

davidwrighton mentioned this pull request Nov 13, 2025
Startup Perf fix backport to dotnet/dotnet dotnet/dotnet#3349
Closed

JulieLeeMSFT assigned davidwrighton Nov 17, 2025

jkotas mentioned this pull request Nov 21, 2025
Reduce types loaded on startup significantly #120459
Merged

mangod9 added Servicing-consider Issue for next servicing release review and removed NO-MERGE The PR is not ready for merge yet (see discussion for detailed reasons) labels Nov 24, 2025

jkotas approved these changes Nov 26, 2025
View reviewed changes

Merge branch 'release/10.0' into backport/pr-120459-to-release/10.0
9ef9eb5

build-analysisBot mentioned this pull request Nov 26, 2025
[release/10.0] Assert Interop.Sys.LSeek(this, 0, Interop.Sys.SeekWhence.SEEK_CUR) >= 0 in System.Net.XXX tests #121940
Closed

ViktorHofer added this to the 10.0.2 milestone Dec 1, 2025

rbhanda added Servicing-approved Approved for servicing release and removed Servicing-consider Issue for next servicing release review labels Dec 1, 2025

JulieLeeMSFT merged commit 1425a40 into release/10.0Dec 2, 2025
104 of 108 checks passed

dotnet-maestroBot mentioned this pull request Dec 2, 2025
[release/10.0.1xx] Source code updates from dotnet/runtime dotnet/dotnet#3642
Merged

jkotas deleted the backport/pr-120459-to-release/10.0 branch December 4, 2025 01:58

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