This is a follow-up to many allocations recognized in dotnet#20448.

A lot of methods ultimately call through CustomAttributes.GetCustomAttributes(). In the inherited search path (default for most searches above), the inheritance path of a class is traversed, resulting in an array allocation per crawled type, a copy to the overall List<object> and then after that - in current code - an array allocation from that list and a typed array allocation it's copied to.

However, in the common miss case as simple as:
typeof(T).GetCustomAttributes(typeof(TAttr), true);
...and many other overloads, all the same path underneath...

We can avoid the last 2 arrays in the miss case. We have the List<object> to go off of. If that's a zero-entry list, we can return an Array.Empty<TAttr>(). That's effectively what this change does.

While converting the entire attribute pipeline to generics is problematic and has issue since some object[] return abstracts aren't sealed, we can at least somewhat trivially cache an array per attribute type (only one static, ultimately from Array.Empty<T> underneath) and return that for the miss case.

There are far more wins to be had here, but they require more changes.

…'s inherited path (#20779)

* Optimization: avoid 2 array allocations in inherited attribute misses

This is a follow-up to many allocations recognized in #20448.

A lot of methods ultimately call through CustomAttributes.GetCustomAttributes(). In the inherited search path (default for most searches above), the inheritance path of a class is traversed, resulting in an array allocation per crawled type, a copy to the overall List<object> and then after that - in current code - an array allocation from that list and a typed array allocation it's copied to.

However, in the common miss case as simple as:
typeof(T).GetCustomAttributes(typeof(TAttr), true);
...and many other overloads, all the same path underneath...

We can avoid the last 2 arrays in the miss case. We have the List<object> to go off of. If that's a zero-entry list, we can return an Array.Empty<TAttr>(). That's effectively what this change does.

While converting the entire attribute pipeline to generics is problematic and has issue since some object[] return abstracts aren't sealed, we can at least somewhat trivially cache an array per attribute type (only one static, ultimately from Array.Empty<T> underneath) and return that for the miss case.

There are far more wins to be had here, but they require more changes.

* Move RuntimeType empty array cache generation to Attribute.CreateAttributeArrayHelper

This exposes Attribute.CreateAttributeArrayHelper to internal and uses it directly on the RuntimeType caching for empty arrays. Though this allocated 1 additional array overall, it's simpler, faster to init, and still is an infinite win over the per-call allocations before this overall changesets.

* CustomAttributes: remove needless array copy in the inherited hit case

This removes a .ToArray() for the sake of Array.Copy() where a simple for loop suffices and removes the allocation. Reversing the "empty" result checks is also just a bit cleaner here.

This also expands the same fix to the MemberInfo path.

Note: should DRY these up too (longstanding issue) - but let's do that in a separate commit for clarity.

* GetCusomAttributes: use ListBuilder<object> for inheritance crawls

This exposes RuntimeType.ListBuilder<T> for internal usage and replaces the List<T> allocation in GetCustomAttributes() paths to reduce allocations and increase performance in the inherited crawl paths (which is the default for many optional-parameter methods in layers above).

Note: there is a subtle behavior depending on previous-null (not possible with a struct now) in AttributeUsageCheck() that I believe still behaves correctly, but could use another set of eyes and a full test suite run to confirm. object[] attributes was removed there simply because it wasn't used before - only cleaning up.

* Attribute caching: use Array.CreateInstance() directly on RuntimeType

This also reverts the CreateAttributeArrayHelper => internal change, since it's no longer needed.

* Ref passing for RuntimeType.ListBuilder<object> & CustomAttribute simplification

This fixes the struct passing duplication and tweaks how we're creating arrays a bit, centralizing the zero-element checks to cover all cases as well as simplify the per-method code to rely on the fact this is happening underneath.

When looking for compiler generated async state machine types and methods, we need not look at parents in the reflection path. This introduces additional overhead in both .IsDefined() and .GetCustomAttributes<T>() in every path.

See the short circuit path in: https://github.com/dotnet/coreclr/blob/57f8358221a3c4ad7f1608f625bc3c5936618505/src/System.Private.CoreLib/src/System/Reflection/CustomAttribute.cs#L1315-L1320

We can avoid the list allocation, the array from it, and the resulting combined array by not looking for inherited attributed members that cannot exist for our purposes of creating a stack trace.

…'s inherited path (dotnet#20779)

* Optimization: avoid 2 array allocations in inherited attribute misses

This is a follow-up to many allocations recognized in dotnet#20448.

A lot of methods ultimately call through CustomAttributes.GetCustomAttributes(). In the inherited search path (default for most searches above), the inheritance path of a class is traversed, resulting in an array allocation per crawled type, a copy to the overall List<object> and then after that - in current code - an array allocation from that list and a typed array allocation it's copied to.

However, in the common miss case as simple as:
typeof(T).GetCustomAttributes(typeof(TAttr), true);
...and many other overloads, all the same path underneath...

We can avoid the last 2 arrays in the miss case. We have the List<object> to go off of. If that's a zero-entry list, we can return an Array.Empty<TAttr>(). That's effectively what this change does.

While converting the entire attribute pipeline to generics is problematic and has issue since some object[] return abstracts aren't sealed, we can at least somewhat trivially cache an array per attribute type (only one static, ultimately from Array.Empty<T> underneath) and return that for the miss case.

There are far more wins to be had here, but they require more changes.

* Move RuntimeType empty array cache generation to Attribute.CreateAttributeArrayHelper

This exposes Attribute.CreateAttributeArrayHelper to internal and uses it directly on the RuntimeType caching for empty arrays. Though this allocated 1 additional array overall, it's simpler, faster to init, and still is an infinite win over the per-call allocations before this overall changesets.

* CustomAttributes: remove needless array copy in the inherited hit case

This removes a .ToArray() for the sake of Array.Copy() where a simple for loop suffices and removes the allocation. Reversing the "empty" result checks is also just a bit cleaner here.

This also expands the same fix to the MemberInfo path.

Note: should DRY these up too (longstanding issue) - but let's do that in a separate commit for clarity.

* GetCusomAttributes: use ListBuilder<object> for inheritance crawls

This exposes RuntimeType.ListBuilder<T> for internal usage and replaces the List<T> allocation in GetCustomAttributes() paths to reduce allocations and increase performance in the inherited crawl paths (which is the default for many optional-parameter methods in layers above).

Note: there is a subtle behavior depending on previous-null (not possible with a struct now) in AttributeUsageCheck() that I believe still behaves correctly, but could use another set of eyes and a full test suite run to confirm. object[] attributes was removed there simply because it wasn't used before - only cleaning up.

* Attribute caching: use Array.CreateInstance() directly on RuntimeType

This also reverts the CreateAttributeArrayHelper => internal change, since it's no longer needed.

* Ref passing for RuntimeType.ListBuilder<object> & CustomAttribute simplification

This fixes the struct passing duplication and tweaks how we're creating arrays a bit, centralizing the zero-element checks to cover all cases as well as simplify the per-method code to rely on the fact this is happening underneath.

…'s inherited path (dotnet/coreclr#20779)

* Optimization: avoid 2 array allocations in inherited attribute misses

This is a follow-up to many allocations recognized in dotnet/coreclr#20448.

A lot of methods ultimately call through CustomAttributes.GetCustomAttributes(). In the inherited search path (default for most searches above), the inheritance path of a class is traversed, resulting in an array allocation per crawled type, a copy to the overall List<object> and then after that - in current code - an array allocation from that list and a typed array allocation it's copied to.

However, in the common miss case as simple as:
typeof(T).GetCustomAttributes(typeof(TAttr), true);
...and many other overloads, all the same path underneath...

We can avoid the last 2 arrays in the miss case. We have the List<object> to go off of. If that's a zero-entry list, we can return an Array.Empty<TAttr>(). That's effectively what this change does.

While converting the entire attribute pipeline to generics is problematic and has issue since some object[] return abstracts aren't sealed, we can at least somewhat trivially cache an array per attribute type (only one static, ultimately from Array.Empty<T> underneath) and return that for the miss case.

There are far more wins to be had here, but they require more changes.

* Move RuntimeType empty array cache generation to Attribute.CreateAttributeArrayHelper

This exposes Attribute.CreateAttributeArrayHelper to internal and uses it directly on the RuntimeType caching for empty arrays. Though this allocated 1 additional array overall, it's simpler, faster to init, and still is an infinite win over the per-call allocations before this overall changesets.

* CustomAttributes: remove needless array copy in the inherited hit case

This removes a .ToArray() for the sake of Array.Copy() where a simple for loop suffices and removes the allocation. Reversing the "empty" result checks is also just a bit cleaner here.

This also expands the same fix to the MemberInfo path.

Note: should DRY these up too (longstanding issue) - but let's do that in a separate commit for clarity.

* GetCusomAttributes: use ListBuilder<object> for inheritance crawls

This exposes RuntimeType.ListBuilder<T> for internal usage and replaces the List<T> allocation in GetCustomAttributes() paths to reduce allocations and increase performance in the inherited crawl paths (which is the default for many optional-parameter methods in layers above).

Note: there is a subtle behavior depending on previous-null (not possible with a struct now) in AttributeUsageCheck() that I believe still behaves correctly, but could use another set of eyes and a full test suite run to confirm. object[] attributes was removed there simply because it wasn't used before - only cleaning up.

* Attribute caching: use Array.CreateInstance() directly on RuntimeType

This also reverts the CreateAttributeArrayHelper => internal change, since it's no longer needed.

* Ref passing for RuntimeType.ListBuilder<object> & CustomAttribute simplification

This fixes the struct passing duplication and tweaks how we're creating arrays a bit, centralizing the zero-element checks to cover all cases as well as simplify the per-method code to rely on the fact this is happening underneath.


Commit migrated from dotnet/coreclr@6d9fc60