Have ConstructorInfo use Activator.CreateInstance() instead of emit for default constructors

[steveharter]

Activator.CreateInstance() was optimized in v6 and made super fast when invoking the default constructor. As shown in the benchmarks below, currently calling a zero-parameter constructor through Activator.CreateInstance(...) is ~1.7x faster than ConstructorInfo. Note that before the 7.0 feature to use IL emit, Activator.CreateInstance(...) used to be ~6x faster than ConstructorInfo.

|                                                                       Method |        Job |              Toolchain |       Mean |      Error |     StdDev |     Median |        Min |        Max | Ratio | RatioSD |  Gen 0 | Allocated | Alloc Ratio |
|----------------------------------------------------------------------------- |----------- |----------------------- |-----------:|-----------:|-----------:|-----------:|-----------:|-----------:|------:|--------:|-------:|----------:|------------:|
|                                       Ctor0_ActivatorCreateInstance_NoParams | Job-VAFQFP | \newinvoke\corerun.exe |   8.700 ns |  0.1857 ns |  0.1646 ns |   8.733 ns |   8.395 ns |   8.999 ns |  1.00 |    0.00 | 0.0054 |      56 B |        1.00 |
|                                                               Ctor0_NoParams | Job-VAFQFP | \newinvoke\corerun.exe |  14.928 ns |  0.5837 ns |  0.6721 ns |  14.697 ns |  14.234 ns |  16.242 ns |  1.00 |    0.00 | 0.0053 |      56 B |        1.00 |

Although Activator is faster than ConstructorInfo that only applies for cases when there is a default constructor. When there are constructor parameters, calling ConstructorInfo is up to 2x faster.

Due to the varying performance of these two APIs, reflection users that need to invoke constructors and want the maximum performance currently need to call ConstructorInfo when there are parameters and Activator when there are no parameters. This issue should make this choice go away by making ConstructorInfo the preferred API going forward for almost all cases by having ConstructorInfo call Activator for default constructors. This also avoids generating IL for these cases which can help with start-up and reduce global memory usage.

Using ConstructorInfo instead of Activator also has the advantage of forcing the caller select the appropriate constructor ahead of time, instead of auto-selecting each time the method is called by inspecting the parameters. If the caller does not know what constructor to call, then continuing to use Activator is fine.

We also need to look at normalizing the exception handling between these two APIs so they have the same Exception semantics for OutOfMemoryException.

Also see #36194 for ideas on exposing "Factory" overloads that will not throw `TargetInvocationException".

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Issue Details

---

Activator.CreateInstance() was optimized in v6 and made super fast when invoking the default constructor. However, as shown in the benchmarks below, currently calling a zero parameter constructor through Activator.CreateInstance(...) is ~1.7x faster than ConstructorInfo. Note that before the 7.0 feature to use IL emit, Activator.CreateInstance(...) used to be ~6x faster than ConstructorInfo.

|                                                                       Method |        Job |              Toolchain |       Mean |      Error |     StdDev |     Median |        Min |        Max | Ratio | RatioSD |  Gen 0 | Allocated | Alloc Ratio |
|----------------------------------------------------------------------------- |----------- |----------------------- |-----------:|-----------:|-----------:|-----------:|-----------:|-----------:|------:|--------:|-------:|----------:|------------:|
|                                       Ctor0_ActivatorCreateInstance_NoParams | Job-VAFQFP | \newinvoke\corerun.exe |   8.700 ns |  0.1857 ns |  0.1646 ns |   8.733 ns |   8.395 ns |   8.999 ns |  1.00 |    0.00 | 0.0054 |      56 B |        1.00 |
|                                                               Ctor0_NoParams | Job-VAFQFP | \newinvoke\corerun.exe |  14.928 ns |  0.5837 ns |  0.6721 ns |  14.697 ns |  14.234 ns |  16.242 ns |  1.00 |    0.00 | 0.0053 |      56 B |        1.00 |

Although Activator is faster than ConstructorInfo that only applies for cases when there is a default constructor. When there are constructor parameters, calling ConstructorInfo is up to 2x faster.

Due to the varying performance of these two APIs, reflection users that need to invoke constructors and want the maximum performance currently need to call ConstructorInfo when there are parameters and Activator when there are no parameters. This issue should make this choice go away by making ConstructorInfo the preferred API going forward for almost all cases by having ConstructorInfo call Activator for default constructors. This also avoids generating IL for these cases which can help with start-up and reduce global memory usage.

Using ConstructorInfo instead of Activator also has the advantage of forcing the caller select the appropriate constructor ahead of time, instead of auto-selecting each time the method is called by inspecting the parameters. If the caller does not know what constructor to call, then continuing to use Activator is fine.

We also need to look at normalizing the exception handling between these two APIs so they have the same Exception semantics for OutOfMemoryException.

Author:	steveharter
Assignees:	steveharter
Labels:	area-System.Reflection, tenet-performance
Milestone:	8.0.0

[steveharter]

Moving to 9.0.

Note that the existing ConstructorInfo invoke API was made ~1.2x faster with this PR: #88415 which puts it much closer to Activator.CreateInstance (minus the overhead of emit).