Avoid allocation in object construction by reflection

[Yves57]

During an analysis about memory allocations in an ASP.NET Core service (github/dotnet/extensions#693), I have found that there is maybe an optimization in (at least) object construction by reflection.
When constructing an object by reflection, the method MethodBase.CheckArguments() seems to duplicate the parameters (copyOfParameters) because they may be changed by CheckValue(). But this method seems to just return the value as-is in the normal cases. So isn't it possible to do a "lazy allocation" only if necessary?

/cc @pakrym

[jkotas]

because they may be changed by CheckValue()

It is not just because of they may be changed by CheckValue(). It is also protect against cases where the value is change by the caller (e.g. on a different thread) that would violate type safety invariant in the code that follows.

Having said this, there are ways how to optimize this. It just is not as simple as allocating the array lazily.

[Yves57]

Got it!
But the external array modification is probably a very uncommon case. The ASP.NET Core ActivatorUtilities.CreateInstance() is typically a case where this protection seems not useful. Maybe create a new flag BindingFlags.ThreadSafeParameters set by the caller?

[jkotas]

I do not think a new flag is necessary. It should be possible to optimize this for everybody without compromising type safety and security characteristics provided by the current implementation.

[Yves57]

I hope this optimization will be developped! I want to see what kind of trick can avoid this allocation! 😃

[benaadams]

Could change RuntimeMethodHandle::InvokeMethod to take a Span rather than a regular array, then copy to a stack array instead; though not sure there are any examples of passing a Span the the vm

[steveharter]

Moving to future