cgt.un is invalid for comparing a void* with a null type

[Perksey]

Steps to Reproduce

1. Create a method with an is not null comparison on a void* and compile with Debug configuration using the latest Roslyn.
2. Attempt to use this in a Mono-powered application
3. Observe an InvalidProgramException

• The actual problem in context: https://github.com/Ultz/Silk.NET/blob/master/src/Windowing/Silk.NET.SDL/SdlContext.cs
• The related downstream issue: TriangleDroid test app crashes while trying to get GL context via SDL2 dotnet/Silk.NET#389

The generated IL for AssertNotCreated:

nop
ldarg.0      // this
ldfld        void* Silk.NET.SDL.SdlContext::_ctx
ldnull
cgt.un
stloc.0      // V_0
ldloc.0      // V_0
brfalse.s    IL_001a
nop
ldstr        "Context created already."
newobj       instance void [netstandard]System.InvalidOperationException::.ctor(string)
throw
ret

Current Behavior

System.InvalidProgramException: Invalid IL code in Silk.NET.SDL.SdlContext:AssertNotCreated (): IL_0008: cgt.un
  at Silk.NET.SDL.SdlContext.set_Window (Silk.NET.SDL.Window* value) [0x00001] in E:\Code\Silk.NET\src\Windowing\Silk.NET.SDL\SdlContext.cs:48 
  at Silk.NET.SDL.SdlContext..ctor (Silk.NET.SDL.Sdl sdl, Silk.NET.SDL.Window* window, Silk.NET.Core.Contexts.IGLContextSource source, System.ValueTuple`2[Silk.NET.SDL.GLattr,System.Int32][] attributes) [0x0000f] in E:\Code\Silk.NET\src\Windowing\Silk.NET.SDL\SdlContext.cs:32 
  at Silk.NET.Windowing.Sdl.SdlView.get_GLContext () [0x00000] in E:\Code\Silk.NET\src\Windowing\Silk.NET.Windowing.Sdl\SdlView.cs:58 
  at Silk.NET.Windowing.Sdl.SdlView.CoreInitialize (Silk.NET.Windowing.ViewOptions opts, System.Nullable`1[T] additionalFlags, System.Nullable`1[T] x, System.Nullable`1[T] y, System.Nullable`1[T] w, System.Nullable`1[T] h, System.String title, Silk.NET.Core.Contexts.IGLContext sharedContext) [0x0012b] in E:\Code\Silk.NET\src\Windowing\Silk.NET.Windowing.Sdl\SdlView.cs:161 
  at Silk.NET.Windowing.Sdl.SdlView.CoreInitialize (Silk.NET.Windowing.ViewOptions opts) [0x00000] in E:\Code\Silk.NET\src\Windowing\Silk.NET.Windowing.Sdl\SdlView.cs:100 
  at Silk.NET.Windowing.Internals.ViewImplementationBase.Initialize () [0x00011] in E:\Code\Silk.NET\src\Windowing\Silk.NET.Windowing.Common\Internals\ViewImplementationBase.cs:97 
  at Silk.NET.Windowing.WindowExtensions.Run (Silk.NET.Windowing.IView view) [0x0000e] in E:\Code\Silk.NET\src\Windowing\Silk.NET.Windowing.Common\WindowExtensions.cs:47 
  at Triangle.Program.Main (System.String[] args) [0x000d7] in E:\Code\Silk.NET\src\Lab\Triangle\Program.cs:58 
  at TriangleDroid.MainActivity.OnRun () [0x00016] in E:\Code\Silk.NET\src\Lab\TriangleDroid\MainActivity.cs:20 
  at Silk.NET.Windowing.Sdl.Android.SilkActivity.Run () [0x00001] in E:\Code\Silk.NET\src\Windowing\Android\Silk.NET.Windowing.Sdl.Android\Additions\SilkActivity.cs:65 
  at Silk.NET.Windowing.Sdl.Android.SilkActivity.Main () [0x00019] in E:\Code\Silk.NET\src\Windowing\Android\Silk.NET.Windowing.Sdl.Android\Additions\SilkActivity.cs:45 
  at (wrapper native-to-managed) Silk.NET.Windowing.Sdl.Android.SilkActivity.Main()

Expected Behavior

The IL is valid and Mono is able to run the application.

On which platforms did you notice this

[ ] macOS
[x] Linux
[ ] Windows

Version Used:

Awaiting response from downstream user.

[Perksey]

Apparently one of our community contributors has already filed this.

Duplicate of #20709.

Closing this one.