Hybrid AOT is not working for some generic methods

[filipnavara]

Steps to Reproduce

1. Open the attached LurchTableTest project
   LurchTableTest.zip
2. Build the Release configuration
3. Run the resulting executable "bin/Release/LurchTableTest.app/Contents/MacOS/LurchTableTest"

Current Behavior

The application crashes because it couldn't locate an AOTed method and the IL code is stripped.

[ERROR] FATAL UNHANDLED EXCEPTION: System.InvalidProgramException: Invalid IL code in System.Drawing.LurchTable`2<string, LurchTableTest.MainClass/Entry>:InternalInsert<System.Drawing.LurchTable`2/AddInfo<string, LurchTableTest.MainClass/Entry>> (int,string,int&,System.Drawing.LurchTable`2/AddInfo<string, LurchTableTest.MainClass/Entry>&): IL_0000: ret       


  at System.Drawing.LurchTable`2[TKey,TValue].Insert[T] (TKey key, T& value) [0x0002c] in <4bca31772cc24f93bb11f33848657c2b>:0 
  at (wrapper unknown) System.Object.gsharedvt_in()
  at System.Drawing.LurchTable`2[TKey,TValue].set_Item (TKey key, TValue value) [0x0001a] in <4bca31772cc24f93bb11f33848657c2b>:0 
  at LurchTableTest.MainClass.Main (System.String[] args) [0x0002c] in <4bca31772cc24f93bb11f33848657c2b>:0 

Expected Behavior

The program should not crash.

On which platforms did you notice this

[x] macOS
[ ] Linux
[ ] Windows

Version Used:

Mono JIT compiler version 5.8.0.123 (2017-10/38502063cac Thu Feb 1 12:58:29 EST 2018)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
TLS: normal
SIGSEGV: altstack
Notification: kqueue
Architecture: amd64
Disabled: none
Misc: softdebug
LLVM: yes(3.6.0svn-mono-master/8b1520c8aae)
GC: sgen (concurrent by default)

[marek-safar]

/cc @vargaz any ideas, it looks like we AOT less than what we should in this specific case

[vargaz]

The LurchTable class uses some complicated generics with valuetypes, so we fail back to valuetype based sharing, which still has some restrictions around constrained calls, i.e. this one in

  .method private hidebysig instance valuetype System.Drawing.LurchTable`2/InsertResult<!TKey,!TValue> 
          InternalInsert<(class System.Drawing.ICreateOrUpdateValue`2<!TKey,!TValue>) T>(int32 hash,
                                                                                         !TKey key,
                                                                                         [out] int32& added,
                                                                                         !!T& 'value') cil managed
:

    IL_009d:  ldarg.s    'value'
    IL_009f:  ldarg.2
    IL_00a0:  ldloca.s   V_1
    IL_00a2:  constrained. !!T
    IL_00a8:  callvirt   instance bool class System.Drawing.IUpdateValue`2<!TKey,!TValue>::UpdateValue(!0,
                                                                                                       !1&)

[filipnavara]

Are the restrictions documented somewhere? I don't see a big problem with the fact that the AOT fails, but there's no warning/error. Neither is there an option to keep the IL unstripped for the problematic calls.

[vargaz]

The restrictions are hard to describe at a user level. We should probably keep the IL for these methods.

[filipnavara]

I don't quite understand why
InsertResult Insert<T>(TKey key, ref T value) where T : ICreateOrUpdateValue<TKey, TValue>
works and
InsertResult InternalInsert<T>(int hash, TKey key, out int added, ref T value) where T : ICreateOrUpdateValue<TKey, TValue>
doesn't. The constraints look identical to me.

[vargaz]

The problem is the AddInfo struct, generics + structs don't work very well in an AOT environment. As a workaround, I'd suggest getting rid of it and passing the 2 parameters normally.

[marek-safar]

/cc @chamons