To reproduce:

1. Download attached project "Devirtualization_test.zip" and open in Unity
2. Open "SampleScene" scene
3. Set Scripting Backend to IL2CPP
4. Build for iOS or Android
5. Go to "Devirtualization_test/Temp/il2cppOutput/il2cppOutput" and open "Bulk_Assembly-CSharp_0.cpp"

Expected behaviour:
Call to cow.Speak() should read: `String_t* L_18 = Cow_Speak_m1607867742(L_16, /*hidden argument*/NULL);`

Actual behaviour:
Call to cow.Speak() reads: String_t* L_18 = VirtFuncInvoker0< String_t* >::Invoke(4 /* System.String Animal::Speak() */, L_17);

Notes:
- This issue does not reproduce on Windows Standalone and macOS Standalone
- This issue appears only on iOS and Android (IL2CPP)
- You can remove the "sealed" keyword from the Cow class in "FarmAbstract", repeat steps 1 - 5 and notice results are identical
- Could not check on Unity 2017.3 because project becomes corrupted
- Could not check on Unity 2019.1 because of this issue:
https://issuetracker.unity3d.com/issues/crash-on-mono-method-to-ir-when-trying-to-build-after-the-project-was-created-on-older-version-of-unity-net3-dot-5

Reproduced on Unity 2017.4.0f1, 2017.4.15f1, 2018.1.9f2, 2018.2.16f1 and 2018.3.0b10