Add Rethrow and Fix Exn (#208)

* partial progress

* progress

* progress

* progress

* fix

* add another example

* further progress

* formatting fix

* fixes

* undo removal of comment

* example null deref

* comment edit

* progress

* progress

* fix

* add ldlen test

* add unit test for this

* minor edits

* fix test

* edit test

* fix

* bug fix

* updated expected counts

* progress

* translation and tests

* bug fix

* add constrained

* progress

* write warning instead

* bug fix

* fix bug

* undo debug stuff

* typo

* fix

* remove stash markers

* testclass introduction of bug fix

* doc fix

* undo regular control flow from throw through finally

* remove unecessary method

* add ldvirtftn

* remove indent

---------

Co-authored-by: Xiaoyu Liu <lixiaoyu@microsoft.com>

Cilsil.Test/Assets/TestClass.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation.
+// Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 using System;
 using System.IO;

Cilsil/Cil/Parsers/CallParser.cs

@@ -67,7 +67,7 @@ namespace Cilsil.Cil.Parsers
                 // case.
                 if (!(callArgs[0].Type is Tfun methodType))
                 {
-                    Log.WriteError("Unexpected arg on stack: expected function");
+                    Log.WriteWarning("Unexpected arg on stack: expected function");
                     return false;
                 }
                 else

Cilsil/Services/CfgParserService.cs

@@ -199,6 +199,14 @@ namespace Cilsil.Services
                     programState.PushInstruction(methodBody.Instructions.First(), initNode);
                     do
                     {
+                        if (programState.IsTopSnapshotInstructionNull())
+                        {
+                            Log.WriteWarning("Top instruction is null; terminating translation.");
+                            Log.RecordUnfinishedMethod(method.GetCompatibleFullName(),
+                                                       method.Body.Instructions.Count);
+                            translationUnfinished = true;
+                            break;
+                        }
                         iterationCount++;
                         var nextInstruction = programState.PopInstruction();
                         // Checks if there is a node for the offset that we can reuse.

Cilsil/Utils/MethodExceptionHandlers.cs

@@ -41,23 +41,25 @@ namespace Cilsil.Utils
             new Dictionary<Instruction, ExceptionHandler>();
 
         /// <summary>
-        /// Maps offsets within try-blocks of try-catch to the corresponding catch handler set.
+        /// Maps offsets within try-blocks of try-catch to the corresponding catch handler set and
+        /// the length of the try.
         /// </summary>
         public readonly Dictionary<int, 
                                    (List<ExceptionHandlerNode>, int)> TryOffsetToCatchHandlers;
 
         /// <summary>
-        /// Maps offsets within try-blocks of try-finally to the corresponding finally handler.
+        /// Maps offsets within try-blocks of try-finally to the corresponding finally handler and
+        /// the length of the try.
         /// </summary>
         public readonly Dictionary<int, (ExceptionHandler, int)> TryOffsetToFinallyHandler;
 
         /// <summary>
-        /// Maps offsets within catch-blocks to the corresponding catch handler.
+        /// Maps offsets within catch-blocks to the corresponding catch handler and its length.
         /// </summary>
         public readonly Dictionary<int, (ExceptionHandlerNode, int)> CatchOffsetToCatchHandler;
 
         /// <summary>
-        /// Maps offsets within finally-blocks to the corresponding finally handler and the .
+        /// Maps offsets within finally-blocks to the corresponding finally handler and its length.
         /// </summary>
         public readonly Dictionary<int, (ExceptionHandler, int)> FinallyOffsetToFinallyHandler;
         #endregion

Cilsil/Utils/ProgramState.cs

@@ -458,6 +458,15 @@ namespace Cilsil.Utils
                 });
         }
 
+        /// <summary>
+        /// Checks null-state of the top snapshot instruction of the stack.
+        /// </summary>
+        /// <returns><c>True</c> if instruction null; <c>false</c> otherwise.</returns>
+        public bool IsTopSnapshotInstructionNull()
+        {
+            return InstructionsStack.Peek().Instruction == null;
+        }
+
         /// <summary>
         /// Pops an instruction to be parsed.
         /// </summary>