Fix assertion in ReduceNestingTransform: after copying the exitInst, it was possible that the old copy of the exitInst became unreachable.

ICSharpCode.Decompiler/IL/ControlFlow/ConditionDetection.cs

@@ -354,7 +354,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			//assert then block terminates
 			var trueExitInst = GetExit(ifInst.TrueInst);
 			var exitInst = GetExit(block);
-			context.Step("Negate if for desired branch "+trueExitInst, ifInst);
+			context.Step($"InvertIf at IL_{ifInst.StartILOffset:x4}", ifInst);
 			
 			//if the then block terminates, else blocks are redundant, and should not exist
 			Debug.Assert(IsEmpty(ifInst.FalseInst));

ICSharpCode.Decompiler/IL/Transforms/ReduceNestingTransform.cs

@@ -194,6 +194,18 @@ namespace ICSharpCode.Decompiler.IL
 				// if (cond) { ...; exit; }
 				// ...; exit;
 				EnsureEndPointUnreachable(ifInst.TrueInst, exitInst);
+				if (ifInst.FalseInst.HasFlag(InstructionFlags.EndPointUnreachable)) {
+					Debug.Assert(ifInst.HasFlag(InstructionFlags.EndPointUnreachable));
+					Debug.Assert(ifInst.Parent == block);
+					int removeAfter = ifInst.ChildIndex + 1;
+					if (removeAfter < block.Instructions.Count) {
+						// Remove all instructions that ended up dead
+						// (this should just be exitInst itself)
+						Debug.Assert(block.Instructions.SecondToLastOrDefault() == ifInst);
+						Debug.Assert(block.Instructions.Last() == exitInst);
+						block.Instructions.RemoveRange(removeAfter, block.Instructions.Count - removeAfter);
+					}
+				}
 				ExtractElseBlock(ifInst);
 				ifInst = elseIfInst;
 			} while (ifInst != null);