StatementTransform: Run an expensive invariant check slightly less often.

ICSharpCode.Decompiler/IL/Transforms/StatementTransform.cs

@@ -133,7 +133,6 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 				foreach (var transform in children)
 				{
-					Debug.Assert(block.HasFlag(InstructionFlags.EndPointUnreachable));
 					transform.Run(block, pos, ctx);
 #if DEBUG
 					block.Instructions[pos].CheckInvariant(ILPhase.Normal);
@@ -160,6 +159,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					pos--;
 				}
 			}
+			// This invariant can be surprisingly expensive to check if the block has thousands
+			// of instructions and is frequently modified by transforms (invalidating the flags each time)
+			// so we'll check this only once at the end of the block.
+			Debug.Assert(block.HasFlag(InstructionFlags.EndPointUnreachable));
 		}
 	}
 }