Fixed issue in AddCheckedBlocks that could cause variable declaration…

…s to be omitted or placed incorrectly.

ICSharpCode.Decompiler/Ast/Transforms/AddCheckedBlocks.cs

@@ -45,8 +45,20 @@ sealed class CheckedUncheckedAnnotation {
 				1. Use minimum number of checked blocks+expressions
 				2. Prefer checked expressions over checked blocks
 				3. Make the scope of checked expressions as small as possible
-				4. Make the scope of checked blocks as large as possible
+				4. Open checked blocks as late as possible, and close checked blocks as late as possible
 				(where goal 1 has the highest priority)
+				
+				Goal 4a (open checked blocks as late as possible) is necessary so that we don't move variable declarations
+				into checked blocks, as the variable might still be used after the checked block.
+				 (this could cause DeclareVariables to omit the variable declaration, producing incorrect code)
+				Goal 4b (close checked blocks as late as possible) makes the code look nicer in this case:
+				   checked {
+				   	int c = a + b;
+						int r = a + c;
+				   	return r;
+				   }
+				If the checked block was closed as early as possible, the variable r would have to be declared outside
+				 (this would work, but look badly)
 		 */
 
 		#region struct Cost
@@ -257,7 +269,7 @@ Result GetResultFromBlock(BlockStatement block)
 
 			Statement statement = block.Statements.FirstOrDefault();
 			while (true) {
-				// Blocks can be closed 'for free'. We use '<=' so that blocks are closed as late as possible (goal 4)
+				// Blocks can be closed 'for free'. We use '<=' so that blocks are closed as late as possible (goal 4b)
 				if (costCheckedContextUncheckedBlockOpen <= costCheckedContext) {
 					costCheckedContext = costCheckedContextUncheckedBlockOpen;
 					nodesCheckedContext = nodesCheckedContextUncheckedBlockOpen + new InsertedBlock(uncheckedBlockStart, statement, false);
@@ -268,13 +280,13 @@ Result GetResultFromBlock(BlockStatement block)
 				}
 				if (statement == null)
 					break;
-				// Now try opening blocks. We use '<' so that blocks are opened as early as possible. (goal 4)
-				if (costCheckedContext + new Cost(1, 0) < costCheckedContextUncheckedBlockOpen) {
+				// Now try opening blocks. We use '<=' so that blocks are opened as late as possible. (goal 4a)
+				if (costCheckedContext + new Cost(1, 0) <= costCheckedContextUncheckedBlockOpen) {
 					costCheckedContextUncheckedBlockOpen = costCheckedContext + new Cost(1, 0);
 					nodesCheckedContextUncheckedBlockOpen = nodesCheckedContext;
 					uncheckedBlockStart = statement;
 				}
-				if (costUncheckedContext + new Cost(1, 0) < costUncheckedContextCheckedBlockOpen) {
+				if (costUncheckedContext + new Cost(1, 0) <= costUncheckedContextCheckedBlockOpen) {
 					costUncheckedContextCheckedBlockOpen = costUncheckedContext + new Cost(1, 0);
 					nodesUncheckedContextCheckedBlockOpen = nodesUncheckedContext;
 					checkedBlockStart = statement;