Fix logic error and add unreachable after returns

src/librustc/middle/graph.rs

@@ -314,7 +314,7 @@ pub struct DepthFirstTraversal<'g, N:'g, E:'g> {
 impl<'g, N, E> Iterator<&'g N> for DepthFirstTraversal<'g, N, E> {
     fn next(&mut self) -> Option<&'g N> {
         while let Some(idx) = self.stack.pop() {
-            if self.visited.insert(idx.node_id()) {
+            if !self.visited.insert(idx.node_id()) {
                 continue;
             }
             self.graph.each_outgoing_edge(idx, |_, e| -> bool {

src/librustc_trans/trans/expr.rs

@@ -945,6 +945,10 @@ fn trans_rvalue_stmt_unadjusted<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                 if let &Some(ref x) = ex {
                     bcx = trans_into(bcx, &**x, Ignore);
                 }
+                // Mark the end of the block as unreachable. Once we get to
+                // a return expression, there's no more we should be doing
+                // after this.
+                Unreachable(bcx);
                 bcx
             }
         }