Small clean up in y order code.

common/yorder.go

@@ -36,7 +36,11 @@ func NewYOrder(renderFn func(*Block) error, capacity int) *YOrder {
 }
 
 func (yo *YOrder) Reset() {
-	yo.blocks = yo.blocks[:0]
+	blocks := yo.blocks
+	for i := range blocks {
+		blocks[i] = nil
+	}
+	yo.blocks = blocks[:0]
 }
 
 func copyData(data []byte) []byte {
@@ -101,9 +105,11 @@ func (yo *YOrder) Push(x interface{}) {
 	yo.blocks = append(yo.blocks, x.(*Block))
 }
 
-func (yo *YOrder) Pop() (x interface{}) {
-	l := len(yo.blocks)
-	x = yo.blocks[l-1]
-	yo.blocks = yo.blocks[0 : l-1]
+func (yo *YOrder) Pop() interface{} {
+	blocks := yo.blocks
+	l := len(blocks)
+	x := blocks[l-1]
+	blocks[l-1] = nil
+	yo.blocks = blocks[:l-1]
 	return x
 }