Bug 1402284 - Make RedBlackTree::{Insert,Remove} work when the type has a constructor. r=njn

RedBlackTree::{Insert,Remove} allocate an object on the stack for its
RedBlackTreeNode, and that shouldn't have side effects if the type
happens to have a constructor. This will allow to add constructors to
some of the mozjemalloc types.

--HG--
extra : rebase_source : 14dbb7d73c86921701d83156186df5d645530dda

memory/build/rb.h

@@ -67,6 +67,7 @@
 #ifndef RB_H_
 #define RB_H_
 
+#include "mozilla/Alignment.h"
 #include "Utils.h"
 
 enum NodeColor
@@ -327,14 +328,16 @@ private:
 
   void Insert(TreeNode* aNode)
   {
-    TreeNode rbp_i_s;
+    // rbp_i_s is only used as a placeholder for its RedBlackTreeNode. Use
+    // AlignedStorage2 to avoid running the TreeNode base class constructor.
+    mozilla::AlignedStorage2<TreeNode> rbp_i_s;
     TreeNode *rbp_i_g, *rbp_i_p, *rbp_i_c, *rbp_i_t, *rbp_i_u;
     int rbp_i_cmp = 0;
     rbp_i_g = nullptr;
-    rbp_i_s.SetLeft(mRoot);
-    rbp_i_s.SetRight(nullptr);
-    rbp_i_s.SetColor(NodeColor::Black);
-    rbp_i_p = &rbp_i_s;
+    rbp_i_p = rbp_i_s.addr();
+    rbp_i_p->SetLeft(mRoot);
+    rbp_i_p->SetRight(nullptr);
+    rbp_i_p->SetColor(NodeColor::Black);
     rbp_i_c = mRoot;
     /* Iteratively search down the tree for the insertion point,
      * splitting 4-nodes as they are encountered. At the end of each
@@ -405,19 +408,21 @@ private:
       rbp_i_p->SetLeft(aNode);
     }
     /* Update the root and make sure that it is black. */
-    mRoot = rbp_i_s.Left();
+    mRoot = rbp_i_s.addr()->Left();
     mRoot->SetColor(NodeColor::Black);
   }
 
   void Remove(TreeNode* aNode)
   {
-    TreeNode rbp_r_s;
+    // rbp_r_s is only used as a placeholder for its RedBlackTreeNode. Use
+    // AlignedStorage2 to avoid running the TreeNode base class constructor.
+    mozilla::AlignedStorage2<TreeNode> rbp_r_s;
     TreeNode *rbp_r_p, *rbp_r_c, *rbp_r_xp, *rbp_r_t, *rbp_r_u;
     int rbp_r_cmp;
-    rbp_r_s.SetLeft(mRoot);
-    rbp_r_s.SetRight(nullptr);
-    rbp_r_s.SetColor(NodeColor::Black);
-    rbp_r_p = &rbp_r_s;
+    rbp_r_p = rbp_r_s.addr();
+    rbp_r_p->SetLeft(mRoot);
+    rbp_r_p->SetRight(nullptr);
+    rbp_r_p->SetColor(NodeColor::Black);
     rbp_r_c = mRoot;
     rbp_r_xp = nullptr;
     /* Iterate down the tree, but always transform 2-nodes to 3- or
@@ -577,7 +582,7 @@ private:
       }
     }
     /* Update root. */
-    mRoot = rbp_r_s.Left();
+    mRoot = rbp_r_s.addr()->Left();
   }
 
   TreeNode* RotateLeft(TreeNode* aNode)