From 83d6818295cb337b6201fe307e15755df9dcd47f Mon Sep 17 00:00:00 2001
From: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Date: Mon, 22 May 2017 02:38:13 -0700
Subject: [PATCH] speed up 3-level page map access

There is no need to have pointer indirection for root node. This also
helps the case of early free of garbage pointer because we didn't
check root_ pointer for NULL.
---
 src/pagemap.h | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/pagemap.h b/src/pagemap.h
index 50c17db..68b2d24 100644
--- a/src/pagemap.h
+++ b/src/pagemap.h
@@ -229,7 +229,7 @@ class TCMalloc_PageMap3 {
     void* values[LEAF_LENGTH];
   };
 
-  Node* root_;                          // Root of radix tree
+  Node  root_;                          // Root of radix tree
   void* (*allocator_)(size_t);          // Memory allocator
 
   Node* NewNode() {
@@ -245,7 +245,7 @@ class TCMalloc_PageMap3 {
 
   explicit TCMalloc_PageMap3(void* (*allocator)(size_t)) {
     allocator_ = allocator;
-    root_ = NewNode();
+    memset(&root_, 0, sizeof(root_));
   }
 
   ATTRIBUTE_ALWAYS_INLINE
@@ -254,10 +254,10 @@ class TCMalloc_PageMap3 {
     const Number i2 = (k >> LEAF_BITS) & (INTERIOR_LENGTH-1);
     const Number i3 = k & (LEAF_LENGTH-1);
     if ((k >> BITS) > 0 ||
-        root_->ptrs[i1] == NULL || root_->ptrs[i1]->ptrs[i2] == NULL) {
+        root_.ptrs[i1] == NULL || root_.ptrs[i1]->ptrs[i2] == NULL) {
       return NULL;
     }
-    return reinterpret_cast<Leaf*>(root_->ptrs[i1]->ptrs[i2])->values[i3];
+    return reinterpret_cast<Leaf*>(root_.ptrs[i1]->ptrs[i2])->values[i3];
   }
 
   void set(Number k, void* v) {
@@ -265,7 +265,7 @@ class TCMalloc_PageMap3 {
     const Number i1 = k >> (LEAF_BITS + INTERIOR_BITS);
     const Number i2 = (k >> LEAF_BITS) & (INTERIOR_LENGTH-1);
     const Number i3 = k & (LEAF_LENGTH-1);
-    reinterpret_cast<Leaf*>(root_->ptrs[i1]->ptrs[i2])->values[i3] = v;
+    reinterpret_cast<Leaf*>(root_.ptrs[i1]->ptrs[i2])->values[i3] = v;
   }
 
   bool Ensure(Number start, size_t n) {
@@ -278,18 +278,18 @@ class TCMalloc_PageMap3 {
         return false;
 
       // Make 2nd level node if necessary
-      if (root_->ptrs[i1] == NULL) {
+      if (root_.ptrs[i1] == NULL) {
         Node* n = NewNode();
         if (n == NULL) return false;
-        root_->ptrs[i1] = n;
+        root_.ptrs[i1] = n;
       }
 
       // Make leaf node if necessary
-      if (root_->ptrs[i1]->ptrs[i2] == NULL) {
+      if (root_.ptrs[i1]->ptrs[i2] == NULL) {
         Leaf* leaf = reinterpret_cast<Leaf*>((*allocator_)(sizeof(Leaf)));
         if (leaf == NULL) return false;
         memset(leaf, 0, sizeof(*leaf));
-        root_->ptrs[i1]->ptrs[i2] = reinterpret_cast<Node*>(leaf);
+        root_.ptrs[i1]->ptrs[i2] = reinterpret_cast<Node*>(leaf);
       }
 
       // Advance key past whatever is covered by this leaf node
@@ -305,11 +305,11 @@ class TCMalloc_PageMap3 {
     while (k < (Number(1) << BITS)) {
       const Number i1 = k >> (LEAF_BITS + INTERIOR_BITS);
       const Number i2 = (k >> LEAF_BITS) & (INTERIOR_LENGTH-1);
-      if (root_->ptrs[i1] == NULL) {
+      if (root_.ptrs[i1] == NULL) {
         // Advance to next top-level entry
         k = (i1 + 1) << (LEAF_BITS + INTERIOR_BITS);
       } else {
-        Leaf* leaf = reinterpret_cast<Leaf*>(root_->ptrs[i1]->ptrs[i2]);
+        Leaf* leaf = reinterpret_cast<Leaf*>(root_.ptrs[i1]->ptrs[i2]);
         if (leaf != NULL) {
           for (Number i3 = (k & (LEAF_LENGTH-1)); i3 < LEAF_LENGTH; i3++) {
             if (leaf->values[i3] != NULL) {