Add an analysis on memory usage in static asserts

CC #9

ConflictSet.cpp

@@ -247,6 +247,19 @@ struct Node256 : Node {
   uint8_t *partialKey() { return (uint8_t *)(this + 1); }
 };
 
+// Bound memory usage following the analysis in the ART paper
+
+constexpr int kBytesPerKey = 86;
+constexpr int kMinChildrenNode4 = 2;
+constexpr int kMinChildrenNode16 = 5;
+constexpr int kMinChildrenNode48 = 17;
+constexpr int kMinChildrenNode256 = 49;
+
+static_assert(sizeof(Node256) < kMinChildrenNode256 * kBytesPerKey);
+static_assert(sizeof(Node48) < kMinChildrenNode48 * kBytesPerKey);
+static_assert(sizeof(Node16) < kMinChildrenNode16 * kBytesPerKey);
+static_assert(sizeof(Node4) < kMinChildrenNode4 * kBytesPerKey);
+
 // Bounds memory usage in free list, but does not account for memory for partial
 // keys.
 template <class T, size_t kMemoryBound = (1 << 20)>
@@ -332,8 +345,7 @@ uint8_t *Node::partialKey() {
   case Type::Node256:
     return ((Node256 *)this)->partialKey();
   }
-  __builtin_unreachable();
+  __builtin_unreachable(); // GCOVR_EXCL_LINE
-  ; // GCOVR_EXCL_LINE
 }
 
 struct NodeAllocators {
@@ -526,12 +538,6 @@ int getChildGeq(Node *self, int child) {
   return -1;
 }
 
-void setChildrenParents(Node4 *n) {
-  for (int i = 0; i < n->numChildren; ++i) {
-    n->children[i].child->parent = n;
-  }
-}
-
 void setChildrenParents(Node16 *n) {
   for (int i = 0; i < n->numChildren; ++i) {
     n->children[i].child->parent = n;