Remove "memcpy common section to next node"

Do it in a simpler, more robust/type safe way

CMakeLists.txt

@@ -102,8 +102,6 @@ option(DISABLE_TSAN "Disable TSAN" OFF)
 # https://valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.clientreq
 include_directories(SYSTEM ${CMAKE_CURRENT_SOURCE_DIR}/third_party/valgrind)
 
-add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-Wno-invalid-offsetof>)
-
 if(APPLE)
   add_link_options(-Wl,-dead_strip)
 else()

ConflictSet.cpp

@@ -281,7 +281,6 @@ private:
 
 struct Node {
 
-  /* begin section that's copied to the next node */
   union {
     Entry entry;
     /* Set to the forwarding point for this node if releaseDeferred is set */
@@ -292,7 +291,6 @@ struct Node {
   int16_t numChildren;
   bool entryPresent;
   uint8_t parentsIndex;
-  /* end section that's copied to the next node */
 
   /* If set, this node has been replaced and the next node in the forwarding
    * chain is `forwardTo`*/
@@ -322,10 +320,6 @@ Type TaggedNodePointer::getType() {
   return Type(p & uintptr_t(7));
 }
 
-constexpr int kNodeCopyBegin = offsetof(Node, entry);
-constexpr int kNodeCopySize =
-    offsetof(Node, parentsIndex) + sizeof(Node::parentsIndex) - kNodeCopyBegin;
-
 // copyChildrenAndKeyFrom is responsible for copying all
 // public members of Node, copying the partial key, logically copying the
 // children (converting representation if necessary), and updating all the
@@ -431,27 +425,35 @@ struct Node256 : Node {
   size_t size() const { return sizeof(Node256) + getCapacity(); }
 };
 
+template <class To, class From>
+void copyCommon(To &to, const From &from)
+  requires(std::is_base_of_v<Node, To> && std::is_base_of_v<Node, From>)
+{
+  memcpy(&to.entry, &from.entry, sizeof(from.entry));
+  to.parent = from.parent;
+  to.partialKeyLen = from.partialKeyLen;
+  to.numChildren = from.numChildren;
+  to.entryPresent = from.entryPresent;
+  to.parentsIndex = from.parentsIndex;
+}
+
 inline void Node0::copyChildrenAndKeyFrom(const Node0 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   memcpy(partialKey(), &other + 1, partialKeyLen);
 }
 
 inline void Node0::copyChildrenAndKeyFrom(const Node3 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   memcpy(partialKey(), &other + 1, partialKeyLen);
 }
 
 inline void Node3::copyChildrenAndKeyFrom(const Node0 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   memcpy(partialKey(), &other + 1, partialKeyLen);
 }
 
 inline void Node3::copyChildrenAndKeyFrom(const Node3 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   memcpy(index, other.index, kMaxNodes);
   memcpy(children, other.children, kMaxNodes * sizeof(children[0])); // NOLINT
   memcpy(childMaxVersion, other.childMaxVersion,
@@ -464,8 +466,7 @@ inline void Node3::copyChildrenAndKeyFrom(const Node3 &other) {
 }
 
 inline void Node3::copyChildrenAndKeyFrom(const Node16 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   memcpy(index, other.index, kMaxNodes);
   memcpy(children, other.children, kMaxNodes * sizeof(children[0])); // NOLINT
   memcpy(childMaxVersion, other.childMaxVersion,
@@ -478,8 +479,7 @@ inline void Node3::copyChildrenAndKeyFrom(const Node16 &other) {
 }
 
 inline void Node16::copyChildrenAndKeyFrom(const Node3 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   memcpy(index, other.index, Node3::kMaxNodes);
   memcpy(children, other.children,
          Node3::kMaxNodes * sizeof(children[0])); // NOLINT
@@ -494,8 +494,7 @@ inline void Node16::copyChildrenAndKeyFrom(const Node3 &other) {
 }
 
 inline void Node16::copyChildrenAndKeyFrom(const Node16 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   memcpy(index, other.index, sizeof(index));
   for (int i = 0; i < numChildren; ++i) {
     children[i] = other.children[i];
@@ -507,8 +506,7 @@ inline void Node16::copyChildrenAndKeyFrom(const Node16 &other) {
 }
 
 inline void Node16::copyChildrenAndKeyFrom(const Node48 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   int i = 0;
   other.bitSet.forEachSet([&](int c) {
     // Suppress a false positive -Waggressive-loop-optimizations warning
@@ -525,8 +523,7 @@ inline void Node16::copyChildrenAndKeyFrom(const Node48 &other) {
 }
 
 inline void Node48::copyChildrenAndKeyFrom(const Node16 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   assert(numChildren == Node16::kMaxNodes);
   memset(index, -1, sizeof(index));
   memset(children, 0, sizeof(children));
@@ -552,8 +549,7 @@ inline void Node48::copyChildrenAndKeyFrom(const Node16 &other) {
 }
 
 inline void Node48::copyChildrenAndKeyFrom(const Node48 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   bitSet = other.bitSet;
   memcpy(index, other.index, sizeof(index));
   memset(children, 0, sizeof(children));
@@ -573,8 +569,7 @@ inline void Node48::copyChildrenAndKeyFrom(const Node48 &other) {
 }
 
 inline void Node48::copyChildrenAndKeyFrom(const Node256 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   memset(index, -1, sizeof(index));
   memset(children, 0, sizeof(children));
   const auto z = InternalVersionT::zero;
@@ -601,8 +596,7 @@ inline void Node48::copyChildrenAndKeyFrom(const Node256 &other) {
 }
 
 inline void Node256::copyChildrenAndKeyFrom(const Node48 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   bitSet = other.bitSet;
   memset(children, 0, sizeof(children));
   const auto z = InternalVersionT::zero;
@@ -624,8 +618,7 @@ inline void Node256::copyChildrenAndKeyFrom(const Node48 &other) {
 }
 
 inline void Node256::copyChildrenAndKeyFrom(const Node256 &other) {
-  memcpy((char *)this + kNodeCopyBegin, (char *)&other + kNodeCopyBegin,
-         kNodeCopySize);
+  copyCommon(*this, other);
   memset(children, 0, sizeof(children));
   const auto z = InternalVersionT::zero;
   for (auto &v : childMaxVersion) {