Prevent unnecessary shared_ptr copies by accepting a value in SHAMapInnerNode::setChild (#4266)

* Do a move instead of a copy in `SHAMapInnerNode::setChild`

* Create the value directly in the call

Author: greg7mdp

src/ripple/shamap/SHAMapInnerNode.h

@@ -147,7 +147,7 @@ class SHAMapInnerNode final : public SHAMapTreeNode,
     getChildHash(int m) const;
 
     void
-    setChild(int m, std::shared_ptr<SHAMapTreeNode> const& child);
+    setChild(int m, std::shared_ptr<SHAMapTreeNode> child);
 
     void
     shareChild(int m, std::shared_ptr<SHAMapTreeNode> const& child);

src/ripple/shamap/impl/SHAMap.cpp

@@ -118,7 +118,7 @@ SHAMap::dirtyUp(
         assert(branch >= 0);
 
         node = unshareNode(std::move(node), nodeID);
-        node->setChild(branch, child);
+        node->setChild(branch, std::move(child));
 
         child = std::move(node);
     }
@@ -718,7 +718,7 @@ SHAMap::delItem(uint256 const& id)
         stack.pop();
 
         node = unshareNode(std::move(node), nodeID);
-        node->setChild(selectBranch(nodeID, id), prevNode);
+        node->setChild(selectBranch(nodeID, id), std::move(prevNode));
 
         if (!nodeID.isRoot())
         {
@@ -795,8 +795,7 @@ SHAMap::addGiveItem(SHAMapNodeType type, std::shared_ptr<SHAMapItem const> item)
         auto inner = std::static_pointer_cast<SHAMapInnerNode>(node);
         int branch = selectBranch(nodeID, tag);
         assert(inner->isEmptyBranch(branch));
-        auto newNode = makeTypedLeaf(type, std::move(item), cowid_);
-        inner->setChild(branch, newNode);
+        inner->setChild(branch, makeTypedLeaf(type, std::move(item), cowid_));
     }
     else
     {

src/ripple/shamap/impl/SHAMapInnerNode.cpp

@@ -284,7 +284,7 @@ SHAMapInnerNode::getString(const SHAMapNodeID& id) const
 
 // We are modifying an inner node
 void
-SHAMapInnerNode::setChild(int m, std::shared_ptr<SHAMapTreeNode> const& child)
+SHAMapInnerNode::setChild(int m, std::shared_ptr<SHAMapTreeNode> child)
 {
     assert((m >= 0) && (m < branchFactor));
     assert(cowid_ != 0);
@@ -310,7 +310,7 @@ SHAMapInnerNode::setChild(int m, std::shared_ptr<SHAMapTreeNode> const& child)
         auto const childIndex = *getChildIndex(m);
         auto [_, hashes, children] = hashesAndChildren_.getHashesAndChildren();
         hashes[childIndex].zero();
-        children[childIndex] = child;
+        children[childIndex] = std::move(child);
     }
 
     hash_.zero();