Speed up DfgGraph::addGraph

Append whole lists in one go, rather than going item by item.

src/V3Dfg.cpp

@@ -40,10 +40,22 @@ DfgGraph::~DfgGraph() {
 }
 
 void DfgGraph::addGraph(DfgGraph& other) {
-    other.forEachVertex([&](DfgVertex& vtx) {
-        other.removeVertex(vtx);
-        this->addVertex(vtx);
-    });
+    m_size += other.m_size;
+    other.m_size = 0;
+
+    const auto moveVertexList = [this](V3List<DfgVertex*>& src, V3List<DfgVertex*>& dst) {
+        if (DfgVertex* vtxp = src.begin()) {
+            vtxp->m_verticesEnt.moveAppend(src, dst, vtxp);
+            do {
+                vtxp->m_graphp = this;
+                vtxp = vtxp->verticesNext();
+            } while (vtxp);
+        }
+    };
+
+    moveVertexList(other.m_varVertices, m_varVertices);
+    moveVertexList(other.m_constVertices, m_constVertices);
+    moveVertexList(other.m_opVertices, m_opVertices);
 }
 
 std::vector<std::unique_ptr<DfgGraph>> DfgGraph::splitIntoComponents(std::string label) {

src/V3Dfg.h

@@ -536,6 +536,7 @@ public:
 //------------------------------------------------------------------------------
 
 void DfgGraph::addVertex(DfgVertex& vtx) {
+    // Note: changes here need to be replicated in DfgGraph::addGraph
     ++m_size;
     if (vtx.is<DfgConst>()) {
         vtx.m_verticesEnt.pushBack(m_constVertices, &vtx);
@@ -548,6 +549,7 @@ void DfgGraph::addVertex(DfgVertex& vtx) {
 }
 
 void DfgGraph::removeVertex(DfgVertex& vtx) {
+    // Note: changes here need to be replicated in DfgGraph::addGraph
     --m_size;
     if (vtx.is<DfgConst>()) {
         vtx.m_verticesEnt.unlink(m_constVertices, &vtx);

src/V3List.h

@@ -119,6 +119,23 @@ public:
         }
         m_prevp = m_nextp = nullptr;
     }
+    // Remove all nodes from 'oldListr', append them to 'newListr'. 'this' must be a member of the
+    // object at 'selfp', and 'selfp' must be the head of the list in 'oldListr'.
+    void moveAppend(V3List<T>& oldListr, V3List<T>& newListr, T selfp) {
+        UASSERT(selfp == oldListr.m_headp, "Must be head of list to use 'moveAppend'");
+        const size_t offset = (size_t)(uint8_t*)(this) - (size_t)(uint8_t*)(selfp);
+        const T headp = selfp;
+        const T tailp = oldListr.m_tailp;
+        oldListr.reset();
+        if (newListr.empty()) {
+            newListr.m_headp = headp;
+            newListr.m_tailp = tailp;
+        } else {
+            baseToListEnt(newListr.m_tailp, offset)->m_nextp = headp;
+            m_prevp = newListr.m_tailp;
+            newListr.m_tailp = tailp;
+        }
+    }
 };
 
 //============================================================================