Improve next{Physical,Logical} codegen more

ConflictSet.cpp

@@ -1281,6 +1281,41 @@ Node *getChildGeq(Node *self, int child) {
   }
 }
 
+Node *getFirstChild(Node0 *) { return nullptr; }
+Node *getFirstChild(Node3 *self) {
+  return self->numChildren == 0 ? nullptr : self->children[0];
+}
+Node *getFirstChild(Node16 *self) {
+  return self->numChildren == 0 ? nullptr : self->children[0];
+}
+Node *getFirstChild(Node48 *self) {
+  int index = self->index[self->bitSet.firstSetGeq(0)];
+  return index < 0 ? nullptr : self->children[index];
+}
+Node *getFirstChild(Node256 *self) {
+  return self->children[self->bitSet.firstSetGeq(0)];
+}
+
+Node *getFirstChild(Node *self) {
+  // Only require that the node-specific overloads are covered
+  // GCOVR_EXCL_START
+  switch (self->getType()) {
+  case Type_Node0:
+    return getFirstChild(static_cast<Node0 *>(self));
+  case Type_Node3:
+    return getFirstChild(static_cast<Node3 *>(self));
+  case Type_Node16:
+    return getFirstChild(static_cast<Node16 *>(self));
+  case Type_Node48:
+    return getFirstChild(static_cast<Node48 *>(self));
+  case Type_Node256:
+    return getFirstChild(static_cast<Node256 *>(self));
+  default:
+    __builtin_unreachable();
+  }
+  // GCOVR_EXCL_STOP
+}
+
 // Precondition: self has a child
 Node *getFirstChildExists(Node3 *self) {
   assert(self->numChildren > 0);
@@ -1559,36 +1594,45 @@ TaggedNodePointer &getOrCreateChild(TaggedNodePointer &self,
 }
 
 Node *nextPhysical(Node *node) {
-  int index = -1;
+  auto nextChild = getFirstChild(node);
+  if (nextChild != nullptr) {
+    return nextChild;
+  }
   for (;;) {
-    auto nextChild = getChildGeq(node, index + 1);
+    int index = node->parentsIndex;
-    if (nextChild != nullptr) {
-      return nextChild;
-    }
-    index = node->parentsIndex;
     node = node->parent;
     if (node == nullptr) {
       return nullptr;
     }
+    auto nextChild = getChildGeq(node, index + 1);
+    if (nextChild != nullptr) {
+      return nextChild;
+    }
   }
 }
 
 Node *nextLogical(Node *node) {
-  int index = -1;
+  auto nextChild = getFirstChild(node);
+  if (nextChild != nullptr) {
+    node = nextChild;
+    goto downLeftSpine;
+  }
   for (;;) {
-    auto nextChild = getChildGeq(node, index + 1);
+    int index = node->parentsIndex;
-    if (nextChild != nullptr) {
-      for (node = nextChild; !node->entryPresent;
-           node = getFirstChildExists(node)) {
-      }
-      return node;
-    }
-    index = node->parentsIndex;
     node = node->parent;
     if (node == nullptr) {
       return nullptr;
     }
+    auto nextChild = getChildGeq(node, index + 1);
+    if (nextChild != nullptr) {
+      node = nextChild;
+      goto downLeftSpine;
+    }
   }
+downLeftSpine:
+  for (; !node->entryPresent; node = getFirstChildExists(node)) {
+  }
+  return node;
 }
 
 // Invalidates `self`, replacing it with a node of at least capacity.