Avoid branching on type twice in erase

ConflictSet.cpp

@@ -1675,53 +1675,67 @@ void mergeWithChild(Node *&self, WriteContext *tls, ConflictSet::Impl *impl,
   tls->release(self3);
 }
 
-void maybeDownsize(Node *self, WriteContext *tls, ConflictSet::Impl *impl,
+bool needsDownsize(Node *n) {
+  static int minTable[] = {0, kMinChildrenNode3, kMinChildrenNode16,
+                           kMinChildrenNode48, kMinChildrenNode256};
+  return n->numChildren + n->entryPresent < minTable[n->getType()];
+}
+
+void downsize(Node3 *self, WriteContext *tls, ConflictSet::Impl *impl,
               Node *&dontInvalidate) {
-
-#if DEBUG_VERBOSE && !defined(NDEBUG)
-  fprintf(stderr, "maybeDownsize: %s\n", getSearchPathPrintable(self).c_str());
-#endif
-
-  switch (self->getType()) {
-  case Type_Node0:           // GCOVR_EXCL_LINE
-    __builtin_unreachable(); // GCOVR_EXCL_LINE
-  case Type_Node3: {
-    auto *self3 = (Node3 *)self;
   if (self->numChildren == 0) {
     auto *newSelf = tls->allocate<Node0>(self->partialKeyLen);
-      newSelf->copyChildrenAndKeyFrom(*self3);
+    newSelf->copyChildrenAndKeyFrom(*self);
     getInTree(self, impl) = newSelf;
-      tls->release(self3);
+    tls->release(self);
-    } else if (self->numChildren == 1 && !self->entryPresent) {
+  } else {
-      mergeWithChild(getInTree(self, impl), tls, impl, dontInvalidate, self3);
+    assert(self->numChildren == 1 && !self->entryPresent);
+    mergeWithChild(getInTree(self, impl), tls, impl, dontInvalidate, self);
   }
-  } break;
+}
-  case Type_Node16:
+
-    if (self->numChildren + int(self->entryPresent) < kMinChildrenNode16) {
+void downsize(Node16 *self, WriteContext *tls, ConflictSet::Impl *impl) {
-      auto *self16 = (Node16 *)self;
+  assert(self->numChildren + int(self->entryPresent) < kMinChildrenNode16);
   auto *newSelf = tls->allocate<Node3>(self->partialKeyLen);
-      newSelf->copyChildrenAndKeyFrom(*self16);
+  newSelf->copyChildrenAndKeyFrom(*self);
   getInTree(self, impl) = newSelf;
-      tls->release(self16);
+  tls->release(self);
-    }
+}
-    break;
+
-  case Type_Node48:
+void downsize(Node48 *self, WriteContext *tls, ConflictSet::Impl *impl) {
-    if (self->numChildren + int(self->entryPresent) < kMinChildrenNode48) {
+  assert(self->numChildren + int(self->entryPresent) < kMinChildrenNode48);
-      auto *self48 = (Node48 *)self;
   auto *newSelf = tls->allocate<Node16>(self->partialKeyLen);
-      newSelf->copyChildrenAndKeyFrom(*self48);
+  newSelf->copyChildrenAndKeyFrom(*self);
   getInTree(self, impl) = newSelf;
-      tls->release(self48);
+  tls->release(self);
-    }
+}
-    break;
+
-  case Type_Node256:
+void downsize(Node256 *self, WriteContext *tls, ConflictSet::Impl *impl) {
-    if (self->numChildren + int(self->entryPresent) < kMinChildrenNode256) {
+  assert(self->numChildren + int(self->entryPresent) < kMinChildrenNode256);
   auto *self256 = (Node256 *)self;
   auto *newSelf = tls->allocate<Node48>(self->partialKeyLen);
   newSelf->copyChildrenAndKeyFrom(*self256);
   getInTree(self, impl) = newSelf;
   tls->release(self256);
-    }
+}
+
+void downsize(Node *self, WriteContext *tls, ConflictSet::Impl *impl,
+              Node *&dontInvalidate) {
+
+  switch (self->getType()) {
+  case Type_Node0:           // GCOVR_EXCL_LINE
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
+  case Type_Node3:
+    downsize(static_cast<Node3 *>(self), tls, impl, dontInvalidate);
+    break;
+  case Type_Node16:
+    downsize(static_cast<Node16 *>(self), tls, impl);
+    break;
+  case Type_Node48:
+    downsize(static_cast<Node48 *>(self), tls, impl);
+    break;
+  case Type_Node256:
+    downsize(static_cast<Node256 *>(self), tls, impl);
     break;
   default:                   // GCOVR_EXCL_LINE
     __builtin_unreachable(); // GCOVR_EXCL_LINE
@@ -1751,7 +1765,9 @@ Node *erase(Node *self, WriteContext *tls, ConflictSet::Impl *impl,
   self->entryPresent = false;
 
   if (self->numChildren != 0) {
-    maybeDownsize(self, tls, impl, result);
+    if (needsDownsize(self)) {
+      downsize(self, tls, impl, result);
+    }
     return result;
   }
 
@@ -1771,7 +1787,10 @@ Node *erase(Node *self, WriteContext *tls, ConflictSet::Impl *impl,
       parent3->children[i] = parent3->children[i + 1];
       parent3->childMaxVersion[i] = parent3->childMaxVersion[i + 1];
     }
-    assert(parent->numChildren > 0 || parent->entryPresent);
+
+    if (needsDownsize(parent3)) {
+      downsize(parent3, tls, impl, result);
+    }
   } break;
   case Type_Node16: {
     auto *parent16 = static_cast<Node16 *>(parent);
@@ -1784,8 +1803,9 @@ Node *erase(Node *self, WriteContext *tls, ConflictSet::Impl *impl,
       parent16->childMaxVersion[i] = parent16->childMaxVersion[i + 1];
     }
 
-    // By kMinChildrenNode16
+    if (needsDownsize(parent16)) {
-    assert(parent->numChildren > 0);
+      downsize(parent16, tls, impl, result);
+    }
   } break;
   case Type_Node48: {
     auto *parent48 = static_cast<Node48 *>(parent);
@@ -1813,8 +1833,9 @@ Node *erase(Node *self, WriteContext *tls, ConflictSet::Impl *impl,
 
     --parent->numChildren;
 
-    // By kMinChildrenNode48
+    if (needsDownsize(parent48)) {
-    assert(parent->numChildren > 0);
+      downsize(parent48, tls, impl, result);
+    }
   } break;
   case Type_Node256: {
     auto *parent256 = static_cast<Node256 *>(parent);
@@ -1823,16 +1844,14 @@ Node *erase(Node *self, WriteContext *tls, ConflictSet::Impl *impl,
 
     --parent->numChildren;
 
-    // By kMinChildrenNode256
+    if (needsDownsize(parent256)) {
-    assert(parent->numChildren > 0);
+      downsize(parent256, tls, impl, result);
-
+    }
   } break;
   default:                   // GCOVR_EXCL_LINE
     __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 
-  maybeDownsize(parent, tls, impl, result);
-
   return result;
 }