DrupalDefaultEntityController::load(), on the first attempt to load entities, will
- load the raw entities from the database.
- attach fields and possibly more with ::attachLoad() to the entity objects.
On subsequent calls for the same ids, it will get these entities from the cache in $this->entityCache.
This way, it avoids redundant and repeated database queries and calls to ::attachLoad().
However, if DrupalDefaultEntityController::load() is called with a non-empty $condition array, and $ids === FALSE, then repeated calls to load entities by the same conditions will cause each time cause a query, and call ::attachLoad() for entities that are already in the cache.
The entities built this way are later discarded via $entities += $queried_entities.
Even in a case where both $ids and $conditions are provided, if only one id is missing, then ::attachLoad() will be called for all the entities, even those already in cache.
This can be avoided.
I don't know how common it is to repeatedly load entities by the same conditions.
But in case someone does, fixing this will radically reduce the time of this operation.
