Perf improve.

Author: peterwilsoncc

src/wp-includes/class-wp-query.php

@@ -3739,20 +3739,24 @@ public function the_post() {
 		global $post;
 
 		if ( ! $this->in_the_loop ) {
-			if ( 'all' === $this->query_vars['fields'] ) {
+			if ( $this->posts[0] instanceof WP_Post ) {
+				// Full post objects queried.
 				$post_objects = $this->posts;
 			} else {
 				// Only partial objects queried, need to prime the cache for the loop.
-				$post_ids = array();
-				foreach ( $this->posts as $loop_post ) {
-					if ( 'ids' === $this->query_vars['fields'] ) {
-						$post_ids[] = $loop_post;
-					} else {
-						// Partial object (stdClass) queried.
-						$post_ids[] = $loop_post->ID;
-					}
-				}
+				$post_ids = array_reduce(
+					$this->posts,
+					function ( $carry, $post ) {
+						if ( 'ids' === $this->query_vars['fields'] ) {
+							$carry[] = $post;
+						} elseif ( isset( $post->ID ) ) {
+							$carry[] = $post->ID;
+						}
 
+						return $carry;
+					},
+					array()
+				);
 				_prime_post_caches( $post_ids, $this->query_vars['update_post_term_cache'], $this->query_vars['update_post_meta_cache'] );
 				$post_objects = array_map( 'get_post', $post_ids );
 			}
@@ -3776,12 +3780,14 @@ public function the_post() {
 		$post = $this->next_post();
 
 		// Ensure a full post object is available.
-		if ( 'ids' === $this->query_vars['fields'] ) {
-			// Post IDs queried.
-			$post = get_post( $post );
-		} elseif ( 'all' !== $this->query_vars['fields'] ) {
-			// Partial object (stdClass) queried.
-			$post = get_post( $post->ID );
+		if ( ! $post instanceof WP_Post ) {
+			if ( 'ids' === $this->query_vars['fields'] ) {
+				// Post IDs queried.
+				$post = get_post( $post );
+			} elseif ( isset( $post->ID ) ) {
+				// Partial object (stdClass) queried.
+				$post = get_post( $post->ID );
+			}
 		}
 
 		// Set up the global post object for the loop.