Song: embed the Tag object statically into class Song

Reduces overhead because we need to manage only one memory allocation.
According to valgrind/massif, we save 7%.

src/DatabaseHelpers.cxx

@@ -39,9 +39,7 @@ typedef std::set<const char *, StringLess> StringSet;
 static bool
 CollectTags(StringSet &set, TagType tag_type, Song &song)
 {
-	Tag *tag = song.tag;
-	if (tag == nullptr)
-		return true;
+	const Tag *tag = &song.tag;
 
 	bool found = false;
 	for (unsigned i = 0; i < tag->num_items; ++i) {
@@ -108,8 +106,7 @@ StatsVisitSong(DatabaseStats &stats, StringSet &artists, StringSet &albums,
 {
 	++stats.song_count;
 
-	if (song.tag != nullptr)
-		StatsVisitTag(stats, artists, albums, *song.tag);
+	StatsVisitTag(stats, artists, albums, song.tag);
 
 	return true;
 }

src/DatabasePrint.cxx

@@ -70,7 +70,7 @@ PrintSongBrief(Client &client, const Song &song)
 {
 	song_print_uri(client, song);
 
-	if (song.tag != nullptr && song.tag->has_playlist)
+	if (song.tag.has_playlist)
 		/* this song file has an embedded CUE sheet */
 		print_playlist_in_directory(client, song.parent, song.uri);
 
@@ -82,7 +82,7 @@ PrintSongFull(Client &client, const Song &song)
 {
 	song_print_info(client, song);
 
-	if (song.tag != nullptr && song.tag->has_playlist)
+	if (song.tag.has_playlist)
 		/* this song file has an embedded CUE sheet */
 		print_playlist_in_directory(client, song.parent, song.uri);
 

src/DetachedSong.cxx

@@ -25,7 +25,7 @@
 
 DetachedSong::DetachedSong(const Song &other)
 	:uri(other.GetURI().c_str()),
-	 tag(other.tag != nullptr ? *other.tag : Tag()),
+	 tag(other.tag),
 	 mtime(other.mtime),
 	 start_ms(other.start_ms), end_ms(other.end_ms) {}
 

src/PlaylistUpdate.cxx

@@ -49,9 +49,7 @@ UpdatePlaylistSong(const Database &db, DetachedSong &song)
 	}
 
 	song.SetLastModified(original->mtime);
-
-	if (original->tag != nullptr)
-		song.SetTag(*original->tag);
+	song.SetTag(original->tag);
 
 	db.ReturnSong(original);
 	return true;

src/Song.cxx

@@ -29,14 +29,13 @@
 #include <stdlib.h>
 
 inline Song::Song(const char *_uri, size_t uri_length, Directory *_parent)
-	:tag(nullptr), parent(_parent), mtime(0), start_ms(0), end_ms(0)
+	:parent(_parent), mtime(0), start_ms(0), end_ms(0)
 {
 	memcpy(uri, _uri, uri_length + 1);
 }
 
 inline Song::~Song()
 {
-	delete tag;
 }
 
 static Song *
@@ -57,7 +56,7 @@ Song *
 Song::NewFrom(DetachedSong &&other, Directory *parent)
 {
 	Song *song = song_alloc(other.GetURI(), parent);
-	song->tag = new Tag(std::move(other.WritableTag()));
+	song->tag = std::move(other.WritableTag());
 	song->mtime = other.GetLastModified();
 	song->start_ms = other.GetStartMS();
 	song->end_ms = other.GetEndMS();
@@ -101,8 +100,8 @@ Song::GetDuration() const
 	if (end_ms > 0)
 		return (end_ms - start_ms) / 1000.0;
 
-	if (tag == nullptr)
+	if (tag.time <= 0)
 		return 0;
 
-	return tag->time - start_ms / 1000.0;
+	return tag.time - start_ms / 1000.0;
 }

src/Song.hxx

@@ -21,6 +21,7 @@
 #define MPD_SONG_HXX
 
 #include "util/list.h"
+#include "tag/Tag.hxx"
 #include "Compiler.h"
 
 #include <string>
@@ -31,7 +32,6 @@
 #define SONG_FILE	"file: "
 #define SONG_TIME	"Time: "
 
-struct Tag;
 struct Directory;
 class DetachedSong;
 
@@ -49,7 +49,7 @@ struct Song {
 	 */
 	struct list_head siblings;
 
-	Tag *tag;
+	Tag tag;
 
 	/**
 	 * The #Directory that contains this song.  May be nullptr if

src/SongFilter.cxx

@@ -149,7 +149,7 @@ SongFilter::Item::Match(const Song &song) const
 		return StringMatch(uri.c_str());
 	}
 
-	return song.tag != NULL && Match(*song.tag);
+	return Match(song.tag);
 }
 
 bool

src/SongPrint.cxx

@@ -74,8 +74,7 @@ song_print_info(Client &client, const Song &song)
 	if (song.mtime > 0)
 		time_print(client, "Last-Modified", song.mtime);
 
-	if (song.tag != nullptr)
-		tag_print(client, *song.tag);
+	tag_print(client, song.tag);
 }
 
 void

src/SongSave.cxx

@@ -53,8 +53,7 @@ song_save(FILE *fp, const Song &song)
 
 	range_save(fp, song.start_ms, song.end_ms);
 
-	if (song.tag != nullptr)
-		tag_save(fp, *song.tag);
+	tag_save(fp, song.tag);
 
 	fprintf(fp, SONG_MTIME ": %li\n", (long)song.mtime);
 	fprintf(fp, SONG_END "\n");

src/SongSort.cxx

@@ -30,14 +30,6 @@ extern "C" {
 
 #include <stdlib.h>
 
-static const char *
-tag_get_value_checked(const Tag *tag, TagType type)
-{
-	return tag != nullptr
-		? tag->GetValue(type)
-		: nullptr;
-}
-
 static int
 compare_utf8_string(const char *a, const char *b)
 {
@@ -55,11 +47,11 @@ compare_utf8_string(const char *a, const char *b)
  * nullptr.
  */
 static int
-compare_string_tag_item(const Tag *a, const Tag *b,
+compare_string_tag_item(const Tag &a, const Tag &b,
 			TagType type)
 {
-	return compare_utf8_string(tag_get_value_checked(a, type),
-				   tag_get_value_checked(b, type));
+	return compare_utf8_string(a.GetValue(type),
+				   b.GetValue(type));
 }
 
 /**
@@ -82,10 +74,10 @@ compare_number_string(const char *a, const char *b)
 }
 
 static int
-compare_tag_item(const Tag *a, const Tag *b, TagType type)
+compare_tag_item(const Tag &a, const Tag &b, TagType type)
 {
-	return compare_number_string(tag_get_value_checked(a, type),
-				     tag_get_value_checked(b, type));
+	return compare_number_string(a.GetValue(type),
+				     b.GetValue(type));
 }
 
 /* Only used for sorting/searchin a songvec, not general purpose compares */

src/SongUpdate.cxx

@@ -98,8 +98,7 @@ Song::UpdateFile()
 
 	mtime = st.st_mtime;
 
-	delete tag;
-	tag = tag_builder.CommitNew();
+	tag_builder.Commit(tag);
 	return true;
 }
 
@@ -123,8 +122,7 @@ Song::UpdateFileInArchive()
 	if (!tag_stream_scan(path_fs.c_str(), full_tag_handler, &tag_builder))
 		return false;
 
-	delete tag;
-	tag = tag_builder.CommitNew();
+	tag_builder.Commit(tag);
 	return true;
 }
 

src/UpdateContainer.cxx

@@ -113,10 +113,7 @@ update_container_file(Directory &directory,
 		plugin.ScanFile(child_path_fs.c_str(),
 				add_tag_handler, &tag_builder);
 
-		if (tag_builder.IsDefined())
-			song->tag = tag_builder.CommitNew();
-		else
-			tag_builder.Clear();
+		tag_builder.Commit(song->tag);
 
 		db_lock();
 		contdir->AddSong(song);

src/db/ProxyDatabasePlugin.cxx

@@ -524,7 +524,7 @@ Convert(const struct mpd_song *song)
 	for (const auto *i = &tag_table[0]; i->d != TAG_NUM_OF_ITEM_TYPES; ++i)
 		Copy(tag, i->d, song, i->s);
 
-	s->tag = tag.CommitNew();
+	tag.Commit(s->tag);
 
 	return s;
 }

src/db/UpnpDatabasePlugin.cxx

@@ -205,7 +205,7 @@ upnpItemToSong(UPnPDirObject &&dirent, const char *uri)
 		uri = dirent.url.c_str();
 
 	Song *s = Song::NewFile(uri, nullptr);
-	s->tag = new Tag(std::move(dirent.tag));
+	s->tag = std::move(dirent.tag);
 	return s;
 }