refactor: prealloc slices with known sizes

Often thoses are small slices and that cuts down the number of (small) allocations from 2~7 to 1. This is consistent too, always only gets 1.

cmd/ipfs/daemon.go

@@ -704,22 +704,23 @@ func printSwarmAddrs(node *core.IpfsNode) {
 		return
 	}
 
-	var lisAddrs []string
 	ifaceAddrs, err := node.PeerHost.Network().InterfaceListenAddresses()
 	if err != nil {
 		log.Errorf("failed to read listening addresses: %s", err)
 	}
-	for _, addr := range ifaceAddrs {
-		lisAddrs = append(lisAddrs, addr.String())
+	lisAddrs := make([]string, len(ifaceAddrs))
+	for i, addr := range ifaceAddrs {
+		lisAddrs[i] = addr.String()
 	}
 	sort.Strings(lisAddrs)
 	for _, addr := range lisAddrs {
 		fmt.Printf("Swarm listening on %s\n", addr)
 	}
 
-	var addrs []string
-	for _, addr := range node.PeerHost.Addrs() {
-		addrs = append(addrs, addr.String())
+	nodePhostAddrs := node.PeerHost.Addrs()
+	addrs := make([]string, len(nodePhostAddrs))
+	for i, addr := range nodePhostAddrs {
+		addrs[i] = addrs, addr.String()
 	}
 	sort.Strings(addrs)
 	for _, addr := range addrs {

core/commands/sysdiag.go

@@ -134,9 +134,9 @@ func netInfo(online bool, out map[string]interface{}) error {
 		return err
 	}
 
-	var straddrs []string
-	for _, a := range addrs {
-		straddrs = append(straddrs, a.String())
+	straddrs := make([]string, len(addrs))
+	for i, a := range addrs {
+		straddrs[i] = a.String()
 	}
 
 	n["interface_addresses"] = straddrs

core/node/libp2p/addrs.go

@@ -100,13 +100,13 @@ func AddrsFactory(announce []string, appendAnnouce []string, noAnnounce []string
 }
 
 func listenAddresses(addresses []string) ([]ma.Multiaddr, error) {
-	var listen []ma.Multiaddr
-	for _, addr := range addresses {
+	listen := make([]ma.Multiaddr, len(addresses))
+	for i, addr := range addresses {
 		maddr, err := ma.NewMultiaddr(addr)
 		if err != nil {
 			return nil, fmt.Errorf("failure to parse config.Addresses.Swarm: %s", addresses)
 		}
-		listen = append(listen, maddr)
+		listen[i] = maddr
 	}
 
 	return listen, nil

fuse/ipns/ipns_unix.go

@@ -215,7 +215,7 @@ func (r *Root) Forget() {
 func (r *Root) ReadDirAll(ctx context.Context) ([]fuse.Dirent, error) {
 	log.Debug("Root ReadDirAll")
 
-	var listing []fuse.Dirent
+	listing := make([]fuse.Dirent, 0, len(r.Keys)*2)
 	for alias, k := range r.Keys {
 		ent := fuse.Dirent{
 			Name: k.ID().Pretty(),
@@ -290,12 +290,12 @@ func (s *Directory) Lookup(ctx context.Context, name string) (fs.Node, error) {
 
 // ReadDirAll reads the link structure as directory entries
 func (dir *Directory) ReadDirAll(ctx context.Context) ([]fuse.Dirent, error) {
-	var entries []fuse.Dirent
 	listing, err := dir.dir.List(ctx)
 	if err != nil {
 		return nil, err
 	}
-	for _, entry := range listing {
+	entries := make([]fuse.Dirent, len(listing))
+	for i, entry := range listing {
 		dirent := fuse.Dirent{Name: entry.Name}
 
 		switch mfs.NodeType(entry.Type) {
@@ -305,7 +305,7 @@ func (dir *Directory) ReadDirAll(ctx context.Context) ([]fuse.Dirent, error) {
 			dirent.Type = fuse.DT_File
 		}
 
-		entries = append(entries, dirent)
+		entries[i] = dirent
 	}
 
 	if len(entries) > 0 {

profile/profile.go

@@ -125,13 +125,13 @@ func (p *profiler) runProfile(ctx context.Context) error {
 	ctx, cancelFn := context.WithCancel(ctx)
 	defer cancelFn()
 
-	var collectorsToRun []collector
-	for _, name := range p.opts.Collectors {
+	collectorsToRun := make([]collector, len(p.opts.Collectors))
+	for i, name := range p.opts.Collectors {
 		c, ok := collectors[name]
 		if !ok {
 			return fmt.Errorf("unknown collector '%s'", name)
 		}
-		collectorsToRun = append(collectorsToRun, c)
+		collectorsToRun[i] = c
 	}
 
 	results := make(chan profileResult, len(p.opts.Collectors))