cmd/link: make Allsym a slice

Looks a tiny bit faster, which is a surprise. Probably noise.
Motivation is making the LSym structure a little easier to understand.

Linking juju, best of 10:

before: real 0m4.811s user 0m5.582s
after:  real 0m4.611s user 0m5.267s

Change-Id: Idbedaf4a6e6e199036a1bbb6760e98c94ed2c282
Reviewed-on: https://go-review.googlesource.com/20142
Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/link/internal/ld/ar.go

@@ -97,7 +97,7 @@ func hostArchive(name string) {
 	any := true
 	for any {
 		var load []uint64
-		for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+		for _, s := range Ctxt.Allsym {
 			for _, r := range s.R {
 				if r.Sym != nil && r.Sym.Type&obj.SMASK == obj.SXREF {
 					if off := armap[r.Sym.Name]; off != 0 && !loaded[off] {

src/cmd/link/internal/ld/data.go

@@ -1006,7 +1006,7 @@ func addinitarrdata(s *LSym) {
 }
 
 func dosymtype() {
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if len(s.P) > 0 {
 			if s.Type == obj.SBSS {
 				s.Type = obj.SDATA
@@ -1145,7 +1145,7 @@ func dodata() {
 	var last *LSym
 	datap = nil
 
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if !s.Reachable || s.Special != 0 {
 			continue
 		}

src/cmd/link/internal/ld/elf.go

@@ -1361,9 +1361,7 @@ func elfdynhash() {
 	buckets := make([]uint32, nbucket)
 
 	var b int
-	var hc uint32
-	var name string
-	for sy := Ctxt.Allsym; sy != nil; sy = sy.Allsym {
+	for _, sy := range Ctxt.Allsym {
 		if sy.Dynid <= 0 {
 			continue
 		}
@@ -1372,8 +1370,8 @@ func elfdynhash() {
 			need[sy.Dynid] = addelflib(&needlib, sy.Dynimplib, sy.Dynimpvers)
 		}
 
-		name = sy.Extname
-		hc = elfhash([]byte(name))
+		name := sy.Extname
+		hc := elfhash([]byte(name))
 
 		b = int(hc % uint32(nbucket))
 		chain[sy.Dynid] = buckets[b]

src/cmd/link/internal/ld/go.go

@@ -449,7 +449,7 @@ func deadcode() {
 	if Buildmode == BuildmodeShared {
 		// Mark all symbols defined in this library as reachable when
 		// building a shared library.
-		for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+		for _, s := range Ctxt.Allsym {
 			if s.Type != 0 && s.Type != obj.SDYNIMPORT {
 				mark(s)
 			}
@@ -471,7 +471,7 @@ func deadcode() {
 		markflood()
 
 		// keep each beginning with 'typelink.' if the symbol it points at is being kept.
-		for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+		for _, s := range Ctxt.Allsym {
 			if strings.HasPrefix(s.Name, "go.typelink.") {
 				s.Reachable = len(s.R) == 1 && s.R[0].Sym.Reachable
 			}
@@ -503,7 +503,7 @@ func deadcode() {
 		}
 	}
 
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if strings.HasPrefix(s.Name, "go.weak.") {
 			s.Special = 1 // do not lay out in data segment
 			s.Reachable = true
@@ -513,14 +513,13 @@ func deadcode() {
 
 	// record field tracking references
 	var buf bytes.Buffer
-	var p *LSym
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if strings.HasPrefix(s.Name, "go.track.") {
 			s.Special = 1 // do not lay out in data segment
 			s.Hidden = true
 			if s.Reachable {
 				buf.WriteString(s.Name[9:])
-				for p = s.Reachparent; p != nil; p = p.Reachparent {
+				for p := s.Reachparent; p != nil; p = p.Reachparent {
 					buf.WriteString("\t")
 					buf.WriteString(p.Name)
 				}
@@ -543,13 +542,11 @@ func deadcode() {
 }
 
 func doweak() {
-	var t *LSym
-
 	// resolve weak references only if
 	// target symbol will be in binary anyway.
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if strings.HasPrefix(s.Name, "go.weak.") {
-			t = Linkrlookup(Ctxt, s.Name[8:], int(s.Version))
+			t := Linkrlookup(Ctxt, s.Name[8:], int(s.Version))
 			if t != nil && t.Type != 0 && t.Reachable {
 				s.Value = t.Value
 				s.Type = t.Type

src/cmd/link/internal/ld/lib.go

@@ -599,7 +599,7 @@ func loadlib() {
 	if Linkmode == LinkInternal {
 		// Drop all the cgo_import_static declarations.
 		// Turns out we won't be needing them.
-		for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+		for _, s := range Ctxt.Allsym {
 			if s.Type == obj.SHOSTOBJ {
 				// If a symbol was marked both
 				// cgo_import_static and cgo_import_dynamic,
@@ -679,7 +679,7 @@ func loadlib() {
 		// If we have any undefined symbols in external
 		// objects, try to read them from the libgcc file.
 		any := false
-		for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+		for _, s := range Ctxt.Allsym {
 			for _, r := range s.R {
 				if r.Sym != nil && r.Sym.Type&obj.SMASK == obj.SXREF && r.Sym.Name != ".got" {
 					any = true
@@ -1904,7 +1904,7 @@ func genasmsym(put func(*LSym, string, int, int64, int64, int, *LSym)) {
 		put(s, s.Name, 'T', s.Value, s.Size, int(s.Version), nil)
 	}
 
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if s.Hidden || ((s.Name == "" || s.Name[0] == '.') && s.Version == 0 && s.Name != ".rathole" && s.Name != ".TOC.") {
 			continue
 		}

src/cmd/link/internal/ld/link.go

@@ -67,7 +67,6 @@ type LSym struct {
 	Locals      int32
 	Value       int64
 	Size        int64
-	Allsym      *LSym
 	Next        *LSym
 	Sub         *LSym
 	Outer       *LSym
@@ -142,7 +141,7 @@ type Link struct {
 	Windows    int32
 	Goroot     string
 	Hash       map[symVer]*LSym
-	Allsym     *LSym
+	Allsym     []*LSym
 	Nsymbol    int32
 	Tlsg       *LSym
 	Libdir     []string

src/cmd/link/internal/ld/macho.go

@@ -652,7 +652,7 @@ func (x machoscmp) Less(i, j int) bool {
 
 func machogenasmsym(put func(*LSym, string, int, int64, int64, int, *LSym)) {
 	genasmsym(put)
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if s.Type == obj.SDYNIMPORT || s.Type == obj.SHOSTOBJ {
 			if s.Reachable {
 				put(s, "", 'D', 0, 0, 0, nil)

src/cmd/link/internal/ld/pe.go

@@ -487,7 +487,7 @@ func initdynimport() *Dll {
 
 	dr = nil
 	var m *Imp
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if !s.Reachable || s.Type != obj.SDYNIMPORT {
 			continue
 		}
@@ -692,7 +692,7 @@ func (s byExtname) Less(i, j int) bool { return s[i].Extname < s[j].Extname }
 
 func initdynexport() {
 	nexport = 0
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if !s.Reachable || s.Cgoexport&CgoExportDynamic == 0 {
 			continue
 		}

src/cmd/link/internal/ld/sym.go

@@ -57,12 +57,13 @@ var headers = []struct {
 }
 
 func linknew(arch *LinkArch) *Link {
-	ctxt := new(Link)
-	// Preallocate about 2mb for hash
-	ctxt.Hash = make(map[symVer]*LSym, 100000)
-	ctxt.Arch = arch
-	ctxt.Version = obj.HistVersion
-	ctxt.Goroot = obj.Getgoroot()
+	ctxt := &Link{
+		Hash:    make(map[symVer]*LSym, 100000), // preallocate about 2mb for hash
+		Allsym:  make([]*LSym, 0, 100000),
+		Arch:    arch,
+		Version: obj.HistVersion,
+		Goroot:  obj.Getgoroot(),
+	}
 
 	p := obj.Getgoarch()
 	if p != arch.Name {
@@ -168,15 +169,10 @@ func linknewsym(ctxt *Link, symb string, v int) *LSym {
 	s.Plt = -1
 	s.Got = -1
 	s.Name = symb
-	s.Type = 0
 	s.Version = int16(v)
-	s.Value = 0
-	s.Size = 0
 	ctxt.Nsymbol++
 
-	s.Allsym = ctxt.Allsym
-	ctxt.Allsym = s
-
+	ctxt.Allsym = append(ctxt.Allsym, s)
 	return s
 }
 

src/cmd/link/internal/ld/symtab.go

@@ -461,7 +461,7 @@ func symtab() {
 	// within a type they sort by size, so the .* symbols
 	// just defined above will be first.
 	// hide the specific symbols.
-	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
+	for _, s := range Ctxt.Allsym {
 		if !s.Reachable || s.Special != 0 || s.Type != obj.SRODATA {
 			continue
 		}