cmd/internal/gc: remove namebuf variable

namebuf was a global char buffer in the C version of gc, which was
useful for providing common storage for constructing symbol and file
names.  However, now that it's just a global Go string and the string
data is dynamically allocated anyway, it doesn't serve any purpose
except to force extra write barriers everytime it's assigned to.

Also, introduce Lookupf(fmt, args...) as shorthand for
Lookup(fmt.Sprintf(fmt, args...)), which was a very common pattern for
using namebuf.

Passes "go build -toolexec 'toolstash -cmp' -a std".

Notably, this CL shrinks 6g's text section by ~15kB:

$ size toolstash/6g tool/linux_amd64/6g
   text	   data	    bss	    dec	    hex	filename
4600805	 605968	 342988	5549761	 54aec1	toolstash/6g
4585547	 605968	 342956	5534471	 547307	tool/linux_amd64/6g

Change-Id: I98abb44fc7f43a2e2e48425cc9f215cd0be37442
Reviewed-on: https://go-review.googlesource.com/7080Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/internal/gc/closure.go

@@ -174,8 +174,7 @@ func closurename(n *Node) *Sym {
 	} else {
 		Fatal("closurename called for %v", Nconv(n, obj.FmtShort))
 	}
-	namebuf = fmt.Sprintf("%s.%s%d", outer, prefix, gen)
-	n.Sym = Lookup(namebuf)
+	n.Sym = Lookupf("%s.%s%d", outer, prefix, gen)
 	return n.Sym
 }
 
@@ -333,9 +332,7 @@ func transformclosure(xfunc *Node) {
 				// we introduce function param &v *T
 				// and v remains PPARAMREF with &v heapaddr
 				// (accesses will implicitly deref &v).
-				namebuf = fmt.Sprintf("&%s", v.Sym.Name)
-
-				addr = newname(Lookup(namebuf))
+				addr = newname(Lookupf("&%s", v.Sym.Name))
 				addr.Type = Ptrto(v.Type)
 				addr.Class = PPARAM
 				v.Heapaddr = addr
@@ -397,9 +394,7 @@ func transformclosure(xfunc *Node) {
 			} else {
 				// Declare variable holding addresses taken from closure
 				// and initialize in entry prologue.
-				namebuf = fmt.Sprintf("&%s", v.Sym.Name)
-
-				addr = newname(Lookup(namebuf))
+				addr = newname(Lookupf("&%s", v.Sym.Name))
 				addr.Ntype = Nod(OIND, typenod(v.Type), nil)
 				addr.Class = PAUTO
 				addr.Used = true
@@ -557,9 +552,8 @@ func makepartialcall(fn *Node, t0 *Type, meth *Node) *Node {
 	var fld *Node
 	var n *Node
 	for t := getinargx(t0).Type; t != nil; t = t.Down {
-		namebuf = fmt.Sprintf("a%d", i)
+		n = newname(Lookupf("a%d", i))
 		i++
-		n = newname(Lookup(namebuf))
 		n.Class = PPARAM
 		xfunc.Dcl = list(xfunc.Dcl, n)
 		callargs = list(callargs, n)
@@ -577,9 +571,8 @@ func makepartialcall(fn *Node, t0 *Type, meth *Node) *Node {
 	l = nil
 	var retargs *NodeList
 	for t := getoutargx(t0).Type; t != nil; t = t.Down {
-		namebuf = fmt.Sprintf("r%d", i)
+		n = newname(Lookupf("r%d", i))
 		i++
-		n = newname(Lookup(namebuf))
 		n.Class = PPARAMOUT
 		xfunc.Dcl = list(xfunc.Dcl, n)
 		retargs = list(retargs, n)

src/cmd/internal/gc/dcl.go

@@ -645,10 +645,8 @@ func funcargs(nt *Node) {
 
 		if n.Left == nil {
 			// Name so that escape analysis can track it. ~r stands for 'result'.
-			namebuf = fmt.Sprintf("~r%d", gen)
+			n.Left = newname(Lookupf("~r%d", gen))
 			gen++
-
-			n.Left = newname(Lookup(namebuf))
 		}
 
 		// TODO: n->left->missing = 1;
@@ -667,9 +665,8 @@ func funcargs(nt *Node) {
 
 			*nn = *n.Left
 			nn.Orig = nn
-			namebuf = fmt.Sprintf("~b%d", gen)
+			nn.Sym = Lookupf("~b%d", gen)
 			gen++
-			nn.Sym = Lookup(namebuf)
 			n.Left = nn
 		}
 

src/cmd/internal/gc/gen.go

@@ -590,10 +590,8 @@ func Tempname(nn *Node, t *Type) {
 
 	// give each tmp a different name so that there
 	// a chance to registerizer them
-	namebuf = fmt.Sprintf("autotmp_%.4d", statuniqgen)
-
+	s := Lookupf("autotmp_%.4d", statuniqgen)
 	statuniqgen++
-	s := Lookup(namebuf)
 	n := Nod(ONAME, nil, nil)
 	n.Sym = s
 	s.Def = n

src/cmd/internal/gc/go.go

@@ -500,8 +500,6 @@ var safemode int
 
 var nolocalimports int
 
-var namebuf string
-
 var lexbuf bytes.Buffer
 var strbuf bytes.Buffer
 

src/cmd/internal/gc/init.go

@@ -4,8 +4,6 @@
 
 package gc
 
-import "fmt"
-
 //	case OADD:
 //		if(n->right->op == OLITERAL) {
 //			v = n->right->vconst;
@@ -31,8 +29,7 @@ var renameinit_initgen int
 
 func renameinit() *Sym {
 	renameinit_initgen++
-	namebuf = fmt.Sprintf("init.%d", renameinit_initgen)
-	return Lookup(namebuf)
+	return Lookupf("init.%d", renameinit_initgen)
 }
 
 /*
@@ -112,18 +109,14 @@ func fninit(n *NodeList) {
 	var r *NodeList
 
 	// (1)
-	namebuf = "initdone·"
-
-	gatevar := newname(Lookup(namebuf))
+	gatevar := newname(Lookup("initdone·"))
 	addvar(gatevar, Types[TUINT8], PEXTERN)
 
 	// (2)
 	Maxarg = 0
 
-	namebuf = "init"
-
 	fn := Nod(ODCLFUNC, nil, nil)
-	initsym := Lookup(namebuf)
+	initsym := Lookup("init")
 	fn.Nname = newname(initsym)
 	fn.Nname.Defn = fn
 	fn.Nname.Ntype = Nod(OTFUNC, nil, nil)
@@ -169,8 +162,7 @@ func fninit(n *NodeList) {
 	// (9)
 	// could check that it is fn of no args/returns
 	for i := 1; ; i++ {
-		namebuf = fmt.Sprintf("init.%d", i)
-		s := Lookup(namebuf)
+		s := Lookupf("init.%d", i)
 		if s.Def == nil {
 			break
 		}

src/cmd/internal/gc/inl.go

@@ -859,8 +859,7 @@ func inlvar(var_ *Node) *Node {
 
 // Synthesize a variable to store the inlined function's results in.
 func retvar(t *Type, i int) *Node {
-	namebuf = fmt.Sprintf("~r%d", i)
-	n := newname(Lookup(namebuf))
+	n := newname(Lookupf("~r%d", i))
 	n.Type = t.Type
 	n.Class = PAUTO
 	n.Used = true
@@ -872,8 +871,7 @@ func retvar(t *Type, i int) *Node {
 // Synthesize a variable to store the inlined function's arguments
 // when they come from a multiple return call.
 func argvar(t *Type, i int) *Node {
-	namebuf = fmt.Sprintf("~arg%d", i)
-	n := newname(Lookup(namebuf))
+	n := newname(Lookupf("~arg%d", i))
 	n.Type = t.Type
 	n.Class = PAUTO
 	n.Used = true
@@ -886,8 +884,7 @@ var newlabel_inl_label int
 
 func newlabel_inl() *Node {
 	newlabel_inl_label++
-	namebuf = fmt.Sprintf(".inlret%.6d", newlabel_inl_label)
-	n := newname(Lookup(namebuf))
+	n := newname(Lookupf(".inlret%.6d", newlabel_inl_label))
 	n.Etype = 1 // flag 'safe' for escape analysis (no backjumps)
 	return n
 }

src/cmd/internal/gc/lex.go

@@ -559,25 +559,24 @@ func islocalname(name string) bool {
 		strings.HasPrefix(name, "../") || name == ".."
 }
 
-func findpkg(name string) bool {
+func findpkg(name string) (file string, ok bool) {
 	if islocalname(name) {
 		if safemode != 0 || nolocalimports != 0 {
-			return false
+			return "", false
 		}
 
 		// try .a before .6.  important for building libraries:
 		// if there is an array.6 in the array.a library,
 		// want to find all of array.a, not just array.6.
-		namebuf = fmt.Sprintf("%s.a", name)
-
-		if obj.Access(namebuf, 0) >= 0 {
-			return true
+		file = fmt.Sprintf("%s.a", name)
+		if obj.Access(file, 0) >= 0 {
+			return file, true
 		}
-		namebuf = fmt.Sprintf("%s.%c", name, Thearch.Thechar)
-		if obj.Access(namebuf, 0) >= 0 {
-			return true
+		file = fmt.Sprintf("%s.%c", name, Thearch.Thechar)
+		if obj.Access(file, 0) >= 0 {
+			return file, true
 		}
-		return false
+		return "", false
 	}
 
 	// local imports should be canonicalized already.
@@ -587,17 +586,17 @@ func findpkg(name string) bool {
 	_ = q
 	if path.Clean(name) != name {
 		Yyerror("non-canonical import path %q (should be %q)", name, q)
-		return false
+		return "", false
 	}
 
 	for p := idirs; p != nil; p = p.link {
-		namebuf = fmt.Sprintf("%s/%s.a", p.dir, name)
-		if obj.Access(namebuf, 0) >= 0 {
-			return true
+		file = fmt.Sprintf("%s/%s.a", p.dir, name)
+		if obj.Access(file, 0) >= 0 {
+			return file, true
 		}
-		namebuf = fmt.Sprintf("%s/%s.%c", p.dir, name, Thearch.Thechar)
-		if obj.Access(namebuf, 0) >= 0 {
-			return true
+		file = fmt.Sprintf("%s/%s.%c", p.dir, name, Thearch.Thechar)
+		if obj.Access(file, 0) >= 0 {
+			return file, true
 		}
 	}
 
@@ -612,17 +611,17 @@ func findpkg(name string) bool {
 			suffix = "race"
 		}
 
-		namebuf = fmt.Sprintf("%s/pkg/%s_%s%s%s/%s.a", goroot, goos, goarch, suffixsep, suffix, name)
-		if obj.Access(namebuf, 0) >= 0 {
-			return true
+		file = fmt.Sprintf("%s/pkg/%s_%s%s%s/%s.a", goroot, goos, goarch, suffixsep, suffix, name)
+		if obj.Access(file, 0) >= 0 {
+			return file, true
 		}
-		namebuf = fmt.Sprintf("%s/pkg/%s_%s%s%s/%s.%c", goroot, goos, goarch, suffixsep, suffix, name, Thearch.Thechar)
-		if obj.Access(namebuf, 0) >= 0 {
-			return true
+		file = fmt.Sprintf("%s/pkg/%s_%s%s%s/%s.%c", goroot, goos, goarch, suffixsep, suffix, name, Thearch.Thechar)
+		if obj.Access(file, 0) >= 0 {
+			return file, true
 		}
 	}
 
-	return false
+	return "", false
 }
 
 func fakeimport() {
@@ -698,7 +697,8 @@ func importfile(f *Val, line int) {
 		}
 	}
 
-	if !findpkg(path_) {
+	file, found := findpkg(path_)
+	if !found {
 		Yyerror("can't find import: %q", f.U.Sval)
 		errorexit()
 	}
@@ -708,7 +708,6 @@ func importfile(f *Val, line int) {
 	// If we already saw that package, feed a dummy statement
 	// to the lexer to avoid parsing export data twice.
 	if importpkg.Imported != 0 {
-		file := namebuf
 		tag := ""
 		if importpkg.Safe {
 			tag = "safe"
@@ -723,16 +722,13 @@ func importfile(f *Val, line int) {
 
 	var err error
 	var imp *obj.Biobuf
-	imp, err = obj.Bopenr(namebuf)
+	imp, err = obj.Bopenr(file)
 	if err != nil {
 		Yyerror("can't open import: %q: %v", f.U.Sval, err)
 		errorexit()
 	}
 
-	file := namebuf
-
-	n := len(namebuf)
-	if n > 2 && namebuf[n-2] == '.' && namebuf[n-1] == 'a' {
+	if strings.HasSuffix(file, ".a") {
 		if !skiptopkgdef(imp) {
 			Yyerror("import %s: not a package file", file)
 			errorexit()
@@ -757,7 +753,7 @@ func importfile(f *Val, line int) {
 
 	// assume files move (get installed)
 	// so don't record the full path.
-	linehist(file[n-len(path_)-2:], -1, 1) // acts as #pragma lib
+	linehist(file[len(file)-len(path_)-2:], -1, 1) // acts as #pragma lib
 
 	/*
 	 * position the input right
@@ -3162,10 +3158,9 @@ func mkpackage(pkgname string) {
 				p = p[i+1:]
 			}
 		}
-		namebuf = p
-		if i := strings.LastIndex(namebuf, "."); i >= 0 {
-			namebuf = namebuf[:i]
+		if i := strings.LastIndex(p, "."); i >= 0 {
+			p = p[:i]
 		}
-		outfile = fmt.Sprintf("%s.%c", namebuf, Thearch.Thechar)
+		outfile = fmt.Sprintf("%s.%c", p, Thearch.Thechar)
 	}
 }

src/cmd/internal/gc/obj.go

@@ -101,8 +101,8 @@ func dumpobj() {
 			obj.Bputc(bout, 0)
 		}
 		obj.Bseek(bout, startobj-ArhdrSize, 0)
-		namebuf = fmt.Sprintf("_go_.%c", Thearch.Thechar)
-		formathdr(arhdr[:], namebuf, size)
+		name := fmt.Sprintf("_go_.%c", Thearch.Thechar)
+		formathdr(arhdr[:], name, size)
 		obj.Bwrite(bout, arhdr[:])
 	}
 
@@ -199,22 +199,23 @@ func duintptr(s *Sym, off int, v uint64) int {
 var stringsym_gen int
 
 func stringsym(s string) *Sym {
+	var symname string
 	var pkg *Pkg
 	if len(s) > 100 {
 		// huge strings are made static to avoid long names
 		stringsym_gen++
-		namebuf = fmt.Sprintf(".gostring.%d", stringsym_gen)
+		symname = fmt.Sprintf(".gostring.%d", stringsym_gen)
 
 		pkg = localpkg
 	} else {
 		// small strings get named by their contents,
 		// so that multiple modules using the same string
 		// can share it.
-		namebuf = fmt.Sprintf("%q", s)
+		symname = fmt.Sprintf("%q", s)
 		pkg = gostringpkg
 	}
 
-	sym := Pkglookup(namebuf, pkg)
+	sym := Pkglookup(symname, pkg)
 
 	// SymUniq flag indicates that data is generated already
 	if sym.Flags&SymUniq != 0 {
@@ -252,8 +253,8 @@ func slicebytes(nam *Node, s string, len int) {
 	var m int
 
 	slicebytes_gen++
-	namebuf = fmt.Sprintf(".gobytes.%d", slicebytes_gen)
-	sym := Pkglookup(namebuf, localpkg)
+	symname := fmt.Sprintf(".gobytes.%d", slicebytes_gen)
+	sym := Pkglookup(symname, localpkg)
 	sym.Def = newname(sym)
 
 	off := 0

src/cmd/internal/gc/pgen.go

@@ -18,9 +18,8 @@ var makefuncdatasym_nsym int32
 func makefuncdatasym(namefmt string, funcdatakind int64) *Sym {
 	var nod Node
 
-	namebuf = fmt.Sprintf(namefmt, makefuncdatasym_nsym)
+	sym := Lookupf(namefmt, makefuncdatasym_nsym)
 	makefuncdatasym_nsym++
-	sym := Lookup(namebuf)
 	pnod := newname(sym)
 	pnod.Class = PEXTERN
 	Nodconst(&nod, Types[TINT32], funcdatakind)

src/cmd/internal/gc/sinit.go

@@ -517,9 +517,8 @@ func staticassign(l *Node, r *Node, out **NodeList) bool {
  * part of the composite literal.
  */
 func staticname(t *Type, ctxt int) *Node {
-	namebuf = fmt.Sprintf("statictmp_%.4d", statuniqgen)
+	n := newname(Lookupf("statictmp_%.4d", statuniqgen))
 	statuniqgen++
-	n := newname(Lookup(namebuf))
 	if ctxt == 0 {
 		n.Readonly = true
 	}

src/cmd/internal/gc/subr.go

@@ -281,6 +281,10 @@ func Lookup(name string) *Sym {
 	return localpkg.Lookup(name)
 }
 
+func Lookupf(format string, a ...interface{}) *Sym {
+	return Lookup(fmt.Sprintf(format, a...))
+}
+
 func LookupBytes(name []byte) *Sym {
 	return localpkg.LookupBytes(name)
 }

src/cmd/internal/gc/walk.go

@@ -1109,17 +1109,18 @@ func walkexpr(np **Node, init **NodeList) {
 			if Widthreg >= 8 || (et != TUINT64 && et != TINT64) {
 				goto ret
 			}
+			var fn string
 			if et == TINT64 {
-				namebuf = "int64"
+				fn = "int64"
 			} else {
-				namebuf = "uint64"
+				fn = "uint64"
 			}
 			if n.Op == ODIV {
-				namebuf += "div"
+				fn += "div"
 			} else {
-				namebuf += "mod"
+				fn += "mod"
 			}
-			n = mkcall(namebuf, n.Type, init, conv(n.Left, Types[et]), conv(n.Right, Types[et]))
+			n = mkcall(fn, n.Type, init, conv(n.Left, Types[et]), conv(n.Right, Types[et]))
 
 		default:
 			break
@@ -2882,13 +2883,14 @@ func addstr(n *Node, init **NodeList) *Node {
 		args = list(args, conv(l.N, Types[TSTRING]))
 	}
 
+	var fn string
 	if c <= 5 {
 		// small numbers of strings use direct runtime helpers.
 		// note: orderexpr knows this cutoff too.
-		namebuf = fmt.Sprintf("concatstring%d", c)
+		fn = fmt.Sprintf("concatstring%d", c)
 	} else {
 		// large numbers of strings are passed to the runtime as a slice.
-		namebuf = "concatstrings"
+		fn = "concatstrings"
 
 		t := typ(TARRAY)
 		t.Type = Types[TSTRING]
@@ -2901,7 +2903,7 @@ func addstr(n *Node, init **NodeList) *Node {
 		slice.Esc = EscNone
 	}
 
-	cat := syslook(namebuf, 1)
+	cat := syslook(fn, 1)
 	r := Nod(OCALL, cat, nil)
 	r.List = args
 	typecheck(&r, Erv)