cmd/internal/gc, cmd/internal/ld, cmd/internal/obj: teach compiler about local symbols

This lets us avoid loading string constants via the GOT and (together with
http://golang.org/cl/9102) results in the fannkuch benchmark having very similar
register usage with -dynlink as without.

Change-Id: Ic3892b399074982b76773c3e547cfbba5dabb6f9
Reviewed-on: https://go-review.googlesource.com/9103Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/cmd/6g/prog.go

@@ -299,7 +299,7 @@ func proginfo(p *obj.Prog) {
 		if p.As == x86.ALEAQ || info.Flags == gc.Pseudo || p.As == obj.ACALL || p.As == obj.ARET || p.As == obj.AJMP {
 			return
 		}
-		if p.As == obj.ADUFFZERO || p.As == obj.ADUFFCOPY || p.From.Name == obj.NAME_EXTERN || p.To.Name == obj.NAME_EXTERN {
+		if p.As == obj.ADUFFZERO || p.As == obj.ADUFFCOPY || (p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local) || (p.To.Name == obj.NAME_EXTERN && !p.To.Sym.Local) {
 			info.Reguse |= R15
 			info.Regset |= R15
 			return

src/cmd/internal/gc/gsubr.go

@@ -218,11 +218,15 @@ func ggloblnod(nam *Node) {
 	}
 }
 
-func ggloblsym(s *Sym, width int32, flags int8) {
+func ggloblsym(s *Sym, width int32, flags int16) {
 	p := Thearch.Gins(obj.AGLOBL, nil, nil)
 	p.From.Type = obj.TYPE_MEM
 	p.From.Name = obj.NAME_EXTERN
 	p.From.Sym = Linksym(s)
+	if flags&obj.LOCAL != 0 {
+		p.From.Sym.Local = true
+		flags &= ^obj.LOCAL
+	}
 	p.To.Type = obj.TYPE_CONST
 	p.To.Offset = int64(width)
 	p.From3.Offset = int64(flags)

src/cmd/internal/gc/obj.go

@@ -245,7 +245,7 @@ func stringsym(s string) *Sym {
 
 	off = duint8(sym, off, 0)                    // terminating NUL for runtime
 	off = (off + Widthptr - 1) &^ (Widthptr - 1) // round to pointer alignment
-	ggloblsym(sym, int32(off), obj.DUPOK|obj.RODATA)
+	ggloblsym(sym, int32(off), obj.DUPOK|obj.RODATA|obj.LOCAL)
 
 	return sym
 }
@@ -269,7 +269,7 @@ func slicebytes(nam *Node, s string, len int) {
 		off = dsname(sym, off, s[n:n+m])
 	}
 
-	ggloblsym(sym, int32(off), obj.NOPTR)
+	ggloblsym(sym, int32(off), obj.NOPTR|obj.LOCAL)
 
 	if nam.Op != ONAME {
 		Fatal("slicebytes %v", nam)

src/cmd/internal/gc/pgen.go

@@ -161,7 +161,7 @@ func emitptrargsmap() {
 		}
 	}
 
-	ggloblsym(sym, int32(off), obj.RODATA)
+	ggloblsym(sym, int32(off), obj.RODATA|obj.LOCAL)
 }
 
 // Sort the list of stack variables. Autos after anything else,

src/cmd/internal/gc/reflect.go

@@ -814,7 +814,7 @@ func dcommontype(s *Sym, ot int, t *Type) int {
 			for i := 0; i < 2*Widthptr; i++ {
 				duint8(sbits, i, gcmask[i])
 			}
-			ggloblsym(sbits, 2*int32(Widthptr), obj.DUPOK|obj.RODATA)
+			ggloblsym(sbits, 2*int32(Widthptr), obj.DUPOK|obj.RODATA|obj.LOCAL)
 		}
 
 		ot = dsymptr(s, ot, sbits, 0)
@@ -1203,7 +1203,7 @@ ok:
 	}
 
 	ot = dextratype(s, ot, t, xt)
-	ggloblsym(s, int32(ot), int8(dupok|obj.RODATA))
+	ggloblsym(s, int32(ot), int16(dupok|obj.RODATA))
 
 	// generate typelink.foo pointing at s = type.foo.
 	// The linker will leave a table of all the typelinks for
@@ -1229,7 +1229,7 @@ ok:
 		case TARRAY, TCHAN, TFUNC, TMAP:
 			slink := typelinksym(t)
 			dsymptr(slink, 0, s, 0)
-			ggloblsym(slink, int32(Widthptr), int8(dupok|obj.RODATA))
+			ggloblsym(slink, int32(Widthptr), int16(dupok|obj.RODATA))
 		}
 	}
 

src/cmd/internal/ld/objfile.go

@@ -72,8 +72,12 @@ func readsym(ctxt *Link, f *Biobuf, pkg string, pn string) {
 	if v != 0 && v != 1 {
 		log.Fatalf("invalid symbol version %d", v)
 	}
-	dupok := int(rdint(f))
-	dupok &= 1
+	flags := int(rdint(f))
+	dupok := flags & 1
+	local := false
+	if flags&2 != 0 {
+		local = true
+	}
 	size := int(rdint(f))
 	typ := rdsym(ctxt, f, pkg)
 	var data []byte
@@ -125,6 +129,7 @@ overwrite:
 	if s.Size < int64(size) {
 		s.Size = int64(size)
 	}
+	s.Local = local
 	if typ != nil { // if bss sym defined multiple times, take type from any one def
 		s.Gotype = typ
 	}

src/cmd/internal/ld/symtab.go

@@ -373,15 +373,7 @@ func symtab() {
 	// just defined above will be first.
 	// hide the specific symbols.
 	for s := Ctxt.Allsym; s != nil; s = s.Allsym {
-		if !s.Reachable || s.Special != 0 {
-			continue
-		}
-
-		if strings.Contains(s.Name, "..gostring.") || strings.Contains(s.Name, "..gobytes.") {
-			s.Local = true
-		}
-
-		if s.Type != obj.SRODATA {
+		if !s.Reachable || s.Special != 0 || s.Type != obj.SRODATA {
 			continue
 		}
 

src/cmd/internal/obj/link.go

@@ -273,6 +273,7 @@ const (
 	A_ARCHSPECIFIC
 )
 
+// An LSym is the sort of symbol that is written to an object file.
 type LSym struct {
 	Name      string
 	Type      int16
@@ -283,18 +284,25 @@ type LSym struct {
 	Leaf      uint8
 	Seenglobl uint8
 	Onlist    uint8
-	Args      int32
-	Locals    int32
-	Value     int64
-	Size      int64
-	Next      *LSym
-	Gotype    *LSym
-	Autom     *Auto
-	Text      *Prog
-	Etext     *Prog
-	Pcln      *Pcln
-	P         []byte
-	R         []Reloc
+	// Local means make the symbol local even when compiling Go code to reference Go
+	// symbols in other shared libraries, as in this mode symbols are global by
+	// default. "local" here means in the sense of the dynamic linker, i.e. not
+	// visible outside of the module (shared library or executable) that contains its
+	// definition. (When not compiling to support Go shared libraries, all symbols are
+	// local in this sense unless there is a cgo_export_* directive).
+	Local  bool
+	Args   int32
+	Locals int32
+	Value  int64
+	Size   int64
+	Next   *LSym
+	Gotype *LSym
+	Autom  *Auto
+	Text   *Prog
+	Etext  *Prog
+	Pcln   *Pcln
+	P      []byte
+	R      []Reloc
 }
 
 type Pcln struct {

src/cmd/internal/obj/objfile.go

@@ -400,7 +400,11 @@ func writesym(ctxt *Link, b *Biobuf, s *LSym) {
 	wrint(b, int64(s.Type))
 	wrstring(b, s.Name)
 	wrint(b, int64(s.Version))
-	wrint(b, int64(s.Dupok))
+	flags := int64(s.Dupok)
+	if s.Local {
+		flags |= 2
+	}
+	wrint(b, flags)
 	wrint(b, s.Size)
 	wrsym(b, s.Gotype)
 	wrdata(b, s.P)

src/cmd/internal/obj/textflag.go

@@ -30,4 +30,7 @@ const (
 
 	// This function uses its incoming context register.
 	NEEDCTXT = 64
+
+	// When passed to ggloblsym, causes Local to be set to true on the LSym it creates.
+	LOCAL = 128
 )

src/cmd/internal/obj/x86/obj6.go

@@ -251,6 +251,7 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 			p.From.Type = obj.TYPE_MEM
 			p.From.Name = obj.NAME_EXTERN
 			p.From.Sym = s
+			p.From.Sym.Local = true
 			p.From.Offset = 0
 		}
 
@@ -294,6 +295,7 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 			p.From.Type = obj.TYPE_MEM
 			p.From.Name = obj.NAME_EXTERN
 			p.From.Sym = s
+			p.From.Sym.Local = true
 			p.From.Offset = 0
 		}
 	}
@@ -327,11 +329,11 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 	}
 
 	if ctxt.Flag_dynlink {
-		if p.As == ALEAQ && p.From.Type == obj.TYPE_MEM && p.From.Name == obj.NAME_EXTERN {
+		if p.As == ALEAQ && p.From.Type == obj.TYPE_MEM && p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local {
 			p.As = AMOVQ
 			p.From.Type = obj.TYPE_ADDR
 		}
-		if p.From.Type == obj.TYPE_ADDR && p.From.Name == obj.NAME_EXTERN {
+		if p.From.Type == obj.TYPE_ADDR && p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local {
 			if p.As != AMOVQ {
 				ctxt.Diag("do not know how to handle TYPE_ADDR in %v with -dynlink", p)
 			}
@@ -356,12 +358,12 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 			ctxt.Diag("don't know how to handle %v with -dynlink", p)
 		}
 		var source *obj.Addr
-		if p.From.Name == obj.NAME_EXTERN {
-			if p.To.Name == obj.NAME_EXTERN {
+		if p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local {
+			if p.To.Name == obj.NAME_EXTERN && !p.To.Sym.Local {
 				ctxt.Diag("cannot handle NAME_EXTERN on both sides in %v with -dynlink", p)
 			}
 			source = &p.From
-		} else if p.To.Name == obj.NAME_EXTERN {
+		} else if p.To.Name == obj.NAME_EXTERN && !p.To.Sym.Local {
 			source = &p.To
 		} else {
 			return