cmd/compile, cmd/link: stop generating unused go.string.hdr symbols.

name       old s/op    new s/op    delta
LinkCmdGo   0.29 ± 5%   0.29 ± 8%  -2.60%   (p=0.000 n=97+98)

name       old MaxRSS  new MaxRSS  delta
LinkCmdGo   106k ± 4%   105k ± 3%  -1.00%  (p=0.000 n=100+99)

Change-Id: I75a1c3b24ea711a15a5d2eae026b70b97ee7bad4
Reviewed-on: https://go-review.googlesource.com/31030
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>

src/cmd/compile/internal/gc/obj.go

@@ -280,18 +280,7 @@ func dbvec(s *Sym, off int, bv bvec) int {
 	return off
 }
 
-// stringConstantSyms holds the pair of symbols we create for a
-// constant string.
-type stringConstantSyms struct {
-	hdr  *obj.LSym // string header
-	data *obj.LSym // actual string data
-}
-
-// stringConstants maps from the symbol name we use for the string
-// contents to the pair of linker symbols for that string.
-var stringConstants = make(map[string]stringConstantSyms, 100)
-
-func stringsym(s string) (hdr, data *obj.LSym) {
+func stringsym(s string) (data *obj.LSym) {
 	var symname string
 	if len(s) > 100 {
 		// Huge strings are hashed to avoid long names in object files.
@@ -308,33 +297,15 @@ func stringsym(s string) (hdr, data *obj.LSym) {
 	const prefix = "go.string."
 	symdataname := prefix + symname
 
-	// All the strings have the same prefix, so ignore it for map
-	// purposes, but use a slice of the symbol name string to
-	// reduce long-term memory overhead.
-	key := symdataname[len(prefix):]
-
-	if syms, ok := stringConstants[key]; ok {
-		return syms.hdr, syms.data
-	}
-
-	symhdrname := "go.string.hdr." + symname
-
-	symhdr := obj.Linklookup(Ctxt, symhdrname, 0)
 	symdata := obj.Linklookup(Ctxt, symdataname, 0)
 
-	stringConstants[key] = stringConstantSyms{symhdr, symdata}
-
-	// string header
-	off := 0
-	off = dsymptrLSym(symhdr, off, symdata, 0)
-	off = duintxxLSym(symhdr, off, uint64(len(s)), Widthint)
-	ggloblLSym(symhdr, int32(off), obj.DUPOK|obj.RODATA|obj.LOCAL)
-
-	// string data
-	off = dsnameLSym(symdata, 0, s)
-	ggloblLSym(symdata, int32(off), obj.DUPOK|obj.RODATA|obj.LOCAL)
+	if !symdata.Seenglobl {
+		// string data
+		off := dsnameLSym(symdata, 0, s)
+		ggloblLSym(symdata, int32(off), obj.DUPOK|obj.RODATA|obj.LOCAL)
+	}
 
-	return symhdr, symdata
+	return symdata
 }
 
 var slicebytes_gen int
@@ -357,14 +328,6 @@ func slicebytes(nam *Node, s string, len int) {
 	duintxx(nam.Sym, off, uint64(len), Widthint)
 }
 
-func datagostring(sval string, a *obj.Addr) {
-	symhdr, _ := stringsym(sval)
-	a.Type = obj.TYPE_MEM
-	a.Name = obj.NAME_EXTERN
-	a.Sym = symhdr
-	a.Offset = 0
-}
-
 func dsname(s *Sym, off int, t string) int {
 	return dsnameLSym(Linksym(s), off, t)
 }
@@ -465,7 +428,7 @@ func gdatacomplex(nam *Node, cval *Mpcplx) {
 
 func gdatastring(nam *Node, sval string) {
 	s := Linksym(nam.Sym)
-	_, symdata := stringsym(sval)
+	symdata := stringsym(sval)
 	s.WriteAddr(Ctxt, nam.Xoffset, Widthptr, symdata, 0)
 	s.WriteInt(Ctxt, nam.Xoffset+int64(Widthptr), Widthint, int64(len(sval)))
 }

src/cmd/compile/internal/gc/ssa.go

@@ -4525,7 +4525,7 @@ func (s *ssaExport) TypeBytePtr() ssa.Type { return ptrto(Types[TUINT8]) }
 // is the data component of a global string constant containing s.
 func (*ssaExport) StringData(s string) interface{} {
 	// TODO: is idealstring correct?  It might not matter...
-	_, data := stringsym(s)
+	data := stringsym(s)
 	return &ssa.ExternSymbol{Typ: idealstring, Sym: data}
 }
 

src/cmd/internal/obj/link.go

@@ -393,7 +393,6 @@ const (
 	STYPE
 	SSTRING
 	SGOSTRING
-	SGOSTRINGHDR
 	SGOFUNC
 	SGCBITS
 	SRODATA
@@ -417,7 +416,6 @@ const (
 	STYPERELRO
 	SSTRINGRELRO
 	SGOSTRINGRELRO
-	SGOSTRINGHDRRELRO
 	SGOFUNCRELRO
 	SGCBITSRELRO
 	SRODATARELRO
@@ -466,7 +464,6 @@ var ReadOnly = []SymKind{
 	STYPE,
 	SSTRING,
 	SGOSTRING,
-	SGOSTRINGHDR,
 	SGOFUNC,
 	SGCBITS,
 	SRODATA,
@@ -476,14 +473,13 @@ var ReadOnly = []SymKind{
 // RelROMap describes the transformation of read-only symbols to rel-ro
 // symbols.
 var RelROMap = map[SymKind]SymKind{
-	STYPE:        STYPERELRO,
-	SSTRING:      SSTRINGRELRO,
-	SGOSTRING:    SGOSTRINGRELRO,
-	SGOSTRINGHDR: SGOSTRINGHDRRELRO,
-	SGOFUNC:      SGOFUNCRELRO,
-	SGCBITS:      SGCBITSRELRO,
-	SRODATA:      SRODATARELRO,
-	SFUNCTAB:     SFUNCTABRELRO,
+	STYPE:     STYPERELRO,
+	SSTRING:   SSTRINGRELRO,
+	SGOSTRING: SGOSTRINGRELRO,
+	SGOFUNC:   SGOFUNCRELRO,
+	SGCBITS:   SGCBITSRELRO,
+	SRODATA:   SRODATARELRO,
+	SFUNCTAB:  SFUNCTABRELRO,
 }
 
 type Reloc struct {

src/cmd/internal/obj/symkind_string.go

@@ -4,9 +4,9 @@ package obj
 
 import "fmt"
 
-const _SymKind_name = "SxxxSTEXTSELFRXSECTSTYPESSTRINGSGOSTRINGSGOSTRINGHDRSGOFUNCSGCBITSSRODATASFUNCTABSELFROSECTSMACHOPLTSTYPERELROSSTRINGRELROSGOSTRINGRELROSGOSTRINGHDRRELROSGOFUNCRELROSGCBITSRELROSRODATARELROSFUNCTABRELROSTYPELINKSITABLINKSSYMTABSPCLNTABSELFSECTSMACHOSMACHOGOTSWINDOWSSELFGOTSNOPTRDATASINITARRSDATASBSSSNOPTRBSSSTLSBSSSXREFSMACHOSYMSTRSMACHOSYMTABSMACHOINDIRECTPLTSMACHOINDIRECTGOTSFILESFILEPATHSCONSTSDYNIMPORTSHOSTOBJSDWARFSECTSDWARFINFO"
+const _SymKind_name = "SxxxSTEXTSELFRXSECTSTYPESSTRINGSGOSTRINGSGOFUNCSGCBITSSRODATASFUNCTABSELFROSECTSMACHOPLTSTYPERELROSSTRINGRELROSGOSTRINGRELROSGOFUNCRELROSGCBITSRELROSRODATARELROSFUNCTABRELROSTYPELINKSITABLINKSSYMTABSPCLNTABSELFSECTSMACHOSMACHOGOTSWINDOWSSELFGOTSNOPTRDATASINITARRSDATASBSSSNOPTRBSSSTLSBSSSXREFSMACHOSYMSTRSMACHOSYMTABSMACHOINDIRECTPLTSMACHOINDIRECTGOTSFILESFILEPATHSCONSTSDYNIMPORTSHOSTOBJSDWARFSECTSDWARFINFO"
 
-var _SymKind_index = [...]uint16{0, 4, 9, 19, 24, 31, 40, 52, 59, 66, 73, 81, 91, 100, 110, 122, 136, 153, 165, 177, 189, 202, 211, 220, 227, 235, 243, 249, 258, 266, 273, 283, 291, 296, 300, 309, 316, 321, 333, 345, 362, 379, 384, 393, 399, 409, 417, 427, 437}
+var _SymKind_index = [...]uint16{0, 4, 9, 19, 24, 31, 40, 47, 54, 61, 69, 79, 88, 98, 110, 124, 136, 148, 160, 173, 182, 191, 198, 206, 214, 220, 229, 237, 244, 254, 262, 267, 271, 280, 287, 292, 304, 316, 333, 350, 355, 364, 370, 380, 388, 398, 408}
 
 func (i SymKind) String() string {
 	if i < 0 || i >= SymKind(len(_SymKind_index)-1) {

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

@@ -1135,7 +1135,7 @@ func symalign(s *Symbol) int32 {
 	} else if s.Align != 0 {
 		return min
 	}
-	if (strings.HasPrefix(s.Name, "go.string.") && !strings.HasPrefix(s.Name, "go.string.hdr.")) || strings.HasPrefix(s.Name, "type..namedata.") {
+	if strings.HasPrefix(s.Name, "go.string.") || strings.HasPrefix(s.Name, "type..namedata.") {
 		// String data is just bytes.
 		// If we align it, we waste a lot of space to padding.
 		return min
@@ -1336,7 +1336,7 @@ func (ctxt *Link) dodata() {
 			for _, s := range data[symnro] {
 				isRelro := len(s.R) > 0
 				switch s.Type {
-				case obj.STYPE, obj.SGOSTRINGHDR, obj.STYPERELRO, obj.SGOSTRINGHDRRELRO, obj.SGOFUNCRELRO:
+				case obj.STYPE, obj.STYPERELRO, obj.SGOFUNCRELRO:
 					// Symbols are not sorted yet, so it is possible
 					// that an Outer symbol has been changed to a
 					// relro Type before it reaches here.

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

@@ -1890,13 +1890,11 @@ func genasmsym(ctxt *Link, put func(*Link, *Symbol, string, SymbolType, int64, *
 			obj.STYPE,
 			obj.SSTRING,
 			obj.SGOSTRING,
-			obj.SGOSTRINGHDR,
 			obj.SGOFUNC,
 			obj.SGCBITS,
 			obj.STYPERELRO,
 			obj.SSTRINGRELRO,
 			obj.SGOSTRINGRELRO,
-			obj.SGOSTRINGHDRRELRO,
 			obj.SGOFUNCRELRO,
 			obj.SGCBITSRELRO,
 			obj.SRODATARELRO,

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

@@ -435,10 +435,9 @@ func (ctxt *Link) symtab() {
 		return s
 	}
 	var (
-		symgostring    = groupSym("go.string.*", obj.SGOSTRING)
-		symgostringhdr = groupSym("go.string.hdr.*", obj.SGOSTRINGHDR)
-		symgofunc      = groupSym("go.func.*", obj.SGOFUNC)
-		symgcbits      = groupSym("runtime.gcbits.*", obj.SGCBITS)
+		symgostring = groupSym("go.string.*", obj.SGOSTRING)
+		symgofunc   = groupSym("go.func.*", obj.SGOFUNC)
+		symgcbits   = groupSym("runtime.gcbits.*", obj.SGCBITS)
 	)
 
 	var symgofuncrel *Symbol
@@ -508,10 +507,6 @@ func (ctxt *Link) symtab() {
 			s.Type = obj.SGOSTRING
 			s.Attr |= AttrHidden
 			s.Outer = symgostring
-			if strings.HasPrefix(s.Name, "go.string.hdr.") {
-				s.Type = obj.SGOSTRINGHDR
-				s.Outer = symgostringhdr
-			}
 
 		case strings.HasPrefix(s.Name, "runtime.gcbits."):
 			s.Type = obj.SGCBITS