cmd/compile, cmd/link, cmd/newlink: remove support for weak symbols

They were only used for rtype.ptrToThis which David Crawshaw removed a couple
of weeks ago. Removes two traversals of Ctxt.Allsym from the linker but it
doesn't seem to make much difference to performance.

Change-Id: I5c305e0180186f643221d57822d301de4aa18827
Reviewed-on: https://go-review.googlesource.com/20287
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -425,8 +425,6 @@ var typepkg *Pkg // fake package for runtime type info (headers)
 
 var typelinkpkg *Pkg // fake package for runtime type info (data)
 
-var weaktypepkg *Pkg // weak references to runtime type info
-
 var unsafepkg *Pkg // package unsafe
 
 var trackpkg *Pkg // fake package for field tracking

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

@@ -140,11 +140,6 @@ func Main() {
 	itabpkg.Name = "go.itab"
 	itabpkg.Prefix = "go.itab" // not go%2eitab
 
-	weaktypepkg = mkpkg("go.weak.type")
-
-	weaktypepkg.Name = "go.weak.type"
-	weaktypepkg.Prefix = "go.weak.type" // not go%2eweak%2etype
-
 	typelinkpkg = mkpkg("go.typelink")
 	typelinkpkg.Name = "go.typelink"
 	typelinkpkg.Prefix = "go.typelink" // not go%2etypelink

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

@@ -844,15 +844,6 @@ func typename(t *Type) *Node {
 	return n
 }
 
-func weaktypesym(t *Type) *Sym {
-	p := Tconv(t, obj.FmtLeft)
-	s := Pkglookup(p, weaktypepkg)
-
-	//print("weaktypesym: %s -> %+S\n", p, s);
-
-	return s
-}
-
 // isreflexive reports whether t has a reflexive equality operator.
 // That is, if x==x for all x of type t.
 func isreflexive(t *Type) bool {

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

@@ -373,9 +373,6 @@ func mark1(s *LSym, parent *LSym) {
 	if s == nil || s.Attr.Reachable() {
 		return
 	}
-	if strings.HasPrefix(s.Name, "go.weak.") {
-		return
-	}
 	s.Attr |= AttrReachable
 	s.Reachparent = parent
 	markQueue = append(markQueue, s)
@@ -494,14 +491,6 @@ func deadcode() {
 		}
 	}
 
-	for _, s := range Ctxt.Allsym {
-		if strings.HasPrefix(s.Name, "go.weak.") {
-			s.Attr |= AttrSpecial // do not lay out in data segment
-			s.Attr |= AttrReachable
-			s.Attr |= AttrHidden
-		}
-	}
-
 	// record field tracking references
 	var buf bytes.Buffer
 	for _, s := range Ctxt.Allsym {
@@ -532,26 +521,6 @@ func deadcode() {
 	addstrdata(tracksym, buf.String())
 }
 
-func doweak() {
-	// resolve weak references only if
-	// target symbol will be in binary anyway.
-	for _, s := range Ctxt.Allsym {
-		if strings.HasPrefix(s.Name, "go.weak.") {
-			t := Linkrlookup(Ctxt, s.Name[8:], int(s.Version))
-			if t != nil && t.Type != 0 && t.Attr.Reachable() {
-				s.Value = t.Value
-				s.Type = t.Type
-				s.Outer = t
-			} else {
-				s.Type = obj.SCONST
-				s.Value = 0
-			}
-
-			continue
-		}
-	}
-}
-
 func addexport() {
 	if HEADTYPE == obj.Hdarwin {
 		return

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

@@ -216,7 +216,6 @@ func Ldmain() {
 	symtab()
 	dodata()
 	address()
-	doweak()
 	reloc()
 	Thearch.Asmb()
 	undef()

src/cmd/newlink/auto.go

@@ -42,8 +42,7 @@ var linkerDefined = map[string]bool{
 
 // isAuto reports whether sym is an automatically-generated data or constant symbol.
 func (p *Prog) isAuto(sym goobj.SymID) bool {
-	return strings.HasPrefix(sym.Name, "go.weak.") ||
-		strings.HasPrefix(sym.Name, "$f64.") ||
+	return strings.HasPrefix(sym.Name, "$f64.") ||
 		strings.HasPrefix(sym.Name, "$f32.") ||
 		linkerDefined[sym.Name]
 }
@@ -85,24 +84,6 @@ func (p *Prog) autoData() {
 	}
 }
 
-// autoConst defines the automatically generated constant symbols needed by p.
-func (p *Prog) autoConst() {
-	for sym := range p.Missing {
-		switch {
-		case strings.HasPrefix(sym.Name, "go.weak."):
-			// weak symbol resolves to actual symbol if present, or else nil.
-			delete(p.Missing, sym)
-			targ := sym
-			targ.Name = sym.Name[len("go.weak."):]
-			var addr Addr
-			if s := p.Syms[targ]; s != nil {
-				addr = s.Addr
-			}
-			p.defineConst(sym.Name, addr)
-		}
-	}
-}
-
 // defineConst defines a new symbol with the given name and constant address.
 func (p *Prog) defineConst(name string, addr Addr) {
 	sym := goobj.SymID{Name: name}

src/cmd/newlink/auto_test.go

@@ -22,7 +22,6 @@ import (
 // identical 8-byte sequences.
 var autoTests = []string{
 	"testdata/autosection.6",
-	"testdata/autoweak.6",
 }
 
 func TestAuto(t *testing.T) {

src/cmd/newlink/prog.go

@@ -149,7 +149,6 @@ func (p *Prog) link(w io.Writer, mainFile string) {
 	p.runtime()
 	p.autoData()
 	p.layout()
-	p.autoConst()
 	if p.NumError > 0 {
 		return
 	}

src/cmd/newlink/testdata/autoweak.s

@@ -1,30 +0,0 @@
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Test of go.weak symbols.
-
-TEXT start(SB),7,$0
-	MOVQ $autotab(SB),AX
-	MOVQ $autoptr(SB),AX
-	RET
-
-// go.weak.sym should resolve to sym, because sym is in the binary.
-DATA autotab+0(SB)/8, $go·weak·sym(SB)
-DATA autotab+8(SB)/8, $sym(SB)
-
-// go.weak.missingsym should resolve to 0, because missingsym is not in the binary.
-DATA autotab+16(SB)/8, $go·weak·missingsym(SB)
-DATA autotab+24(SB)/8, $0
-
-// go.weak.deadsym should resolve to 0, because deadsym is discarded during dead code removal
-DATA autotab+32(SB)/8, $go·weak·deadsym(SB)
-DATA autotab+40(SB)/8, $0
-
-GLOBL autotab(SB), $48
-
-GLOBL sym(SB), $1
-
-GLOBL deadsym(SB), $1
-
-GLOBL autoptr(SB), $0