src/cmd/compile/internal/gc/pgen.go - go - Git at Google

 // Copyright 2011 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.

 package gc

 import (
 	"cmd/compile/internal/ssa"
 	"cmd/internal/dwarf"
 	"cmd/internal/obj"
 	"cmd/internal/src"
 	"cmd/internal/sys"
 	"fmt"
 	"sort"
 )

 // "Portable" code generation.

 var makefuncdatasym_nsym int

 func makefuncdatasym(pp *Progs, nameprefix string, funcdatakind int64) *Sym {
 	sym := lookupN(nameprefix, makefuncdatasym_nsym)
 	makefuncdatasym_nsym++
 	p := pp.Prog(obj.AFUNCDATA)
 	Addrconst(&p.From, funcdatakind)
 	p.To.Type = obj.TYPE_MEM
 	p.To.Name = obj.NAME_EXTERN
 	p.To.Sym = Linksym(sym)
 	return sym
 }

 // TODO(mdempsky): Update to reference OpVar{Def,Kill,Live} instead
 // and move to plive.go.

 // VARDEF is an annotation for the liveness analysis, marking a place
 // where a complete initialization (definition) of a variable begins.
 // Since the liveness analysis can see initialization of single-word
 // variables quite easy, gvardef is usually only called for multi-word
 // or 'fat' variables, those satisfying isfat(n->type).
 // However, gvardef is also called when a non-fat variable is initialized
 // via a block move; the only time this happens is when you have
 //	return f()
 // for a function with multiple return values exactly matching the return
 // types of the current function.
 //
 // A 'VARDEF x' annotation in the instruction stream tells the liveness
 // analysis to behave as though the variable x is being initialized at that
 // point in the instruction stream. The VARDEF must appear before the
 // actual (multi-instruction) initialization, and it must also appear after
 // any uses of the previous value, if any. For example, if compiling:
 //
 //	x = x[1:]
 //
 // it is important to generate code like:
 //
 //	base, len, cap = pieces of x[1:]
 //	VARDEF x
 //	x = {base, len, cap}
 //
 // If instead the generated code looked like:
 //
 //	VARDEF x
 //	base, len, cap = pieces of x[1:]
 //	x = {base, len, cap}
 //
 // then the liveness analysis would decide the previous value of x was
 // unnecessary even though it is about to be used by the x[1:] computation.
 // Similarly, if the generated code looked like:
 //
 //	base, len, cap = pieces of x[1:]
 //	x = {base, len, cap}
 //	VARDEF x
 //
 // then the liveness analysis will not preserve the new value of x, because
 // the VARDEF appears to have "overwritten" it.
 //
 // VARDEF is a bit of a kludge to work around the fact that the instruction
 // stream is working on single-word values but the liveness analysis
 // wants to work on individual variables, which might be multi-word
 // aggregates. It might make sense at some point to look into letting
 // the liveness analysis work on single-word values as well, although
 // there are complications around interface values, slices, and strings,
 // all of which cannot be treated as individual words.
 //
 // VARKILL is the opposite of VARDEF: it marks a value as no longer needed,
 // even if its address has been taken. That is, a VARKILL annotation asserts
 // that its argument is certainly dead, for use when the liveness analysis
 // would not otherwise be able to deduce that fact.

 func emitptrargsmap() {
 	if Curfn.Func.Nname.Sym.Name == "_" {
 		return
 	}
 	sym := lookup(fmt.Sprintf("%s.args_stackmap", Curfn.Func.Nname.Sym.Name))

 	nptr := int(Curfn.Type.ArgWidth() / int64(Widthptr))
 	bv := bvalloc(int32(nptr) * 2)
 	nbitmap := 1
 	if Curfn.Type.Results().NumFields() > 0 {
 		nbitmap = 2
 	}
 	off := duint32(sym, 0, uint32(nbitmap))
 	off = duint32(sym, off, uint32(bv.n))
 	var xoffset int64
 	if Curfn.IsMethod() {
 		xoffset = 0
 		onebitwalktype1(Curfn.Type.Recvs(), &xoffset, bv)
 	}

 	if Curfn.Type.Params().NumFields() > 0 {
 		xoffset = 0
 		onebitwalktype1(Curfn.Type.Params(), &xoffset, bv)
 	}

 	off = dbvec(sym, off, bv)
 	if Curfn.Type.Results().NumFields() > 0 {
 		xoffset = 0
 		onebitwalktype1(Curfn.Type.Results(), &xoffset, bv)
 		off = dbvec(sym, off, bv)
 	}

 	ggloblsym(sym, int32(off), obj.RODATA|obj.LOCAL)
 }

 // cmpstackvarlt reports whether the stack variable a sorts before b.
 //
 // Sort the list of stack variables. Autos after anything else,
 // within autos, unused after used, within used, things with
 // pointers first, zeroed things first, and then decreasing size.
 // Because autos are laid out in decreasing addresses
 // on the stack, pointers first, zeroed things first and decreasing size
 // really means, in memory, things with pointers needing zeroing at
 // the top of the stack and increasing in size.
 // Non-autos sort on offset.
 func cmpstackvarlt(a, b *Node) bool {
 	if (a.Class == PAUTO) != (b.Class == PAUTO) {
 		return b.Class == PAUTO
 	}

 	if a.Class != PAUTO {
 		return a.Xoffset < b.Xoffset
 	}

 	if a.Used() != b.Used() {
 		return a.Used()
 	}

 	ap := haspointers(a.Type)
 	bp := haspointers(b.Type)
 	if ap != bp {
 		return ap
 	}

 	ap = a.Name.Needzero()
 	bp = b.Name.Needzero()
 	if ap != bp {
 		return ap
 	}

 	if a.Type.Width != b.Type.Width {
 		return a.Type.Width > b.Type.Width
 	}

 	return a.Sym.Name < b.Sym.Name
 }

 // byStackvar implements sort.Interface for []*Node using cmpstackvarlt.
 type byStackVar []*Node

 func (s byStackVar) Len() int           { return len(s) }
 func (s byStackVar) Less(i, j int) bool { return cmpstackvarlt(s[i], s[j]) }
 func (s byStackVar) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }

 var scratchFpMem *Node

 func (s *ssafn) AllocFrame(f *ssa.Func) {
 	s.stksize = 0
 	s.stkptrsize = 0
 	fn := s.curfn.Func

 	// Mark the PAUTO's unused.
 	for _, ln := range fn.Dcl {
 		if ln.Class == PAUTO {
 			ln.SetUsed(false)
 		}
 	}

 	for _, l := range f.RegAlloc {
 		if ls, ok := l.(ssa.LocalSlot); ok {
 			ls.N.(*Node).SetUsed(true)
 		}

 	}

 	scratchUsed := false
 	for _, b := range f.Blocks {
 		for _, v := range b.Values {
 			switch a := v.Aux.(type) {
 			case *ssa.ArgSymbol:
 				a.Node.(*Node).SetUsed(true)
 			case *ssa.AutoSymbol:
 				a.Node.(*Node).SetUsed(true)
 			}

 			if !scratchUsed {
 				scratchUsed = v.Op.UsesScratch()
 			}
 		}
 	}

 	if f.Config.NeedsFpScratch {
 		scratchFpMem = tempAt(src.NoXPos, s.curfn, Types[TUINT64])
 		scratchFpMem.SetUsed(scratchUsed)
 	}

 	sort.Sort(byStackVar(fn.Dcl))

 	// Reassign stack offsets of the locals that are used.
 	for i, n := range fn.Dcl {
 		if n.Op != ONAME || n.Class != PAUTO {
 			continue
 		}
 		if !n.Used() {
 			fn.Dcl = fn.Dcl[:i]
 			break
 		}

 		dowidth(n.Type)
 		w := n.Type.Width
 		if w >= thearch.MAXWIDTH || w < 0 {
 			Fatalf("bad width")
 		}
 		s.stksize += w
 		s.stksize = Rnd(s.stksize, int64(n.Type.Align))
 		if haspointers(n.Type) {
 			s.stkptrsize = s.stksize
 		}
 		if thearch.LinkArch.InFamily(sys.MIPS, sys.MIPS64, sys.ARM, sys.ARM64, sys.PPC64, sys.S390X) {
 			s.stksize = Rnd(s.stksize, int64(Widthptr))
 		}
 		if s.stksize >= 1<<31 {
 			yyerrorl(s.curfn.Pos, "stack frame too large (>2GB)")
 		}

 		n.Xoffset = -s.stksize
 	}

 	s.stksize = Rnd(s.stksize, int64(Widthreg))
 	s.stkptrsize = Rnd(s.stkptrsize, int64(Widthreg))
 }

 func compile(fn *Node) {
 	if Newproc == nil {
 		Newproc = Sysfunc("newproc")
 		Deferproc = Sysfunc("deferproc")
 		Deferreturn = Sysfunc("deferreturn")
 		Duffcopy = Sysfunc("duffcopy")
 		Duffzero = Sysfunc("duffzero")
 		panicindex = Sysfunc("panicindex")
 		panicslice = Sysfunc("panicslice")
 		panicdivide = Sysfunc("panicdivide")
 		growslice = Sysfunc("growslice")
 		panicdottypeE = Sysfunc("panicdottypeE")
 		panicdottypeI = Sysfunc("panicdottypeI")
 		panicnildottype = Sysfunc("panicnildottype")
 		assertE2I = Sysfunc("assertE2I")
 		assertE2I2 = Sysfunc("assertE2I2")
 		assertI2I = Sysfunc("assertI2I")
 		assertI2I2 = Sysfunc("assertI2I2")
 	}

 	Curfn = fn
 	dowidth(fn.Type)

 	if fn.Nbody.Len() == 0 {
 		emitptrargsmap()
 		return
 	}

 	saveerrors()

 	order(fn)
 	if nerrors != 0 {
 		return
 	}

 	walk(fn)
 	if nerrors != 0 {
 		return
 	}
 	checkcontrolflow(fn)
 	if nerrors != 0 {
 		return
 	}
 	if instrumenting {
 		instrument(fn)
 	}
 	if nerrors != 0 {
 		return
 	}

 	// From this point, there should be no uses of Curfn. Enforce that.
 	Curfn = nil

 	// Build an SSA backend function.
 	ssafn := buildssa(fn)
 	if nerrors != 0 {
 		return
 	}

 	pp := newProgs(fn)
 	genssa(ssafn, pp)
 	fieldtrack(pp.Text.From.Sym, fn.Func.FieldTrack)
 	pp.Flush()
 }

 func debuginfo(fnsym *obj.LSym, curfn interface{}) []*dwarf.Var {
 	fn := curfn.(*Node)
 	if expect := Linksym(fn.Func.Nname.Sym); fnsym != expect {
 		Fatalf("unexpected fnsym: %v != %v", fnsym, expect)
 	}

 	var vars []*dwarf.Var
 	for _, n := range fn.Func.Dcl {
 		if n.Op != ONAME { // might be OTYPE or OLITERAL
 			continue
 		}

 		var name obj.AddrName
 		var abbrev int
 		offs := n.Xoffset

 		switch n.Class {
 		case PAUTO:
 			if !n.Used() {
 				continue
 			}
 			name = obj.NAME_AUTO

 			abbrev = dwarf.DW_ABRV_AUTO
 			if Ctxt.FixedFrameSize() == 0 {
 				offs -= int64(Widthptr)
 			}
 			if obj.Framepointer_enabled(obj.GOOS, obj.GOARCH) {
 				offs -= int64(Widthptr)
 			}

 		case PPARAM, PPARAMOUT:
 			name = obj.NAME_PARAM

 			abbrev = dwarf.DW_ABRV_PARAM
 			offs += Ctxt.FixedFrameSize()

 		default:
 			continue
 		}

 		gotype := Linksym(ngotype(n))
 		fnsym.Autom = append(fnsym.Autom, &obj.Auto{
 			Asym:    obj.Linklookup(Ctxt, n.Sym.Name, 0),
 			Aoffset: int32(n.Xoffset),
 			Name:    name,
 			Gotype:  gotype,
 		})

 		if n.IsAutoTmp() {
 			continue
 		}

 		typename := dwarf.InfoPrefix + gotype.Name[len("type."):]
 		vars = append(vars, &dwarf.Var{
 			Name:   n.Sym.Name,
 			Abbrev: abbrev,
 			Offset: int32(offs),
 			Type:   obj.Linklookup(Ctxt, typename, 0),
 		})
 	}

 	// Stable sort so that ties are broken with declaration order.
 	sort.Stable(dwarf.VarsByOffset(vars))

 	return vars
 }

 // fieldtrack adds R_USEFIELD relocations to fnsym to record any
 // struct fields that it used.
 func fieldtrack(fnsym *obj.LSym, tracked map[*Sym]struct{}) {
 	if fnsym == nil {
 		return
 	}
 	if obj.Fieldtrack_enabled == 0 || len(tracked) == 0 {
 		return
 	}

 	trackSyms := make([]*Sym, 0, len(tracked))
 	for sym := range tracked {
 		trackSyms = append(trackSyms, sym)
 	}
 	sort.Sort(symByName(trackSyms))
 	for _, sym := range trackSyms {
 		r := obj.Addrel(fnsym)
 		r.Sym = Linksym(sym)
 		r.Type = obj.R_USEFIELD
 	}
 }

 type symByName []*Sym

 func (a symByName) Len() int           { return len(a) }
 func (a symByName) Less(i, j int) bool { return a[i].Name < a[j].Name }
 func (a symByName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
	// Copyright 2011 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.

	package gc

	import (
	"cmd/compile/internal/ssa"
	"cmd/internal/dwarf"
	"cmd/internal/obj"
	"cmd/internal/src"
	"cmd/internal/sys"
	"fmt"
	"sort"
	)

	// "Portable" code generation.

	var makefuncdatasym_nsym int

	func makefuncdatasym(pp Progs, nameprefix string, funcdatakind int64) Sym {
	sym := lookupN(nameprefix, makefuncdatasym_nsym)
	makefuncdatasym_nsym++
	p := pp.Prog(obj.AFUNCDATA)
	Addrconst(&p.From, funcdatakind)
	p.To.Type = obj.TYPE_MEM
	p.To.Name = obj.NAME_EXTERN
	p.To.Sym = Linksym(sym)
	return sym
	}

	// TODO(mdempsky): Update to reference OpVar{Def,Kill,Live} instead
	// and move to plive.go.

	// VARDEF is an annotation for the liveness analysis, marking a place
	// where a complete initialization (definition) of a variable begins.
	// Since the liveness analysis can see initialization of single-word
	// variables quite easy, gvardef is usually only called for multi-word
	// or 'fat' variables, those satisfying isfat(n->type).
	// However, gvardef is also called when a non-fat variable is initialized
	// via a block move; the only time this happens is when you have
	// return f()
	// for a function with multiple return values exactly matching the return
	// types of the current function.
	//
	// A 'VARDEF x' annotation in the instruction stream tells the liveness
	// analysis to behave as though the variable x is being initialized at that
	// point in the instruction stream. The VARDEF must appear before the
	// actual (multi-instruction) initialization, and it must also appear after
	// any uses of the previous value, if any. For example, if compiling:
	//
	// x = x[1:]
	//
	// it is important to generate code like:
	//
	// base, len, cap = pieces of x[1:]
	// VARDEF x
	// x = {base, len, cap}
	//
	// If instead the generated code looked like:
	//
	// VARDEF x
	// base, len, cap = pieces of x[1:]
	// x = {base, len, cap}
	//
	// then the liveness analysis would decide the previous value of x was
	// unnecessary even though it is about to be used by the x[1:] computation.
	// Similarly, if the generated code looked like:
	//
	// base, len, cap = pieces of x[1:]
	// x = {base, len, cap}
	// VARDEF x
	//
	// then the liveness analysis will not preserve the new value of x, because
	// the VARDEF appears to have "overwritten" it.
	//
	// VARDEF is a bit of a kludge to work around the fact that the instruction
	// stream is working on single-word values but the liveness analysis
	// wants to work on individual variables, which might be multi-word
	// aggregates. It might make sense at some point to look into letting
	// the liveness analysis work on single-word values as well, although
	// there are complications around interface values, slices, and strings,
	// all of which cannot be treated as individual words.
	//
	// VARKILL is the opposite of VARDEF: it marks a value as no longer needed,
	// even if its address has been taken. That is, a VARKILL annotation asserts
	// that its argument is certainly dead, for use when the liveness analysis
	// would not otherwise be able to deduce that fact.

	func emitptrargsmap() {
	if Curfn.Func.Nname.Sym.Name == "_" {
	return
	}
	sym := lookup(fmt.Sprintf("%s.args_stackmap", Curfn.Func.Nname.Sym.Name))

	nptr := int(Curfn.Type.ArgWidth() / int64(Widthptr))
	bv := bvalloc(int32(nptr) * 2)
	nbitmap := 1
	if Curfn.Type.Results().NumFields() > 0 {
	nbitmap = 2
	}
	off := duint32(sym, 0, uint32(nbitmap))
	off = duint32(sym, off, uint32(bv.n))
	var xoffset int64
	if Curfn.IsMethod() {
	xoffset = 0
	onebitwalktype1(Curfn.Type.Recvs(), &xoffset, bv)
	}

	if Curfn.Type.Params().NumFields() > 0 {
	xoffset = 0
	onebitwalktype1(Curfn.Type.Params(), &xoffset, bv)
	}

	off = dbvec(sym, off, bv)
	if Curfn.Type.Results().NumFields() > 0 {
	xoffset = 0
	onebitwalktype1(Curfn.Type.Results(), &xoffset, bv)
	off = dbvec(sym, off, bv)
	}

	ggloblsym(sym, int32(off), obj.RODATA\|obj.LOCAL)
	}

	// cmpstackvarlt reports whether the stack variable a sorts before b.
	//
	// Sort the list of stack variables. Autos after anything else,
	// within autos, unused after used, within used, things with
	// pointers first, zeroed things first, and then decreasing size.
	// Because autos are laid out in decreasing addresses
	// on the stack, pointers first, zeroed things first and decreasing size
	// really means, in memory, things with pointers needing zeroing at
	// the top of the stack and increasing in size.
	// Non-autos sort on offset.
	func cmpstackvarlt(a, b *Node) bool {
	if (a.Class == PAUTO) != (b.Class == PAUTO) {
	return b.Class == PAUTO
	}

	if a.Class != PAUTO {
	return a.Xoffset < b.Xoffset
	}

	if a.Used() != b.Used() {
	return a.Used()
	}

	ap := haspointers(a.Type)
	bp := haspointers(b.Type)
	if ap != bp {
	return ap
	}

	ap = a.Name.Needzero()
	bp = b.Name.Needzero()
	if ap != bp {
	return ap
	}

	if a.Type.Width != b.Type.Width {
	return a.Type.Width > b.Type.Width
	}

	return a.Sym.Name < b.Sym.Name
	}

	// byStackvar implements sort.Interface for []*Node using cmpstackvarlt.
	type byStackVar []*Node

	func (s byStackVar) Len() int { return len(s) }
	func (s byStackVar) Less(i, j int) bool { return cmpstackvarlt(s[i], s[j]) }
	func (s byStackVar) Swap(i, j int) { s[i], s[j] = s[j], s[i] }

	var scratchFpMem *Node

	func (s ssafn) AllocFrame(f ssa.Func) {
	s.stksize = 0
	s.stkptrsize = 0
	fn := s.curfn.Func

	// Mark the PAUTO's unused.
	for _, ln := range fn.Dcl {
	if ln.Class == PAUTO {
	ln.SetUsed(false)
	}
	}

	for _, l := range f.RegAlloc {
	if ls, ok := l.(ssa.LocalSlot); ok {
	ls.N.(*Node).SetUsed(true)
	}

	}

	scratchUsed := false
	for _, b := range f.Blocks {
	for _, v := range b.Values {
	switch a := v.Aux.(type) {
	case *ssa.ArgSymbol:
	a.Node.(*Node).SetUsed(true)
	case *ssa.AutoSymbol:
	a.Node.(*Node).SetUsed(true)
	}

	if !scratchUsed {
	scratchUsed = v.Op.UsesScratch()
	}
	}
	}

	if f.Config.NeedsFpScratch {
	scratchFpMem = tempAt(src.NoXPos, s.curfn, Types[TUINT64])
	scratchFpMem.SetUsed(scratchUsed)
	}

	sort.Sort(byStackVar(fn.Dcl))

	// Reassign stack offsets of the locals that are used.
	for i, n := range fn.Dcl {
	if n.Op != ONAME \|\| n.Class != PAUTO {
	continue
	}
	if !n.Used() {
	fn.Dcl = fn.Dcl[:i]
	break
	}

	dowidth(n.Type)
	w := n.Type.Width
	if w >= thearch.MAXWIDTH \|\| w < 0 {
	Fatalf("bad width")
	}
	s.stksize += w
	s.stksize = Rnd(s.stksize, int64(n.Type.Align))
	if haspointers(n.Type) {
	s.stkptrsize = s.stksize
	}
	if thearch.LinkArch.InFamily(sys.MIPS, sys.MIPS64, sys.ARM, sys.ARM64, sys.PPC64, sys.S390X) {
	s.stksize = Rnd(s.stksize, int64(Widthptr))
	}
	if s.stksize >= 1<<31 {
	yyerrorl(s.curfn.Pos, "stack frame too large (>2GB)")
	}

	n.Xoffset = -s.stksize
	}

	s.stksize = Rnd(s.stksize, int64(Widthreg))
	s.stkptrsize = Rnd(s.stkptrsize, int64(Widthreg))
	}

	func compile(fn *Node) {
	if Newproc == nil {
	Newproc = Sysfunc("newproc")
	Deferproc = Sysfunc("deferproc")
	Deferreturn = Sysfunc("deferreturn")
	Duffcopy = Sysfunc("duffcopy")
	Duffzero = Sysfunc("duffzero")
	panicindex = Sysfunc("panicindex")
	panicslice = Sysfunc("panicslice")
	panicdivide = Sysfunc("panicdivide")
	growslice = Sysfunc("growslice")
	panicdottypeE = Sysfunc("panicdottypeE")
	panicdottypeI = Sysfunc("panicdottypeI")
	panicnildottype = Sysfunc("panicnildottype")
	assertE2I = Sysfunc("assertE2I")
	assertE2I2 = Sysfunc("assertE2I2")
	assertI2I = Sysfunc("assertI2I")
	assertI2I2 = Sysfunc("assertI2I2")
	}

	Curfn = fn
	dowidth(fn.Type)

	if fn.Nbody.Len() == 0 {
	emitptrargsmap()
	return
	}

	saveerrors()

	order(fn)
	if nerrors != 0 {
	return
	}

	walk(fn)
	if nerrors != 0 {
	return
	}
	checkcontrolflow(fn)
	if nerrors != 0 {
	return
	}
	if instrumenting {
	instrument(fn)
	}
	if nerrors != 0 {
	return
	}

	// From this point, there should be no uses of Curfn. Enforce that.
	Curfn = nil

	// Build an SSA backend function.
	ssafn := buildssa(fn)
	if nerrors != 0 {
	return
	}

	pp := newProgs(fn)
	genssa(ssafn, pp)
	fieldtrack(pp.Text.From.Sym, fn.Func.FieldTrack)
	pp.Flush()
	}

	func debuginfo(fnsym obj.LSym, curfn interface{}) []dwarf.Var {
	fn := curfn.(*Node)
	if expect := Linksym(fn.Func.Nname.Sym); fnsym != expect {
	Fatalf("unexpected fnsym: %v != %v", fnsym, expect)
	}

	var vars []*dwarf.Var
	for _, n := range fn.Func.Dcl {
	if n.Op != ONAME { // might be OTYPE or OLITERAL
	continue
	}

	var name obj.AddrName
	var abbrev int
	offs := n.Xoffset

	switch n.Class {
	case PAUTO:
	if !n.Used() {
	continue
	}
	name = obj.NAME_AUTO

	abbrev = dwarf.DW_ABRV_AUTO
	if Ctxt.FixedFrameSize() == 0 {
	offs -= int64(Widthptr)
	}
	if obj.Framepointer_enabled(obj.GOOS, obj.GOARCH) {
	offs -= int64(Widthptr)
	}

	case PPARAM, PPARAMOUT:
	name = obj.NAME_PARAM

	abbrev = dwarf.DW_ABRV_PARAM
	offs += Ctxt.FixedFrameSize()

	default:
	continue
	}

	gotype := Linksym(ngotype(n))
	fnsym.Autom = append(fnsym.Autom, &obj.Auto{
	Asym: obj.Linklookup(Ctxt, n.Sym.Name, 0),
	Aoffset: int32(n.Xoffset),
	Name: name,
	Gotype: gotype,
	})

	if n.IsAutoTmp() {
	continue
	}

	typename := dwarf.InfoPrefix + gotype.Name[len("type."):]
	vars = append(vars, &dwarf.Var{
	Name: n.Sym.Name,
	Abbrev: abbrev,
	Offset: int32(offs),
	Type: obj.Linklookup(Ctxt, typename, 0),
	})
	}

	// Stable sort so that ties are broken with declaration order.
	sort.Stable(dwarf.VarsByOffset(vars))

	return vars
	}

	// fieldtrack adds R_USEFIELD relocations to fnsym to record any
	// struct fields that it used.
	func fieldtrack(fnsym obj.LSym, tracked map[Sym]struct{}) {
	if fnsym == nil {
	return
	}
	if obj.Fieldtrack_enabled == 0 \|\| len(tracked) == 0 {
	return
	}

	trackSyms := make([]*Sym, 0, len(tracked))
	for sym := range tracked {
	trackSyms = append(trackSyms, sym)
	}
	sort.Sort(symByName(trackSyms))
	for _, sym := range trackSyms {
	r := obj.Addrel(fnsym)
	r.Sym = Linksym(sym)
	r.Type = obj.R_USEFIELD
	}
	}

	type symByName []*Sym

	func (a symByName) Len() int { return len(a) }
	func (a symByName) Less(i, j int) bool { return a[i].Name < a[j].Name }
	func (a symByName) Swap(i, j int) { a[i], a[j] = a[j], a[i] }