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/compile/internal/types"
 	"cmd/internal/dwarf"
 	"cmd/internal/obj"
 	"cmd/internal/objabi"
 	"cmd/internal/src"
 	"cmd/internal/sys"
 	"fmt"
 	"math"
 	"math/rand"
 	"sort"
 	"sync"
 	"time"
 )

 // "Portable" code generation.

 var (
 	nBackendWorkers int     // number of concurrent backend workers, set by a compiler flag
 	compilequeue    []*Node // functions waiting to be compiled
 )

 func emitptrargsmap() {
 	if Curfn.funcname() == "_" {
 		return
 	}
 	sym := lookup(fmt.Sprintf("%s.args_stackmap", Curfn.funcname()))
 	lsym := sym.Linksym()

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

 	ggloblsym(lsym, 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.Name.Used() != b.Name.Used() {
 		return a.Name.Used()
 	}

 	ap := types.Haspointers(a.Type)
 	bp := types.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] }

 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.Name.SetUsed(false)
 		}
 	}

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

 	scratchUsed := false
 	for _, b := range f.Blocks {
 		for _, v := range b.Values {
 			switch a := v.Aux.(type) {
 			case *ssa.ArgSymbol:
 				n := a.Node.(*Node)
 				// Don't modify nodfp; it is a global.
 				if n != nodfp {
 					n.Name.SetUsed(true)
 				}
 			case *ssa.AutoSymbol:
 				a.Node.(*Node).Name.SetUsed(true)
 			}

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

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

 	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.Name.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 types.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))
 		}
 		n.Xoffset = -s.stksize
 	}

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

 func compile(fn *Node) {
 	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
 	}
 	if instrumenting {
 		instrument(fn)
 	}

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

 	// Set up the function's LSym early to avoid data races with the assemblers.
 	fn.Func.initLSym()

 	if compilenow() {
 		compileSSA(fn, 0)
 	} else {
 		compilequeue = append(compilequeue, fn)
 	}
 }

 // compilenow reports whether to compile immediately.
 // If functions are not compiled immediately,
 // they are enqueued in compilequeue,
 // which is drained by compileFunctions.
 func compilenow() bool {
 	return nBackendWorkers == 1 && Debug_compilelater == 0
 }

 const maxStackSize = 1 << 31

 // compileSSA builds an SSA backend function,
 // uses it to generate a plist,
 // and flushes that plist to machine code.
 // worker indicates which of the backend workers is doing the processing.
 func compileSSA(fn *Node, worker int) {
 	ssafn := buildssa(fn, worker)
 	pp := newProgs(fn, worker)
 	genssa(ssafn, pp)
 	if pp.Text.To.Offset < maxStackSize {
 		pp.Flush()
 	} else {
 		largeStackFramesMu.Lock()
 		largeStackFrames = append(largeStackFrames, fn.Pos)
 		largeStackFramesMu.Unlock()
 	}
 	// fieldtrack must be called after pp.Flush. See issue 20014.
 	fieldtrack(pp.Text.From.Sym, fn.Func.FieldTrack)
 	pp.Free()
 }

 func init() {
 	if raceEnabled {
 		rand.Seed(time.Now().UnixNano())
 	}
 }

 // compileFunctions compiles all functions in compilequeue.
 // It fans out nBackendWorkers to do the work
 // and waits for them to complete.
 func compileFunctions() {
 	if len(compilequeue) != 0 {
 		sizeCalculationDisabled = true // not safe to calculate sizes concurrently
 		if raceEnabled {
 			// Randomize compilation order to try to shake out races.
 			tmp := make([]*Node, len(compilequeue))
 			perm := rand.Perm(len(compilequeue))
 			for i, v := range perm {
 				tmp[v] = compilequeue[i]
 			}
 			copy(compilequeue, tmp)
 		} else {
 			// Compile the longest functions first,
 			// since they're most likely to be the slowest.
 			// This helps avoid stragglers.
 			obj.SortSlice(compilequeue, func(i, j int) bool {
 				return compilequeue[i].Nbody.Len() > compilequeue[j].Nbody.Len()
 			})
 		}
 		var wg sync.WaitGroup
 		c := make(chan *Node, nBackendWorkers)
 		for i := 0; i < nBackendWorkers; i++ {
 			wg.Add(1)
 			go func(worker int) {
 				for fn := range c {
 					compileSSA(fn, worker)
 				}
 				wg.Done()
 			}(i)
 		}
 		for _, fn := range compilequeue {
 			c <- fn
 		}
 		close(c)
 		compilequeue = nil
 		wg.Wait()
 		sizeCalculationDisabled = false
 	}
 }

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

 	var automDecls []*Node
 	// Populate Automs for fn.
 	for _, n := range fn.Func.Dcl {
 		if n.Op != ONAME { // might be OTYPE or OLITERAL
 			continue
 		}
 		var name obj.AddrName
 		switch n.Class() {
 		case PAUTO:
 			if !n.Name.Used() {
 				Fatalf("debuginfo unused node (AllocFrame should truncate fn.Func.Dcl)")
 			}
 			name = obj.NAME_AUTO
 		case PPARAM, PPARAMOUT:
 			name = obj.NAME_PARAM
 		default:
 			continue
 		}
 		automDecls = append(automDecls, n)
 		gotype := ngotype(n).Linksym()
 		fnsym.Func.Autom = append(fnsym.Func.Autom, &obj.Auto{
 			Asym:    Ctxt.Lookup(n.Sym.Name),
 			Aoffset: int32(n.Xoffset),
 			Name:    name,
 			Gotype:  gotype,
 		})
 	}

 	var dwarfVars []*dwarf.Var
 	var decls []*Node
 	if Ctxt.Flag_locationlists && Ctxt.Flag_optimize {
 		decls, dwarfVars = createComplexVars(fn, debugInfo)
 	} else {
 		decls, dwarfVars = createSimpleVars(automDecls)
 	}

 	var varScopes []ScopeID
 	for _, decl := range decls {
 		var scope ScopeID
 		if !decl.Name.Captured() && !decl.Name.Byval() {
 			// n.Pos of captured variables is their first
 			// use in the closure but they should always
 			// be assigned to scope 0 instead.
 			// TODO(mdempsky): Verify this.
 			scope = findScope(fn.Func.Marks, decl.Pos)
 		}
 		varScopes = append(varScopes, scope)
 	}
 	return assembleScopes(fnsym, fn, dwarfVars, varScopes)
 }

 // createSimpleVars creates a DWARF entry for every variable declared in the
 // function, claiming that they are permanently on the stack.
 func createSimpleVars(automDecls []*Node) ([]*Node, []*dwarf.Var) {
 	var vars []*dwarf.Var
 	var decls []*Node
 	for _, n := range automDecls {
 		if n.IsAutoTmp() {
 			continue
 		}
 		var abbrev int
 		offs := n.Xoffset

 		switch n.Class() {
 		case PAUTO:
 			abbrev = dwarf.DW_ABRV_AUTO
 			if Ctxt.FixedFrameSize() == 0 {
 				offs -= int64(Widthptr)
 			}
 			if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
 				offs -= int64(Widthptr)
 			}

 		case PPARAM, PPARAMOUT:
 			abbrev = dwarf.DW_ABRV_PARAM
 			offs += Ctxt.FixedFrameSize()
 		default:
 			Fatalf("createSimpleVars unexpected type %v for node %v", n.Class(), n)
 		}

 		typename := dwarf.InfoPrefix + typesymname(n.Type)
 		decls = append(decls, n)
 		vars = append(vars, &dwarf.Var{
 			Name:        n.Sym.Name,
 			Abbrev:      abbrev,
 			StackOffset: int32(offs),
 			Type:        Ctxt.Lookup(typename),
 		})
 	}
 	return decls, vars
 }

 type varPart struct {
 	varOffset int64
 	slot      ssa.SlotID
 	locs      ssa.VarLocList
 }

 func createComplexVars(fn *Node, debugInfo *ssa.FuncDebug) ([]*Node, []*dwarf.Var) {
 	for _, locList := range debugInfo.Variables {
 		for _, loc := range locList.Locations {
 			if loc.StartProg != nil {
 				loc.StartPC = loc.StartProg.Pc
 			}
 			if loc.EndProg != nil {
 				loc.EndPC = loc.EndProg.Pc
 			}
 			if Debug_locationlist == 0 {
 				loc.EndProg = nil
 				loc.StartProg = nil
 			}
 		}
 	}

 	// Group SSA variables by the user variable they were decomposed from.
 	varParts := map[*Node][]varPart{}
 	for slotID, locList := range debugInfo.Variables {
 		if len(locList.Locations) == 0 {
 			continue
 		}
 		slot := debugInfo.Slots[slotID]
 		for slot.SplitOf != nil {
 			slot = slot.SplitOf
 		}
 		n := slot.N.(*Node)
 		varParts[n] = append(varParts[n], varPart{varOffset(slot), ssa.SlotID(slotID), locList})
 	}

 	// Produce a DWARF variable entry for each user variable.
 	// Don't iterate over the map -- that's nondeterministic, and
 	// createComplexVar has side effects. Instead, go by slot.
 	var decls []*Node
 	var vars []*dwarf.Var
 	for _, slot := range debugInfo.Slots {
 		for slot.SplitOf != nil {
 			slot = slot.SplitOf
 		}
 		n := slot.N.(*Node)
 		parts := varParts[n]
 		if parts == nil {
 			continue
 		}

 		// Get the order the parts need to be in to represent the memory
 		// of the decomposed user variable.
 		sort.Sort(partsByVarOffset(parts))

 		if dvar := createComplexVar(debugInfo, n, parts); dvar != nil {
 			decls = append(decls, n)
 			vars = append(vars, dvar)
 		}
 	}
 	return decls, vars
 }

 // varOffset returns the offset of slot within the user variable it was
 // decomposed from. This has nothing to do with its stack offset.
 func varOffset(slot *ssa.LocalSlot) int64 {
 	offset := slot.Off
 	for ; slot.SplitOf != nil; slot = slot.SplitOf {
 		offset += slot.SplitOffset
 	}
 	return offset
 }

 type partsByVarOffset []varPart

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

 // createComplexVar builds a DWARF variable entry and location list representing n.
 func createComplexVar(debugInfo *ssa.FuncDebug, n *Node, parts []varPart) *dwarf.Var {
 	slots := debugInfo.Slots
 	var offs int64 // base stack offset for this kind of variable
 	var abbrev int
 	switch n.Class() {
 	case PAUTO:
 		abbrev = dwarf.DW_ABRV_AUTO_LOCLIST
 		if Ctxt.FixedFrameSize() == 0 {
 			offs -= int64(Widthptr)
 		}
 		if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
 			offs -= int64(Widthptr)
 		}

 	case PPARAM, PPARAMOUT:
 		abbrev = dwarf.DW_ABRV_PARAM_LOCLIST
 		offs += Ctxt.FixedFrameSize()
 	default:
 		return nil
 	}

 	gotype := ngotype(n).Linksym()
 	typename := dwarf.InfoPrefix + gotype.Name[len("type."):]
 	// The stack offset is used as a sorting key, so for decomposed
 	// variables just give it the lowest one. It's not used otherwise.
 	stackOffset := debugInfo.Slots[parts[0].slot].N.(*Node).Xoffset + offs
 	dvar := &dwarf.Var{
 		Name:        n.Sym.Name,
 		Abbrev:      abbrev,
 		Type:        Ctxt.Lookup(typename),
 		StackOffset: int32(stackOffset),
 	}

 	if Debug_locationlist != 0 {
 		Ctxt.Logf("Building location list for %+v. Parts:\n", n)
 		for _, part := range parts {
 			Ctxt.Logf("\t%v => %v\n", debugInfo.Slots[part.slot], part.locs)
 		}
 	}

 	// Given a variable that's been decomposed into multiple parts,
 	// its location list may need a new entry after the beginning or
 	// end of every location entry for each of its parts. For example:
 	//
 	// [variable]    [pc range]
 	// string.ptr    |----|-----|    |----|
 	// string.len    |------------|  |--|
 	// ... needs a location list like:
 	// string        |----|-----|-|  |--|-|
 	//
 	// Note that location entries may or may not line up with each other,
 	// and some of the result will only have one or the other part.
 	//
 	// To build the resulting list:
 	// - keep a "current" pointer for each part
 	// - find the next transition point
 	// - advance the current pointer for each part up to that transition point
 	// - build the piece for the range between that transition point and the next
 	// - repeat

 	curLoc := make([]int, len(slots))

 	// findBoundaryAfter finds the next beginning or end of a piece after currentPC.
 	findBoundaryAfter := func(currentPC int64) int64 {
 		min := int64(math.MaxInt64)
 		for slot, part := range parts {
 			// For each part, find the first PC greater than current. Doesn't
 			// matter if it's a start or an end, since we're looking for any boundary.
 			// If it's the new winner, save it.
 		onePart:
 			for i := curLoc[slot]; i < len(part.locs.Locations); i++ {
 				for _, pc := range [2]int64{part.locs.Locations[i].StartPC, part.locs.Locations[i].EndPC} {
 					if pc > currentPC {
 						if pc < min {
 							min = pc
 						}
 						break onePart
 					}
 				}
 			}
 		}
 		return min
 	}
 	var start int64
 	end := findBoundaryAfter(0)
 	for {
 		// Advance to the next chunk.
 		start = end
 		end = findBoundaryAfter(start)
 		if end == math.MaxInt64 {
 			break
 		}

 		dloc := dwarf.Location{StartPC: start, EndPC: end}
 		if Debug_locationlist != 0 {
 			Ctxt.Logf("Processing range %x -> %x\n", start, end)
 		}

 		// Advance curLoc to the last location that starts before/at start.
 		// After this loop, if there's a location that covers [start, end), it will be current.
 		// Otherwise the current piece will be too early.
 		for _, part := range parts {
 			choice := -1
 			for i := curLoc[part.slot]; i < len(part.locs.Locations); i++ {
 				if part.locs.Locations[i].StartPC > start {
 					break //overshot
 				}
 				choice = i // best yet
 			}
 			if choice != -1 {
 				curLoc[part.slot] = choice
 			}
 			if Debug_locationlist != 0 {
 				Ctxt.Logf("\t %v => %v", slots[part.slot], curLoc[part.slot])
 			}
 		}
 		if Debug_locationlist != 0 {
 			Ctxt.Logf("\n")
 		}
 		// Assemble the location list entry for this chunk.
 		present := 0
 		for _, part := range parts {
 			dpiece := dwarf.Piece{
 				Length: slots[part.slot].Type.Size(),
 			}
 			locIdx := curLoc[part.slot]
 			if locIdx >= len(part.locs.Locations) ||
 				start >= part.locs.Locations[locIdx].EndPC ||
 				end <= part.locs.Locations[locIdx].StartPC {
 				if Debug_locationlist != 0 {
 					Ctxt.Logf("\t%v: missing", slots[part.slot])
 				}
 				dpiece.Missing = true
 				dloc.Pieces = append(dloc.Pieces, dpiece)
 				continue
 			}
 			present++
 			loc := part.locs.Locations[locIdx]
 			if Debug_locationlist != 0 {
 				Ctxt.Logf("\t%v: %v", slots[part.slot], loc)
 			}
 			if loc.OnStack {
 				dpiece.OnStack = true
 				dpiece.StackOffset = int32(offs + slots[part.slot].Off + slots[part.slot].N.(*Node).Xoffset)
 			} else {
 				for reg := 0; reg < len(debugInfo.Registers); reg++ {
 					if loc.Registers&(1<<uint8(reg)) != 0 {
 						dpiece.RegNum = Ctxt.Arch.DWARFRegisters[debugInfo.Registers[reg].ObjNum()]
 					}
 				}
 			}
 			dloc.Pieces = append(dloc.Pieces, dpiece)
 		}
 		if present == 0 {
 			if Debug_locationlist != 0 {
 				Ctxt.Logf(" -> totally missing\n")
 			}
 			continue
 		}
 		// Extend the previous entry if possible.
 		if len(dvar.LocationList) > 0 {
 			prev := &dvar.LocationList[len(dvar.LocationList)-1]
 			if prev.EndPC == dloc.StartPC && len(prev.Pieces) == len(dloc.Pieces) {
 				equal := true
 				for i := range prev.Pieces {
 					if prev.Pieces[i] != dloc.Pieces[i] {
 						equal = false
 					}
 				}
 				if equal {
 					prev.EndPC = end
 					if Debug_locationlist != 0 {
 						Ctxt.Logf("-> merged with previous, now %#v\n", prev)
 					}
 					continue
 				}
 			}
 		}
 		dvar.LocationList = append(dvar.LocationList, dloc)
 		if Debug_locationlist != 0 {
 			Ctxt.Logf("-> added: %#v\n", dloc)
 		}
 	}
 	return dvar
 }

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

 	trackSyms := make([]*types.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 = sym.Linksym()
 		r.Type = objabi.R_USEFIELD
 	}
 }

 type symByName []*types.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/compile/internal/types"
	"cmd/internal/dwarf"
	"cmd/internal/obj"
	"cmd/internal/objabi"
	"cmd/internal/src"
	"cmd/internal/sys"
	"fmt"
	"math"
	"math/rand"
	"sort"
	"sync"
	"time"
	)

	// "Portable" code generation.

	var (
	nBackendWorkers int // number of concurrent backend workers, set by a compiler flag
	compilequeue []*Node // functions waiting to be compiled
	)

	func emitptrargsmap() {
	if Curfn.funcname() == "_" {
	return
	}
	sym := lookup(fmt.Sprintf("%s.args_stackmap", Curfn.funcname()))
	lsym := sym.Linksym()

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

	ggloblsym(lsym, 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.Name.Used() != b.Name.Used() {
	return a.Name.Used()
	}

	ap := types.Haspointers(a.Type)
	bp := types.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] }

	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.Name.SetUsed(false)
	}
	}

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

	scratchUsed := false
	for _, b := range f.Blocks {
	for _, v := range b.Values {
	switch a := v.Aux.(type) {
	case *ssa.ArgSymbol:
	n := a.Node.(*Node)
	// Don't modify nodfp; it is a global.
	if n != nodfp {
	n.Name.SetUsed(true)
	}
	case *ssa.AutoSymbol:
	a.Node.(*Node).Name.SetUsed(true)
	}

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

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

	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.Name.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 types.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))
	}
	n.Xoffset = -s.stksize
	}

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

	func compile(fn *Node) {
	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
	}
	if instrumenting {
	instrument(fn)
	}

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

	// Set up the function's LSym early to avoid data races with the assemblers.
	fn.Func.initLSym()

	if compilenow() {
	compileSSA(fn, 0)
	} else {
	compilequeue = append(compilequeue, fn)
	}
	}

	// compilenow reports whether to compile immediately.
	// If functions are not compiled immediately,
	// they are enqueued in compilequeue,
	// which is drained by compileFunctions.
	func compilenow() bool {
	return nBackendWorkers == 1 && Debug_compilelater == 0
	}

	const maxStackSize = 1 << 31

	// compileSSA builds an SSA backend function,
	// uses it to generate a plist,
	// and flushes that plist to machine code.
	// worker indicates which of the backend workers is doing the processing.
	func compileSSA(fn *Node, worker int) {
	ssafn := buildssa(fn, worker)
	pp := newProgs(fn, worker)
	genssa(ssafn, pp)
	if pp.Text.To.Offset < maxStackSize {
	pp.Flush()
	} else {
	largeStackFramesMu.Lock()
	largeStackFrames = append(largeStackFrames, fn.Pos)
	largeStackFramesMu.Unlock()
	}
	// fieldtrack must be called after pp.Flush. See issue 20014.
	fieldtrack(pp.Text.From.Sym, fn.Func.FieldTrack)
	pp.Free()
	}

	func init() {
	if raceEnabled {
	rand.Seed(time.Now().UnixNano())
	}
	}

	// compileFunctions compiles all functions in compilequeue.
	// It fans out nBackendWorkers to do the work
	// and waits for them to complete.
	func compileFunctions() {
	if len(compilequeue) != 0 {
	sizeCalculationDisabled = true // not safe to calculate sizes concurrently
	if raceEnabled {
	// Randomize compilation order to try to shake out races.
	tmp := make([]*Node, len(compilequeue))
	perm := rand.Perm(len(compilequeue))
	for i, v := range perm {
	tmp[v] = compilequeue[i]
	}
	copy(compilequeue, tmp)
	} else {
	// Compile the longest functions first,
	// since they're most likely to be the slowest.
	// This helps avoid stragglers.
	obj.SortSlice(compilequeue, func(i, j int) bool {
	return compilequeue[i].Nbody.Len() > compilequeue[j].Nbody.Len()
	})
	}
	var wg sync.WaitGroup
	c := make(chan *Node, nBackendWorkers)
	for i := 0; i < nBackendWorkers; i++ {
	wg.Add(1)
	go func(worker int) {
	for fn := range c {
	compileSSA(fn, worker)
	}
	wg.Done()
	}(i)
	}
	for _, fn := range compilequeue {
	c <- fn
	}
	close(c)
	compilequeue = nil
	wg.Wait()
	sizeCalculationDisabled = false
	}
	}

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

	var automDecls []*Node
	// Populate Automs for fn.
	for _, n := range fn.Func.Dcl {
	if n.Op != ONAME { // might be OTYPE or OLITERAL
	continue
	}
	var name obj.AddrName
	switch n.Class() {
	case PAUTO:
	if !n.Name.Used() {
	Fatalf("debuginfo unused node (AllocFrame should truncate fn.Func.Dcl)")
	}
	name = obj.NAME_AUTO
	case PPARAM, PPARAMOUT:
	name = obj.NAME_PARAM
	default:
	continue
	}
	automDecls = append(automDecls, n)
	gotype := ngotype(n).Linksym()
	fnsym.Func.Autom = append(fnsym.Func.Autom, &obj.Auto{
	Asym: Ctxt.Lookup(n.Sym.Name),
	Aoffset: int32(n.Xoffset),
	Name: name,
	Gotype: gotype,
	})
	}

	var dwarfVars []*dwarf.Var
	var decls []*Node
	if Ctxt.Flag_locationlists && Ctxt.Flag_optimize {
	decls, dwarfVars = createComplexVars(fn, debugInfo)
	} else {
	decls, dwarfVars = createSimpleVars(automDecls)
	}

	var varScopes []ScopeID
	for _, decl := range decls {
	var scope ScopeID
	if !decl.Name.Captured() && !decl.Name.Byval() {
	// n.Pos of captured variables is their first
	// use in the closure but they should always
	// be assigned to scope 0 instead.
	// TODO(mdempsky): Verify this.
	scope = findScope(fn.Func.Marks, decl.Pos)
	}
	varScopes = append(varScopes, scope)
	}
	return assembleScopes(fnsym, fn, dwarfVars, varScopes)
	}

	// createSimpleVars creates a DWARF entry for every variable declared in the
	// function, claiming that they are permanently on the stack.
	func createSimpleVars(automDecls []Node) ([]Node, []*dwarf.Var) {
	var vars []*dwarf.Var
	var decls []*Node
	for _, n := range automDecls {
	if n.IsAutoTmp() {
	continue
	}
	var abbrev int
	offs := n.Xoffset

	switch n.Class() {
	case PAUTO:
	abbrev = dwarf.DW_ABRV_AUTO
	if Ctxt.FixedFrameSize() == 0 {
	offs -= int64(Widthptr)
	}
	if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
	offs -= int64(Widthptr)
	}

	case PPARAM, PPARAMOUT:
	abbrev = dwarf.DW_ABRV_PARAM
	offs += Ctxt.FixedFrameSize()
	default:
	Fatalf("createSimpleVars unexpected type %v for node %v", n.Class(), n)
	}

	typename := dwarf.InfoPrefix + typesymname(n.Type)
	decls = append(decls, n)
	vars = append(vars, &dwarf.Var{
	Name: n.Sym.Name,
	Abbrev: abbrev,
	StackOffset: int32(offs),
	Type: Ctxt.Lookup(typename),
	})
	}
	return decls, vars
	}

	type varPart struct {
	varOffset int64
	slot ssa.SlotID
	locs ssa.VarLocList
	}

	func createComplexVars(fn Node, debugInfo ssa.FuncDebug) ([]Node, []dwarf.Var) {
	for _, locList := range debugInfo.Variables {
	for _, loc := range locList.Locations {
	if loc.StartProg != nil {
	loc.StartPC = loc.StartProg.Pc
	}
	if loc.EndProg != nil {
	loc.EndPC = loc.EndProg.Pc
	}
	if Debug_locationlist == 0 {
	loc.EndProg = nil
	loc.StartProg = nil
	}
	}
	}

	// Group SSA variables by the user variable they were decomposed from.
	varParts := map[*Node][]varPart{}
	for slotID, locList := range debugInfo.Variables {
	if len(locList.Locations) == 0 {
	continue
	}
	slot := debugInfo.Slots[slotID]
	for slot.SplitOf != nil {
	slot = slot.SplitOf
	}
	n := slot.N.(*Node)
	varParts[n] = append(varParts[n], varPart{varOffset(slot), ssa.SlotID(slotID), locList})
	}

	// Produce a DWARF variable entry for each user variable.
	// Don't iterate over the map -- that's nondeterministic, and
	// createComplexVar has side effects. Instead, go by slot.
	var decls []*Node
	var vars []*dwarf.Var
	for _, slot := range debugInfo.Slots {
	for slot.SplitOf != nil {
	slot = slot.SplitOf
	}
	n := slot.N.(*Node)
	parts := varParts[n]
	if parts == nil {
	continue
	}

	// Get the order the parts need to be in to represent the memory
	// of the decomposed user variable.
	sort.Sort(partsByVarOffset(parts))

	if dvar := createComplexVar(debugInfo, n, parts); dvar != nil {
	decls = append(decls, n)
	vars = append(vars, dvar)
	}
	}
	return decls, vars
	}

	// varOffset returns the offset of slot within the user variable it was
	// decomposed from. This has nothing to do with its stack offset.
	func varOffset(slot *ssa.LocalSlot) int64 {
	offset := slot.Off
	for ; slot.SplitOf != nil; slot = slot.SplitOf {
	offset += slot.SplitOffset
	}
	return offset
	}

	type partsByVarOffset []varPart

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

	// createComplexVar builds a DWARF variable entry and location list representing n.
	func createComplexVar(debugInfo ssa.FuncDebug, n Node, parts []varPart) *dwarf.Var {
	slots := debugInfo.Slots
	var offs int64 // base stack offset for this kind of variable
	var abbrev int
	switch n.Class() {
	case PAUTO:
	abbrev = dwarf.DW_ABRV_AUTO_LOCLIST
	if Ctxt.FixedFrameSize() == 0 {
	offs -= int64(Widthptr)
	}
	if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
	offs -= int64(Widthptr)
	}

	case PPARAM, PPARAMOUT:
	abbrev = dwarf.DW_ABRV_PARAM_LOCLIST
	offs += Ctxt.FixedFrameSize()
	default:
	return nil
	}

	gotype := ngotype(n).Linksym()
	typename := dwarf.InfoPrefix + gotype.Name[len("type."):]
	// The stack offset is used as a sorting key, so for decomposed
	// variables just give it the lowest one. It's not used otherwise.
	stackOffset := debugInfo.Slots[parts[0].slot].N.(*Node).Xoffset + offs
	dvar := &dwarf.Var{
	Name: n.Sym.Name,
	Abbrev: abbrev,
	Type: Ctxt.Lookup(typename),
	StackOffset: int32(stackOffset),
	}

	if Debug_locationlist != 0 {
	Ctxt.Logf("Building location list for %+v. Parts:\n", n)
	for _, part := range parts {
	Ctxt.Logf("\t%v => %v\n", debugInfo.Slots[part.slot], part.locs)
	}
	}

	// Given a variable that's been decomposed into multiple parts,
	// its location list may need a new entry after the beginning or
	// end of every location entry for each of its parts. For example:
	//
	// [variable] [pc range]
	// string.ptr \|----\|-----\| \|----\|
	// string.len \|------------\| \|--\|
	// ... needs a location list like:
	// string \|----\|-----\|-\| \|--\|-\|
	//
	// Note that location entries may or may not line up with each other,
	// and some of the result will only have one or the other part.
	//
	// To build the resulting list:
	// - keep a "current" pointer for each part
	// - find the next transition point
	// - advance the current pointer for each part up to that transition point
	// - build the piece for the range between that transition point and the next
	// - repeat

	curLoc := make([]int, len(slots))

	// findBoundaryAfter finds the next beginning or end of a piece after currentPC.
	findBoundaryAfter := func(currentPC int64) int64 {
	min := int64(math.MaxInt64)
	for slot, part := range parts {
	// For each part, find the first PC greater than current. Doesn't
	// matter if it's a start or an end, since we're looking for any boundary.
	// If it's the new winner, save it.
	onePart:
	for i := curLoc[slot]; i < len(part.locs.Locations); i++ {
	for _, pc := range [2]int64{part.locs.Locations[i].StartPC, part.locs.Locations[i].EndPC} {
	if pc > currentPC {
	if pc < min {
	min = pc
	}
	break onePart
	}
	}
	}
	}
	return min
	}
	var start int64
	end := findBoundaryAfter(0)
	for {
	// Advance to the next chunk.
	start = end
	end = findBoundaryAfter(start)
	if end == math.MaxInt64 {
	break
	}

	dloc := dwarf.Location{StartPC: start, EndPC: end}
	if Debug_locationlist != 0 {
	Ctxt.Logf("Processing range %x -> %x\n", start, end)
	}

	// Advance curLoc to the last location that starts before/at start.
	// After this loop, if there's a location that covers [start, end), it will be current.
	// Otherwise the current piece will be too early.
	for _, part := range parts {
	choice := -1
	for i := curLoc[part.slot]; i < len(part.locs.Locations); i++ {
	if part.locs.Locations[i].StartPC > start {
	break //overshot
	}
	choice = i // best yet
	}
	if choice != -1 {
	curLoc[part.slot] = choice
	}
	if Debug_locationlist != 0 {
	Ctxt.Logf("\t %v => %v", slots[part.slot], curLoc[part.slot])
	}
	}
	if Debug_locationlist != 0 {
	Ctxt.Logf("\n")
	}
	// Assemble the location list entry for this chunk.
	present := 0
	for _, part := range parts {
	dpiece := dwarf.Piece{
	Length: slots[part.slot].Type.Size(),
	}
	locIdx := curLoc[part.slot]
	if locIdx >= len(part.locs.Locations) \|\|
	start >= part.locs.Locations[locIdx].EndPC \|\|
	end <= part.locs.Locations[locIdx].StartPC {
	if Debug_locationlist != 0 {
	Ctxt.Logf("\t%v: missing", slots[part.slot])
	}
	dpiece.Missing = true
	dloc.Pieces = append(dloc.Pieces, dpiece)
	continue
	}
	present++
	loc := part.locs.Locations[locIdx]
	if Debug_locationlist != 0 {
	Ctxt.Logf("\t%v: %v", slots[part.slot], loc)
	}
	if loc.OnStack {
	dpiece.OnStack = true
	dpiece.StackOffset = int32(offs + slots[part.slot].Off + slots[part.slot].N.(*Node).Xoffset)
	} else {
	for reg := 0; reg < len(debugInfo.Registers); reg++ {
	if loc.Registers&(1<<uint8(reg)) != 0 {
	dpiece.RegNum = Ctxt.Arch.DWARFRegisters[debugInfo.Registers[reg].ObjNum()]
	}
	}
	}
	dloc.Pieces = append(dloc.Pieces, dpiece)
	}
	if present == 0 {
	if Debug_locationlist != 0 {
	Ctxt.Logf(" -> totally missing\n")
	}
	continue
	}
	// Extend the previous entry if possible.
	if len(dvar.LocationList) > 0 {
	prev := &dvar.LocationList[len(dvar.LocationList)-1]
	if prev.EndPC == dloc.StartPC && len(prev.Pieces) == len(dloc.Pieces) {
	equal := true
	for i := range prev.Pieces {
	if prev.Pieces[i] != dloc.Pieces[i] {
	equal = false
	}
	}
	if equal {
	prev.EndPC = end
	if Debug_locationlist != 0 {
	Ctxt.Logf("-> merged with previous, now %#v\n", prev)
	}
	continue
	}
	}
	}
	dvar.LocationList = append(dvar.LocationList, dloc)
	if Debug_locationlist != 0 {
	Ctxt.Logf("-> added: %#v\n", dloc)
	}
	}
	return dvar
	}

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

	trackSyms := make([]*types.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 = sym.Linksym()
	r.Type = objabi.R_USEFIELD
	}
	}

	type symByName []*types.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] }