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

 // Copyright 2009 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 (
 	"bytes"
 	"cmd/compile/internal/types"
 	"fmt"
 	"sort"
 )

 // sizeCalculationDisabled indicates whether it is safe
 // to calculate Types' widths and alignments. See dowidth.
 var sizeCalculationDisabled bool

 // machine size and rounding alignment is dictated around
 // the size of a pointer, set in betypeinit (see ../amd64/galign.go).
 var defercalc int

 func Rnd(o int64, r int64) int64 {
 	if r < 1 || r > 8 || r&(r-1) != 0 {
 		Fatalf("rnd %d", r)
 	}
 	return (o + r - 1) &^ (r - 1)
 }

 // expandiface computes the method set for interface type t by
 // expanding embedded interfaces.
 func expandiface(t *types.Type) {
 	seen := make(map[*types.Sym]*types.Field)
 	var methods []*types.Field

 	addMethod := func(m *types.Field, explicit bool) {
 		switch prev := seen[m.Sym]; {
 		case prev == nil:
 			seen[m.Sym] = m
 		case langSupported(1, 14, t.Pkg()) && !explicit && types.Identical(m.Type, prev.Type):
 			return
 		default:
 			yyerrorl(m.Pos, "duplicate method %s", m.Sym.Name)
 		}
 		methods = append(methods, m)
 	}

 	for _, m := range t.Methods().Slice() {
 		if m.Sym == nil {
 			continue
 		}

 		checkwidth(m.Type)
 		addMethod(m, true)
 	}

 	for _, m := range t.Methods().Slice() {
 		if m.Sym != nil {
 			continue
 		}

 		if !m.Type.IsInterface() {
 			yyerrorl(m.Pos, "interface contains embedded non-interface %v", m.Type)
 			m.SetBroke(true)
 			t.SetBroke(true)
 			// Add to fields so that error messages
 			// include the broken embedded type when
 			// printing t.
 			// TODO(mdempsky): Revisit this.
 			methods = append(methods, m)
 			continue
 		}

 		// Embedded interface: duplicate all methods
 		// (including broken ones, if any) and add to t's
 		// method set.
 		for _, t1 := range m.Type.Fields().Slice() {
 			f := types.NewField()
 			f.Pos = m.Pos // preserve embedding position
 			f.Sym = t1.Sym
 			f.Type = t1.Type
 			f.SetBroke(t1.Broke())
 			addMethod(f, false)
 		}
 	}

 	sort.Sort(methcmp(methods))

 	if int64(len(methods)) >= thearch.MAXWIDTH/int64(Widthptr) {
 		yyerrorl(typePos(t), "interface too large")
 	}
 	for i, m := range methods {
 		m.Offset = int64(i) * int64(Widthptr)
 	}

 	// Access fields directly to avoid recursively calling dowidth
 	// within Type.Fields().
 	t.Extra.(*types.Interface).Fields.Set(methods)
 }

 func widstruct(errtype *types.Type, t *types.Type, o int64, flag int) int64 {
 	starto := o
 	maxalign := int32(flag)
 	if maxalign < 1 {
 		maxalign = 1
 	}
 	lastzero := int64(0)
 	for _, f := range t.Fields().Slice() {
 		if f.Type == nil {
 			// broken field, just skip it so that other valid fields
 			// get a width.
 			continue
 		}

 		dowidth(f.Type)
 		if int32(f.Type.Align) > maxalign {
 			maxalign = int32(f.Type.Align)
 		}
 		if f.Type.Align > 0 {
 			o = Rnd(o, int64(f.Type.Align))
 		}
 		f.Offset = o
 		if n := asNode(f.Nname); n != nil {
 			// addrescapes has similar code to update these offsets.
 			// Usually addrescapes runs after widstruct,
 			// in which case we could drop this,
 			// but function closure functions are the exception.
 			// NOTE(rsc): This comment may be stale.
 			// It's possible the ordering has changed and this is
 			// now the common case. I'm not sure.
 			if n.Name.Param.Stackcopy != nil {
 				n.Name.Param.Stackcopy.Xoffset = o
 				n.Xoffset = 0
 			} else {
 				n.Xoffset = o
 			}
 		}

 		w := f.Type.Width
 		if w < 0 {
 			Fatalf("invalid width %d", f.Type.Width)
 		}
 		if w == 0 {
 			lastzero = o
 		}
 		o += w
 		maxwidth := thearch.MAXWIDTH
 		// On 32-bit systems, reflect tables impose an additional constraint
 		// that each field start offset must fit in 31 bits.
 		if maxwidth < 1<<32 {
 			maxwidth = 1<<31 - 1
 		}
 		if o >= maxwidth {
 			yyerrorl(typePos(errtype), "type %L too large", errtype)
 			o = 8 // small but nonzero
 		}
 	}

 	// For nonzero-sized structs which end in a zero-sized thing, we add
 	// an extra byte of padding to the type. This padding ensures that
 	// taking the address of the zero-sized thing can't manufacture a
 	// pointer to the next object in the heap. See issue 9401.
 	if flag == 1 && o > starto && o == lastzero {
 		o++
 	}

 	// final width is rounded
 	if flag != 0 {
 		o = Rnd(o, int64(maxalign))
 	}
 	t.Align = uint8(maxalign)

 	// type width only includes back to first field's offset
 	t.Width = o - starto

 	return o
 }

 // findTypeLoop searches for an invalid type declaration loop involving
 // type t and reports whether one is found. If so, path contains the
 // loop.
 //
 // path points to a slice used for tracking the sequence of types
 // visited. Using a pointer to a slice allows the slice capacity to
 // grow and limit reallocations.
 func findTypeLoop(t *types.Type, path *[]*types.Type) bool {
 	// We implement a simple DFS loop-finding algorithm. This
 	// could be faster, but type cycles are rare.

 	if t.Sym != nil {
 		// Declared type. Check for loops and otherwise
 		// recurse on the type expression used in the type
 		// declaration.

 		for i, x := range *path {
 			if x == t {
 				*path = (*path)[i:]
 				return true
 			}
 		}

 		*path = append(*path, t)
 		if p := asNode(t.Nod).Name.Param; p != nil && findTypeLoop(p.Ntype.Type, path) {
 			return true
 		}
 		*path = (*path)[:len(*path)-1]
 	} else {
 		// Anonymous type. Recurse on contained types.

 		switch t.Etype {
 		case TARRAY:
 			if findTypeLoop(t.Elem(), path) {
 				return true
 			}
 		case TSTRUCT:
 			for _, f := range t.Fields().Slice() {
 				if findTypeLoop(f.Type, path) {
 					return true
 				}
 			}
 		case TINTER:
 			for _, m := range t.Methods().Slice() {
 				if m.Type.IsInterface() { // embedded interface
 					if findTypeLoop(m.Type, path) {
 						return true
 					}
 				}
 			}
 		}
 	}

 	return false
 }

 func reportTypeLoop(t *types.Type) {
 	if t.Broke() {
 		return
 	}

 	var l []*types.Type
 	if !findTypeLoop(t, &l) {
 		Fatalf("failed to find type loop for: %v", t)
 	}

 	// Rotate loop so that the earliest type declaration is first.
 	i := 0
 	for j, t := range l[1:] {
 		if typePos(t).Before(typePos(l[i])) {
 			i = j + 1
 		}
 	}
 	l = append(l[i:], l[:i]...)

 	var msg bytes.Buffer
 	fmt.Fprintf(&msg, "invalid recursive type %v\n", l[0])
 	for _, t := range l {
 		fmt.Fprintf(&msg, "\t%v: %v refers to\n", linestr(typePos(t)), t)
 		t.SetBroke(true)
 	}
 	fmt.Fprintf(&msg, "\t%v: %v", linestr(typePos(l[0])), l[0])
 	yyerrorl(typePos(l[0]), msg.String())
 }

 // dowidth calculates and stores the size and alignment for t.
 // If sizeCalculationDisabled is set, and the size/alignment
 // have not already been calculated, it calls Fatal.
 // This is used to prevent data races in the back end.
 func dowidth(t *types.Type) {
 	// Calling dowidth when typecheck tracing enabled is not safe.
 	// See issue #33658.
 	if enableTrace && skipDowidthForTracing {
 		return
 	}
 	if Widthptr == 0 {
 		Fatalf("dowidth without betypeinit")
 	}

 	if t == nil {
 		return
 	}

 	if t.Width == -2 {
 		reportTypeLoop(t)
 		t.Width = 0
 		t.Align = 1
 		return
 	}

 	if t.WidthCalculated() {
 		return
 	}

 	if sizeCalculationDisabled {
 		if t.Broke() {
 			// break infinite recursion from Fatal call below
 			return
 		}
 		t.SetBroke(true)
 		Fatalf("width not calculated: %v", t)
 	}

 	// break infinite recursion if the broken recursive type
 	// is referenced again
 	if t.Broke() && t.Width == 0 {
 		return
 	}

 	// defer checkwidth calls until after we're done
 	defercheckwidth()

 	lno := lineno
 	if asNode(t.Nod) != nil {
 		lineno = asNode(t.Nod).Pos
 	}

 	t.Width = -2
 	t.Align = 0 // 0 means use t.Width, below

 	et := t.Etype
 	switch et {
 	case TFUNC, TCHAN, TMAP, TSTRING:
 		break

 	// simtype == 0 during bootstrap
 	default:
 		if simtype[t.Etype] != 0 {
 			et = simtype[t.Etype]
 		}
 	}

 	var w int64
 	switch et {
 	default:
 		Fatalf("dowidth: unknown type: %v", t)

 	// compiler-specific stuff
 	case TINT8, TUINT8, TBOOL:
 		// bool is int8
 		w = 1

 	case TINT16, TUINT16:
 		w = 2

 	case TINT32, TUINT32, TFLOAT32:
 		w = 4

 	case TINT64, TUINT64, TFLOAT64:
 		w = 8
 		t.Align = uint8(Widthreg)

 	case TCOMPLEX64:
 		w = 8
 		t.Align = 4

 	case TCOMPLEX128:
 		w = 16
 		t.Align = uint8(Widthreg)

 	case TPTR:
 		w = int64(Widthptr)
 		checkwidth(t.Elem())

 	case TUNSAFEPTR:
 		w = int64(Widthptr)

 	case TINTER: // implemented as 2 pointers
 		w = 2 * int64(Widthptr)
 		t.Align = uint8(Widthptr)
 		expandiface(t)

 	case TCHAN: // implemented as pointer
 		w = int64(Widthptr)

 		checkwidth(t.Elem())

 		// make fake type to check later to
 		// trigger channel argument check.
 		t1 := types.NewChanArgs(t)
 		checkwidth(t1)

 	case TCHANARGS:
 		t1 := t.ChanArgs()
 		dowidth(t1) // just in case
 		if t1.Elem().Width >= 1<<16 {
 			yyerrorl(typePos(t1), "channel element type too large (>64kB)")
 		}
 		w = 1 // anything will do

 	case TMAP: // implemented as pointer
 		w = int64(Widthptr)
 		checkwidth(t.Elem())
 		checkwidth(t.Key())

 	case TFORW: // should have been filled in
 		reportTypeLoop(t)
 		w = 1 // anything will do

 	case TANY:
 		// dummy type; should be replaced before use.
 		Fatalf("dowidth any")

 	case TSTRING:
 		if sizeofString == 0 {
 			Fatalf("early dowidth string")
 		}
 		w = sizeofString
 		t.Align = uint8(Widthptr)

 	case TARRAY:
 		if t.Elem() == nil {
 			break
 		}

 		dowidth(t.Elem())
 		if t.Elem().Width != 0 {
 			cap := (uint64(thearch.MAXWIDTH) - 1) / uint64(t.Elem().Width)
 			if uint64(t.NumElem()) > cap {
 				yyerrorl(typePos(t), "type %L larger than address space", t)
 			}
 		}
 		w = t.NumElem() * t.Elem().Width
 		t.Align = t.Elem().Align

 	case TSLICE:
 		if t.Elem() == nil {
 			break
 		}
 		w = sizeofSlice
 		checkwidth(t.Elem())
 		t.Align = uint8(Widthptr)

 	case TSTRUCT:
 		if t.IsFuncArgStruct() {
 			Fatalf("dowidth fn struct %v", t)
 		}
 		w = widstruct(t, t, 0, 1)

 	// make fake type to check later to
 	// trigger function argument computation.
 	case TFUNC:
 		t1 := types.NewFuncArgs(t)
 		checkwidth(t1)
 		w = int64(Widthptr) // width of func type is pointer

 	// function is 3 cated structures;
 	// compute their widths as side-effect.
 	case TFUNCARGS:
 		t1 := t.FuncArgs()
 		w = widstruct(t1, t1.Recvs(), 0, 0)
 		w = widstruct(t1, t1.Params(), w, Widthreg)
 		w = widstruct(t1, t1.Results(), w, Widthreg)
 		t1.Extra.(*types.Func).Argwid = w
 		if w%int64(Widthreg) != 0 {
 			Warn("bad type %v %d\n", t1, w)
 		}
 		t.Align = 1
 	}

 	if Widthptr == 4 && w != int64(int32(w)) {
 		yyerrorl(typePos(t), "type %v too large", t)
 	}

 	t.Width = w
 	if t.Align == 0 {
 		if w == 0 || w > 8 || w&(w-1) != 0 {
 			Fatalf("invalid alignment for %v", t)
 		}
 		t.Align = uint8(w)
 	}

 	lineno = lno

 	resumecheckwidth()
 }

 // when a type's width should be known, we call checkwidth
 // to compute it.  during a declaration like
 //
 //	type T *struct { next T }
 //
 // it is necessary to defer the calculation of the struct width
 // until after T has been initialized to be a pointer to that struct.
 // similarly, during import processing structs may be used
 // before their definition.  in those situations, calling
 // defercheckwidth() stops width calculations until
 // resumecheckwidth() is called, at which point all the
 // checkwidths that were deferred are executed.
 // dowidth should only be called when the type's size
 // is needed immediately.  checkwidth makes sure the
 // size is evaluated eventually.

 var deferredTypeStack []*types.Type

 func checkwidth(t *types.Type) {
 	if t == nil {
 		return
 	}

 	// function arg structs should not be checked
 	// outside of the enclosing function.
 	if t.IsFuncArgStruct() {
 		Fatalf("checkwidth %v", t)
 	}

 	if defercalc == 0 {
 		dowidth(t)
 		return
 	}

 	// if type has not yet been pushed on deferredTypeStack yet, do it now
 	if !t.Deferwidth() {
 		t.SetDeferwidth(true)
 		deferredTypeStack = append(deferredTypeStack, t)
 	}
 }

 func defercheckwidth() {
 	defercalc++
 }

 func resumecheckwidth() {
 	if defercalc == 1 {
 		for len(deferredTypeStack) > 0 {
 			t := deferredTypeStack[len(deferredTypeStack)-1]
 			deferredTypeStack = deferredTypeStack[:len(deferredTypeStack)-1]
 			t.SetDeferwidth(false)
 			dowidth(t)
 		}
 	}

 	defercalc--
 }
	// Copyright 2009 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 (
	"bytes"
	"cmd/compile/internal/types"
	"fmt"
	"sort"
	)

	// sizeCalculationDisabled indicates whether it is safe
	// to calculate Types' widths and alignments. See dowidth.
	var sizeCalculationDisabled bool

	// machine size and rounding alignment is dictated around
	// the size of a pointer, set in betypeinit (see ../amd64/galign.go).
	var defercalc int

	func Rnd(o int64, r int64) int64 {
	if r < 1 \|\| r > 8 \|\| r&(r-1) != 0 {
	Fatalf("rnd %d", r)
	}
	return (o + r - 1) &^ (r - 1)
	}

	// expandiface computes the method set for interface type t by
	// expanding embedded interfaces.
	func expandiface(t *types.Type) {
	seen := make(map[types.Sym]types.Field)
	var methods []*types.Field

	addMethod := func(m *types.Field, explicit bool) {
	switch prev := seen[m.Sym]; {
	case prev == nil:
	seen[m.Sym] = m
	case langSupported(1, 14, t.Pkg()) && !explicit && types.Identical(m.Type, prev.Type):
	return
	default:
	yyerrorl(m.Pos, "duplicate method %s", m.Sym.Name)
	}
	methods = append(methods, m)
	}

	for _, m := range t.Methods().Slice() {
	if m.Sym == nil {
	continue
	}

	checkwidth(m.Type)
	addMethod(m, true)
	}

	for _, m := range t.Methods().Slice() {
	if m.Sym != nil {
	continue
	}

	if !m.Type.IsInterface() {
	yyerrorl(m.Pos, "interface contains embedded non-interface %v", m.Type)
	m.SetBroke(true)
	t.SetBroke(true)
	// Add to fields so that error messages
	// include the broken embedded type when
	// printing t.
	// TODO(mdempsky): Revisit this.
	methods = append(methods, m)
	continue
	}

	// Embedded interface: duplicate all methods
	// (including broken ones, if any) and add to t's
	// method set.
	for _, t1 := range m.Type.Fields().Slice() {
	f := types.NewField()
	f.Pos = m.Pos // preserve embedding position
	f.Sym = t1.Sym
	f.Type = t1.Type
	f.SetBroke(t1.Broke())
	addMethod(f, false)
	}
	}

	sort.Sort(methcmp(methods))

	if int64(len(methods)) >= thearch.MAXWIDTH/int64(Widthptr) {
	yyerrorl(typePos(t), "interface too large")
	}
	for i, m := range methods {
	m.Offset = int64(i) * int64(Widthptr)
	}

	// Access fields directly to avoid recursively calling dowidth
	// within Type.Fields().
	t.Extra.(*types.Interface).Fields.Set(methods)
	}

	func widstruct(errtype types.Type, t types.Type, o int64, flag int) int64 {
	starto := o
	maxalign := int32(flag)
	if maxalign < 1 {
	maxalign = 1
	}
	lastzero := int64(0)
	for _, f := range t.Fields().Slice() {
	if f.Type == nil {
	// broken field, just skip it so that other valid fields
	// get a width.
	continue
	}

	dowidth(f.Type)
	if int32(f.Type.Align) > maxalign {
	maxalign = int32(f.Type.Align)
	}
	if f.Type.Align > 0 {
	o = Rnd(o, int64(f.Type.Align))
	}
	f.Offset = o
	if n := asNode(f.Nname); n != nil {
	// addrescapes has similar code to update these offsets.
	// Usually addrescapes runs after widstruct,
	// in which case we could drop this,
	// but function closure functions are the exception.
	// NOTE(rsc): This comment may be stale.
	// It's possible the ordering has changed and this is
	// now the common case. I'm not sure.
	if n.Name.Param.Stackcopy != nil {
	n.Name.Param.Stackcopy.Xoffset = o
	n.Xoffset = 0
	} else {
	n.Xoffset = o
	}
	}

	w := f.Type.Width
	if w < 0 {
	Fatalf("invalid width %d", f.Type.Width)
	}
	if w == 0 {
	lastzero = o
	}
	o += w
	maxwidth := thearch.MAXWIDTH
	// On 32-bit systems, reflect tables impose an additional constraint
	// that each field start offset must fit in 31 bits.
	if maxwidth < 1<<32 {
	maxwidth = 1<<31 - 1
	}
	if o >= maxwidth {
	yyerrorl(typePos(errtype), "type %L too large", errtype)
	o = 8 // small but nonzero
	}
	}

	// For nonzero-sized structs which end in a zero-sized thing, we add
	// an extra byte of padding to the type. This padding ensures that
	// taking the address of the zero-sized thing can't manufacture a
	// pointer to the next object in the heap. See issue 9401.
	if flag == 1 && o > starto && o == lastzero {
	o++
	}

	// final width is rounded
	if flag != 0 {
	o = Rnd(o, int64(maxalign))
	}
	t.Align = uint8(maxalign)

	// type width only includes back to first field's offset
	t.Width = o - starto

	return o
	}

	// findTypeLoop searches for an invalid type declaration loop involving
	// type t and reports whether one is found. If so, path contains the
	// loop.
	//
	// path points to a slice used for tracking the sequence of types
	// visited. Using a pointer to a slice allows the slice capacity to
	// grow and limit reallocations.
	func findTypeLoop(t types.Type, path []*types.Type) bool {
	// We implement a simple DFS loop-finding algorithm. This
	// could be faster, but type cycles are rare.

	if t.Sym != nil {
	// Declared type. Check for loops and otherwise
	// recurse on the type expression used in the type
	// declaration.

	for i, x := range *path {
	if x == t {
	path = (path)[i:]
	return true
	}
	}

	path = append(path, t)
	if p := asNode(t.Nod).Name.Param; p != nil && findTypeLoop(p.Ntype.Type, path) {
	return true
	}
	path = (path)[:len(*path)-1]
	} else {
	// Anonymous type. Recurse on contained types.

	switch t.Etype {
	case TARRAY:
	if findTypeLoop(t.Elem(), path) {
	return true
	}
	case TSTRUCT:
	for _, f := range t.Fields().Slice() {
	if findTypeLoop(f.Type, path) {
	return true
	}
	}
	case TINTER:
	for _, m := range t.Methods().Slice() {
	if m.Type.IsInterface() { // embedded interface
	if findTypeLoop(m.Type, path) {
	return true
	}
	}
	}
	}
	}

	return false
	}

	func reportTypeLoop(t *types.Type) {
	if t.Broke() {
	return
	}

	var l []*types.Type
	if !findTypeLoop(t, &l) {
	Fatalf("failed to find type loop for: %v", t)
	}

	// Rotate loop so that the earliest type declaration is first.
	i := 0
	for j, t := range l[1:] {
	if typePos(t).Before(typePos(l[i])) {
	i = j + 1
	}
	}
	l = append(l[i:], l[:i]...)

	var msg bytes.Buffer
	fmt.Fprintf(&msg, "invalid recursive type %v\n", l[0])
	for _, t := range l {
	fmt.Fprintf(&msg, "\t%v: %v refers to\n", linestr(typePos(t)), t)
	t.SetBroke(true)
	}
	fmt.Fprintf(&msg, "\t%v: %v", linestr(typePos(l[0])), l[0])
	yyerrorl(typePos(l[0]), msg.String())
	}

	// dowidth calculates and stores the size and alignment for t.
	// If sizeCalculationDisabled is set, and the size/alignment
	// have not already been calculated, it calls Fatal.
	// This is used to prevent data races in the back end.
	func dowidth(t *types.Type) {
	// Calling dowidth when typecheck tracing enabled is not safe.
	// See issue #33658.
	if enableTrace && skipDowidthForTracing {
	return
	}
	if Widthptr == 0 {
	Fatalf("dowidth without betypeinit")
	}

	if t == nil {
	return
	}

	if t.Width == -2 {
	reportTypeLoop(t)
	t.Width = 0
	t.Align = 1
	return
	}

	if t.WidthCalculated() {
	return
	}

	if sizeCalculationDisabled {
	if t.Broke() {
	// break infinite recursion from Fatal call below
	return
	}
	t.SetBroke(true)
	Fatalf("width not calculated: %v", t)
	}

	// break infinite recursion if the broken recursive type
	// is referenced again
	if t.Broke() && t.Width == 0 {
	return
	}

	// defer checkwidth calls until after we're done
	defercheckwidth()

	lno := lineno
	if asNode(t.Nod) != nil {
	lineno = asNode(t.Nod).Pos
	}

	t.Width = -2
	t.Align = 0 // 0 means use t.Width, below

	et := t.Etype
	switch et {
	case TFUNC, TCHAN, TMAP, TSTRING:
	break

	// simtype == 0 during bootstrap
	default:
	if simtype[t.Etype] != 0 {
	et = simtype[t.Etype]
	}
	}

	var w int64
	switch et {
	default:
	Fatalf("dowidth: unknown type: %v", t)

	// compiler-specific stuff
	case TINT8, TUINT8, TBOOL:
	// bool is int8
	w = 1

	case TINT16, TUINT16:
	w = 2

	case TINT32, TUINT32, TFLOAT32:
	w = 4

	case TINT64, TUINT64, TFLOAT64:
	w = 8
	t.Align = uint8(Widthreg)

	case TCOMPLEX64:
	w = 8
	t.Align = 4

	case TCOMPLEX128:
	w = 16
	t.Align = uint8(Widthreg)

	case TPTR:
	w = int64(Widthptr)
	checkwidth(t.Elem())

	case TUNSAFEPTR:
	w = int64(Widthptr)

	case TINTER: // implemented as 2 pointers
	w = 2 * int64(Widthptr)
	t.Align = uint8(Widthptr)
	expandiface(t)

	case TCHAN: // implemented as pointer
	w = int64(Widthptr)

	checkwidth(t.Elem())

	// make fake type to check later to
	// trigger channel argument check.
	t1 := types.NewChanArgs(t)
	checkwidth(t1)

	case TCHANARGS:
	t1 := t.ChanArgs()
	dowidth(t1) // just in case
	if t1.Elem().Width >= 1<<16 {
	yyerrorl(typePos(t1), "channel element type too large (>64kB)")
	}
	w = 1 // anything will do

	case TMAP: // implemented as pointer
	w = int64(Widthptr)
	checkwidth(t.Elem())
	checkwidth(t.Key())

	case TFORW: // should have been filled in
	reportTypeLoop(t)
	w = 1 // anything will do

	case TANY:
	// dummy type; should be replaced before use.
	Fatalf("dowidth any")

	case TSTRING:
	if sizeofString == 0 {
	Fatalf("early dowidth string")
	}
	w = sizeofString
	t.Align = uint8(Widthptr)

	case TARRAY:
	if t.Elem() == nil {
	break
	}

	dowidth(t.Elem())
	if t.Elem().Width != 0 {
	cap := (uint64(thearch.MAXWIDTH) - 1) / uint64(t.Elem().Width)
	if uint64(t.NumElem()) > cap {
	yyerrorl(typePos(t), "type %L larger than address space", t)
	}
	}
	w = t.NumElem() * t.Elem().Width
	t.Align = t.Elem().Align

	case TSLICE:
	if t.Elem() == nil {
	break
	}
	w = sizeofSlice
	checkwidth(t.Elem())
	t.Align = uint8(Widthptr)

	case TSTRUCT:
	if t.IsFuncArgStruct() {
	Fatalf("dowidth fn struct %v", t)
	}
	w = widstruct(t, t, 0, 1)

	// make fake type to check later to
	// trigger function argument computation.
	case TFUNC:
	t1 := types.NewFuncArgs(t)
	checkwidth(t1)
	w = int64(Widthptr) // width of func type is pointer

	// function is 3 cated structures;
	// compute their widths as side-effect.
	case TFUNCARGS:
	t1 := t.FuncArgs()
	w = widstruct(t1, t1.Recvs(), 0, 0)
	w = widstruct(t1, t1.Params(), w, Widthreg)
	w = widstruct(t1, t1.Results(), w, Widthreg)
	t1.Extra.(*types.Func).Argwid = w
	if w%int64(Widthreg) != 0 {
	Warn("bad type %v %d\n", t1, w)
	}
	t.Align = 1
	}

	if Widthptr == 4 && w != int64(int32(w)) {
	yyerrorl(typePos(t), "type %v too large", t)
	}

	t.Width = w
	if t.Align == 0 {
	if w == 0 \|\| w > 8 \|\| w&(w-1) != 0 {
	Fatalf("invalid alignment for %v", t)
	}
	t.Align = uint8(w)
	}

	lineno = lno

	resumecheckwidth()
	}

	// when a type's width should be known, we call checkwidth
	// to compute it. during a declaration like
	//
	// type T *struct { next T }
	//
	// it is necessary to defer the calculation of the struct width
	// until after T has been initialized to be a pointer to that struct.
	// similarly, during import processing structs may be used
	// before their definition. in those situations, calling
	// defercheckwidth() stops width calculations until
	// resumecheckwidth() is called, at which point all the
	// checkwidths that were deferred are executed.
	// dowidth should only be called when the type's size
	// is needed immediately. checkwidth makes sure the
	// size is evaluated eventually.

	var deferredTypeStack []*types.Type

	func checkwidth(t *types.Type) {
	if t == nil {
	return
	}

	// function arg structs should not be checked
	// outside of the enclosing function.
	if t.IsFuncArgStruct() {
	Fatalf("checkwidth %v", t)
	}

	if defercalc == 0 {
	dowidth(t)
	return
	}

	// if type has not yet been pushed on deferredTypeStack yet, do it now
	if !t.Deferwidth() {
	t.SetDeferwidth(true)
	deferredTypeStack = append(deferredTypeStack, t)
	}
	}

	func defercheckwidth() {
	defercalc++
	}

	func resumecheckwidth() {
	if defercalc == 1 {
	for len(deferredTypeStack) > 0 {
	t := deferredTypeStack[len(deferredTypeStack)-1]
	deferredTypeStack = deferredTypeStack[:len(deferredTypeStack)-1]
	t.SetDeferwidth(false)
	dowidth(t)
	}
	}

	defercalc--
	}