cmd/compile: add and use new Fields type

Analogous to the Nodes type used as a more space efficient []*Node
representation.

Passes toolstash -cmp.

Change-Id: I8341e45304777d6e4200bd36dadc935b07ccf3ff
Reviewed-on: https://go-review.googlesource.com/20793Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -1269,9 +1269,7 @@ func addmethod(msym *Sym, t *Type, tpkg *Pkg, local, nointerface bool) {
 	n := Nod(ODCLFIELD, newname(msym), nil)
 	n.Type = t
 
-	var d *Field // last found
 	for f, it := IterMethods(pa); f != nil; f = it.Next() {
-		d = f
 		if msym.Name != f.Sym.Name {
 			continue
 		}
@@ -1291,11 +1289,7 @@ func addmethod(msym *Sym, t *Type, tpkg *Pkg, local, nointerface bool) {
 		Fatalf("imported method name %v in wrong package %s\n", Sconv(f.Sym, FmtSign), tpkg.Name)
 	}
 
-	if d == nil {
-		pa.Method = f
-	} else {
-		d.Down = f
-	}
+	pa.Methods().Append(f)
 }
 
 func funccompile(n *Node) {

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

@@ -602,24 +602,24 @@ func typefmt(t *Type, flag FmtFlag) string {
 	case TINTER:
 		var buf bytes.Buffer
 		buf.WriteString("interface {")
-		for t1, it := IterFields(t); t1 != nil; t1 = it.Next() {
+		for i, f := range t.Fields().Slice() {
+			if i != 0 {
+				buf.WriteString(";")
+			}
 			buf.WriteString(" ")
 			switch {
-			case t1.Sym == nil:
+			case f.Sym == nil:
 				// Check first that a symbol is defined for this type.
 				// Wrong interface definitions may have types lacking a symbol.
 				break
-			case exportname(t1.Sym.Name):
-				buf.WriteString(Sconv(t1.Sym, FmtShort))
+			case exportname(f.Sym.Name):
+				buf.WriteString(Sconv(f.Sym, FmtShort))
 			default:
-				buf.WriteString(Sconv(t1.Sym, FmtUnsigned))
-			}
-			buf.WriteString(Tconv(t1.Type, FmtShort))
-			if t1.Down != nil {
-				buf.WriteString(";")
+				buf.WriteString(Sconv(f.Sym, FmtUnsigned))
 			}
+			buf.WriteString(Tconv(f.Type, FmtShort))
 		}
-		if t.Fields != nil {
+		if t.NumFields() != 0 {
 			buf.WriteString(" ")
 		}
 		buf.WriteString("}")
@@ -679,32 +679,27 @@ func typefmt(t *Type, flag FmtFlag) string {
 		var buf bytes.Buffer
 		if t.Funarg {
 			buf.WriteString("(")
+			var flag1 FmtFlag
 			if fmtmode == FTypeId || fmtmode == FErr { // no argument names on function signature, and no "noescape"/"nosplit" tags
-				for t1, it := IterFields(t); t1 != nil; t1 = it.Next() {
-					buf.WriteString(Fldconv(t1, FmtShort))
-					if t1.Down != nil {
-						buf.WriteString(", ")
-					}
-				}
-			} else {
-				for t1, it := IterFields(t); t1 != nil; t1 = it.Next() {
-					buf.WriteString(Fldconv(t1, 0))
-					if t1.Down != nil {
-						buf.WriteString(", ")
-					}
+				flag1 = FmtShort
+			}
+			for i, f := range t.Fields().Slice() {
+				if i != 0 {
+					buf.WriteString(", ")
 				}
+				buf.WriteString(Fldconv(f, flag1))
 			}
 			buf.WriteString(")")
 		} else {
 			buf.WriteString("struct {")
-			for t1, it := IterFields(t); t1 != nil; t1 = it.Next() {
-				buf.WriteString(" ")
-				buf.WriteString(Fldconv(t1, FmtLong))
-				if t1.Down != nil {
+			for i, f := range t.Fields().Slice() {
+				if i != 0 {
 					buf.WriteString(";")
 				}
+				buf.WriteString(" ")
+				buf.WriteString(Fldconv(f, FmtLong))
 			}
-			if t.Fields != nil {
+			if t.NumFields() != 0 {
 				buf.WriteString(" ")
 			}
 			buf.WriteString("}")

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

@@ -285,7 +285,7 @@ func methods(t *Type) []*Sig {
 	// make list of methods for t,
 	// generating code if necessary.
 	var ms []*Sig
-	for f, it2 := IterAllMethods(mt); f != nil; f = it2.Next() {
+	for _, f := range mt.AllMethods().Slice() {
 		if f.Type.Etype != TFUNC || f.Type.Thistuple == 0 {
 			Fatalf("non-method on %v method %v %v\n", mt, f.Sym, f)
 		}

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

@@ -1725,12 +1725,10 @@ func adddot(n *Node) *Node {
 // the actual methods.
 type Symlink struct {
 	field     *Field
-	link      *Symlink
-	good      bool
 	followptr bool
 }
 
-var slist *Symlink
+var slist []Symlink
 
 func expand0(t *Type, followptr bool) {
 	u := t
@@ -1740,17 +1738,12 @@ func expand0(t *Type, followptr bool) {
 	}
 
 	if u.Etype == TINTER {
-		var sl *Symlink
 		for f, it := IterFields(u); f != nil; f = it.Next() {
 			if f.Sym.Flags&SymUniq != 0 {
 				continue
 			}
 			f.Sym.Flags |= SymUniq
-			sl = new(Symlink)
-			sl.field = f
-			sl.link = slist
-			sl.followptr = followptr
-			slist = sl
+			slist = append(slist, Symlink{field: f, followptr: followptr})
 		}
 
 		return
@@ -1758,17 +1751,12 @@ func expand0(t *Type, followptr bool) {
 
 	u = methtype(t, 0)
 	if u != nil {
-		var sl *Symlink
 		for f, it := IterMethods(u); f != nil; f = it.Next() {
 			if f.Sym.Flags&SymUniq != 0 {
 				continue
 			}
 			f.Sym.Flags |= SymUniq
-			sl = new(Symlink)
-			sl.field = f
-			sl.link = slist
-			sl.followptr = followptr
-			slist = sl
+			slist = append(slist, Symlink{field: f, followptr: followptr})
 		}
 	}
 }
@@ -1808,7 +1796,7 @@ out:
 }
 
 func expandmeth(t *Type) {
-	if t == nil || t.Xmethod != nil {
+	if t == nil || t.AllMethods().Len() != 0 {
 		return
 	}
 
@@ -1819,41 +1807,40 @@ func expandmeth(t *Type) {
 	}
 
 	// generate all reachable methods
-	slist = nil
-
+	slist = slist[:0]
 	expand1(t, true, false)
 
 	// check each method to be uniquely reachable
-	for sl := slist; sl != nil; sl = sl.link {
+	var ms []*Field
+	for i, sl := range slist {
+		slist[i].field = nil
 		sl.field.Sym.Flags &^= SymUniq
+
 		var f *Field
 		if path, _ := dotpath(sl.field.Sym, t, &f, false); path == nil {
 			continue
 		}
+
 		// dotpath may have dug out arbitrary fields, we only want methods.
-		if f.Type.Etype == TFUNC && f.Type.Thistuple > 0 {
-			sl.good = true
-			sl.field = f
+		if f.Type.Etype != TFUNC || f.Type.Thistuple == 0 {
+			continue
 		}
+
+		// add it to the base type method list
+		f = f.Copy()
+		f.Embedded = 1 // needs a trampoline
+		if sl.followptr {
+			f.Embedded = 2
+		}
+		ms = append(ms, f)
 	}
 
 	for f, it := IterMethods(t); f != nil; f = it.Next() {
 		f.Sym.Flags &^= SymUniq
 	}
 
-	t.Xmethod = t.Method
-	for sl := slist; sl != nil; sl = sl.link {
-		if sl.good {
-			// add it to the base type method list
-			f := sl.field.Copy()
-			f.Embedded = 1 // needs a trampoline
-			if sl.followptr {
-				f.Embedded = 2
-			}
-			f.Down = t.Xmethod
-			t.Xmethod = f
-		}
-	}
+	ms = append(ms, t.Methods().Slice()...)
+	t.AllMethods().Set(ms)
 }
 
 // Given funarg struct list, return list of ODCLFIELD Node fn args.

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

@@ -123,8 +123,8 @@ type Type struct {
 	Intuple   int
 	Outnamed  bool
 
-	Method  *Field
-	Xmethod *Field
+	methods    Fields
+	allMethods Fields
 
 	Sym    *Sym
 	Vargen int32 // unique name for OTYPE/ONAME
@@ -137,7 +137,7 @@ type Type struct {
 	Width int64
 
 	// TSTRUCT
-	Fields *Field // first struct field
+	fields Fields
 
 	Down *Type // key type in TMAP; next struct in Funarg TSTRUCT
 
@@ -172,7 +172,48 @@ type Field struct {
 	Type  *Type   // field type
 	Width int64   // TODO(mdempsky): Rename to offset.
 	Note  *string // literal string annotation
-	Down  *Field  // next struct field
+}
+
+// Fields is a pointer to a slice of *Field.
+// This saves space in Types that do not have fields or methods
+// compared to a simple slice of *Field.
+type Fields struct {
+	s *[]*Field
+}
+
+// Len returns the number of entries in f.
+func (f *Fields) Len() int {
+	if f.s == nil {
+		return 0
+	}
+	return len(*f.s)
+}
+
+// Slice returns the entries in f as a slice.
+// Changes to the slice entries will be reflected in f.
+func (f *Fields) Slice() []*Field {
+	if f.s == nil {
+		return nil
+	}
+	return *f.s
+}
+
+// Set sets f to a slice.
+// This takes ownership of the slice.
+func (f *Fields) Set(s []*Field) {
+	if len(s) != 0 {
+		f.s = &s
+	} else {
+		f.s = nil
+	}
+}
+
+// Append appends entries to f.
+func (f *Fields) Append(s ...*Field) {
+	if f.s == nil {
+		f.s = new([]*Field)
+	}
+	*f.s = append(*f.s, s...)
 }
 
 // typ returns a new Type of the specified kind.
@@ -213,49 +254,38 @@ func (f *Field) Copy() *Field {
 // Iter provides an abstraction for iterating across struct fields and
 // interface methods.
 type Iter struct {
-	x *Field
+	s []*Field
 }
 
 // IterFields returns the first field or method in struct or interface type t
 // and an Iter value to continue iterating across the rest.
 func IterFields(t *Type) (*Field, Iter) {
-	if t.Etype != TSTRUCT && t.Etype != TINTER {
-		Fatalf("IterFields: type %v does not have fields", t)
-	}
-	return RawIter(t.Fields)
+	return t.Fields().Iter()
 }
 
 // IterMethods returns the first method in type t's method set
 // and an Iter value to continue iterating across the rest.
 // IterMethods does not include promoted methods.
 func IterMethods(t *Type) (*Field, Iter) {
-	// TODO(mdempsky): Validate t?
-	return RawIter(t.Method)
-}
-
-// IterAllMethods returns the first (possibly promoted) method in type t's
-// method set and an Iter value to continue iterating across the rest.
-func IterAllMethods(t *Type) (*Field, Iter) {
-	// TODO(mdempsky): Validate t?
-	return RawIter(t.Xmethod)
+	return t.Methods().Iter()
 }
 
-// RawIter returns field t and an Iter value to continue iterating across
-// its successor fields. Most code should instead use one of the IterXXX
-// functions above.
-func RawIter(t *Field) (*Field, Iter) {
-	i := Iter{x: t}
+// Iter returns the first field in fs and an Iter value to continue iterating
+// across its successor fields.
+// Deprecated: New code should use Slice instead.
+func (fs *Fields) Iter() (*Field, Iter) {
+	i := Iter{s: fs.Slice()}
 	f := i.Next()
 	return f, i
 }
 
 // Next returns the next field or method, if any.
 func (i *Iter) Next() *Field {
-	if i.x == nil {
+	if len(i.s) == 0 {
 		return nil
 	}
-	f := i.x
-	i.x = f.Down
+	f := i.s[0]
+	i.s = i.s[1:]
 	return f
 }
 
@@ -311,40 +341,37 @@ func (t *Type) Key() *Type {
 	return t.Down
 }
 
+func (t *Type) Methods() *Fields {
+	// TODO(mdempsky): Validate t?
+	return &t.methods
+}
+
+func (t *Type) AllMethods() *Fields {
+	// TODO(mdempsky): Validate t?
+	return &t.allMethods
+}
+
+func (t *Type) Fields() *Fields {
+	if t.Etype != TSTRUCT && t.Etype != TINTER {
+		Fatalf("Fields: type %v does not have fields", t)
+	}
+	return &t.fields
+}
+
 // Field returns the i'th field/method of struct/interface type t.
 func (t *Type) Field(i int) *Field {
-	// TODO: store fields in a slice so we can
-	// look them up by index in constant time.
-	for f, it := IterFields(t); f != nil; f = it.Next() {
-		if i == 0 {
-			return f
-		}
-		i--
-	}
-	panic("not enough fields")
+	return t.Fields().Slice()[i]
 }
 
 // FieldSlice returns a slice of containing all fields/methods of
 // struct/interface type t.
 func (t *Type) FieldSlice() []*Field {
-	var s []*Field
-	for f, it := IterFields(t); f != nil; f = it.Next() {
-		s = append(s, f)
-	}
-	return s
+	return t.Fields().Slice()
 }
 
 // SetFields sets struct/interface type t's fields/methods to fields.
 func (t *Type) SetFields(fields []*Field) {
-	if t.Etype != TSTRUCT && t.Etype != TINTER {
-		Fatalf("SetFields: type %v does not have fields", t)
-	}
-	var next *Field
-	for i := len(fields) - 1; i >= 0; i-- {
-		fields[i].Down = next
-		next = fields[i]
-	}
-	t.Fields = next
+	t.Fields().Set(fields)
 }
 
 func (t *Type) Size() int64 {
@@ -649,11 +676,7 @@ func (t *Type) PtrTo() ssa.Type {
 }
 
 func (t *Type) NumFields() int {
-	n := 0
-	for f, it := IterFields(t); f != nil; f = it.Next() {
-		n++
-	}
-	return n
+	return t.Fields().Len()
 }
 func (t *Type) FieldType(i int) ssa.Type {
 	return t.Field(i).Type

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

@@ -2362,9 +2362,9 @@ func twoarg(n *Node) bool {
 	return true
 }
 
-func lookdot1(errnode *Node, s *Sym, t *Type, f *Field, dostrcmp int) *Field {
+func lookdot1(errnode *Node, s *Sym, t *Type, fs *Fields, dostrcmp int) *Field {
 	var r *Field
-	for f, it := RawIter(f); f != nil; f = it.Next() {
+	for _, f := range fs.Slice() {
 		if dostrcmp != 0 && f.Sym.Name == s.Name {
 			return f
 		}
@@ -2395,7 +2395,7 @@ func looktypedot(n *Node, t *Type, dostrcmp int) bool {
 	s := n.Right.Sym
 
 	if t.Etype == TINTER {
-		f1 := lookdot1(n, s, t, t.Fields, dostrcmp)
+		f1 := lookdot1(n, s, t, t.Fields(), dostrcmp)
 		if f1 == nil {
 			return false
 		}
@@ -2415,7 +2415,7 @@ func looktypedot(n *Node, t *Type, dostrcmp int) bool {
 	}
 
 	expandmeth(mt)
-	f2 := lookdot1(n, s, mt, mt.Xmethod, dostrcmp)
+	f2 := lookdot1(n, s, mt, mt.AllMethods(), dostrcmp)
 	if f2 == nil {
 		return false
 	}
@@ -2455,7 +2455,7 @@ func lookdot(n *Node, t *Type, dostrcmp int) *Field {
 	dowidth(t)
 	var f1 *Field
 	if t.Etype == TSTRUCT || t.Etype == TINTER {
-		f1 = lookdot1(n, s, t, t.Fields, dostrcmp)
+		f1 = lookdot1(n, s, t, t.Fields(), dostrcmp)
 	}
 
 	var f2 *Field
@@ -2464,7 +2464,7 @@ func lookdot(n *Node, t *Type, dostrcmp int) *Field {
 		if mt != nil {
 			// Use f2->method, not f2->xmethod: adddot has
 			// already inserted all the necessary embedded dots.
-			f2 = lookdot1(n, s, mt, mt.Method, dostrcmp)
+			f2 = lookdot1(n, s, mt, mt.Methods(), dostrcmp)
 		}
 	}
 
@@ -3103,7 +3103,7 @@ func typecheckcomplit(np **Node) {
 					}
 				}
 
-				f := lookdot1(nil, s, t, t.Fields, 0)
+				f := lookdot1(nil, s, t, t.Fields(), 0)
 				if f == nil {
 					Yyerror("unknown %v field '%v' in struct literal", t, s)
 					continue
@@ -3524,8 +3524,8 @@ func copytype(n *Node, t *Type) {
 	if n.Name != nil {
 		t.Vargen = n.Name.Vargen
 	}
-	t.Method = nil
-	t.Xmethod = nil
+	t.methods = Fields{}
+	t.allMethods = Fields{}
 	t.Nod = nil
 	t.Printed = false
 	t.Deferwidth = false