cmd/compile: change ODOT and friends to use Sym, not Right

The Node type ODOT and its variants all represent a selector, with a
simple name to the right of the dot.  Before this change this was
represented by using an ONAME Node in the Right field.  This ONAME node
served no useful purpose.  This CL changes these Node types to store the
symbol in the Sym field instead, thus not requiring allocating a Node
for each selector.

When compiling x/tools/go/types this CL eliminates nearly 5000 calls to
newname and reduces the total number of Nodes allocated by about 6.6%.
It seems to cut compilation time by 1 to 2 percent.

Getting this right was somewhat subtle, and I added two dubious changes
to produce the exact same output as before.  One is to ishairy in
inl.go: the ONAME node increased the cost of ODOT and friends by 1, and
I retained that, although really ODOT is not more expensive than any
other node.  The other is to varexpr in walk.go: because the ONAME in
the Right field of an ODOT has no class, varexpr would always return
false for an ODOT, although in fact for some ODOT's it seemingly ought
to return true; I added an && false for now.  I will send separate CLs,
that will break toolstash -cmp, to clean these up.

This CL passes toolstash -cmp.

Change-Id: I4af8a10cc59078c436130ce472f25abc3a9b2f80
Reviewed-on: https://go-review.googlesource.com/20890
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/amd64/gsubr.go

@@ -112,7 +112,7 @@ func ginscmp(op gc.Op, t *gc.Type, n1, n2 *gc.Node, likely int) *obj.Prog {
 	// A special case to make write barriers more efficient.
 	// Comparing the first field of a named struct can be done directly.
 	base := n1
-	if n1.Op == gc.ODOT && n1.Left.Type.Etype == gc.TSTRUCT && n1.Left.Type.Field(0).Sym == n1.Right.Sym {
+	if n1.Op == gc.ODOT && n1.Left.Type.Etype == gc.TSTRUCT && n1.Left.Type.Field(0).Sym == n1.Sym {
 		base = n1.Left
 	}
 

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

@@ -242,7 +242,7 @@ func genhash(sym *Sym, t *Type) {
 			if algtype1(f.Type, nil) != AMEM {
 				hashel := hashfor(f.Type)
 				call := Nod(OCALL, hashel, nil)
-				nx := Nod(OXDOT, np, newname(f.Sym)) // TODO: fields from other packages?
+				nx := NodSym(OXDOT, np, f.Sym) // TODO: fields from other packages?
 				na := Nod(OADDR, nx, nil)
 				na.Etype = 1 // no escape to heap
 				call.List.Append(na)
@@ -258,7 +258,7 @@ func genhash(sym *Sym, t *Type) {
 			// h = hashel(&p.first, size, h)
 			hashel := hashmem(f.Type)
 			call := Nod(OCALL, hashel, nil)
-			nx := Nod(OXDOT, np, newname(f.Sym)) // TODO: fields from other packages?
+			nx := NodSym(OXDOT, np, f.Sym) // TODO: fields from other packages?
 			na := Nod(OADDR, nx, nil)
 			na.Etype = 1 // no escape to heap
 			call.List.Append(na)
@@ -436,7 +436,7 @@ func geneq(sym *Sym, t *Type) {
 
 			// Compare non-memory fields with field equality.
 			if algtype1(f.Type, nil) != AMEM {
-				and(eqfield(np, nq, newname(f.Sym)))
+				and(eqfield(np, nq, f.Sym))
 				i++
 				continue
 			}
@@ -449,11 +449,11 @@ func geneq(sym *Sym, t *Type) {
 			if s := fields[i:next]; len(s) <= 2 {
 				// Two or fewer fields: use plain field equality.
 				for _, f := range s {
-					and(eqfield(np, nq, newname(f.Sym)))
+					and(eqfield(np, nq, f.Sym))
 				}
 			} else {
 				// More than two fields: use memequal.
-				and(eqmem(np, nq, newname(f.Sym), size))
+				and(eqmem(np, nq, f.Sym, size))
 			}
 			i = next
 		}
@@ -502,19 +502,19 @@ func geneq(sym *Sym, t *Type) {
 
 // eqfield returns the node
 // 	p.field == q.field
-func eqfield(p *Node, q *Node, field *Node) *Node {
-	nx := Nod(OXDOT, p, field)
-	ny := Nod(OXDOT, q, field)
+func eqfield(p *Node, q *Node, field *Sym) *Node {
+	nx := NodSym(OXDOT, p, field)
+	ny := NodSym(OXDOT, q, field)
 	ne := Nod(OEQ, nx, ny)
 	return ne
 }
 
 // eqmem returns the node
 // 	memequal(&p.field, &q.field [, size])
-func eqmem(p *Node, q *Node, field *Node, size int64) *Node {
-	nx := Nod(OADDR, Nod(OXDOT, p, field), nil)
+func eqmem(p *Node, q *Node, field *Sym, size int64) *Node {
+	nx := Nod(OADDR, NodSym(OXDOT, p, field), nil)
 	nx.Etype = 1 // does not escape
-	ny := Nod(OADDR, Nod(OXDOT, q, field), nil)
+	ny := Nod(OADDR, NodSym(OXDOT, q, field), nil)
 	ny.Etype = 1 // does not escape
 	typecheck(&nx, Erv)
 	typecheck(&ny, Erv)

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

@@ -890,7 +890,7 @@ func (p *exporter) node(n *Node) {
 
 	case ODOT, ODOTPTR, ODOTMETH, ODOTINTER, OXDOT:
 		p.node(n.Left)
-		p.sym(n.Right.Sym)
+		p.sym(n.Sym)
 
 	case ODOTTYPE, ODOTTYPE2:
 		p.node(n.Left)

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

@@ -658,7 +658,7 @@ func (p *importer) node() *Node {
 			obj.Used = true
 			return oldname(s)
 		}
-		return Nod(OXDOT, obj, newname(sel))
+		return NodSym(OXDOT, obj, sel)
 
 	case ODOTTYPE, ODOTTYPE2:
 		n.Left = p.node()

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

@@ -802,7 +802,7 @@ func cgen_wbptr(n, res *Node) {
 	}
 
 	wbVar := syslook("writeBarrier")
-	wbEnabled := Nod(ODOT, wbVar, newname(wbVar.Type.Field(0).Sym))
+	wbEnabled := NodSym(ODOT, wbVar, wbVar.Type.Field(0).Sym)
 	wbEnabled = typecheck(&wbEnabled, Erv)
 	pbr := Thearch.Ginscmp(ONE, Types[TUINT8], wbEnabled, Nodintconst(0), -1)
 	Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &src, &dst)
@@ -2440,11 +2440,6 @@ func cgen_callinter(n *Node, res *Node, proc int) {
 		Fatalf("cgen_callinter: not ODOTINTER %v", Oconv(i.Op, 0))
 	}
 
-	f := i.Right // field
-	if f.Op != ONAME {
-		Fatalf("cgen_callinter: not ONAME %v", Oconv(f.Op, 0))
-	}
-
 	i = i.Left // interface
 
 	if !i.Addable {

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

@@ -462,7 +462,7 @@ func walkclosure(func_ *Node, init *Nodes) *Node {
 	return clos
 }
 
-func typecheckpartialcall(fn *Node, sym *Node) {
+func typecheckpartialcall(fn *Node, sym *Sym) {
 	switch fn.Op {
 	case ODOTINTER, ODOTMETH:
 		break
@@ -474,21 +474,21 @@ func typecheckpartialcall(fn *Node, sym *Node) {
 	// Create top-level function.
 	xfunc := makepartialcall(fn, fn.Type, sym)
 	fn.Func = xfunc.Func
-	fn.Right = sym
+	fn.Right = newname(sym)
 	fn.Op = OCALLPART
 	fn.Type = xfunc.Type
 }
 
 var makepartialcall_gopkg *Pkg
 
-func makepartialcall(fn *Node, t0 *Type, meth *Node) *Node {
+func makepartialcall(fn *Node, t0 *Type, meth *Sym) *Node {
 	var p string
 
 	rcvrtype := fn.Left.Type
-	if exportname(meth.Sym.Name) {
-		p = fmt.Sprintf("(%v).%s-fm", Tconv(rcvrtype, FmtLeft|FmtShort), meth.Sym.Name)
+	if exportname(meth.Name) {
+		p = fmt.Sprintf("(%v).%s-fm", Tconv(rcvrtype, FmtLeft|FmtShort), meth.Name)
 	} else {
-		p = fmt.Sprintf("(%v).(%v)-fm", Tconv(rcvrtype, FmtLeft|FmtShort), Sconv(meth.Sym, FmtLeft))
+		p = fmt.Sprintf("(%v).(%v)-fm", Tconv(rcvrtype, FmtLeft|FmtShort), Sconv(meth, FmtLeft))
 	}
 	basetype := rcvrtype
 	if Isptr[rcvrtype.Etype] {
@@ -592,7 +592,7 @@ func makepartialcall(fn *Node, t0 *Type, meth *Node) *Node {
 		body = append(body, Nod(OAS, ptr, Nod(OADDR, cv, nil)))
 	}
 
-	call := Nod(OCALL, Nod(OXDOT, ptr, meth), nil)
+	call := Nod(OCALL, NodSym(OXDOT, ptr, meth), nil)
 	call.List.Set(callargs)
 	call.Isddd = ddd
 	if t0.Results().NumFields() == 0 {

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

@@ -1432,7 +1432,7 @@ func (c *nowritebarrierrecChecker) visitcode(n *Node) {
 func (c *nowritebarrierrecChecker) visitcall(n *Node) {
 	fn := n.Left
 	if n.Op == OCALLMETH {
-		fn = n.Left.Right.Sym.Def
+		fn = n.Left.Sym.Def
 	}
 	if fn == nil || fn.Op != ONAME || fn.Class != PFUNC || fn.Name.Defn == nil {
 		return

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

@@ -131,7 +131,7 @@ func (v *bottomUpVisitor) visitcode(n *Node, min uint32) uint32 {
 	if n.Op == OCALLFUNC || n.Op == OCALLMETH {
 		fn := n.Left
 		if n.Op == OCALLMETH {
-			fn = n.Left.Right.Sym.Def
+			fn = n.Left.Sym.Def
 		}
 		if fn != nil && fn.Op == ONAME && fn.Class == PFUNC && fn.Name.Defn != nil {
 			m := v.visit(fn.Name.Defn)
@@ -1421,7 +1421,7 @@ func esccall(e *EscState, n *Node, up *Node) {
 		indirect = fn.Op != ONAME || fn.Class != PFUNC
 
 	case OCALLMETH:
-		fn = n.Left.Right.Sym.Def
+		fn = n.Left.Sym.Def
 		if fn != nil {
 			fntype = fn.Type
 		} else {

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

@@ -1249,12 +1249,7 @@ func exprfmt(n *Node, prec int) string {
 		}
 		return ":"
 
-	case OXDOT,
-		ODOT,
-		ODOTPTR,
-		ODOTINTER,
-		ODOTMETH,
-		OCALLPART:
+	case OCALLPART:
 		var f string
 		f += exprfmt(n.Left, nprec)
 		if n.Right == nil || n.Right.Sym == nil {
@@ -1264,6 +1259,16 @@ func exprfmt(n *Node, prec int) string {
 		f += fmt.Sprintf(".%v", Sconv(n.Right.Sym, FmtShort|FmtByte))
 		return f
 
+	case OXDOT, ODOT, ODOTPTR, ODOTINTER, ODOTMETH:
+		var f string
+		f += exprfmt(n.Left, nprec)
+		if n.Sym == nil {
+			f += ".<nil>"
+			return f
+		}
+		f += fmt.Sprintf(".%v", Sconv(n.Sym, FmtShort|FmtByte))
+		return f
+
 	case ODOTTYPE, ODOTTYPE2:
 		var f string
 		f += exprfmt(n.Left, nprec)

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

@@ -948,7 +948,7 @@ func cgen_callmeth(n *Node, proc int) {
 
 	n2 := *n
 	n2.Op = OCALLFUNC
-	n2.Left = l.Right
+	n2.Left = newname(l.Sym)
 	n2.Left.Type = l.Type
 
 	if n2.Left.Op == ONAME {

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

@@ -416,7 +416,7 @@ func Naddr(a *obj.Addr, n *Node) {
 		// A special case to make write barriers more efficient.
 		// Taking the address of the first field of a named struct
 		// is the same as taking the address of the struct.
-		if n.Left.Type.Etype != TSTRUCT || n.Left.Type.Field(0).Sym != n.Right.Sym {
+		if n.Left.Type.Etype != TSTRUCT || n.Left.Type.Field(0).Sym != n.Sym {
 			Debug['h'] = 1
 			Dump("naddr", n)
 			Fatalf("naddr: bad %v %v", Oconv(n.Op, 0), Ctxt.Dconv(a))

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

@@ -220,6 +220,13 @@ func ishairy(n *Node, budget *int) bool {
 		ODCLTYPE, // can't print yet
 		ORETJMP:
 		return true
+
+	case ODOT, ODOTPTR, ODOTMETH, ODOTINTER:
+		// These used to store the symbol name as an ONAME in
+		// the Right field, meaning that it cost one budget
+		// unit.  Stay compatible for now.
+		// TODO(iant): Remove this.
+		(*budget)--
 	}
 
 	(*budget)--

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

@@ -1793,7 +1793,7 @@ func (p *parser) new_dotname(obj *Node) *Node {
 		obj.Used = true
 		return oldname(s)
 	}
-	return Nod(OXDOT, obj, newname(sel))
+	return NodSym(OXDOT, obj, sel)
 }
 
 func (p *parser) dotname() *Node {

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

@@ -226,27 +226,27 @@ func walkrange(n *Node) {
 		hit := prealloc[n]
 		hit.Type = th
 		n.Left = nil
-		keyname := newname(th.Field(0).Sym) // depends on layout of iterator struct.  See reflect.go:hiter
-		valname := newname(th.Field(1).Sym) // ditto
+		keysym := th.Field(0).Sym // depends on layout of iterator struct.  See reflect.go:hiter
+		valsym := th.Field(1).Sym // ditto
 
 		fn := syslook("mapiterinit")
 
 		substArgTypes(&fn, t.Key(), t.Type, th)
 		init = append(init, mkcall1(fn, nil, nil, typename(t), ha, Nod(OADDR, hit, nil)))
-		n.Left = Nod(ONE, Nod(ODOT, hit, keyname), nodnil())
+		n.Left = Nod(ONE, NodSym(ODOT, hit, keysym), nodnil())
 
 		fn = syslook("mapiternext")
 		substArgTypes(&fn, th)
 		n.Right = mkcall1(fn, nil, nil, Nod(OADDR, hit, nil))
 
-		key := Nod(ODOT, hit, keyname)
+		key := NodSym(ODOT, hit, keysym)
 		key = Nod(OIND, key, nil)
 		if v1 == nil {
 			body = nil
 		} else if v2 == nil {
 			body = []*Node{Nod(OAS, v1, key)}
 		} else {
-			val := Nod(ODOT, hit, valname)
+			val := NodSym(ODOT, hit, valsym)
 			val = Nod(OIND, val, nil)
 			a := Nod(OAS2, nil, nil)
 			a.List.Set([]*Node{v1, v2})

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

@@ -574,10 +574,10 @@ func structlit(ctxt int, pass int, n *Node, var_ *Node, init *Nodes) {
 		case OARRAYLIT:
 			if value.Type.Bound < 0 {
 				if pass == 1 && ctxt != 0 {
-					a = Nod(ODOT, var_, newname(index.Sym))
+					a = NodSym(ODOT, var_, index.Sym)
 					slicelit(ctxt, value, a, init)
 				} else if pass == 2 && ctxt == 0 {
-					a = Nod(ODOT, var_, newname(index.Sym))
+					a = NodSym(ODOT, var_, index.Sym)
 					slicelit(ctxt, value, a, init)
 				} else if pass == 3 {
 					break
@@ -585,12 +585,12 @@ func structlit(ctxt int, pass int, n *Node, var_ *Node, init *Nodes) {
 				continue
 			}
 
-			a = Nod(ODOT, var_, newname(index.Sym))
+			a = NodSym(ODOT, var_, index.Sym)
 			arraylit(ctxt, pass, value, a, init)
 			continue
 
 		case OSTRUCTLIT:
-			a = Nod(ODOT, var_, newname(index.Sym))
+			a = NodSym(ODOT, var_, index.Sym)
 			structlit(ctxt, pass, value, a, init)
 			continue
 		}
@@ -605,7 +605,7 @@ func structlit(ctxt int, pass int, n *Node, var_ *Node, init *Nodes) {
 
 		// build list of var.field = expr
 		setlineno(value)
-		a = Nod(ODOT, var_, newname(index.Sym))
+		a = NodSym(ODOT, var_, index.Sym)
 
 		a = Nod(OAS, a, value)
 		typecheck(&a, Etop)
@@ -904,7 +904,7 @@ func maplit(ctxt int, n *Node, var_ *Node, init *Nodes) {
 				a = Nodintconst(b)
 
 				a = Nod(OINDEX, vstat, a)
-				a = Nod(ODOT, a, newname(syma))
+				a = NodSym(ODOT, a, syma)
 				a = Nod(OAS, a, index)
 				typecheck(&a, Etop)
 				walkexpr(&a, init)
@@ -916,7 +916,7 @@ func maplit(ctxt int, n *Node, var_ *Node, init *Nodes) {
 				a = Nodintconst(b)
 
 				a = Nod(OINDEX, vstat, a)
-				a = Nod(ODOT, a, newname(symb))
+				a = NodSym(ODOT, a, symb)
 				a = Nod(OAS, a, value)
 				typecheck(&a, Etop)
 				walkexpr(&a, init)
@@ -935,11 +935,11 @@ func maplit(ctxt int, n *Node, var_ *Node, init *Nodes) {
 
 		a = Nod(OINDEX, vstat, index)
 		a.Bounded = true
-		a = Nod(ODOT, a, newname(symb))
+		a = NodSym(ODOT, a, symb)
 
 		r := Nod(OINDEX, vstat, index)
 		r.Bounded = true
-		r = Nod(ODOT, r, newname(syma))
+		r = NodSym(ODOT, r, syma)
 		r = Nod(OINDEX, var_, r)
 
 		r = Nod(OAS, r, a)

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

@@ -2326,16 +2326,14 @@ func (s *state) call(n *Node, k callKind) *ssa.Value {
 		if fn.Op != ODOTMETH {
 			Fatalf("OCALLMETH: n.Left not an ODOTMETH: %v", fn)
 		}
-		if fn.Right.Op != ONAME {
-			Fatalf("OCALLMETH: n.Left.Right not a ONAME: %v", fn.Right)
-		}
 		if k == callNormal {
-			sym = fn.Right.Sym
+			sym = fn.Sym
 			break
 		}
-		n2 := *fn.Right
+		n2 := newname(fn.Sym)
 		n2.Class = PFUNC
-		closure = s.expr(&n2)
+		n2.Lineno = fn.Lineno
+		closure = s.expr(n2)
 		// Note: receiver is already assigned in n.List, so we don't
 		// want to set it here.
 	case OCALLINTER:
@@ -3967,14 +3965,14 @@ func AutoVar(v *ssa.Value) (*Node, int64) {
 // fieldIdx finds the index of the field referred to by the ODOT node n.
 func fieldIdx(n *Node) int {
 	t := n.Left.Type
-	f := n.Right
+	f := n.Sym
 	if t.Etype != TSTRUCT {
 		panic("ODOT's LHS is not a struct")
 	}
 
 	var i int
 	for _, t1 := range t.Fields().Slice() {
-		if t1.Sym != f.Sym {
+		if t1.Sym != f {
 			i++
 			continue
 		}

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

@@ -339,6 +339,14 @@ func Nod(op Op, nleft *Node, nright *Node) *Node {
 	return n
 }
 
+// NodSym makes a Node with Op op and with the Left field set to left
+// and the Sym field set to sym. This is for ODOT and friends.
+func NodSym(op Op, left *Node, sym *Sym) *Node {
+	n := Nod(op, left, nil)
+	n.Sym = sym
+	return n
+}
+
 func saveorignode(n *Node) {
 	if n.Orig != nil {
 		return
@@ -1677,10 +1685,7 @@ func adddot(n *Node) *Node {
 		return n
 	}
 
-	if n.Right.Op != ONAME {
-		return n
-	}
-	s := n.Right.Sym
+	s := n.Sym
 	if s == nil {
 		return n
 	}
@@ -1689,7 +1694,7 @@ func adddot(n *Node) *Node {
 	case path != nil:
 		// rebuild elided dots
 		for c := len(path) - 1; c >= 0; c-- {
-			n.Left = Nod(ODOT, n.Left, newname(path[c].field.Sym))
+			n.Left = NodSym(ODOT, n.Left, path[c].field.Sym)
 			n.Left.Implicit = true
 		}
 	case ambig:
@@ -1960,7 +1965,7 @@ func genwrapper(rcvr *Type, method *Field, newnam *Sym, iface int) {
 		fn.Nbody.Append(n)
 	}
 
-	dot := adddot(Nod(OXDOT, this.Left, newname(method.Sym)))
+	dot := adddot(NodSym(OXDOT, this.Left, method.Sym))
 
 	// generate call
 	if !instrumenting && Isptr[rcvr.Etype] && Isptr[methodrcvr.Etype] && method.Embedded != 0 && !isifacemethod(method.Type) {

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

@@ -595,14 +595,14 @@ func (s *typeSwitch) walk(sw *Node) {
 
 	if !isnilinter(cond.Right.Type) {
 		// Load type from itab.
-		typ = Nod(ODOTPTR, typ, nil)
+		typ = NodSym(ODOTPTR, typ, nil)
 		typ.Type = Ptrto(Types[TUINT8])
 		typ.Typecheck = 1
 		typ.Xoffset = int64(Widthptr) // offset of _type in runtime.itab
 		typ.Bounded = true            // guaranteed not to fault
 	}
 	// Load hash from type.
-	h := Nod(ODOTPTR, typ, nil)
+	h := NodSym(ODOTPTR, typ, nil)
 	h.Type = Types[TUINT32]
 	h.Typecheck = 1
 	h.Xoffset = int64(2 * Widthptr) // offset of hash in runtime._type

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

@@ -249,11 +249,11 @@ const (
 	ODCLTYPE  // type Int int
 
 	ODELETE    // delete(Left, Right)
-	ODOT       // Left.Right (Left is of struct type)
-	ODOTPTR    // Left.Right (Left is of pointer to struct type)
-	ODOTMETH   // Left.Right (Left is non-interface, Right is method name)
-	ODOTINTER  // Left.Right (Left is interface, Right is method name)
-	OXDOT      // Left.Right (before rewrite to one of the preceding)
+	ODOT       // Left.Sym (Left is of struct type)
+	ODOTPTR    // Left.Sym (Left is of pointer to struct type)
+	ODOTMETH   // Left.Sym (Left is non-interface, Right is method name)
+	ODOTINTER  // Left.Sym (Left is interface, Right is method name)
+	OXDOT      // Left.Sym (before rewrite to one of the preceding)
 	ODOTTYPE   // Left.Right or Left.Type (.Right during parsing, .Type once resolved)
 	ODOTTYPE2  // Left.Right or Left.Type (.Right during parsing, .Type once resolved; on rhs of OAS2DOTTYPE)
 	OEQ        // Left == Right

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

@@ -252,17 +252,22 @@ func typecheck1(np **Node, top int) {
 		*np = n
 	}()
 
-	if n.Sym != nil {
-		if n.Op == ONAME && n.Etype != 0 && top&Ecall == 0 {
-			Yyerror("use of builtin %v not in function call", n.Sym)
-			n.Type = nil
-			return
-		}
+	switch n.Op {
+	case OXDOT, ODOT, ODOTPTR, ODOTMETH, ODOTINTER:
+		// n.Sym is a field/method name, not a variable.
+	default:
+		if n.Sym != nil {
+			if n.Op == ONAME && n.Etype != 0 && top&Ecall == 0 {
+				Yyerror("use of builtin %v not in function call", n.Sym)
+				n.Type = nil
+				return
+			}
 
-		typecheckdef(n)
-		if n.Op == ONONAME {
-			n.Type = nil
-			return
+			typecheckdef(n)
+			if n.Op == ONONAME {
+				n.Type = nil
+				return
+			}
 		}
 	}
 
@@ -819,11 +824,6 @@ OpSwitch:
 		typecheck(&n.Left, Erv|Etype)
 
 		defaultlit(&n.Left, nil)
-		if n.Right.Op != ONAME {
-			Yyerror("rhs of . must be a name") // impossible
-			n.Type = nil
-			return
-		}
 
 		t := n.Left.Type
 		if t == nil {
@@ -832,14 +832,14 @@ OpSwitch:
 			return
 		}
 
-		r := n.Right
+		s := n.Sym
 
 		if n.Left.Op == OTYPE {
 			if !looktypedot(n, t, 0) {
 				if looktypedot(n, t, 1) {
-					Yyerror("%v undefined (cannot refer to unexported method %v)", n, n.Right.Sym)
+					Yyerror("%v undefined (cannot refer to unexported method %v)", n, n.Sym)
 				} else {
-					Yyerror("%v undefined (type %v has no method %v)", n, t, n.Right.Sym)
+					Yyerror("%v undefined (type %v has no method %v)", n, t, n.Sym)
 				}
 				n.Type = nil
 				return
@@ -856,7 +856,7 @@ OpSwitch:
 			if n.Name == nil {
 				n.Name = new(Name)
 			}
-			n.Sym = n.Right.Sym
+			n.Right = newname(n.Sym)
 			n.Type = methodfunc(n.Type, n.Left.Type)
 			n.Xoffset = 0
 			n.Class = PFUNC
@@ -874,7 +874,7 @@ OpSwitch:
 			checkwidth(t)
 		}
 
-		if isblank(n.Right) {
+		if isblanksym(n.Sym) {
 			Yyerror("cannot refer to blank field or method")
 			n.Type = nil
 			return
@@ -892,13 +892,13 @@ OpSwitch:
 
 			case lookdot(n, t, 1) != nil:
 				// Field or method matches by name, but it is not exported.
-				Yyerror("%v undefined (cannot refer to unexported field or method %v)", n, n.Right.Sym)
+				Yyerror("%v undefined (cannot refer to unexported field or method %v)", n, n.Sym)
 
 			default:
 				if mt := lookdot(n, t, 2); mt != nil { // Case-insensitive lookup.
-					Yyerror("%v undefined (type %v has no field or method %v, but does have %v)", n, n.Left.Type, n.Right.Sym, mt.Sym)
+					Yyerror("%v undefined (type %v has no field or method %v, but does have %v)", n, n.Left.Type, n.Sym, mt.Sym)
 				} else {
-					Yyerror("%v undefined (type %v has no field or method %v)", n, n.Left.Type, n.Right.Sym)
+					Yyerror("%v undefined (type %v has no field or method %v)", n, n.Left.Type, n.Sym)
 				}
 			}
 			n.Type = nil
@@ -910,7 +910,7 @@ OpSwitch:
 			if top&Ecall != 0 {
 				ok |= Ecall
 			} else {
-				typecheckpartialcall(n, r)
+				typecheckpartialcall(n, s)
 				ok |= Erv
 			}
 
@@ -2392,7 +2392,7 @@ func lookdot1(errnode *Node, s *Sym, t *Type, fs *Fields, dostrcmp int) *Field {
 }
 
 func looktypedot(n *Node, t *Type, dostrcmp int) bool {
-	s := n.Right.Sym
+	s := n.Sym
 
 	if t.Etype == TINTER {
 		f1 := lookdot1(n, s, t, t.Fields(), dostrcmp)
@@ -2400,7 +2400,7 @@ func looktypedot(n *Node, t *Type, dostrcmp int) bool {
 			return false
 		}
 
-		n.Right = methodname(n.Right, t)
+		n.Sym = methodsym(n.Sym, t, 0)
 		n.Xoffset = f1.Width
 		n.Type = f1.Type
 		n.Op = ODOTINTER
@@ -2426,7 +2426,7 @@ func looktypedot(n *Node, t *Type, dostrcmp int) bool {
 		return false
 	}
 
-	n.Right = methodname(n.Right, t)
+	n.Sym = methodsym(n.Sym, t, 0)
 	n.Xoffset = f2.Width
 	n.Type = f2.Type
 	n.Op = ODOTMETH
@@ -2450,7 +2450,7 @@ type typeSym struct {
 var dotField = map[typeSym]*Field{}
 
 func lookdot(n *Node, t *Type, dostrcmp int) *Field {
-	s := n.Right.Sym
+	s := n.Sym
 
 	dowidth(t)
 	var f1 *Field
@@ -2474,7 +2474,7 @@ func lookdot(n *Node, t *Type, dostrcmp int) *Field {
 			return f1
 		}
 		if f2 != nil {
-			Yyerror("%v is both field and method", n.Right.Sym)
+			Yyerror("%v is both field and method", n.Sym)
 		}
 		if f1.Width == BADWIDTH {
 			Fatalf("lookdot badwidth %v %p", f1, f1)
@@ -2516,7 +2516,7 @@ func lookdot(n *Node, t *Type, dostrcmp int) *Field {
 				n.Left.Implicit = true
 				typecheck(&n.Left, Etype|Erv)
 			} else if tt.Etype == Tptr && tt.Type.Etype == Tptr && Eqtype(derefall(tt), derefall(rcvr)) {
-				Yyerror("calling method %v with receiver %v requires explicit dereference", n.Right, Nconv(n.Left, FmtLong))
+				Yyerror("calling method %v with receiver %v requires explicit dereference", n.Sym, Nconv(n.Left, FmtLong))
 				for tt.Etype == Tptr {
 					// Stop one level early for method with pointer receiver.
 					if rcvr.Etype == Tptr && tt.Type.Etype != Tptr {
@@ -2545,7 +2545,7 @@ func lookdot(n *Node, t *Type, dostrcmp int) *Field {
 			return nil
 		}
 
-		n.Right = methodname(n.Right, n.Left.Type)
+		n.Sym = methodsym(n.Sym, n.Left.Type, 0)
 		n.Xoffset = f2.Width
 		n.Type = f2.Type
 
@@ -3232,7 +3232,7 @@ func samesafeexpr(l *Node, r *Node) bool {
 		return l == r
 
 	case ODOT, ODOTPTR:
-		return l.Right != nil && r.Right != nil && l.Right.Sym == r.Right.Sym && samesafeexpr(l.Left, r.Left)
+		return l.Sym != nil && r.Sym != nil && l.Sym == r.Sym && samesafeexpr(l.Left, r.Left)
 
 	case OIND:
 		return samesafeexpr(l.Left, r.Left)

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

@@ -2480,12 +2480,17 @@ func varexpr(n *Node) bool {
 		OPAREN,
 		OANDAND,
 		OOROR,
-		ODOT, // but not ODOTPTR
 		OCONV,
 		OCONVNOP,
 		OCONVIFACE,
 		ODOTTYPE:
 		return varexpr(n.Left) && varexpr(n.Right)
+
+	case ODOT: // but not ODOTPTR
+		// The original code always returned false for ODOT,
+		// because n.Right would be an ONAME with n.Class not set.
+		// TODO(iant): Fix this to remove "&& false".
+		return varexpr(n.Left) && false
 	}
 
 	// Be conservative.
@@ -3234,8 +3239,8 @@ func walkcompare(np **Node, init *Nodes) {
 			if isblanksym(t1.Sym) {
 				continue
 			}
-			li = Nod(OXDOT, l, newname(t1.Sym))
-			ri = Nod(OXDOT, r, newname(t1.Sym))
+			li = NodSym(OXDOT, l, t1.Sym)
+			ri = NodSym(OXDOT, r, t1.Sym)
 			a = Nod(n.Op, li, ri)
 			if expr == nil {
 				expr = a
@@ -3295,9 +3300,7 @@ func samecheap(a *Node, b *Node) bool {
 			return a == b
 
 		case ODOT, ODOTPTR:
-			ar = a.Right
-			br = b.Right
-			if ar.Op != ONAME || br.Op != ONAME || ar.Sym != br.Sym {
+			if a.Sym != b.Sym {
 				return false
 			}
 
@@ -3815,7 +3818,7 @@ func usefield(n *Node) {
 	case ODOT, ODOTPTR:
 		break
 	}
-	if n.Right == nil {
+	if n.Sym == nil {
 		// No field name.  This DOTPTR was built by the compiler for access
 		// to runtime data structures.  Ignore.
 		return
@@ -3825,9 +3828,9 @@ func usefield(n *Node) {
 	if Isptr[t.Etype] {
 		t = t.Type
 	}
-	field := dotField[typeSym{t.Orig, n.Right.Sym}]
+	field := dotField[typeSym{t.Orig, n.Sym}]
 	if field == nil {
-		Fatalf("usefield %v %v without paramfld", n.Left.Type, n.Right.Sym)
+		Fatalf("usefield %v %v without paramfld", n.Left.Type, n.Sym)
 	}
 	if field.Note == nil || !strings.Contains(*field.Note, "go:\"track\"") {
 		return

src/cmd/compile/internal/x86/gsubr.go

@@ -639,7 +639,7 @@ func ginscmp(op gc.Op, t *gc.Type, n1, n2 *gc.Node, likely int) *obj.Prog {
 	// A special case to make write barriers more efficient.
 	// Comparing the first field of a named struct can be done directly.
 	base := n1
-	if n1.Op == gc.ODOT && n1.Left.Type.Etype == gc.TSTRUCT && n1.Left.Type.Field(0).Sym == n1.Right.Sym {
+	if n1.Op == gc.ODOT && n1.Left.Type.Etype == gc.TSTRUCT && n1.Left.Type.Field(0).Sym == n1.Sym {
 		base = n1.Left
 	}