cmd/compile: convert Func.Cvars from *NodeList to *[]*Node

Passes toolstash -cmp.

Update #14473.

Change-Id: I7285175b1992a29033fdc9e81d6f30545e5cc30d
Reviewed-on: https://go-review.googlesource.com/19967Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -67,9 +67,7 @@ func closurebody(body *NodeList) *Node {
 	// ordinary ones in the symbol table; see oldname.
 	// unhook them.
 	// make the list of pointers for the closure call.
-	var v *Node
-	for l := func_.Func.Cvars; l != nil; l = l.Next {
-		v = l.N
+	for _, v := range func_.Func.Cvars() {
 		v.Name.Param.Closure.Name.Param.Closure = v.Name.Param.Outer
 		v.Name.Param.Outerexpr = oldname(v.Sym)
 	}
@@ -78,10 +76,8 @@ func closurebody(body *NodeList) *Node {
 }
 
 func typecheckclosure(func_ *Node, top int) {
-	var n *Node
-
-	for l := func_.Func.Cvars; l != nil; l = l.Next {
-		n = l.N.Name.Param.Closure
+	for _, ln := range func_.Func.Cvars() {
+		n := ln.Name.Param.Closure
 		if !n.Name.Captured {
 			n.Name.Captured = true
 			if n.Name.Decldepth == 0 {
@@ -221,7 +217,6 @@ func makeclosure(func_ *Node) *Node {
 // We use value capturing for values <= 128 bytes that are never reassigned
 // after capturing (effectively constant).
 func capturevars(xfunc *Node) {
-	var v *Node
 	var outer *Node
 
 	lno := int(lineno)
@@ -229,8 +224,7 @@ func capturevars(xfunc *Node) {
 
 	func_ := xfunc.Func.Closure
 	func_.Func.Enter = nil
-	for l := func_.Func.Cvars; l != nil; l = l.Next {
-		v = l.N
+	for _, v := range func_.Func.Cvars() {
 		if v.Type == nil {
 			// if v->type is nil, it means v looked like it was
 			// going to be used in the closure but wasn't.
@@ -310,11 +304,9 @@ func transformclosure(xfunc *Node) {
 		original_dcl := xfunc.Func.Dcl
 		xfunc.Func.Dcl = nil
 
-		var v *Node
 		var addr *Node
 		var fld *Type
-		for l := func_.Func.Cvars; l != nil; l = l.Next {
-			v = l.N
+		for _, v := range func_.Func.Cvars() {
 			if v.Op == OXXX {
 				continue
 			}
@@ -363,10 +355,8 @@ func transformclosure(xfunc *Node) {
 		var body *NodeList
 		offset := int64(Widthptr)
 		var addr *Node
-		var v *Node
 		var cv *Node
-		for l := func_.Func.Cvars; l != nil; l = l.Next {
-			v = l.N
+		for _, v := range func_.Func.Cvars() {
 			if v.Op == OXXX {
 				continue
 			}
@@ -417,7 +407,7 @@ func transformclosure(xfunc *Node) {
 
 func walkclosure(func_ *Node, init **NodeList) *Node {
 	// If no closure vars, don't bother wrapping.
-	if func_.Func.Cvars == nil {
+	if len(func_.Func.Cvars()) == 0 {
 		return func_.Func.Closure.Func.Nname
 	}
 
@@ -439,9 +429,7 @@ func walkclosure(func_ *Node, init **NodeList) *Node {
 
 	typ.List = list1(Nod(ODCLFIELD, newname(Lookup(".F")), typenod(Types[TUINTPTR])))
 	var typ1 *Node
-	var v *Node
-	for l := func_.Func.Cvars; l != nil; l = l.Next {
-		v = l.N
+	for _, v := range func_.Func.Cvars() {
 		if v.Op == OXXX {
 			continue
 		}

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

@@ -426,7 +426,7 @@ func oldname(s *Sym) *Node {
 			n.Name.Param.Closure = c
 			c.Name.Param.Closure = n
 			c.Xoffset = 0
-			Curfn.Func.Cvars = list(Curfn.Func.Cvars, c)
+			Curfn.Func.CvarAppend(c)
 		}
 
 		// return ref to closure var, not original

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

@@ -864,9 +864,7 @@ func esc(e *EscState, n *Node, up *Node) {
 		// Link addresses of captured variables to closure.
 	case OCLOSURE:
 		var a *Node
-		var v *Node
-		for ll := n.Func.Cvars; ll != nil; ll = ll.Next {
-			v = ll.N
+		for _, v := range n.Func.Cvars() {
 			if v.Op == OXXX { // unnamed out argument; see dcl.go:/^funcargs
 				continue
 			}

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

@@ -1137,7 +1137,7 @@ func orderexpr(np **Node, order *Order, lhs *Node) {
 		}
 
 	case OCLOSURE:
-		if n.Noescape && n.Func.Cvars != nil {
+		if n.Noescape && len(n.Func.Cvars()) > 0 {
 			prealloc[n] = ordertemp(Types[TUINT8], order, false) // walk will fill in correct type
 		}
 

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

@@ -475,7 +475,7 @@ func staticassign(l *Node, r *Node, out **NodeList) bool {
 		break
 
 	case OCLOSURE:
-		if r.Func.Cvars == nil {
+		if len(r.Func.Cvars()) == 0 {
 			// Closures with no captured variables are globals,
 			// so the assignment can be done at link time.
 			n := *l

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

@@ -151,9 +151,9 @@ type Func struct {
 	Shortname  *Node
 	Enter      *NodeList
 	Exit       *NodeList
-	Cvars      *NodeList // closure params
-	Dcl        []*Node   // autodcl for this func/closure
-	Inldcl     []*Node   // copy of dcl for use in inlining
+	cvars      *[]*Node // closure params
+	Dcl        []*Node  // autodcl for this func/closure
+	Inldcl     []*Node  // copy of dcl for use in inlining
 	Closgen    int
 	Outerfunc  *Node
 	Fieldtrack []*Type
@@ -177,6 +177,27 @@ type Func struct {
 	Needctxt bool   // function uses context register (has closure variables)
 }
 
+// Cvars returns the closure variables for this Func.
+// These are referenced variables that are defined in enclosing
+// functions.
+// The cvars field is a pointer to save space, since most Func values
+// have no cvars.
+func (f *Func) Cvars() []*Node {
+	if f.cvars == nil {
+		return nil
+	}
+	return *f.cvars
+}
+
+// AppendCvar appends a new closure variable.
+func (f *Func) CvarAppend(n *Node) {
+	if f.cvars == nil {
+		f.cvars = &[]*Node{n}
+	} else {
+		*f.cvars = append(*f.cvars, n)
+	}
+}
+
 type Op uint8
 
 // Node ops.