cmd/compile: convert externdecl to []*Node

This one of a set of changes to make the transition away from NodeList
easier by removing cases in which NodeList doesn't act semi-trivially like a
[]*Node.

This CL was originally prepared by Josh Bleecher Snyder <josharian@gmail.com>.

This change passes go build -toolexec 'toolstash -cmp' -a std.

Change-Id: Ifd73501e06e8ea5efd028b6d473b3e5d1b07a5ac
Reviewed-on: https://go-review.googlesource.com/14570Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -182,7 +182,7 @@ func declare(n *Node, ctxt uint8) {
 
 	gen := 0
 	if ctxt == PEXTERN {
-		externdcl = list(externdcl, n)
+		externdcl = append(externdcl, n)
 		if dflag() {
 			fmt.Printf("\t%v global decl %v %p\n", Ctxt.Line(int(lineno)), s, n)
 		}

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

@@ -584,7 +584,7 @@ var maxfltval [NTYPE]*Mpflt
 
 var xtop *NodeList
 
-var externdcl *NodeList
+var externdcl []*Node
 
 var exportlist []*Node
 

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

@@ -464,9 +464,9 @@ func Main() {
 	}
 
 	// Phase 9: Check external declarations.
-	for l := externdcl; l != nil; l = l.Next {
-		if l.N.Op == ONAME {
-			typecheck(&l.N, Erv)
+	for i, n := range externdcl {
+		if n.Op == ONAME {
+			typecheck(&externdcl[i], Erv)
 		}
 	}
 

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

@@ -72,10 +72,7 @@ func dumpobj() {
 
 	fmt.Fprintf(bout, "\n!\n")
 
-	var externs *NodeList
-	if externdcl != nil {
-		externs = externdcl.End
-	}
+	externs := len(externdcl)
 
 	dumpglobls()
 	dumptypestructs()
@@ -83,8 +80,8 @@ func dumpobj() {
 	// Dump extra globals.
 	tmp := externdcl
 
-	if externs != nil {
-		externdcl = externs.Next
+	if externdcl != nil {
+		externdcl = externdcl[externs:]
 	}
 	dumpglobls()
 	externdcl = tmp
@@ -110,8 +107,7 @@ func dumpglobls() {
 	var n *Node
 
 	// add globals
-	for l := externdcl; l != nil; l = l.Next {
-		n = l.N
+	for _, n := range externdcl {
 		if n.Op != ONAME {
 			continue
 		}
@@ -126,7 +122,6 @@ func dumpglobls() {
 			continue
 		}
 		dowidth(n.Type)
-
 		ggloblnod(n)
 	}
 

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

@@ -1317,8 +1317,7 @@ func dumptypestructs() {
 	var n *Node
 
 	// copy types from externdcl list to signatlist
-	for l := externdcl; l != nil; l = l.Next {
-		n = l.N
+	for _, n := range externdcl {
 		if n.Op != OTYPE {
 			continue
 		}

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

@@ -1584,34 +1584,33 @@ func Ptrto(t *Type) *Type {
 }
 
 func frame(context int) {
-	var l *NodeList
-
 	if context != 0 {
 		fmt.Printf("--- external frame ---\n")
-		l = externdcl
-	} else if Curfn != nil {
-		fmt.Printf("--- %v frame ---\n", Curfn.Func.Nname.Sym)
-		l = Curfn.Func.Dcl
-	} else {
+		for _, n := range externdcl {
+			printframenode(n)
+		}
 		return
 	}
 
-	var n *Node
-	var w int64
-	for ; l != nil; l = l.Next {
-		n = l.N
-		w = -1
+	if Curfn != nil {
+		fmt.Printf("--- %v frame ---\n", Curfn.Func.Nname.Sym)
+		for l := Curfn.Func.Dcl; l != nil; l = l.Next {
+			printframenode(l.N)
+		}
+	}
+}
+
+func printframenode(n *Node) {
+	w := int64(-1)
 	if n.Type != nil {
 		w = n.Type.Width
 	}
 	switch n.Op {
 	case ONAME:
 		fmt.Printf("%v %v G%d %v width=%d\n", Oconv(int(n.Op), 0), n.Sym, n.Name.Vargen, n.Type, w)
-
 	case OTYPE:
 		fmt.Printf("%v %v width=%d\n", Oconv(int(n.Op), 0), n.Type, w)
 	}
-	}
 }
 
 /*