cmd/compile: remove unused Label fields

Updates #16357.

Change-Id: I37f04d83134b5e1e7f6ba44eb9a566758ef594d3
Reviewed-on: https://go-review.googlesource.com/29350
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -8,9 +8,6 @@ package gc
 
 import "fmt"
 
-// TODO: labellist should become part of a "compilation state" for functions.
-var labellist []*Label
-
 func Sysfunc(name string) *Node {
 	n := newname(Pkglookup(name, Runtimepkg))
 	n.Class = PFUNC
@@ -182,13 +179,6 @@ func moveToHeap(n *Node) {
 	}
 }
 
-func clearlabels() {
-	for _, l := range labellist {
-		l.Sym.Label = nil
-	}
-	labellist = labellist[:0]
-}
-
 // make a new Node off the books
 func tempname(nn *Node, t *Type) {
 	if Curfn == nil {

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

@@ -54,17 +54,7 @@ type Sym struct {
 }
 
 type Label struct {
-	Sym *Sym
 	Def *Node
-	Use []*Node
-
-	// for use during gen
-	Gotopc   *obj.Prog // pointer to unresolved gotos
-	Labelpc  *obj.Prog // pointer to code
-	Breakpc  *obj.Prog // pointer to code
-	Continpc *obj.Prog // pointer to code
-
-	Used bool // for "label defined and not used" error
 }
 
 type SymFlags uint8

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

@@ -338,9 +338,6 @@ func compile(fn *Node) {
 
 	saveerrors()
 
-	// set up domain for labels
-	clearlabels()
-
 	if Curfn.Type.FuncType().Outnamed {
 		// add clearing of the output parameters
 		for _, t := range Curfn.Type.Results().Fields().Slice() {