cmd/compile: remove Label type

With the removal of the old backend,
a Label is just a Node.

Passes toolstash -cmp.

Change-Id: Ia62cb00fbc551efb75a4ed4dc6ed54fca0831dbf
Reviewed-on: https://go-review.googlesource.com/32216
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -589,9 +589,10 @@ func (e *EscState) escfunc(fn *Node) {
 // Mark labels that have no backjumps to them as not increasing e.loopdepth.
 // Walk hasn't generated (goto|label).Left.Sym.Label yet, so we'll cheat
 // and set it to one of the following two. Then in esc we'll clear it again.
-var looping Label
-
-var nonlooping Label
+var (
+	looping    Node
+	nonlooping Node
+)
 
 func (e *EscState) escloopdepthlist(l Nodes) {
 	for _, n := range l.Slice() {

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

@@ -47,16 +47,12 @@ type Sym struct {
 	Block      int32  // blocknumber to catch redeclaration
 	Lastlineno int32  // last declaration for diagnostic
 
-	Label   *Label // corresponding label (ephemeral)
-	Origpkg *Pkg   // original package for . import
+	Label   *Node // corresponding label (ephemeral)
+	Origpkg *Pkg  // original package for . import
 	Lsym    *obj.LSym
 	Fsym    *Sym // funcsym
 }
 
-type Label struct {
-	Def *Node
-}
-
 type SymFlags uint8
 
 const (

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

@@ -3841,7 +3841,7 @@ func markbreak(n *Node, implicit *Node) {
 		} else {
 			lab := n.Left.Sym.Label
 			if lab != nil {
-				lab.Def.SetHasBreak(true)
+				lab.SetHasBreak(true)
 			}
 		}
 
@@ -3872,9 +3872,7 @@ func markbreaklist(l Nodes, implicit *Node) {
 		if n.Op == OLABEL && i+1 < len(s) && n.Name.Defn == s[i+1] {
 			switch n.Name.Defn.Op {
 			case OFOR, OSWITCH, OTYPESW, OSELECT, ORANGE:
-				lab := new(Label)
-				lab.Def = n.Name.Defn
-				n.Left.Sym.Label = lab
+				n.Left.Sym.Label = n.Name.Defn
 				markbreak(n.Name.Defn, n.Name.Defn)
 				n.Left.Sym.Label = nil
 				i++