cmd/compile: move Used from gc.Node to gc.Name

Node.Used was written to from the backend
concurrently with reads of Node.Class
for the same ONAME Nodes.
I do not know why it was not failing consistently
under the race detector, but it is a race.

This is likely also a problem with Node.HasVal and Node.HasOpt.
They will be handled in a separate CL.

Fix Used by moving it to gc.Name and making it a separate bool.
There was one non-Name use of Used, marking OLABELs as used.
That is no longer needed, now that goto and label checking
happens early in the front end.

Leave the getters and setters in place,
to ease changing the representation in the future
(or changing to an interface!).

Updates #20144

Change-Id: I9bec7c6d33dcb129a4cfa9d338462ea33087f9f7
Reviewed-on: https://go-review.googlesource.com/42015
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -398,7 +398,7 @@ func transformclosure(xfunc *Node) {
 				addr := newname(lookup("&" + v.Sym.Name))
 				addr.Type = types.NewPtr(v.Type)
 				addr.SetClass(PAUTO)
-				addr.SetUsed(true)
+				addr.Name.SetUsed(true)
 				addr.Name.Curfn = xfunc
 				xfunc.Func.Dcl = append(xfunc.Func.Dcl, addr)
 				v.Name.Param.Heapaddr = addr
@@ -622,7 +622,7 @@ func makepartialcall(fn *Node, t0 *types.Type, meth *types.Sym) *Node {
 	}
 	ptr := newname(lookup("rcvr"))
 	ptr.SetClass(PAUTO)
-	ptr.SetUsed(true)
+	ptr.Name.SetUsed(true)
 	ptr.Name.Curfn = xfunc
 	xfunc.Func.Dcl = append(xfunc.Func.Dcl, ptr)
 	var body []*Node

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

@@ -1443,7 +1443,7 @@ func (e *EscState) initEscRetval(call *Node, fntype *types.Type) {
 		ret.SetClass(PAUTO)
 		ret.Name.Curfn = Curfn
 		e.nodeEscState(ret).Loopdepth = e.loopdepth
-		ret.SetUsed(true)
+		ret.Name.SetUsed(true)
 		ret.Pos = call.Pos
 		cE.Retval.Append(ret)
 	}

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

@@ -520,11 +520,11 @@ func (n *Node) jconv(s fmt.State, flag FmtFlag) {
 	}
 
 	if c == 0 && n.HasCall() {
-		fmt.Fprintf(s, " hascall")
+		fmt.Fprint(s, " hascall")
 	}
 
-	if c == 0 && n.Used() {
-		fmt.Fprintf(s, " used(%v)", n.Used())
+	if c == 0 && n.Name != nil && n.Name.Used() {
+		fmt.Fprint(s, " used")
 	}
 }
 

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

@@ -71,13 +71,13 @@ func tempnamel(pos src.XPos, curfn *Node, nn *Node, t *types.Type) {
 func temp(t *types.Type) *Node {
 	var n Node
 	tempnamel(lineno, Curfn, &n, t)
-	asNode(n.Sym.Def).SetUsed(true)
+	asNode(n.Sym.Def).Name.SetUsed(true)
 	return n.Orig
 }
 
 func tempAt(pos src.XPos, curfn *Node, t *types.Type) *Node {
 	var n Node
 	tempnamel(pos, curfn, &n, t)
-	asNode(n.Sym.Def).SetUsed(true)
+	asNode(n.Sym.Def).Name.SetUsed(true)
 	return n.Orig
 }

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

@@ -745,7 +745,6 @@ func mkinlcall1(n *Node, fn *Node, isddd bool) *Node {
 	body := subst.list(fn.Func.Inl)
 
 	lab := nod(OLABEL, retlabel, nil)
-	lab.SetUsed(true) // avoid 'not used' when function doesn't have return
 	body = append(body, lab)
 
 	typecheckslice(body, Etop)
@@ -817,7 +816,7 @@ func inlvar(var_ *Node) *Node {
 	n := newname(var_.Sym)
 	n.Type = var_.Type
 	n.SetClass(PAUTO)
-	n.SetUsed(true)
+	n.Name.SetUsed(true)
 	n.Name.Curfn = Curfn // the calling function, not the called one
 	n.SetAddrtaken(var_.Addrtaken())
 
@@ -830,7 +829,7 @@ func retvar(t *types.Field, i int) *Node {
 	n := newname(lookupN("~r", i))
 	n.Type = t.Type
 	n.SetClass(PAUTO)
-	n.SetUsed(true)
+	n.Name.SetUsed(true)
 	n.Name.Curfn = Curfn // the calling function, not the called one
 	Curfn.Func.Dcl = append(Curfn.Func.Dcl, n)
 	return n
@@ -842,7 +841,7 @@ func argvar(t *types.Type, i int) *Node {
 	n := newname(lookupN("~arg", i))
 	n.Type = t.Elem()
 	n.SetClass(PAUTO)
-	n.SetUsed(true)
+	n.Name.SetUsed(true)
 	n.Name.Curfn = Curfn // the calling function, not the called one
 	Curfn.Func.Dcl = append(Curfn.Func.Dcl, n)
 	return n

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

@@ -1046,7 +1046,7 @@ func clearImports() {
 			// leave s->block set to cause redeclaration
 			// errors if a conflicting top-level name is
 			// introduced by a different file.
-			if !asNode(s.Def).Used() && nsyntaxerrors == 0 {
+			if !asNode(s.Def).Name.Used() && nsyntaxerrors == 0 {
 				pkgnotused(asNode(s.Def).Pos, asNode(s.Def).Name.Pkg.Path, s.Name)
 			}
 			s.Def = nil
@@ -1056,9 +1056,9 @@ func clearImports() {
 		if IsAlias(s) {
 			// throw away top-level name left over
 			// from previous import . "x"
-			if asNode(s.Def).Name != nil && asNode(s.Def).Name.Pack != nil && !asNode(s.Def).Name.Pack.Used() && nsyntaxerrors == 0 {
+			if asNode(s.Def).Name != nil && asNode(s.Def).Name.Pack != nil && !asNode(s.Def).Name.Pack.Name.Used() && nsyntaxerrors == 0 {
 				pkgnotused(asNode(s.Def).Name.Pack.Pos, asNode(s.Def).Name.Pack.Name.Pkg.Path, "")
-				asNode(s.Def).Name.Pack.SetUsed(true)
+				asNode(s.Def).Name.Pack.Name.SetUsed(true)
 			}
 
 			s.Def = nil

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

@@ -449,7 +449,7 @@ func (p *noder) expr(expr syntax.Expr) *Node {
 		// parser.new_dotname
 		obj := p.expr(expr.X)
 		if obj.Op == OPACK {
-			obj.SetUsed(true)
+			obj.Name.SetUsed(true)
 			return oldname(restrictlookup(expr.Sel.Value, obj.Name.Pkg))
 		}
 		return p.setlineno(expr, nodSym(OXDOT, obj, p.name(expr.Sel)))
@@ -611,7 +611,7 @@ func (p *noder) packname(expr syntax.Expr) *types.Sym {
 	case *syntax.Name:
 		name := p.name(expr)
 		if n := oldname(name); n.Name != nil && n.Name.Pack != nil {
-			n.Name.Pack.SetUsed(true)
+			n.Name.Pack.Name.SetUsed(true)
 		}
 		return name
 	case *syntax.SelectorExpr:
@@ -621,7 +621,7 @@ func (p *noder) packname(expr syntax.Expr) *types.Sym {
 			yyerror("%v is not a package", name)
 			pkg = localpkg
 		} else {
-			asNode(name.Def).SetUsed(true)
+			asNode(name.Def).Name.SetUsed(true)
 			pkg = asNode(name.Def).Name.Pkg
 		}
 		return restrictlookup(expr.Sel.Value, pkg)
@@ -1125,7 +1125,7 @@ func (p *noder) pragma(pos src.Pos, text string) syntax.Pragma {
 func mkname(sym *types.Sym) *Node {
 	n := oldname(sym)
 	if n.Name != nil && n.Name.Pack != nil {
-		n.Name.Pack.SetUsed(true)
+		n.Name.Pack.Name.SetUsed(true)
 	}
 	return n
 }

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

@@ -80,8 +80,8 @@ func cmpstackvarlt(a, b *Node) bool {
 		return a.Xoffset < b.Xoffset
 	}
 
-	if a.Used() != b.Used() {
-		return a.Used()
+	if a.Name.Used() != b.Name.Used() {
+		return a.Name.Used()
 	}
 
 	ap := types.Haspointers(a.Type)
@@ -118,13 +118,13 @@ func (s *ssafn) AllocFrame(f *ssa.Func) {
 	// Mark the PAUTO's unused.
 	for _, ln := range fn.Dcl {
 		if ln.Class() == PAUTO {
-			ln.SetUsed(false)
+			ln.Name.SetUsed(false)
 		}
 	}
 
 	for _, l := range f.RegAlloc {
 		if ls, ok := l.(ssa.LocalSlot); ok {
-			ls.N.(*Node).SetUsed(true)
+			ls.N.(*Node).Name.SetUsed(true)
 		}
 	}
 
@@ -136,10 +136,10 @@ func (s *ssafn) AllocFrame(f *ssa.Func) {
 				n := a.Node.(*Node)
 				// Don't modify nodfp; it is a global.
 				if n != nodfp {
-					n.SetUsed(true)
+					n.Name.SetUsed(true)
 				}
 			case *ssa.AutoSymbol:
-				a.Node.(*Node).SetUsed(true)
+				a.Node.(*Node).Name.SetUsed(true)
 			}
 
 			if !scratchUsed {
@@ -159,7 +159,7 @@ func (s *ssafn) AllocFrame(f *ssa.Func) {
 		if n.Op != ONAME || n.Class() != PAUTO {
 			continue
 		}
-		if !n.Used() {
+		if !n.Name.Used() {
 			fn.Dcl = fn.Dcl[:i]
 			break
 		}
@@ -308,7 +308,7 @@ func debuginfo(fnsym *obj.LSym, curfn interface{}) []*dwarf.Var {
 
 		switch n.Class() {
 		case PAUTO:
-			if !n.Used() {
+			if !n.Name.Used() {
 				Fatalf("debuginfo unused node (AllocFrame should truncate fn.Func.Dcl)")
 			}
 			name = obj.NAME_AUTO

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

@@ -25,8 +25,19 @@ func typeWithPointers() *types.Type {
 	return t
 }
 
+func markUsed(n *Node) *Node {
+	n.Name.SetUsed(true)
+	return n
+}
+
+func markNeedZero(n *Node) *Node {
+	n.Name.SetNeedzero(true)
+	return n
+}
+
 func nodeWithClass(n Node, c Class) *Node {
 	n.SetClass(c)
+	n.Name = new(Name)
 	return &n
 }
 
@@ -72,13 +83,13 @@ func TestCmpstackvar(t *testing.T) {
 			true,
 		},
 		{
-			nodeWithClass(Node{flags: nodeUsed}, PAUTO),
+			markUsed(nodeWithClass(Node{}, PAUTO)),
 			nodeWithClass(Node{}, PAUTO),
 			true,
 		},
 		{
 			nodeWithClass(Node{}, PAUTO),
-			nodeWithClass(Node{flags: nodeUsed}, PAUTO),
+			markUsed(nodeWithClass(Node{}, PAUTO)),
 			false,
 		},
 		{
@@ -92,13 +103,13 @@ func TestCmpstackvar(t *testing.T) {
 			true,
 		},
 		{
-			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{flags: nameNeedzero}}, PAUTO),
+			markNeedZero(nodeWithClass(Node{Type: &types.Type{}}, PAUTO)),
 			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}}, PAUTO),
 			true,
 		},
 		{
 			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}}, PAUTO),
-			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{flags: nameNeedzero}}, PAUTO),
+			markNeedZero(nodeWithClass(Node{Type: &types.Type{}}, PAUTO)),
 			false,
 		},
 		{
@@ -112,18 +123,18 @@ func TestCmpstackvar(t *testing.T) {
 			true,
 		},
 		{
-			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
-			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "xyz"}}, PAUTO),
+			nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
+			nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "xyz"}}, PAUTO),
 			true,
 		},
 		{
-			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
-			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
+			nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
+			nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
 			false,
 		},
 		{
-			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "xyz"}}, PAUTO),
-			nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
+			nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "xyz"}}, PAUTO),
+			nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
 			false,
 		},
 	}
@@ -141,34 +152,34 @@ func TestCmpstackvar(t *testing.T) {
 
 func TestStackvarSort(t *testing.T) {
 	inp := []*Node{
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PFUNC),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Xoffset: 0, Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PFUNC),
-		nodeWithClass(Node{Xoffset: 10, Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PFUNC),
-		nodeWithClass(Node{Xoffset: 20, Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PFUNC),
-		nodeWithClass(Node{flags: nodeUsed, Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: typeWithoutPointers(), Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{flags: nameNeedzero}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{Width: 1}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{Width: 2}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "xyz"}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PFUNC),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PAUTO),
+		nodeWithClass(Node{Xoffset: 0, Type: &types.Type{}, Sym: &types.Sym{}}, PFUNC),
+		nodeWithClass(Node{Xoffset: 10, Type: &types.Type{}, Sym: &types.Sym{}}, PFUNC),
+		nodeWithClass(Node{Xoffset: 20, Type: &types.Type{}, Sym: &types.Sym{}}, PFUNC),
+		markUsed(nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PAUTO)),
+		nodeWithClass(Node{Type: typeWithoutPointers(), Sym: &types.Sym{}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PAUTO),
+		markNeedZero(nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PAUTO)),
+		nodeWithClass(Node{Type: &types.Type{Width: 1}, Sym: &types.Sym{}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{Width: 2}, Sym: &types.Sym{}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "xyz"}}, PAUTO),
 	}
 	want := []*Node{
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PFUNC),
-		nodeWithClass(Node{Xoffset: 0, Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PFUNC),
-		nodeWithClass(Node{Xoffset: 10, Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PFUNC),
-		nodeWithClass(Node{Xoffset: 20, Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PFUNC),
-		nodeWithClass(Node{flags: nodeUsed, Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{flags: nameNeedzero}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{Width: 2}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{Width: 1}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
-		nodeWithClass(Node{Type: &types.Type{}, Name: &Name{}, Sym: &types.Sym{Name: "xyz"}}, PAUTO),
-		nodeWithClass(Node{Type: typeWithoutPointers(), Name: &Name{}, Sym: &types.Sym{}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PFUNC),
+		nodeWithClass(Node{Xoffset: 0, Type: &types.Type{}, Sym: &types.Sym{}}, PFUNC),
+		nodeWithClass(Node{Xoffset: 10, Type: &types.Type{}, Sym: &types.Sym{}}, PFUNC),
+		nodeWithClass(Node{Xoffset: 20, Type: &types.Type{}, Sym: &types.Sym{}}, PFUNC),
+		markUsed(nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PAUTO)),
+		markNeedZero(nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PAUTO)),
+		nodeWithClass(Node{Type: &types.Type{Width: 2}, Sym: &types.Sym{}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{Width: 1}, Sym: &types.Sym{}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "abc"}}, PAUTO),
+		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "xyz"}}, PAUTO),
+		nodeWithClass(Node{Type: typeWithoutPointers(), Sym: &types.Sym{}}, PAUTO),
 	}
 	// haspointers updates Type.Haspointers as a side effect, so
 	// exercise this function on all inputs so that reflect.DeepEqual

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

@@ -250,7 +250,7 @@ func (lv *Liveness) valueEffects(v *ssa.Value) (pos int32, effect liveEffect) {
 	// variable" ICEs (issue 19632).
 	switch v.Op {
 	case ssa.OpVarDef, ssa.OpVarKill, ssa.OpVarLive, ssa.OpKeepAlive:
-		if !n.Used() {
+		if !n.Name.Used() {
 			return -1, 0
 		}
 	}

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

@@ -4964,7 +4964,7 @@ func (e *ssafn) namedAuto(name string, typ ssa.Type, pos src.XPos) ssa.GCNode {
 	n.Orig = n
 
 	s.Def = asTypesNode(n)
-	asNode(s.Def).SetUsed(true)
+	asNode(s.Def).Name.SetUsed(true)
 	n.Sym = s
 	n.Type = t
 	n.SetClass(PAUTO)

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

@@ -93,7 +93,6 @@ const (
 	_, nodeNoescape // func arguments do not escape; TODO(rsc): move Noescape to Func struct (see CL 7360)
 	_, nodeBounded  // bounds check unnecessary
 	_, nodeAddable  // addressable
-	_, nodeUsed     // for variable/label declared and not used error
 	_, nodeHasCall  // expression contains a function call
 	_, nodeLikely   // if statement condition likely
 	_, nodeHasVal   // node.E contains a Val
@@ -121,7 +120,6 @@ func (n *Node) NonNil() bool                { return n.flags&nodeNonNil != 0 }
 func (n *Node) Noescape() bool              { return n.flags&nodeNoescape != 0 }
 func (n *Node) Bounded() bool               { return n.flags&nodeBounded != 0 }
 func (n *Node) Addable() bool               { return n.flags&nodeAddable != 0 }
-func (n *Node) Used() bool                  { return n.flags&nodeUsed != 0 }
 func (n *Node) HasCall() bool               { return n.flags&nodeHasCall != 0 }
 func (n *Node) Likely() bool                { return n.flags&nodeLikely != 0 }
 func (n *Node) HasVal() bool                { return n.flags&nodeHasVal != 0 }
@@ -148,7 +146,6 @@ func (n *Node) SetNonNil(b bool)                { n.flags.set(nodeNonNil, b) }
 func (n *Node) SetNoescape(b bool)              { n.flags.set(nodeNoescape, b) }
 func (n *Node) SetBounded(b bool)               { n.flags.set(nodeBounded, b) }
 func (n *Node) SetAddable(b bool)               { n.flags.set(nodeAddable, b) }
-func (n *Node) SetUsed(b bool)                  { n.flags.set(nodeUsed, b) }
 func (n *Node) SetHasCall(b bool)               { n.flags.set(nodeHasCall, b) }
 func (n *Node) SetLikely(b bool)                { n.flags.set(nodeLikely, b) }
 func (n *Node) SetHasVal(b bool)                { n.flags.set(nodeHasVal, b) }
@@ -231,6 +228,7 @@ type Name struct {
 	Vargen    int32      // unique name for ONAME within a function.  Function outputs are numbered starting at one.
 	Funcdepth int32
 
+	used  bool // for variable declared and not used error
 	flags bitset8
 }
 
@@ -249,6 +247,7 @@ func (n *Name) Byval() bool     { return n.flags&nameByval != 0 }
 func (n *Name) Needzero() bool  { return n.flags&nameNeedzero != 0 }
 func (n *Name) Keepalive() bool { return n.flags&nameKeepalive != 0 }
 func (n *Name) AutoTemp() bool  { return n.flags&nameAutoTemp != 0 }
+func (n *Name) Used() bool      { return n.used }
 
 func (n *Name) SetCaptured(b bool)  { n.flags.set(nameCaptured, b) }
 func (n *Name) SetReadonly(b bool)  { n.flags.set(nameReadonly, b) }
@@ -256,6 +255,7 @@ func (n *Name) SetByval(b bool)     { n.flags.set(nameByval, b) }
 func (n *Name) SetNeedzero(b bool)  { n.flags.set(nameNeedzero, b) }
 func (n *Name) SetKeepalive(b bool) { n.flags.set(nameKeepalive, b) }
 func (n *Name) SetAutoTemp(b bool)  { n.flags.set(nameAutoTemp, b) }
+func (n *Name) SetUsed(b bool)      { n.used = b }
 
 type Param struct {
 	Ntype    *Node

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

@@ -323,7 +323,7 @@ OpSwitch:
 				return n
 			}
 
-			n.SetUsed(true)
+			n.Name.SetUsed(true)
 		}
 
 		ok |= Erv

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

@@ -461,5 +461,5 @@ func finishUniverse() {
 	nodfp = newname(lookup(".fp"))
 	nodfp.Type = types.Types[TINT32]
 	nodfp.SetClass(PPARAM)
-	nodfp.SetUsed(true)
+	nodfp.Name.SetUsed(true)
 }

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

@@ -37,21 +37,21 @@ func walk(fn *Node) {
 
 	// Propagate the used flag for typeswitch variables up to the NONAME in it's definition.
 	for _, ln := range fn.Func.Dcl {
-		if ln.Op == ONAME && (ln.Class() == PAUTO || ln.Class() == PAUTOHEAP) && ln.Name.Defn != nil && ln.Name.Defn.Op == OTYPESW && ln.Used() {
-			ln.Name.Defn.Left.SetUsed(true)
+		if ln.Op == ONAME && (ln.Class() == PAUTO || ln.Class() == PAUTOHEAP) && ln.Name.Defn != nil && ln.Name.Defn.Op == OTYPESW && ln.Name.Used() {
+			ln.Name.Defn.Left.Name.SetUsed(true)
 		}
 	}
 
 	for _, ln := range fn.Func.Dcl {
-		if ln.Op != ONAME || (ln.Class() != PAUTO && ln.Class() != PAUTOHEAP) || ln.Sym.Name[0] == '&' || ln.Used() {
+		if ln.Op != ONAME || (ln.Class() != PAUTO && ln.Class() != PAUTOHEAP) || ln.Sym.Name[0] == '&' || ln.Name.Used() {
 			continue
 		}
 		if defn := ln.Name.Defn; defn != nil && defn.Op == OTYPESW {
-			if defn.Left.Used() {
+			if defn.Left.Name.Used() {
 				continue
 			}
 			yyerrorl(defn.Left.Pos, "%v declared and not used", ln.Sym)
-			defn.Left.SetUsed(true) // suppress repeats
+			defn.Left.Name.SetUsed(true) // suppress repeats
 		} else {
 			yyerrorl(ln.Pos, "%v declared and not used", ln.Sym)
 		}