[dev.regabi] cmd/compile: add ir.NewDeclNameAt

This allows directly creating an ONONAME, which is a primordial Name
before having its Op initialized. Then after an Op is assigned, we
never allow it to be reassigned.

Passes buildall w/ toolstash -cmp.

Change-Id: Ibc2f413dc68c0af6a96abfe653c25ce31b184287
Reviewed-on: https://go-review.googlesource.com/c/go/+/274620
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -122,16 +122,6 @@ func declare(n *ir.Name, ctxt ir.Class) {
 	autoexport(n, ctxt)
 }
 
-func addvar(n *ir.Name, t *types.Type, ctxt ir.Class) {
-	if n == nil || n.Sym() == nil || (n.Op() != ir.ONAME && n.Op() != ir.ONONAME) || t == nil {
-		base.Fatalf("addvar: n=%v t=%v nil", n, t)
-	}
-
-	n.SetOp(ir.ONAME)
-	declare(n, ctxt)
-	n.SetType(t)
-}
-
 // declare variables from grammar
 // new_name_list (type | [type] = expr_list)
 func variter(vl []ir.Node, t ir.Ntype, el []ir.Node) []ir.Node {
@@ -192,16 +182,6 @@ func variter(vl []ir.Node, t ir.Ntype, el []ir.Node) []ir.Node {
 	return init
 }
 
-// newnoname returns a new ONONAME Node associated with symbol s.
-func newnoname(s *types.Sym) ir.Node {
-	if s == nil {
-		base.Fatalf("newnoname nil")
-	}
-	n := ir.NewNameAt(base.Pos, s)
-	n.SetOp(ir.ONONAME)
-	return n
-}
-
 // newFuncNameAt generates a new name node for a function or method.
 func newFuncNameAt(pos src.XPos, s *types.Sym, fn *ir.Func) *ir.Name {
 	if fn.Nname != nil {
@@ -213,14 +193,6 @@ func newFuncNameAt(pos src.XPos, s *types.Sym, fn *ir.Func) *ir.Name {
 	return n
 }
 
-// this generates a new name node for a name
-// being declared.
-func dclname(s *types.Sym) *ir.Name {
-	n := NewName(s)
-	n.SetOp(ir.ONONAME) // caller will correct it
-	return n
-}
-
 func anonfield(typ *types.Type) *ir.Field {
 	return symfield(nil, typ)
 }
@@ -243,7 +215,7 @@ func oldname(s *types.Sym) ir.Node {
 		// Maybe a top-level declaration will come along later to
 		// define s. resolve will check s.Def again once all input
 		// source has been processed.
-		return newnoname(s)
+		return ir.NewDeclNameAt(base.Pos, s)
 	}
 
 	if Curfn != nil && n.Op() == ir.ONAME && n.Name().Curfn != nil && n.Name().Curfn != Curfn {

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

@@ -85,7 +85,7 @@ func importsym(ipkg *types.Pkg, s *types.Sym, op ir.Op) ir.Node {
 			base.Fatalf("missing ONONAME for %v\n", s)
 		}
 
-		n = dclname(s)
+		n = ir.NewDeclNameAt(src.NoXPos, s)
 		s.SetPkgDef(n)
 		s.Importdef = ipkg
 	}

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

@@ -175,7 +175,7 @@ func iimport(pkg *types.Pkg, in *bio.Reader) (fingerprint goobj.FingerprintType)
 			if s.Def != nil {
 				base.Fatalf("unexpected definition for %v: %v", s, ir.AsNode(s.Def))
 			}
-			s.Def = npos(src.NoXPos, dclname(s))
+			s.Def = ir.NewDeclNameAt(src.NoXPos, s)
 		}
 	}
 
@@ -833,7 +833,7 @@ func (r *importReader) node() ir.Node {
 	case ir.OTYPESW:
 		n := ir.NodAt(r.pos(), ir.OTYPESW, nil, nil)
 		if s := r.ident(); s != nil {
-			n.SetLeft(npos(n.Pos(), newnoname(s)))
+			n.SetLeft(ir.NewDeclNameAt(n.Pos(), s))
 		}
 		right, _ := r.exprsOrNil()
 		n.SetRight(right)
@@ -962,7 +962,7 @@ func (r *importReader) node() ir.Node {
 	// statements
 	case ir.ODCL:
 		pos := r.pos()
-		lhs := npos(pos, dclname(r.ident()))
+		lhs := ir.NewDeclNameAt(pos, r.ident())
 		typ := ir.TypeNode(r.typ())
 		return npos(pos, liststmt(variter([]ir.Node{lhs}, typ, nil))) // TODO(gri) avoid list creation
 

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

@@ -516,9 +516,7 @@ func (p *noder) declNames(names []*syntax.Name) []ir.Node {
 }
 
 func (p *noder) declName(name *syntax.Name) *ir.Name {
-	n := dclname(p.name(name))
-	n.SetPos(p.pos(name))
-	return n
+	return ir.NewDeclNameAt(p.pos(name), p.name(name))
 }
 
 func (p *noder) funcDecl(fun *syntax.FuncDecl) ir.Node {

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

@@ -371,7 +371,8 @@ func staticname(t *types.Type) ir.Node {
 	// Don't use lookupN; it interns the resulting string, but these are all unique.
 	n := NewName(lookup(fmt.Sprintf("%s%d", obj.StaticNamePref, statuniqgen)))
 	statuniqgen++
-	addvar(n, t, ir.PEXTERN)
+	declare(n, ir.PEXTERN)
+	n.SetType(t)
 	n.Sym().Linksym().Set(obj.AttrLocal, true)
 	return n
 }

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

@@ -108,7 +108,7 @@ func initUniverse() {
 
 	defBasic := func(kind types.Kind, pkg *types.Pkg, name string) *types.Type {
 		sym := pkg.Lookup(name)
-		n := ir.NewNameAt(src.NoXPos, sym)
+		n := ir.NewDeclNameAt(src.NoXPos, sym)
 		n.SetOp(ir.OTYPE)
 		t := types.NewBasic(kind, n)
 		n.SetType(t)
@@ -145,7 +145,7 @@ func initUniverse() {
 
 	// error type
 	s := ir.BuiltinPkg.Lookup("error")
-	n := ir.NewNameAt(src.NoXPos, s)
+	n := ir.NewDeclNameAt(src.NoXPos, s)
 	n.SetOp(ir.OTYPE)
 	types.ErrorType = types.NewNamed(n)
 	types.ErrorType.SetUnderlying(makeErrorInterface())

src/cmd/compile/internal/ir/name.go

@@ -123,18 +123,27 @@ type Name struct {
 }
 
 // NewNameAt returns a new ONAME Node associated with symbol s at position pos.
-// The caller is responsible for setting n.Name.Curfn.
+// The caller is responsible for setting Curfn.
 func NewNameAt(pos src.XPos, sym *types.Sym) *Name {
 	if sym == nil {
 		base.Fatalf("NewNameAt nil")
 	}
-	return newNameAt(pos, sym)
+	return newNameAt(pos, ONAME, sym)
+}
+
+// NewDeclNameAt returns a new ONONAME Node associated with symbol s at position pos.
+// The caller is responsible for setting Curfn.
+func NewDeclNameAt(pos src.XPos, sym *types.Sym) *Name {
+	if sym == nil {
+		base.Fatalf("NewDeclNameAt nil")
+	}
+	return newNameAt(pos, ONONAME, sym)
 }
 
 // newNameAt is like NewNameAt but allows sym == nil.
-func newNameAt(pos src.XPos, sym *types.Sym) *Name {
+func newNameAt(pos src.XPos, op Op, sym *types.Sym) *Name {
 	n := new(Name)
-	n.op = ONAME
+	n.op = op
 	n.pos = pos
 	n.orig = n
 	n.sym = sym
@@ -163,10 +172,13 @@ func (n *Name) SetIota(x int64)               { n.offset = x }
 func (*Name) CanBeNtype() {}
 
 func (n *Name) SetOp(op Op) {
+	if n.op != ONONAME {
+		base.Fatalf("%v already has Op %v", n, n.op)
+	}
 	switch op {
 	default:
 		panic(n.no("SetOp " + op.String()))
-	case OLITERAL, ONONAME, ONAME, OTYPE, OIOTA:
+	case OLITERAL, ONAME, OTYPE, OIOTA:
 		n.op = op
 	}
 }

src/cmd/compile/internal/ir/node.go

@@ -802,9 +802,7 @@ func NodAt(pos src.XPos, op Op, nleft, nright Node) Node {
 	case OLABEL:
 		return NewLabelStmt(pos, nil)
 	case OLITERAL, OTYPE, OIOTA:
-		n := newNameAt(pos, nil)
-		n.SetOp(op)
-		return n
+		return newNameAt(pos, op, nil)
 	case OMAKECHAN, OMAKEMAP, OMAKESLICE, OMAKESLICECOPY:
 		return NewMakeExpr(pos, op, nleft, nright)
 	case OMETHEXPR: