cmd/compile: add newnamel, use in tempAt

newnamel is newname but with no dependency on lineno or Curfn.
This makes it suitable for use in a concurrent back end.
Use it now to make tempAt global-free.

The decision to push the assignment to n.Name.Curfn
to the caller of newnamel is based on mdempsky's
comments in #19683 that he'd like to do that
for callers of newname as well.

Passes toolstash-check. No compiler performance impact.

Updates #19683
Updates #15756

Change-Id: Idc461a1716916d268c9ff323129830d9a6e4a4d9
Reviewed-on: https://go-review.googlesource.com/39191
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -195,12 +195,12 @@ func autotmpname(n int) string {
 }
 
 // make a new Node off the books
-func tempname(nn *Node, t *Type) {
-	if Curfn == nil {
+func tempnamel(pos src.XPos, curfn *Node, nn *Node, t *Type) {
+	if curfn == nil {
 		Fatalf("no curfn for tempname")
 	}
-	if Curfn.Func.Closure != nil && Curfn.Op == OCLOSURE {
-		Dump("tempname", Curfn)
+	if curfn.Func.Closure != nil && curfn.Op == OCLOSURE {
+		Dump("tempname", curfn)
 		Fatalf("adding tempname to wrong closure function")
 	}
 	if t == nil {
@@ -208,17 +208,17 @@ func tempname(nn *Node, t *Type) {
 	}
 
 	s := &Sym{
-		Name: autotmpname(len(Curfn.Func.Dcl)),
+		Name: autotmpname(len(curfn.Func.Dcl)),
 		Pkg:  localpkg,
 	}
-	n := newname(s)
+	n := newnamel(pos, s)
 	s.Def = n
 	n.Type = t
 	n.Class = PAUTO
 	n.Esc = EscNever
-	n.Name.Curfn = Curfn
+	n.Name.Curfn = curfn
 	n.Name.SetAutoTemp(true)
-	Curfn.Func.Dcl = append(Curfn.Func.Dcl, n)
+	curfn.Func.Dcl = append(curfn.Func.Dcl, n)
 
 	dowidth(t)
 	*nn = *n
@@ -226,16 +226,14 @@ func tempname(nn *Node, t *Type) {
 
 func temp(t *Type) *Node {
 	var n Node
-	tempname(&n, t)
+	tempnamel(lineno, Curfn, &n, t)
 	n.Sym.Def.SetUsed(true)
 	return n.Orig
 }
 
 func tempAt(pos src.XPos, curfn *Node, t *Type) *Node {
-	// TODO(mdempsky/josharian): Remove all reads and writes of lineno and Curfn.
-	lineno = pos
-	Curfn = curfn
-	n := temp(t)
-	Curfn = nil
-	return n
+	var n Node
+	tempnamel(pos, curfn, &n, t)
+	n.Sym.Def.SetUsed(true)
+	return n.Orig
 }

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

@@ -365,8 +365,16 @@ func nodl(pos src.XPos, op Op, nleft, nright *Node) *Node {
 
 // newname returns a new ONAME Node associated with symbol s.
 func newname(s *Sym) *Node {
+	n := newnamel(lineno, s)
+	n.Name.Curfn = Curfn
+	return n
+}
+
+// newname returns a new ONAME Node associated with symbol s at position pos.
+// The caller is responsible for setting n.Name.Curfn.
+func newnamel(pos src.XPos, s *Sym) *Node {
 	if s == nil {
-		Fatalf("newname nil")
+		Fatalf("newnamel nil")
 	}
 
 	var x struct {
@@ -379,8 +387,7 @@ func newname(s *Sym) *Node {
 	n.Name.Param = &x.Param
 
 	n.Op = ONAME
-	n.Pos = lineno
-	n.Name.Curfn = Curfn
+	n.Pos = pos
 	n.Orig = n
 
 	n.Sym = s