cmd/compile: move Node.Paramfld to Node.Param.Field

$ sizeof -p cmd/compile/internal/gc Node
Node 264
$

Change-Id: I5c90089dcf5df51c874250f28a1bc3ec32f764b9
Reviewed-on: https://go-review.googlesource.com/10522Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

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

@@ -913,7 +913,7 @@ func tofunargs(l *NodeList) *Type {
 
 		// esc.c needs to find f given a PPARAM to add the tag.
 		if l.N.Left != nil && l.N.Left.Class == PPARAM {
-			l.N.Left.Paramfld = f
+			l.N.Left.Param.Field = f
 		}
 
 		*tp = f

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

@@ -1774,7 +1774,7 @@ func esctag(e *EscState, func_ *Node) {
 		case EscNone, // not touched by escflood
 			EscReturn:
 			if haspointers(ll.N.Type) { // don't bother tagging for scalars
-				ll.N.Paramfld.Note = mktag(int(ll.N.Esc))
+				ll.N.Param.Field.Note = mktag(int(ll.N.Esc))
 			}
 
 		case EscHeap, // touched by escflood, moved to heap

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

@@ -448,8 +448,8 @@ func compile(fn *Node) {
 	gcargs = makefuncdatasym("gcargs·%d", obj.FUNCDATA_ArgsPointerMaps)
 	gclocals = makefuncdatasym("gclocals·%d", obj.FUNCDATA_LocalsPointerMaps)
 
-	for t := Curfn.Paramfld; t != nil; t = t.Down {
-		gtrack(tracksym(t.Type))
+	for _, t := range Curfn.Func.Fieldtrack {
+		gtrack(tracksym(t))
 	}
 
 	for l := fn.Func.Dcl; l != nil; l = l.Next {

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

@@ -33,15 +33,12 @@ type Node struct {
 	Defn  *Node // ONAME: initializing assignment; OLABEL: labeled statement
 	Pack  *Node // real package for import . names
 	Curfn *Node // function for local variables
-	Paramfld *Type // TFIELD for this PPARAM; also for ODOT, curfn
 	Alloc *Node // allocation call
 	Param *Param
 
 	// OPACK
 	Pkg *Pkg
 
-	// OARRAYLIT, OMAPLIT, OSTRUCTLIT.
-
 	// Escape analysis.
 	Escflowsrc *NodeList // flow(this, src)
 	Escretval  *NodeList // on OCALLxxx, list of dummy return values
@@ -116,6 +113,9 @@ type Param struct {
 	Outerexpr  *Node // expression copied into closure for variable
 	Stackparam *Node // OPARAM node referring to stack copy of param
 
+	// ONAME PPARAM
+	Field *Type // TFIELD in arg struct
+
 	// ONAME closure param with PPARAMREF
 	Outer   *Node // outer PPARAMREF in nested closure
 	Closure *Node // ONAME/PHEAP <-> ONAME/PPARAMREF
@@ -132,6 +132,7 @@ type Func struct {
 	Inldcl     *NodeList // copy of dcl for use in inlining
 	Closgen    int
 	Outerfunc  *Node
+	Fieldtrack []*Type
 
 	Inl     *NodeList // copy of the body for use in inlining
 	InlCost int32

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

@@ -2489,6 +2489,15 @@ func derefall(t *Type) *Type {
 	return t
 }
 
+type typeSym struct {
+	t *Type
+	s *Sym
+}
+
+// dotField maps (*Type, *Sym) pairs to the corresponding struct field (*Type with Etype==TFIELD).
+// It is a cache for use during usefield in walk.go, only enabled when field tracking.
+var dotField = map[typeSym]*Type{}
+
 func lookdot(n *Node, t *Type, dostrcmp int) *Type {
 	s := n.Right.Sym
 
@@ -2521,7 +2530,9 @@ func lookdot(n *Node, t *Type, dostrcmp int) *Type {
 		}
 		n.Xoffset = f1.Width
 		n.Type = f1.Type
-		n.Paramfld = f1
+		if obj.Fieldtrack_enabled > 0 {
+			dotField[typeSym{t, s}] = f1
+		}
 		if t.Etype == TINTER {
 			if Isptr[n.Left.Type.Etype] {
 				n.Left = Nod(OIND, n.Left, nil) // implicitstar

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

@@ -3857,7 +3857,11 @@ func usefield(n *Node) {
 		break
 	}
 
-	field := n.Paramfld
+	t := n.Left.Type
+	if Isptr[t.Etype] {
+		t = t.Type
+	}
+	field := dotField[typeSym{t, n.Right.Sym}]
 	if field == nil {
 		Fatal("usefield %v %v without paramfld", n.Left.Type, n.Right.Sym)
 	}
@@ -3881,10 +3885,7 @@ func usefield(n *Node) {
 		Yyerror("tracked field must be exported (upper case)")
 	}
 
-	l := typ(0)
-	l.Type = field
-	l.Down = Curfn.Paramfld
-	Curfn.Paramfld = l
+	Curfn.Func.Fieldtrack = append(Curfn.Func.Fieldtrack, field)
 }
 
 func candiscardlist(l *NodeList) bool {