cmd/compile/internal/gc: introduce type for decl contexts/storage classes

Change-Id: I956e27fa07f16060b8f41b986d991c36557f7c12
Reviewed-on: https://go-review.googlesource.com/16332Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -151,7 +151,7 @@ var vargen int
 
 var declare_typegen int
 
-func declare(n *Node, ctxt uint8) {
+func declare(n *Node, ctxt Class) {
 	if ctxt == PDISCARD {
 		return
 	}
@@ -217,12 +217,12 @@ func declare(n *Node, ctxt uint8) {
 	s.Def = n
 	n.Name.Vargen = int32(gen)
 	n.Name.Funcdepth = Funcdepth
-	n.Class = uint8(ctxt)
+	n.Class = ctxt
 
 	autoexport(n, ctxt)
 }
 
-func addvar(n *Node, t *Type, ctxt uint8) {
+func addvar(n *Node, t *Type, ctxt Class) {
 	if n == nil || n.Sym == nil || (n.Op != ONAME && n.Op != ONONAME) || t == nil {
 		Fatalf("addvar: n=%v t=%v nil", n, t)
 	}

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

@@ -72,7 +72,7 @@ func exportedsym(sym *Sym) bool {
 	return sym.Pkg == localpkg && exportname(sym.Name)
 }
 
-func autoexport(n *Node, ctxt uint8) {
+func autoexport(n *Node, ctxt Class) {
 	if n == nil || n.Sym == nil {
 		return
 	}

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

@@ -333,9 +333,13 @@ const (
 	Cboth = Crecv | Csend
 )
 
-// declaration context
+// The Class of a variable/function describes the "storage class"
+// of a variable or function. During parsing, storage classes are
+// called declaration contexts.
+type Class uint8
+
 const (
-	Pxxx      = uint8(iota)
+	Pxxx      Class = iota
 	PEXTERN         // global variable
 	PAUTO           // local variables
 	PPARAM          // input arguments
@@ -345,7 +349,7 @@ const (
 
 	PDISCARD // discard during parse of duplicate import
 
-	PHEAP = uint8(1 << 7) // an extra bit to identify an escaped variable
+	PHEAP = 1 << 7 // an extra bit to identify an escaped variable
 )
 
 const (
@@ -587,7 +591,7 @@ var importlist []*Node // imported functions and methods with inlinable bodies
 
 var funcsyms []*Node
 
-var dclcontext uint8 // PEXTERN/PAUTO
+var dclcontext Class // PEXTERN/PAUTO
 
 var incannedimport int
 

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

@@ -818,7 +818,7 @@ func checkparam(fn *Node, p *obj.Prog, n *Node) {
 		return
 	}
 	var a *Node
-	var class uint8
+	var class Class
 	for l := fn.Func.Dcl; l != nil; l = l.Next {
 		a = l.N
 		class = a.Class &^ PHEAP

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

@@ -48,7 +48,7 @@ type Node struct {
 	Addable     bool  // addressable
 	Etype       uint8 // op for OASOP, etype for OTYPE, exclam for export, 6g saved reg
 	Bounded     bool  // bounds check unnecessary
-	Class       uint8 // PPARAM, PAUTO, PEXTERN, etc
+	Class       Class // PPARAM, PAUTO, PEXTERN, etc
 	Embedded    uint8 // ODCLFIELD embedded type
 	Colas       bool  // OAS resulting from :=
 	Diag        uint8 // already printed error about this

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

@@ -288,7 +288,7 @@ func walkstmt(np **Node) {
 			// so that reorder3 can fix up conflicts
 			var rl *NodeList
 
-			var cl uint8
+			var cl Class
 			for ll := Curfn.Func.Dcl; ll != nil; ll = ll.Next {
 				cl = ll.N.Class &^ PHEAP
 				if cl == PAUTO {