cmd/compile: add Node.IsMethod helper

Changes generated with eg:

func before(n *gc.Node) bool { return n.Type.Recv() != nil }
func after(n *gc.Node) bool  { return n.IsMethod() }

func before(n *gc.Node) bool { return n.Type.Recv() == nil }
func after(n *gc.Node) bool  { return !n.IsMethod() }

Change-Id: I28e544490d17bbdc06ab11ed32464af5802ab206
Reviewed-on: https://go-review.googlesource.com/28968
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -116,7 +116,7 @@ func reexportdep(n *Node) {
 			}
 
 			// nodes for method calls.
-			if n.Type == nil || n.Type.Recv() != nil {
+			if n.Type == nil || n.IsMethod() {
 				break
 			}
 			fallthrough

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

@@ -32,7 +32,7 @@ import "fmt"
 // Get the function's package. For ordinary functions it's on the ->sym, but for imported methods
 // the ->sym can be re-used in the local package, so peel it off the receiver's type.
 func fnpkg(fn *Node) *Pkg {
-	if fn.Type.Recv() != nil {
+	if fn.IsMethod() {
 		// method
 		rcvr := fn.Type.Recv().Type
 
@@ -615,7 +615,7 @@ func mkinlcall1(n *Node, fn *Node, isddd bool) *Node {
 	}
 
 	// assign receiver.
-	if fn.Type.Recv() != nil && n.Left.Op == ODOTMETH {
+	if fn.IsMethod() && n.Left.Op == ODOTMETH {
 		// method call with a receiver.
 		t := fn.Type.Recv()
 
@@ -679,7 +679,7 @@ func mkinlcall1(n *Node, fn *Node, isddd bool) *Node {
 	li := 0
 
 	// TODO: if len(nlist) == 1 but multiple args, check that n->list->n is a call?
-	if fn.Type.Recv() != nil && n.Left.Op != ODOTMETH {
+	if fn.IsMethod() && n.Left.Op != ODOTMETH {
 		// non-method call to method
 		if n.List.Len() == 0 {
 			Fatalf("non-method call to method without first arg: %+v", n)

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

@@ -144,7 +144,7 @@ func emitptrargsmap() {
 	off := duint32(sym, 0, uint32(nbitmap))
 	off = duint32(sym, off, uint32(bv.n))
 	var xoffset int64
-	if Curfn.Type.Recv() != nil {
+	if Curfn.IsMethod() {
 		xoffset = 0
 		onebitwalktype1(Curfn.Type.Recvs(), &xoffset, bv)
 	}

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

@@ -1038,6 +1038,12 @@ func Is64(t *Type) bool {
 	return false
 }
 
+// IsMethod reports whether n is a method.
+// n must be a function or a method.
+func (n *Node) IsMethod() bool {
+	return n.Type.Recv() != nil
+}
+
 // SliceBounds returns n's slice bounds: low, high, and max in expr[low:high:max].
 // n must be a slice expression. max is nil if n is a simple slice expression.
 func (n *Node) SliceBounds() (low, high, max *Node) {

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

@@ -860,7 +860,7 @@ OpSwitch:
 				return n
 			}
 
-			if n.Type.Etype != TFUNC || n.Type.Recv() == nil {
+			if n.Type.Etype != TFUNC || !n.IsMethod() {
 				Yyerror("type %v has no method %1v", n.Left.Type, n.Right.Sym)
 				n.Type = nil
 				return n