cmd/compile: refactor method expression detection

Eliminates lots of ad hoc code for recognizing the same thing in
different ways.

Passes toolstash-check.

Change-Id: Ic0bb005308e96331b4ef30f455b860e476725b61
Reviewed-on: https://go-review.googlesource.com/73190
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -1192,7 +1192,7 @@ func (p *exporter) expr(n *Node) {
 		// Special case: explicit name of func (*T) method(...) is turned into pkg.(*T).method,
 		// but for export, this should be rendered as (*pkg.T).meth.
 		// These nodes have the special property that they are names with a left OTYPE and a right ONAME.
-		if n.Left != nil && n.Left.Op == OTYPE && n.Right != nil && n.Right.Op == ONAME {
+		if n.isMethodExpression() {
 			p.op(OXDOT)
 			p.pos(n)
 			p.expr(n.Left) // n.Left.Op == OTYPE

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

@@ -112,10 +112,10 @@ func reexportdep(n *Node) {
 	switch n.Op {
 	case ONAME:
 		switch n.Class() {
+		case PFUNC:
 			// methods will be printed along with their type
 			// nodes for T.Method expressions
-		case PFUNC:
-			if n.Left != nil && n.Left.Op == OTYPE {
+			if n.isMethodExpression() {
 				break
 			}
 

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

@@ -244,7 +244,7 @@ func (v *hairyVisitor) visit(n *Node) bool {
 			break
 		}
 
-		if n.isMethodCalledAsFunction() {
+		if n.Left.isMethodExpression() {
 			if d := asNode(n.Left.Sym.Def); d != nil && d.Func.Inl.Len() != 0 {
 				v.budget -= d.Func.InlCost
 				break
@@ -536,7 +536,7 @@ func inlnode(n *Node) *Node {
 		}
 		if n.Left.Func != nil && n.Left.Func.Inl.Len() != 0 && !isIntrinsicCall(n) { // normal case
 			n = mkinlcall(n, n.Left, n.Isddd())
-		} else if n.isMethodCalledAsFunction() && asNode(n.Left.Sym.Def) != nil {
+		} else if n.Left.isMethodExpression() && asNode(n.Left.Sym.Def) != nil {
 			n = mkinlcall(n, asNode(n.Left.Sym.Def), n.Isddd())
 		} else if n.Left.Op == OCLOSURE {
 			if f := inlinableClosure(n.Left); f != nil {
@@ -1095,7 +1095,3 @@ func (subst *inlsubst) updatedPos(xpos src.XPos) src.XPos {
 	pos.SetBase(newbase)
 	return Ctxt.PosTable.XPos(pos)
 }
-
-func (n *Node) isMethodCalledAsFunction() bool {
-	return n.Left.Op == ONAME && n.Left.Left != nil && n.Left.Left.Op == OTYPE && n.Left.Right != nil && n.Left.Right.Op == ONAME
-}

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

@@ -44,7 +44,7 @@ func init1(n *Node, out *[]*Node) {
 		init1(n1, out)
 	}
 
-	if n.Left != nil && n.Type != nil && n.Left.Op == OTYPE && n.Class() == PFUNC {
+	if n.isMethodExpression() {
 		// Methods called as Type.Method(receiver, ...).
 		// Definitions for method expressions are stored in type->nname.
 		init1(asNode(n.Type.FuncType().Nname), out)

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

@@ -209,6 +209,11 @@ func (n *Node) mayBeShared() bool {
 	return false
 }
 
+// isMethodExpression reports whether n represents a method expression T.M.
+func (n *Node) isMethodExpression() bool {
+	return n.Op == ONAME && n.Left != nil && n.Left.Op == OTYPE && n.Right != nil && n.Right.Op == ONAME
+}
+
 // funcname returns the name of the function n.
 func (n *Node) funcname() string {
 	if n == nil || n.Func == nil || n.Func.Nname == nil {

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

@@ -2709,7 +2709,7 @@ notenough:
 			// call is the expression being called, not the overall call.
 			// Method expressions have the form T.M, and the compiler has
 			// rewritten those to ONAME nodes but left T in Left.
-			if call.Op == ONAME && call.Left != nil && call.Left.Op == OTYPE {
+			if call.isMethodExpression() {
 				yyerror("not enough arguments in call to method expression %v%s", call, details)
 			} else {
 				yyerror("not enough arguments in call to %v%s", call, details)