cmd/compile/internal/noder: explicit receiver expression handling

This CL adds a helper expression code for receiver addressing; i.e.,
the implicit addressing, dereferencing, and field selections involved
in changing the `x` in `x.M()` into an appropriate expression to pass
as an argument to the method.

Change-Id: I9be933e2a38c8f94f6a85d95b54f34164e5efb0a
Reviewed-on: https://go-review.googlesource.com/c/go/+/421820
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>

src/cmd/compile/internal/noder/codes.go

@@ -57,6 +57,7 @@ const (
 	exprMake
 	exprNil
 	exprFuncInst
+	exprRecv
 )
 
 type codeAssign int

src/cmd/compile/internal/noder/reader.go

@@ -1914,6 +1914,19 @@ func (r *reader) expr() (res ir.Node) {
 		}
 		return typecheck.Expr(ir.NewBinaryExpr(pos, op, x, y))
 
+	case exprRecv:
+		x := r.expr()
+		pos := r.pos()
+		for i, n := 0, r.Len(); i < n; i++ {
+			x = Implicit(DotField(pos, x, r.Len()))
+		}
+		if r.Bool() { // needs deref
+			x = Implicit(Deref(pos, x.Type().Elem(), x))
+		} else if r.Bool() { // needs addr
+			x = Implicit(Addr(pos, x))
+		}
+		return x
+
 	case exprCall:
 		fun := r.expr()
 		if r.Bool() { // method call

src/cmd/compile/internal/noder/writer.go

@@ -1540,7 +1540,7 @@ func (w *writer) expr(expr syntax.Expr) {
 
 		case types2.MethodVal:
 			w.Code(exprMethodVal)
-			w.expr(expr.X)
+			w.recvExpr(expr, sel)
 			w.pos(expr)
 			w.selector(sel.Obj())
 
@@ -1697,7 +1697,7 @@ func (w *writer) expr(expr syntax.Expr) {
 		writeFunExpr := func() {
 			if selector, ok := unparen(expr.Fun).(*syntax.SelectorExpr); ok {
 				if sel, ok := w.p.info.Selections[selector]; ok && sel.Kind() == types2.MethodVal {
-					w.expr(selector.X)
+					w.recvExpr(selector, sel)
 					w.Bool(true) // method call
 					w.pos(selector)
 					w.selector(sel.Obj())
@@ -1741,6 +1741,40 @@ func (w *writer) optExpr(expr syntax.Expr) {
 	}
 }
 
+// recvExpr writes out expr.X, but handles any implicit addressing,
+// dereferencing, and field selections.
+func (w *writer) recvExpr(expr *syntax.SelectorExpr, sel *types2.Selection) types2.Type {
+	index := sel.Index()
+	implicits := index[:len(index)-1]
+
+	w.Code(exprRecv)
+	w.expr(expr.X)
+	w.pos(expr)
+	w.Len(len(implicits))
+
+	typ := w.p.typeOf(expr.X)
+	for _, ix := range implicits {
+		typ = deref2(typ).Underlying().(*types2.Struct).Field(ix).Type()
+		w.Len(ix)
+	}
+
+	isPtrTo := func(from, to types2.Type) bool {
+		if from, ok := from.(*types2.Pointer); ok {
+			return types2.Identical(from.Elem(), to)
+		}
+		return false
+	}
+
+	recv := sel.Obj().(*types2.Func).Type().(*types2.Signature).Recv().Type()
+	if w.Bool(isPtrTo(typ, recv)) { // needs deref
+		typ = recv
+	} else if w.Bool(isPtrTo(recv, typ)) { // needs addr
+		typ = recv
+	}
+
+	return typ
+}
+
 // multiExpr writes a sequence of expressions, where the i'th value is
 // implicitly converted to dstType(i). It also handles when exprs is a
 // single, multi-valued expression (e.g., the multi-valued argument in