cmd/compile: simplify noding for struct embedding

Since golang.org/cl/31670, we've stopped using the 'embedded' function
for handling struct embeddings within package export data. Now the
only remaining use is for Go source files, which allows for some
substantial simplifications:

1. CenterDot never appears within Go source files, so that logic can
simply be removed.

2. The field name will always be declared in the local package.

Passes toolstash-check.

Change-Id: I59505f62824206dd5de0782918f98fbef6e93224
Reviewed-on: https://go-review.googlesource.com/58790
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -760,33 +760,6 @@ func tointerface0(t *types.Type, l []*Node) *types.Type {
 	return t
 }
 
-func embedded(s *types.Sym, pkg *types.Pkg) *Node {
-	const (
-		CenterDot = 0xB7
-	)
-	// Names sometimes have disambiguation junk
-	// appended after a center dot. Discard it when
-	// making the name for the embedded struct field.
-	name := s.Name
-
-	if i := strings.Index(s.Name, string(CenterDot)); i >= 0 {
-		name = s.Name[:i]
-	}
-
-	var n *Node
-	if exportname(name) {
-		n = newname(lookup(name))
-	} else if s.Pkg == builtinpkg {
-		// The name of embedded builtins belongs to pkg.
-		n = newname(pkg.Lookup(name))
-	} else {
-		n = newname(s.Pkg.Lookup(name))
-	}
-	n = nod(ODCLFIELD, n, oldname(s))
-	n.SetEmbedded(true)
-	return n
-}
-
 func fakeRecv() *Node {
 	return anonfield(types.FakeRecvType())
 }

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

@@ -689,7 +689,11 @@ func (p *noder) embedded(typ syntax.Expr) *Node {
 		}
 		typ = op.X
 	}
-	n := embedded(p.packname(typ), localpkg)
+
+	sym := p.packname(typ)
+	n := nod(ODCLFIELD, newname(lookup(sym.Name)), oldname(sym))
+	n.SetEmbedded(true)
+
 	if isStar {
 		n.Right = p.nod(op, OIND, n.Right, nil)
 	}