cmd/compile/internal/gc: simplify export info

Followup to previous typenod CL. Changes export data format, but only
the compiler-specific section, so no version bump.

Change-Id: I0c21737141f3d257366b29b2a9211bc7217c39ee
Reviewed-on: https://go-review.googlesource.com/39797
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

@@ -1273,10 +1273,6 @@ func (p *exporter) expr(n *Node) {
 		p.op(ODOTTYPE)
 		p.pos(n)
 		p.expr(n.Left)
-		if n.Right != nil {
-			Fatalf("impossible")
-		}
-		p.bool(false)
 		p.typ(n.Type)
 
 	case OINDEX, OINDEXMAP:
@@ -1311,13 +1307,8 @@ func (p *exporter) expr(n *Node) {
 	case OCONV, OCONVIFACE, OCONVNOP, OARRAYBYTESTR, OARRAYRUNESTR, OSTRARRAYBYTE, OSTRARRAYRUNE, ORUNESTR:
 		p.op(OCONV)
 		p.pos(n)
+		p.expr(n.Left)
 		p.typ(n.Type)
-		if n.Left != nil {
-			p.expr(n.Left)
-			p.op(OEND)
-		} else {
-			p.exprList(n.List) // emits terminating OEND
-		}
 
 	case OREAL, OIMAG, OAPPEND, OCAP, OCLOSE, ODELETE, OLEN, OMAKE, ONEW, OPANIC, ORECOVER, OPRINT, OPRINTN:
 		p.op(op)

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

@@ -960,9 +960,6 @@ func (p *importer) node() *Node {
 
 	case ODOTTYPE:
 		n := nodl(p.pos(), ODOTTYPE, p.expr(), nil)
-		if p.bool() {
-			Fatalf("impossible")
-		}
 		n.Type = p.typ()
 		return n
 
@@ -986,13 +983,8 @@ func (p *importer) node() *Node {
 	// 	unreachable - mapped to OCONV case below by exporter
 
 	case OCONV:
-		n := nodl(p.pos(), OCONV, nil, nil)
+		n := nodl(p.pos(), OCONV, p.expr(), nil)
 		n.Type = p.typ()
-		exprs := p.exprList()
-		if len(exprs) != 1 {
-			Fatalf("impossible")
-		}
-		n.Left = exprs[0]
 		return n
 
 	case OCOPY, OCOMPLEX, OREAL, OIMAG, OAPPEND, OCAP, OCLOSE, ODELETE, OLEN, OMAKE, ONEW, OPANIC, ORECOVER, OPRINT, OPRINTN: