cmd/compile: allow importing and exporting of ODYANMICDOTTYPE[2]

Fixes #49027

Change-Id: I4520b5c754027bfffbc5cd92c9c27002b248c99a
Reviewed-on: https://go-review.googlesource.com/c/go/+/356569
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

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

@@ -1888,6 +1888,14 @@ func (w *exportWriter) expr(n ir.Node) {
 		w.expr(n.X)
 		w.typ(n.Type())
 
+	case ir.ODYNAMICDOTTYPE, ir.ODYNAMICDOTTYPE2:
+		n := n.(*ir.DynamicTypeAssertExpr)
+		w.op(n.Op())
+		w.pos(n.Pos())
+		w.expr(n.X)
+		w.expr(n.T)
+		w.typ(n.Type())
+
 	case ir.OINDEX, ir.OINDEXMAP:
 		n := n.(*ir.IndexExpr)
 		if go117ExportTypes {

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

@@ -1457,6 +1457,11 @@ func (r *importReader) node() ir.Node {
 		}
 		return n
 
+	case ir.ODYNAMICDOTTYPE, ir.ODYNAMICDOTTYPE2:
+		n := ir.NewDynamicTypeAssertExpr(r.pos(), op, r.expr(), r.expr())
+		n.SetType(r.typ())
+		return n
+
 	case ir.OINDEX, ir.OINDEXMAP:
 		n := ir.NewIndexExpr(r.pos(), r.expr(), r.expr())
 		if go117ExportTypes {

test/typeparam/issue49027.dir/a.go

@@ -0,0 +1,21 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package a
+
+func Conv(v interface{}) string {
+	return conv[string](v)
+}
+
+func conv[T any](v interface{}) T {
+	return v.(T)
+}
+
+func Conv2(v interface{}) (string, bool) {
+	return conv2[string](v)
+}
+func conv2[T any](v interface{}) (T, bool) {
+	x, ok := v.(T)
+	return x, ok
+}

test/typeparam/issue49027.dir/main.go

@@ -0,0 +1,25 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"a"
+	"fmt"
+)
+
+func main() {
+	s := "foo"
+	x := a.Conv(s)
+	if x != s {
+		panic(fmt.Sprintf("got %s wanted %s", x, s))
+	}
+	y, ok := a.Conv2(s)
+	if !ok {
+		panic("conversion failed")
+	}
+	if y != s {
+		panic(fmt.Sprintf("got %s wanted %s", y, s))
+	}
+}

test/typeparam/issue49027.go

@@ -0,0 +1,7 @@
+// rundir -G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ignored