cmd/compile: allow export/import OSLICE2ARRPTR

Updates #395
Fixes #45665

Change-Id: Iaf053c0439a573e9193d40942fbdb22ac3b4d3bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/312070
Trust: Cuong Manh Le <[email protected]>
Run-TryBot: Cuong Manh Le <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: cuonglm

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

@@ -1677,7 +1677,7 @@ func (w *exportWriter) expr(n ir.Node) {
 			w.op(ir.OEND)
 		}
 
-	case ir.OCONV, ir.OCONVIFACE, ir.OCONVNOP, ir.OBYTES2STR, ir.ORUNES2STR, ir.OSTR2BYTES, ir.OSTR2RUNES, ir.ORUNESTR:
+	case ir.OCONV, ir.OCONVIFACE, ir.OCONVNOP, ir.OBYTES2STR, ir.ORUNES2STR, ir.OSTR2BYTES, ir.OSTR2RUNES, ir.ORUNESTR, ir.OSLICE2ARRPTR:
 		n := n.(*ir.ConvExpr)
 		if go117ExportTypes {
 			w.op(n.Op())

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

@@ -1262,7 +1262,7 @@ func (r *importReader) node() ir.Node {
 		}
 		return n
 
-	case ir.OCONV, ir.OCONVIFACE, ir.OCONVNOP, ir.OBYTES2STR, ir.ORUNES2STR, ir.OSTR2BYTES, ir.OSTR2RUNES, ir.ORUNESTR:
+	case ir.OCONV, ir.OCONVIFACE, ir.OCONVNOP, ir.OBYTES2STR, ir.ORUNES2STR, ir.OSTR2BYTES, ir.OSTR2RUNES, ir.ORUNESTR, ir.OSLICE2ARRPTR:
 		if !go117ExportTypes && op != ir.OCONV {
 			// 	unreachable - mapped to OCONV case by exporter
 			goto error

test/fixedbugs/issue45665.go

@@ -0,0 +1,15 @@
+// compile
+
+// 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
+
+func main() {
+	Get([]string{"a", "b"})
+}
+
+func Get(ss []string) *[2]string {
+	return (*[2]string)(ss)
+}