cmd/compile: fix case where init info of OAS node is dropped

When an OAS node is converted to an OSELRECV2 node in tcSelect(), the
possible DCL node in the Init field was being dropped, since a
completely new node was being created and the Init field was not set. I
don't expect n.Init() to be set for the ORECV case, but the code now
deals with that too.

Fixed bug in both tcSelect() and transformSelect().

Fixes #48289

Change-Id: I09918a70f7cbaa4aa9a17546169f908a8787df15
Reviewed-on: https://go-review.googlesource.com/c/go/+/348569
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -554,6 +554,7 @@ func transformSelect(sel *ir.SelectStmt) {
 				}
 				selrecv.Def = def
 				selrecv.SetTypecheck(1)
+				selrecv.SetInit(n.Init())
 				ncase.Comm = selrecv
 			}
 			switch n.Op() {

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

@@ -395,10 +395,11 @@ func tcSelect(sel *ir.SelectStmt) {
 			n := Stmt(ncase.Comm)
 			ncase.Comm = n
 			oselrecv2 := func(dst, recv ir.Node, def bool) {
-				n := ir.NewAssignListStmt(n.Pos(), ir.OSELRECV2, []ir.Node{dst, ir.BlankNode}, []ir.Node{recv})
-				n.Def = def
-				n.SetTypecheck(1)
-				ncase.Comm = n
+				selrecv := ir.NewAssignListStmt(n.Pos(), ir.OSELRECV2, []ir.Node{dst, ir.BlankNode}, []ir.Node{recv})
+				selrecv.Def = def
+				selrecv.SetTypecheck(1)
+				selrecv.SetInit(n.Init())
+				ncase.Comm = selrecv
 			}
 			switch n.Op() {
 			default:

test/fixedbugs/issue48289.go

@@ -0,0 +1,28 @@
+// run
+
+// 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 "fmt"
+
+func main() {
+	ch := make(chan int, 1)
+
+	var ptrs [2]*int
+	for i := range ptrs {
+		ch <- i
+		select {
+		case x := <-ch:
+			ptrs[i] = &x
+		}
+	}
+
+	for i, ptr := range ptrs {
+		if *ptr != i {
+			panic(fmt.Sprintf("got *ptr %d, want %d", *ptr, i))
+		}
+	}
+}