cmd/compile: fix late expand_calls leaf type for OpStructSelect/OpArraySelect

For the example in #43551, before late call expansion, the OpArg type is
decomposed to int64. But the late call expansion is currently decompose
it to "x.Key" instead.

This CL make expand_calls decompose further for struct { 1-field type }
and array [1]elem.

This matches the previous rules for early decompose args:

(StructSelect (StructMake1 x)) => x
(ArraySelect (ArrayMake1 x)) => x

Fixes #43551

Change-Id: I2f1ebe18cb81cb967f494331c3d237535d2859e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/282332
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

Author: cuonglm

src/cmd/compile/internal/ssa/expand_calls.go

@@ -194,7 +194,8 @@ func expandCalls(f *Func) {
 				}
 				break
 			}
-			if leaf.Op == OpIData {
+			switch leaf.Op {
+			case OpIData, OpStructSelect, OpArraySelect:
 				leafType = removeTrivialWrapperTypes(leaf.Type)
 			}
 			aux := selector.Aux

test/fixedbugs/issue43551.dir/a.go

@@ -0,0 +1,13 @@
+package a
+
+type S struct {
+	a Key
+}
+
+func (s S) A() Key {
+	return s.a
+}
+
+type Key struct {
+	key int64
+}

test/fixedbugs/issue43551.dir/b.go

@@ -0,0 +1,14 @@
+// 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 b
+
+import "./a"
+
+type S a.S
+type Key a.Key
+
+func (s S) A() Key {
+	return Key(a.S(s).A())
+}

test/fixedbugs/issue43551.go

@@ -0,0 +1,7 @@
+// compiledir
+
+// 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