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>

3 files changed, 34 insertions, 0 deletions

diff --git a/test/fixedbugs/issue43551.dir/a.go b/test/fixedbugs/issue43551.dir/a.go
new file mode 100644
index 0000000000..d890dd0c65
--- /dev/null
+++ b/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
+}
diff --git a/test/fixedbugs/issue43551.dir/b.go b/test/fixedbugs/issue43551.dir/b.go
new file mode 100644
index 0000000000..ba062bf14c
--- /dev/null
+++ b/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())
+}
diff --git a/test/fixedbugs/issue43551.go b/test/fixedbugs/issue43551.go
new file mode 100644
index 0000000000..b83fbd7af1
--- /dev/null
+++ b/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