cmd/compile: correct leaf type when "selecting" singleton register-sized struct

Two part fix:
1) bring the type "correction" forward from a later CL in the expand calls series
2) when a leaf-selwect is rewritten in place, update the type (it might have been
   changed by the type correction in 1).

Fixes #41736.

Change-Id: Id097efd10481bf0ad92aaead81a7207221c144b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/259203
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

1 files changed, 105 insertions, 0 deletions

diff --git a/test/fixedbugs/issue41736.go b/test/fixedbugs/issue41736.go
new file mode 100644
index 0000000000..36f127f4fb
--- /dev/null
+++ b/test/fixedbugs/issue41736.go
@@ -0,0 +1,105 @@
+// compile
+
+// Copyright 2020 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 p
+
+type I struct {
+	x int64
+}
+
+type F struct {
+	x float64
+}
+
+type C struct {
+	x *complex128
+}
+
+type D struct {
+	x complex64
+}
+
+type A [1]*complex128
+
+//go:noinline
+func (i I) X() C {
+	cx := complex(0, float64(i.x))
+	return C{&cx}
+}
+
+//go:noinline
+func (f F) X() C {
+	cx := complex(f.x, 0)
+	return C{&cx}
+}
+
+//go:noinline
+func (c C) X() C {
+	cx := complex(imag(*c.x), real(*c.x))
+	return C{&cx}
+}
+
+//go:noinline
+func (d D) X() C {
+	cx := complex(float64(imag(d.x)), -float64(real(d.x)))
+	return C{&cx}
+}
+
+//go:noinline
+func (a A) X() C {
+	cx := complex(-float64(imag(*a[0])), float64(real(*a[0])))
+	return C{&cx}
+}
+
+//go:noinline
+func (i I) id() I {
+	return i
+}
+
+//go:noinline
+func (f F) id() F {
+	return f
+}
+
+//go:noinline
+func (c C) id() C {
+	return c
+}
+
+//go:noinline
+func (d D) id() D {
+	return d
+}
+
+//go:noinline
+func (a A) id() A {
+	return a
+}
+
+type T interface {
+	X() C
+}
+
+func G(x []T) []T {
+	var y []T
+	for _, a := range x {
+		var v T
+		switch u := a.(type) {
+		case I:
+			v = u.id()
+		case F:
+			v = u.id()
+		case C:
+			v = u.id()
+		case D:
+			v = u.id()
+		case A:
+			v = u.id()
+		}
+		y = append(y, v)
+	}
+	return y
+}