cmd/compile: fixed which-result confusion in presence of 0-width types

A function returning multiple results, some of them zero-width,
will have more than one result present at an offset.  Be sure
that offset AND type match.

Includes test.

Change-Id: I3eb1f56116d989b4e73f533fefabb1bf554c901b
Reviewed-on: https://go-review.googlesource.com/c/go/+/297169
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

2 files changed, 34 insertions, 0 deletions

diff --git a/test/abi/f_ret_z_not.go b/test/abi/f_ret_z_not.go
new file mode 100644
index 0000000000..b072aea75e
--- /dev/null
+++ b/test/abi/f_ret_z_not.go
@@ -0,0 +1,33 @@
+// 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"
+
+type Z struct {
+}
+
+type NZ struct {
+	x, y int
+}
+
+//go:noinline
+func f(x,y int) (Z,NZ,Z) {
+	var z Z
+	return z,NZ{x,y},z
+}
+
+//go:noinline
+func g() (Z,NZ,Z) {
+	a,b,c := f(3,4)
+	return c,b,a
+}
+
+func main() {
+	_,b,_ := g()
+	fmt.Println(b.x+b.y)
+}
diff --git a/test/abi/f_ret_z_not.out b/test/abi/f_ret_z_not.out
new file mode 100644
index 0000000000..7f8f011eb7
--- /dev/null
+++ b/test/abi/f_ret_z_not.out
@@ -0,0 +1 @@
+7