cmd/compile: implement too-big-to-SSA struct passing in registers

Added a test that exercises named results

Change-Id: Ie228b68f4f846266595a95e0f65a6e4b8bf79635
Reviewed-on: https://go-review.googlesource.com/c/go/+/297029
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

2 files changed, 104 insertions, 0 deletions

diff --git a/test/abi/named_results.go b/test/abi/named_results.go
new file mode 100644
index 0000000000..eaaadb184f
--- /dev/null
+++ b/test/abi/named_results.go
@@ -0,0 +1,91 @@
+// run
+
+//go:build !wasm
+// +build !wasm
+
+// 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"
+)
+
+var sink *string
+
+var y int
+
+//go:registerparams
+//go:noinline
+func F(a, b, c *int) (x int) {
+	x = *a
+	G(&x)
+	x += *b
+	G(&x)
+	x += *c
+	G(&x)
+	return
+}
+
+//go:registerparams
+//go:noinline
+func G(x *int) {
+	y += *x
+	fmt.Println("y = ", y)
+}
+
+//go:registerparams
+//go:noinline
+func X() {
+	*sink += " !!!!!!!!!!!!!!!"
+}
+
+//go:registerparams
+//go:noinline
+func H(s, t string) (result string) { // result leaks to heap
+	result = "Aloha! " + s + " " + t
+	sink = &result
+	r := ""
+	if len(s) <= len(t) {
+		r = "OKAY! "
+		X()
+	}
+	return r + result
+}
+
+//go:registerparams
+//go:noinline
+func K(s, t string) (result string) { // result spills
+	result = "Aloha! " + s + " " + t
+	r := ""
+	if len(s) <= len(t) {
+		r = "OKAY! "
+		X()
+	}
+	return r + result
+}
+
+func main() {
+	a, b, c := 1, 4, 16
+	x := F(&a, &b, &c)
+	fmt.Printf("x = %d\n", x)
+
+	y := H("Hello", "World!")
+	fmt.Println("len(y) =", len(y))
+	fmt.Println("y =", y)
+	z := H("Hello", "Pal!")
+	fmt.Println("len(z) =", len(z))
+	fmt.Println("z =", z)
+
+	fmt.Println()
+
+	y = K("Hello", "World!")
+	fmt.Println("len(y) =", len(y))
+	fmt.Println("y =", y)
+	z = K("Hello", "Pal!")
+	fmt.Println("len(z) =", len(z))
+	fmt.Println("z =", z)
+
+}
diff --git a/test/abi/named_results.out b/test/abi/named_results.out
new file mode 100644
index 0000000000..02f12e806d
--- /dev/null
+++ b/test/abi/named_results.out
@@ -0,0 +1,13 @@
+y =  1
+y =  6
+y =  27
+x = 21
+len(y) = 41
+y = OKAY! Aloha! Hello World! !!!!!!!!!!!!!!!
+len(z) = 17
+z = Aloha! Hello Pal!
+
+len(y) = 25
+y = OKAY! Aloha! Hello World!
+len(z) = 17
+z = Aloha! Hello Pal!