cmd/compile: load results into registers on open defer return path

When a function panics then recovers, it needs to return to the
caller with named results having the correct values. For
in-register results, we need to load them into registers at the
defer return path.

For non-open-coded defers, we already generate correct code, as
the defer return path is part of the SSA CFG and contains the
instructions that are the same as an ordinary return statement,
including putting the results to the right places.

For open-coded defers, we have a special code generation that
emits a disconnected block that currently contains only the
deferreturn call and a RET instruction. It leaves the result
registers unset. This CL adds instructions that load the result
registers on that path.

Updates #40724.

Change-Id: I1f60514da644fd5fb4b4871a1153c62f42927282
Reviewed-on: https://go-review.googlesource.com/c/go/+/307231
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/test/abi/defer_recover_results.go b/test/abi/defer_recover_results.go
new file mode 100644
index 0000000000..7787f26f4c
--- /dev/null
+++ b/test/abi/defer_recover_results.go
@@ -0,0 +1,36 @@
+// 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.
+
+// Test that when a function recovers from a panic, it
+// returns the correct results to the caller (in particular,
+// setting the result registers correctly).
+
+package main
+
+type S struct {
+	x uint8
+	y uint16
+	z uint32
+	w float64
+}
+
+var a0, b0, c0, d0 = 10, "hello", S{1, 2, 3, 4}, [2]int{111, 222}
+
+//go:noinline
+//go:registerparams
+func F() (a int, b string, _ int, c S, d [2]int) {
+	a, b, c, d = a0, b0, c0, d0
+	defer func() { recover() }()
+	panic("XXX")
+	return
+}
+
+func main() {
+	a1, b1, zero, c1, d1 := F()
+	if a1 != a0 || b1 != b0 || c1 != c0 || d1 != d0 || zero != 0 { // unnamed result gets zero value
+		panic("FAIL")
+	}
+}