cmd/compile: rework marking of dead hidden closure functions

This patch generalizes the code in the inliner that marks unreferenced
hidden closure functions as dead. Rather than doing the marking on the
fly (previous approach), this new approach does a single pass at the
end of inlining, which catches more dead functions.

Fixes #59638.
Updates #59404.
Updates #59547.

Change-Id: I54fd63e9e37c9123b08a3e7def7d1989919bba91
Reviewed-on: https://go-review.googlesource.com/c/go/+/484859
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 65 insertions, 0 deletions

diff --git a/test/fixedbugs/issue59638.go b/test/fixedbugs/issue59638.go
new file mode 100644
index 0000000000..bba6265322
--- /dev/null
+++ b/test/fixedbugs/issue59638.go
@@ -0,0 +1,65 @@
+// build -gcflags=-l=4
+
+// Copyright 2023 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 Interface interface {
+	MonitoredResource() (resType string, labels map[string]string)
+	Done()
+}
+
+func Autodetect(x int) Interface {
+	return func() Interface {
+		func() Interface {
+			x++
+			Do(func() {
+				var ad, gd Interface
+
+				go func() {
+					defer gd.Done()
+					ad = aad()
+				}()
+				go func() {
+					defer ad.Done()
+					gd = aad()
+					defer func() { recover() }()
+				}()
+
+				autoDetected = ad
+				if gd != nil {
+					autoDetected = gd
+				}
+			})
+			return autoDetected
+		}()
+		return nil
+	}()
+}
+
+var autoDetected Interface
+var G int
+
+type If int
+
+func (x If) MonitoredResource() (resType string, labels map[string]string) {
+	return "", nil
+}
+
+//go:noinline
+func (x If) Done() {
+	G++
+}
+
+//go:noinline
+func Do(fn func()) {
+	fn()
+}
+
+//go:noinline
+func aad() Interface {
+	var x If
+	return x
+}