cmd/compile: copy captured dictionary var to local var

When starting a closure that needs a dictionary, copy the closure
variable to a local variable. This lets child closures capture that
dictionary variable correctly.

This is a better fix for #47684, which does not cause problems
like #47723.

Fixes #47723
Update #47684

Change-Id: Ib5d9ffc68a5142e28daa7d0d75683e7a35508540
Reviewed-on: https://go-review.googlesource.com/c/go/+/343871
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/test/typeparam/issue47723.go b/test/typeparam/issue47723.go
new file mode 100644
index 0000000000..9ef60402b2
--- /dev/null
+++ b/test/typeparam/issue47723.go
@@ -0,0 +1,23 @@
+// run -gcflags=-G=3
+
+// 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
+
+func f[_ any]() int {
+	var a [1]int
+	_ = func() int {
+		return func() int {
+			return 0
+		}()
+	}()
+	return a[func() int {
+		return 0
+	}()]
+}
+
+func main() {
+	f[int]()
+}