cmd/compile: deadcode unreferenced hidden closures during inlining
When a closure is inlined, it may contain other hidden closures, which
the inliner will duplicate, rendering the original nested closures as
unreachable. Because they are unreachable, they don't get processed in
escape analysis, meaning that go/defer statements don't get rewritten,
which can then in turn trigger errors in walk. This patch looks for
nested hidden closures and marks them as dead, so that they can be
skipped later on in the compilation flow. NB: if during escape
analysis we rediscover a hidden closure (due to an explicit reference)
that was previously marked dead, revive it at that point.
Fixes #59404.
Change-Id: I76db1e9cf1ee38bd1147aeae823f916dbbbf081b
Reviewed-on: https://go-review.googlesource.com/c/go/+/482355
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Than McIntosh <thanm@google.com> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com> Reviewed-by: Cherry Mui <cherryyz@google.com>