From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: [committed] libstdc++: Fix visit<void>(v) for non-void visitors [PR106589]
Date: Tue, 23 Aug 2022 16:39:12 +0100 [thread overview]
Message-ID: <20220823153912.229679-1-jwakely@redhat.com> (raw)
Tested powerpc64le-linux, pushed to trunk. Backport to gcc-12 needed.
-- >8 --
The optimization for the common case of std::visit forgot to handle the
edge case of passing zero variants to a non-void visitor and converting
the result to void.
libstdc++-v3/ChangeLog:
PR libstdc++/106589
* include/std/variant (__do_visit): Handle is_void<R> for zero
argument case.
* testsuite/20_util/variant/visit_r.cc: Check std::visit<void>(v).
---
libstdc++-v3/include/std/variant | 7 ++++++-
libstdc++-v3/testsuite/20_util/variant/visit_r.cc | 8 ++++++++
2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index f8f15665433..c234b54421e 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1728,7 +1728,12 @@ namespace __variant
{
// Get the silly case of visiting no variants out of the way first.
if constexpr (sizeof...(_Variants) == 0)
- return std::forward<_Visitor>(__visitor)();
+ {
+ if constexpr (is_void_v<_Result_type>)
+ return (void) std::forward<_Visitor>(__visitor)();
+ else
+ return std::forward<_Visitor>(__visitor)();
+ }
else
{
constexpr size_t __max = 11; // "These go to eleven."
diff --git a/libstdc++-v3/testsuite/20_util/variant/visit_r.cc b/libstdc++-v3/testsuite/20_util/variant/visit_r.cc
index 712459f25e3..c77b259c386 100644
--- a/libstdc++-v3/testsuite/20_util/variant/visit_r.cc
+++ b/libstdc++-v3/testsuite/20_util/variant/visit_r.cc
@@ -54,10 +54,18 @@ void test02()
std::visit<const void>(Visitor(), v);
}
+void test03()
+{
+ // PR libstdc++/106589 - visit<void> rejects lambdas that do not return void
+ auto visitor = []{ return 0; };
+ std::visit<void>(visitor);
+ std::visit<void>(static_cast<int(*)()>(visitor));
+}
int
main()
{
test01();
test02();
+ test03();
}
--
2.37.2
reply other threads:[~2022-08-23 15:39 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220823153912.229679-1-jwakely@redhat.com \
--to=jwakely@redhat.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=libstdc++@gcc.gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).