From: Marek Polacek <polacek@redhat.com>
To: Jason Merrill <jason@redhat.com>, GCC Patches <gcc-patches@gcc.gnu.org>
Subject: [PATCH] c++: further -Wdangling-reference refinement [PR107532]
Date: Fri, 17 Mar 2023 16:29:08 -0400 [thread overview]
Message-ID: <20230317202908.42800-1-polacek@redhat.com> (raw)
Based on <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107532#c24>,
it seems like we should treat *any* class with a reference member
as a reference wrapper. This simplifies the code so I'm happy to
make that change.
The patch, however, does not suppress the warning in
int i = 42;
auto const& v = std::get<0>(std::tuple<int&>(i));
Since reference_like_class_p already checks for std::pair<const T&, const T&>
maybe it could also check for std::tuple<T&, ...>. I don't know if we
want to make that change in GCC 13, or move -Wdangling-reference to
-Wextra for GCC 13 and perhaps move it back to -Wall in GCC 14.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
PR c++/107532
gcc/cp/ChangeLog:
* call.cc (reference_like_class_p): Don't look for a constructor.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wdangling-reference11.C: New test.
---
gcc/cp/call.cc | 35 +++++++------------
.../g++.dg/warn/Wdangling-reference11.C | 23 ++++++++++++
2 files changed, 35 insertions(+), 23 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Wdangling-reference11.C
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index c01e7b82457..00d56a157b6 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -13781,8 +13781,9 @@ std_pair_ref_ref_p (tree t)
/* Return true if a class CTYPE is either std::reference_wrapper or
std::ref_view, or a reference wrapper class. We consider a class
- a reference wrapper class if it has a reference member and a
- constructor taking the same reference type. */
+ a reference wrapper class if it has a reference member. We no
+ longer check that it has a constructor taking the same reference type
+ since that approach still generated too many false positives. */
static bool
reference_like_class_p (tree ctype)
@@ -13798,31 +13799,19 @@ reference_like_class_p (tree ctype)
if (decl_in_std_namespace_p (tdecl))
{
tree name = DECL_NAME (tdecl);
- return (name
- && (id_equal (name, "reference_wrapper")
- || id_equal (name, "span")
- || id_equal (name, "ref_view")));
+ if (name
+ && (id_equal (name, "reference_wrapper")
+ || id_equal (name, "span")
+ || id_equal (name, "ref_view")))
+ return true;
}
for (tree fields = TYPE_FIELDS (ctype);
fields;
fields = DECL_CHAIN (fields))
- {
- if (TREE_CODE (fields) != FIELD_DECL || DECL_ARTIFICIAL (fields))
- continue;
- tree type = TREE_TYPE (fields);
- if (!TYPE_REF_P (type))
- continue;
- /* OK, the field is a reference member. Do we have a constructor
- taking its type? */
- for (tree fn : ovl_range (CLASSTYPE_CONSTRUCTORS (ctype)))
- {
- tree args = FUNCTION_FIRST_USER_PARMTYPE (fn);
- if (args
- && same_type_p (TREE_VALUE (args), type)
- && TREE_CHAIN (args) == void_list_node)
- return true;
- }
- }
+ if (TREE_CODE (fields) == FIELD_DECL
+ && !DECL_ARTIFICIAL (fields)
+ && TYPE_REF_P (TREE_TYPE (fields)))
+ return true;
return false;
}
diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference11.C b/gcc/testsuite/g++.dg/warn/Wdangling-reference11.C
new file mode 100644
index 00000000000..667618e7196
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference11.C
@@ -0,0 +1,23 @@
+// PR c++/107532
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wdangling-reference" }
+
+struct R
+{
+ int& r;
+ int& get() { return r; }
+ int&& rget() { return static_cast<int&&>(r); }
+};
+
+int main()
+{
+ int i = 42;
+ int& l = R{i}.get(); // { dg-bogus "dangling reference" }
+ int const& cl = R{i}.get(); // { dg-bogus "dangling reference" }
+ int&& r = R{i}.rget(); // { dg-bogus "dangling reference" }
+ int const&& cr = R{i}.rget(); // { dg-bogus "dangling reference" }
+ (void) l;
+ (void) r;
+ (void) cr;
+ (void) cl;
+}
base-commit: ae7190e345a8d80310835cb83b3b41ef2aeb0d37
--
2.39.2
next reply other threads:[~2023-03-17 20:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-17 20:29 Marek Polacek [this message]
2023-03-18 12:35 ` Jason Merrill
2023-03-20 22:06 ` [PATCH v2] " Marek Polacek
2023-03-21 14:31 ` Jason Merrill
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=20230317202908.42800-1-polacek@redhat.com \
--to=polacek@redhat.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=jason@redhat.com \
/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).