From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 1734) id 8EA4D38582BC; Tue, 15 Nov 2022 00:17:29 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 8EA4D38582BC DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1668471451; bh=aN1Gfz+8IWs6mI7GucqMcQDDqMLKUyxJF0F6q4y6Hbc=; h=From:To:Subject:Date:From; b=cjgd4g8wuQyHTFcfCbOK+UQ75SeM+tsWpORRjT4MxLlAAk5NFY6PNb5LAGx8gpGO9 KOexfdZ0dnmIfaG+ImrsSybVghK+2Dsodx7ohDFecbqbEoO0dKSd2+6gQ1wcAMYtB+ mg6rlxT+ii2/NVQFLPoOebYYs5+iQhhytRbPaGyM= MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Marek Polacek To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-4038] c++: Disable -Wdangling-reference when initing T& X-Act-Checkin: gcc X-Git-Author: Marek Polacek X-Git-Refname: refs/heads/trunk X-Git-Oldrev: aa37a91cab19855ae6b0c6660eff8511b7a81436 X-Git-Newrev: 080b4cf6bd8622c7dff6299f9103184d518ca93f Message-Id: <20221115001731.8EA4D38582BC@sourceware.org> Date: Tue, 15 Nov 2022 00:17:29 +0000 (GMT) List-Id: https://gcc.gnu.org/g:080b4cf6bd8622c7dff6299f9103184d518ca93f commit r13-4038-g080b4cf6bd8622c7dff6299f9103184d518ca93f Author: Marek Polacek Date: Fri Nov 11 12:01:54 2022 -0500 c++: Disable -Wdangling-reference when initing T& Non-const lvalue references can't bind to a temporary, so the warning should not be emitted if we're initializing something of that type. I'm not disabling the warning when the function itself returns a non-const lvalue reference, that would regress at least const int &r = std::any_cast(std::any()); in Wdangling-reference2.C where the any_cast returns an int&. Unfortunately, this patch means we'll stop diagnosing int& fn(int&& x) { return static_cast(x); } void test () { int &r = fn(4); } where there's a genuine dangling reference. OTOH, the patch should suppress false positives with iterators, like: auto &candidate = *candidates.begin (); and arguably that's more important than detecting some relatively obscure cases. It's probably not worth it making the warning more complicated by, for instance, not warning when a fn returns 'int&' but takes 'const int&' (because then it can't return its argument). gcc/cp/ChangeLog: * call.cc (maybe_warn_dangling_reference): Don't warn when initializing a non-const lvalue reference. gcc/testsuite/ChangeLog: * g++.dg/cpp23/elision4.C: Remove dg-warning. * g++.dg/warn/Wdangling-reference1.C: Turn dg-warning into dg-bogus. * g++.dg/warn/Wdangling-reference7.C: New test. Diff: --- gcc/cp/call.cc | 10 ++++++++-- gcc/testsuite/g++.dg/cpp23/elision4.C | 4 ++-- gcc/testsuite/g++.dg/warn/Wdangling-reference1.C | 4 ++-- gcc/testsuite/g++.dg/warn/Wdangling-reference7.C | 16 ++++++++++++++++ 4 files changed, 28 insertions(+), 6 deletions(-) diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index bd3b64a7e26..ef618d5c485 100644 --- a/gcc/cp/call.cc +++ b/gcc/cp/call.cc @@ -13679,8 +13679,14 @@ maybe_warn_dangling_reference (const_tree decl, tree init) { if (!warn_dangling_reference) return; - if (!(TYPE_REF_OBJ_P (TREE_TYPE (decl)) - || std_pair_ref_ref_p (TREE_TYPE (decl)))) + tree type = TREE_TYPE (decl); + /* Only warn if what we're initializing has type T&& or const T&, or + std::pair. (A non-const lvalue reference can't + bind to a temporary.) */ + if (!((TYPE_REF_OBJ_P (type) + && (TYPE_REF_IS_RVALUE (type) + || CP_TYPE_CONST_P (TREE_TYPE (type)))) + || std_pair_ref_ref_p (type))) return; /* Don't suppress the diagnostic just because the call comes from a system header. If the DECL is not in a system header, or if diff --git a/gcc/testsuite/g++.dg/cpp23/elision4.C b/gcc/testsuite/g++.dg/cpp23/elision4.C index d39053ad741..77dcffcdaad 100644 --- a/gcc/testsuite/g++.dg/cpp23/elision4.C +++ b/gcc/testsuite/g++.dg/cpp23/elision4.C @@ -34,6 +34,6 @@ T& temporary2(T&& x) { return static_cast(x); } void test () { - int& r1 = temporary1 (42); // { dg-warning "dangling reference" } - int& r2 = temporary2 (42); // { dg-warning "dangling reference" } + int& r1 = temporary1 (42); + int& r2 = temporary2 (42); } diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference1.C b/gcc/testsuite/g++.dg/warn/Wdangling-reference1.C index 97c81ee716c..1718c28165e 100644 --- a/gcc/testsuite/g++.dg/warn/Wdangling-reference1.C +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference1.C @@ -139,6 +139,6 @@ struct Y { // x1 = Y::operator int&& (&TARGET_EXPR ) int&& x1 = Y(); // { dg-warning "dangling reference" } int&& x2 = Y{}; // { dg-warning "dangling reference" } -int& x3 = Y(); // { dg-warning "dangling reference" } -int& x4 = Y{}; // { dg-warning "dangling reference" } +int& x3 = Y(); // { dg-bogus "dangling reference" } +int& x4 = Y{}; // { dg-bogus "dangling reference" } const int& t1 = Y().foo(10); // { dg-warning "dangling reference" } diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference7.C b/gcc/testsuite/g++.dg/warn/Wdangling-reference7.C new file mode 100644 index 00000000000..4b0de2d8670 --- /dev/null +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference7.C @@ -0,0 +1,16 @@ +// { dg-do compile { target c++11 } } +// { dg-options "-Wdangling-reference" } + +int& ref(const int&); +int&& rref(const int&); + +void +g () +{ + const int& r1 = ref (1); // { dg-warning "dangling reference" } + int& r2 = ref (2); // { dg-bogus "dangling reference" } + auto& r3 = ref (3); // { dg-bogus "dangling reference" } + int&& r4 = rref (4); // { dg-warning "dangling reference" } + auto&& r5 = rref (5); // { dg-warning "dangling reference" } + const int&& r6 = rref (6); // { dg-warning "dangling reference" } +}