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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id de26-20020a05620a371a00b0077f0a79ee55sm8472706qkb.133.2023.12.18.11.50.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Dec 2023 11:50:23 -0800 (PST) From: Patrick Palka To: gcc-patches@gcc.gnu.org Cc: jason@redhat.com, Patrick Palka Subject: [PATCH] c++: bad direct reference binding [PR113064] Date: Mon, 18 Dec 2023 14:50:21 -0500 Message-ID: <20231218195021.1244349-1-ppalka@redhat.com> X-Mailer: git-send-email 2.43.0.76.g1a87c842ec MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-13.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gcc-patches-bounces+incoming=patchwork.ozlabs.org@gcc.gnu.org Bootstrappde and regtested on x86_64-pc-linux-gnu, does this look OK for trunk? -- >8 -- When computing a direct conversion to reference type fails and yields a bad conversion, reference_binding incorrectly commits to that conversion rather than attempting a conversion via a temporary. This leads to us rejecting the first testcase because the direct bad conversion to B&& via the && conversion operator prevents us from considering the (good) conversion via a temporary and the & conversion operator (and similarly for the second more elaborate testcase). This patch fixes this by making reference_binding not prematurely commit to such a bad direct conversion. We still fall back to such a bad direct conversion if using a temporary also fails (otherwise the diagnostic for cpp0x/explicit7.C regresses). PR c++/113064 gcc/cp/ChangeLog: * call.cc (reference_binding): Still try a conversion via a temporary if a direct conversion was bad. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/rv-conv4.C: New test. * g++.dg/cpp0x/rv-conv5.C: New test. --- gcc/cp/call.cc | 22 ++++++++++++++++++---- gcc/testsuite/g++.dg/cpp0x/rv-conv4.C | 16 ++++++++++++++++ gcc/testsuite/g++.dg/cpp0x/rv-conv5.C | 23 +++++++++++++++++++++++ 3 files changed, 57 insertions(+), 4 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/rv-conv4.C create mode 100644 gcc/testsuite/g++.dg/cpp0x/rv-conv5.C diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index 6ac87a298b2..b5d90359160 100644 --- a/gcc/cp/call.cc +++ b/gcc/cp/call.cc @@ -1739,6 +1739,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, tsubst_flags_t complain) { conversion *conv = NULL; + conversion *bad_direct_conv = nullptr; tree to = TREE_TYPE (rto); tree from = rfrom; tree tfrom; @@ -1925,13 +1926,23 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, z_candidate *cand = build_user_type_conversion_1 (rto, expr, flags, complain); if (cand) - return cand->second_conv; + { + if (!cand->second_conv->bad_p) + return cand->second_conv; + + /* Direct reference binding wasn't successful and yielded + a bad conversion. Proceed with trying to use a temporary + instead, and if that also fails then we'll return this bad + conversion rather than no conversion for sake of better + diagnostics. */ + bad_direct_conv = cand->second_conv; + } } /* From this point on, we conceptually need temporaries, even if we elide them. Only the cases above are "direct bindings". */ if (flags & LOOKUP_NO_TEMP_BIND) - return NULL; + return bad_direct_conv ? bad_direct_conv : nullptr; /* [over.ics.rank] @@ -1972,6 +1983,9 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, there's no strictly viable candidate. */ if (!maybe_valid_p && (flags & LOOKUP_SHORTCUT_BAD_CONVS)) { + if (bad_direct_conv) + return bad_direct_conv; + conv = alloc_conversion (ck_deferred_bad); conv->bad_p = true; return conv; @@ -1995,7 +2009,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, conv = implicit_conversion (to, from, expr, c_cast_p, flags, complain); if (!conv) - return NULL; + return bad_direct_conv ? bad_direct_conv : nullptr; if (conv->user_conv_p) { @@ -2018,7 +2032,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, = reference_binding (rto, ftype, NULL_TREE, c_cast_p, sflags, complain); if (!new_second) - return NULL; + return bad_direct_conv ? bad_direct_conv : nullptr; conv = merge_conversion_sequences (t, new_second); gcc_assert (maybe_valid_p || conv->bad_p); return conv; diff --git a/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C b/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C new file mode 100644 index 00000000000..fea2e57531a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C @@ -0,0 +1,16 @@ +// PR c++/113064 +// { dg-do compile { target c++11 } } + +struct B { }; + +struct A { + operator B() &; // #1 + operator B&&() &&; // #2 +}; + +void g(B&&); + +int main() { + A a; + g(a); +} diff --git a/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C b/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C new file mode 100644 index 00000000000..dcb6fc6f76f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C @@ -0,0 +1,23 @@ +// PR c++/113064 +// { dg-do compile { target c++11 } } + +struct no_copy { + no_copy() = default; + + no_copy(const no_copy&) = delete; + no_copy(no_copy&&); + + no_copy& operator=(const no_copy&) = delete; + no_copy& operator=(no_copy&&); +}; + +struct A { + operator no_copy() &; + operator no_copy&&() && = delete; +}; + +int main() { + no_copy nc; + A a; + nc = a; +}