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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id h4sm3537179qtb.67.2021.10.01.06.30.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Oct 2021 06:30:42 -0700 (PDT) Message-ID: Date: Fri, 1 Oct 2021 09:30:41 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.2 Subject: Re: [PATCH] c++: Implement C++20 -Wdeprecated-array-compare [PR97573] To: Marek Polacek Cc: GCC Patches References: <20210930145031.23104-1-polacek@redhat.com> <7962e5b5-9e10-60f8-9a4e-26e86040a542@redhat.com> From: Jason Merrill In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-13.4 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, NICE_REPLY_A, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 01 Oct 2021 13:30:54 -0000 On 9/30/21 17:56, Marek Polacek wrote: > On Thu, Sep 30, 2021 at 03:34:24PM -0400, Jason Merrill wrote: >> On 9/30/21 10:50, Marek Polacek wrote: >>> This patch addresses one of my leftovers from GCC 11. C++20 introduced >>> [depr.array.comp]: >>> "Equality and relational comparisons between two operands of array type are >>> deprecated." >>> so this patch adds -Wdeprecated-array-compare (enabled by default in C++20). >> >> Why not enable it by default in all modes? It was always pretty dubious >> code. > > Sure, it could be done, but it kind of complicates things: we'd probably > need a different option and a different message because it seems incorrect > to say "deprecated" in e.g. C++17 when this was only deprecated in C++20. The warning could say "deprecated in C++20", which is always true? > I'd rather not add another option; if it stays -Wdeprecated-array-compare > but -Wno-deprecated doesn't turn it off that also seems weird. > > I could rename it to -Warray-compare, enable by -Wall, and only > append "is deprecated" to the warning message in C++20. Does that seem > better? That sounds fine too. >>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? >>> >>> PR c++/97573 >>> >>> gcc/c-family/ChangeLog: >>> >>> * c-opts.c (c_common_post_options): In C++20, turn on >>> -Wdeprecated-array-compare. >>> * c.opt (Wdeprecated-array-compare): New option. >>> >>> gcc/cp/ChangeLog: >>> >>> * typeck.c (do_warn_deprecated_array_compare): New. >>> (cp_build_binary_op): Call it for equality and relational comparisons. >>> >>> gcc/ChangeLog: >>> >>> * doc/invoke.texi: Document -Wdeprecated-array-compare. >>> >>> gcc/testsuite/ChangeLog: >>> >>> * g++.dg/tree-ssa/pr15791-1.C: Add dg-warning. >>> * g++.dg/cpp2a/array-comp1.C: New test. >>> * g++.dg/cpp2a/array-comp2.C: New test. >>> * g++.dg/cpp2a/array-comp3.C: New test. >>> --- >>> gcc/c-family/c-opts.c | 5 ++++ >>> gcc/c-family/c.opt | 4 +++ >>> gcc/cp/typeck.c | 28 +++++++++++++++++++ >>> gcc/doc/invoke.texi | 19 ++++++++++++- >>> gcc/testsuite/g++.dg/cpp2a/array-comp1.C | 34 +++++++++++++++++++++++ >>> gcc/testsuite/g++.dg/cpp2a/array-comp2.C | 31 +++++++++++++++++++++ >>> gcc/testsuite/g++.dg/cpp2a/array-comp3.C | 29 +++++++++++++++++++ >>> gcc/testsuite/g++.dg/tree-ssa/pr15791-1.C | 2 +- >>> 8 files changed, 150 insertions(+), 2 deletions(-) >>> create mode 100644 gcc/testsuite/g++.dg/cpp2a/array-comp1.C >>> create mode 100644 gcc/testsuite/g++.dg/cpp2a/array-comp2.C >>> create mode 100644 gcc/testsuite/g++.dg/cpp2a/array-comp3.C >>> >>> diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c >>> index 3eaab5e1530..00b52cc5e12 100644 >>> --- a/gcc/c-family/c-opts.c >>> +++ b/gcc/c-family/c-opts.c >>> @@ -962,6 +962,11 @@ c_common_post_options (const char **pfilename) >>> warn_deprecated_enum_float_conv, >>> cxx_dialect >= cxx20 && warn_deprecated); >>> + /* -Wdeprecated-array-compare is enabled by default in C++20. */ >>> + SET_OPTION_IF_UNSET (&global_options, &global_options_set, >>> + warn_deprecated_array_compare, >>> + cxx_dialect >= cxx20 && warn_deprecated); >>> + >>> /* Declone C++ 'structors if -Os. */ >>> if (flag_declone_ctor_dtor == -1) >>> flag_declone_ctor_dtor = optimize_size; >>> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt >>> index 9c151d19870..a4f0ea68594 100644 >>> --- a/gcc/c-family/c.opt >>> +++ b/gcc/c-family/c.opt >>> @@ -540,6 +540,10 @@ Wdeprecated >>> C C++ ObjC ObjC++ CPP(cpp_warn_deprecated) CppReason(CPP_W_DEPRECATED) >>> ; Documented in common.opt >>> +Wdeprecated-array-compare >>> +C++ ObjC++ Var(warn_deprecated_array_compare) Warning >>> +Warn about deprecated comparisons between two operands of array type. >>> + >>> Wdeprecated-copy >>> C++ ObjC++ Var(warn_deprecated_copy) Warning LangEnabledBy(C++ ObjC++, Wextra) >>> Mark implicitly-declared copy operations as deprecated if the class has a >>> diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c >>> index a2398dbe660..1e3a41104d6 100644 >>> --- a/gcc/cp/typeck.c >>> +++ b/gcc/cp/typeck.c >>> @@ -40,6 +40,7 @@ along with GCC; see the file COPYING3. If not see >>> #include "attribs.h" >>> #include "asan.h" >>> #include "gimplify.h" >>> +#include "tree-pretty-print.h" >>> static tree cp_build_addr_expr_strict (tree, tsubst_flags_t); >>> static tree cp_build_function_call (tree, tree, tsubst_flags_t); >>> @@ -4725,6 +4726,21 @@ do_warn_enum_conversions (location_t loc, enum tree_code code, tree type0, >>> } >>> } >>> +/* Warn about C++20 [depr.array.comp] array comparisons: "Equality >>> + and relational comparisons between two operands of array type are >>> + deprecated." */ >>> + >>> +static inline void >>> +do_warn_deprecated_array_compare (location_t location, tree_code code, >>> + tree op0, tree op1) >>> +{ >>> + if (warning_at (location, OPT_Wdeprecated_array_compare, >>> + "comparison between two arrays is deprecated")) >>> + inform (location, "use unary %<+%> which decays operands to pointers " >>> + "or %<&%D[0] %s &%D[0]%> to compare the addresses", >>> + op0, op_symbol_code (code), op1); >>> +} >>> + >>> /* Build a binary-operation expression without default conversions. >>> CODE is the kind of expression to build. >>> LOCATION is the location_t of the operator in the source code. >>> @@ -5289,6 +5305,11 @@ cp_build_binary_op (const op_location_t &location, >>> warning_at (location, OPT_Waddress, >>> "comparison with string literal results in " >>> "unspecified behavior"); >>> + else if (TREE_CODE (TREE_TYPE (orig_op0)) == ARRAY_TYPE >>> + && TREE_CODE (TREE_TYPE (orig_op1)) == ARRAY_TYPE) >>> + do_warn_deprecated_array_compare (location, code, >>> + stripped_orig_op0, >>> + stripped_orig_op1); >>> } >>> build_type = boolean_type_node; >>> @@ -5559,6 +5580,13 @@ cp_build_binary_op (const op_location_t &location, >>> "comparison with string literal results " >>> "in unspecified behavior"); >>> } >>> + else if (TREE_CODE (TREE_TYPE (orig_op0)) == ARRAY_TYPE >>> + && TREE_CODE (TREE_TYPE (orig_op1)) == ARRAY_TYPE >>> + && code != SPACESHIP_EXPR >> >> What happens if you try to compare them with <=>? > > That's always an error so printing a warning is redundant. > > Marek >