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[130.44.146.16]) by smtp.gmail.com with ESMTPSA id jt4-20020a05621427e400b00699047948besm2646817qvb.59.2024.04.02.10.15.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 Apr 2024 10:15:01 -0700 (PDT) Message-ID: <0edab1e1-8cf3-41fe-a220-30930b302a41@redhat.com> Date: Tue, 2 Apr 2024 13:15:00 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] c++: make __is_array return false for T[0] [PR114479] To: Marek Polacek , GCC Patches References: <20240401175034.44681-1-polacek@redhat.com> From: Jason Merrill In-Reply-To: <20240401175034.44681-1-polacek@redhat.com> 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=-12.3 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_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 4/1/24 13:50, Marek Polacek wrote: > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > -- >8 -- > When we switched to using the __is_array built-in trait to implement > std::is_array in r14-6623-g7fd9c349e45534, we started saying that > T[0] is an array. There are various opinions as to whether that is > the best answer, but it seems prudent to keep the GCC 13 result. > > PR c++/114479 > > gcc/cp/ChangeLog: > > * semantics.cc (trait_expr_value) : Return false > for zero-sized arrays. > > gcc/testsuite/ChangeLog: > > * g++.dg/ext/is_array.C: Extend. > --- > gcc/cp/semantics.cc | 4 +++- > gcc/testsuite/g++.dg/ext/is_array.C | 12 ++++++++++++ > 2 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc > index 9838331d2a9..f561c119dfd 100644 > --- a/gcc/cp/semantics.cc > +++ b/gcc/cp/semantics.cc > @@ -12439,7 +12439,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2) > return CP_AGGREGATE_TYPE_P (type1); > > case CPTK_IS_ARRAY: > - return type_code1 == ARRAY_TYPE; > + return (type_code1 == ARRAY_TYPE > + /* We don't want to report T[0] as being an array type. */ Please elaborate that this is for compatibility with an implementation of is_array by template argument deduction, because compute_array_index_type_loc rejects a zero-size array in SFINAE context. OK with that adjustment. > + && !(TYPE_SIZE (type1) && integer_zerop (TYPE_SIZE (type1)))); > > case CPTK_IS_ASSIGNABLE: > return is_xible (MODIFY_EXPR, type1, type2); > diff --git a/gcc/testsuite/g++.dg/ext/is_array.C b/gcc/testsuite/g++.dg/ext/is_array.C > index f1a6e08b87a..84993266629 100644 > --- a/gcc/testsuite/g++.dg/ext/is_array.C > +++ b/gcc/testsuite/g++.dg/ext/is_array.C > @@ -1,4 +1,5 @@ > // { dg-do compile { target c++11 } } > +// { dg-options "" } > > #define SA(X) static_assert((X),#X) > > @@ -10,18 +11,29 @@ > > class ClassType { }; > > +constexpr int sz0 = 0; > +constexpr int sz2 = 2; > + > SA_TEST_CATEGORY(__is_array, int[2], true); > SA_TEST_CATEGORY(__is_array, int[], true); > +SA_TEST_CATEGORY(__is_array, int[0], false); > SA_TEST_CATEGORY(__is_array, int[2][3], true); > SA_TEST_CATEGORY(__is_array, int[][3], true); > +SA_TEST_CATEGORY(__is_array, int[0][3], false); > +SA_TEST_CATEGORY(__is_array, int[3][0], false); > SA_TEST_CATEGORY(__is_array, float*[2], true); > SA_TEST_CATEGORY(__is_array, float*[], true); > SA_TEST_CATEGORY(__is_array, float*[2][3], true); > SA_TEST_CATEGORY(__is_array, float*[][3], true); > SA_TEST_CATEGORY(__is_array, ClassType[2], true); > SA_TEST_CATEGORY(__is_array, ClassType[], true); > +SA_TEST_CATEGORY(__is_array, ClassType[0], false); > SA_TEST_CATEGORY(__is_array, ClassType[2][3], true); > SA_TEST_CATEGORY(__is_array, ClassType[][3], true); > +SA_TEST_CATEGORY(__is_array, ClassType[0][3], false); > +SA_TEST_CATEGORY(__is_array, ClassType[2][0], false); > +SA_TEST_CATEGORY(__is_array, int[sz2], true); > +SA_TEST_CATEGORY(__is_array, int[sz0], false); > > // Sanity check. > SA_TEST_CATEGORY(__is_array, ClassType, false); > > base-commit: bba118db3f63cb1e3953a014aa3ac2ad89908950