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[2603:7000:9500:34a5::1db4]) by smtp.gmail.com with ESMTPSA id f8-20020a05620a15a800b007671b599cf5sm3125019qkk.40.2023.07.13.11.54.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Jul 2023 11:54:27 -0700 (PDT) Date: Thu, 13 Jul 2023 14:54:25 -0400 From: Marek Polacek To: Jason Merrill Cc: GCC Patches Subject: [PATCH v2] c++: wrong error with static constexpr var in tmpl [PR109876] Message-ID: References: <20230526231805.406578-1-polacek@redhat.com> <460bf6aa-a336-7ac2-0434-c8dcfd8d0b87@redhat.com> MIME-Version: 1.0 In-Reply-To: <460bf6aa-a336-7ac2-0434-c8dcfd8d0b87@redhat.com> User-Agent: Mutt/2.2.9 (2022-11-12) X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-12.5 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,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 List-Id: On Fri, May 26, 2023 at 09:47:10PM -0400, Jason Merrill wrote: > On 5/26/23 19:18, Marek Polacek wrote: > > Since r8-509, we'll no longer create a static temporary var for > > the initializer '{ 1, 2 }' for num in the attached test because > > the code in finish_compound_literal is now guarded by > > '&& fcl_context == fcl_c99' but it's fcl_functional here. This > > causes us to reject num as non-constant when evaluating it in > > a template. > > > > Jason's idea was to treat num as value-dependent even though it > > actually isn't. This patch implements that suggestion. > > > > The is_really_empty_class check is sort of non-obvious but the > > comment should explain why I added it. > > > > Co-authored-by: Jason Merrill > > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > > > PR c++/109876 > > > > gcc/cp/ChangeLog: > > > > * pt.cc (value_dependent_expression_p) : Treat a > > constexpr-declared non-constant variable as value-dependent. > > > > gcc/testsuite/ChangeLog: > > > > * g++.dg/cpp0x/constexpr-template12.C: New test. > > * g++.dg/cpp1z/constexpr-template1.C: New test. > > --- > > gcc/cp/pt.cc | 12 ++++++ > > .../g++.dg/cpp0x/constexpr-template12.C | 38 +++++++++++++++++++ > > .../g++.dg/cpp1z/constexpr-template1.C | 25 ++++++++++++ > > 3 files changed, 75 insertions(+) > > create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C > > create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C > > > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc > > index 7fb3e75bceb..38fd8070705 100644 > > --- a/gcc/cp/pt.cc > > +++ b/gcc/cp/pt.cc > > @@ -27969,6 +27969,18 @@ value_dependent_expression_p (tree expression) > > else if (TYPE_REF_P (TREE_TYPE (expression))) > > /* FIXME cp_finish_decl doesn't fold reference initializers. */ > > return true; > > + /* We have a constexpr variable and we're processing a template. When > > + there's lifetime extension involved (for which finish_compound_literal > > + used to create a temporary), we'll not be able to evaluate the > > + variable until instantiating, so pretend it's value-dependent. */ > > + else if (DECL_DECLARED_CONSTEXPR_P (expression) > > + && !TREE_CONSTANT (expression) > > + /* When there's nothing to initialize, we'll never mark the > > + VAR_DECL TREE_CONSTANT, therefore it would remain > > + value-dependent and we wouldn't instantiate. */ Sorry it's taken so long to get back to this. > Interesting. Can we change that (i.e. mark it TREE_CONSTANT) rather than > work around it here? I think we can. Maybe as in the below: -- >8 -- Since r8-509, we'll no longer create a static temporary var for the initializer '{ 1, 2 }' for num in the attached test because the code in finish_compound_literal is now guarded by '&& fcl_context == fcl_c99' but it's fcl_functional here. This causes us to reject num as non-constant when evaluating it in a template. Jason's idea was to treat num as value-dependent even though it actually isn't. This patch implements that suggestion. We weren't marking objects whose type is an empty class type constant. This patch changes that so that v_d_e_p doesn't need to check is_really_empty_class. Co-authored-by: Jason Merrill Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? PR c++/109876 gcc/cp/ChangeLog: * decl.cc (cp_finish_decl): Set TREE_CONSTANT when initializing an object of empty class type. * pt.cc (value_dependent_expression_p) : Treat a constexpr-declared non-constant variable as value-dependent. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/constexpr-template12.C: New test. * g++.dg/cpp1z/constexpr-template1.C: New test. * g++.dg/cpp1z/constexpr-template2.C: New test. --- gcc/cp/decl.cc | 13 +++++-- gcc/cp/pt.cc | 7 ++++ .../g++.dg/cpp0x/constexpr-template12.C | 38 +++++++++++++++++++ .../g++.dg/cpp1z/constexpr-template1.C | 25 ++++++++++++ .../g++.dg/cpp1z/constexpr-template2.C | 25 ++++++++++++ 5 files changed, 105 insertions(+), 3 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc index 60f107d50c4..792ab330dd0 100644 --- a/gcc/cp/decl.cc +++ b/gcc/cp/decl.cc @@ -8200,7 +8200,6 @@ void cp_finish_decl (tree decl, tree init, bool init_const_expr_p, tree asmspec_tree, int flags) { - tree type; vec *cleanups = NULL; const char *asmspec = NULL; int was_readonly = 0; @@ -8220,7 +8219,7 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p, /* Parameters are handled by store_parm_decls, not cp_finish_decl. */ gcc_assert (TREE_CODE (decl) != PARM_DECL); - type = TREE_TYPE (decl); + tree type = TREE_TYPE (decl); if (type == error_mark_node) return; @@ -8410,7 +8409,7 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p, if (decl_maybe_constant_var_p (decl) /* FIXME setting TREE_CONSTANT on refs breaks the back end. */ && !TYPE_REF_P (type)) - TREE_CONSTANT (decl) = 1; + TREE_CONSTANT (decl) = true; } /* This is handled mostly by gimplify.cc, but we have to deal with not warning about int x = x; as it is a GCC extension to turn off @@ -8421,6 +8420,14 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p, && !warning_enabled_at (DECL_SOURCE_LOCATION (decl), OPT_Winit_self)) suppress_warning (decl, OPT_Winit_self); } + else if (VAR_P (decl) + && COMPLETE_TYPE_P (type) + && !TYPE_REF_P (type) + && !dependent_type_p (type) + && is_really_empty_class (type, /*ignore_vptr*/false)) + /* We have no initializer but there's nothing to initialize anyway. + Treat DECL as constant due to c++/109876. */ + TREE_CONSTANT (decl) = true; if (flag_openmp && TREE_CODE (decl) == FUNCTION_DECL diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index fa15b75b9c5..255d18b9539 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -27983,6 +27983,13 @@ value_dependent_expression_p (tree expression) else if (TYPE_REF_P (TREE_TYPE (expression))) /* FIXME cp_finish_decl doesn't fold reference initializers. */ return true; + /* We have a constexpr variable and we're processing a template. When + there's lifetime extension involved (for which finish_compound_literal + used to create a temporary), we'll not be able to evaluate the + variable until instantiating, so pretend it's value-dependent. */ + else if (DECL_DECLARED_CONSTEXPR_P (expression) + && !TREE_CONSTANT (expression)) + return true; return false; case DYNAMIC_CAST_EXPR: diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C new file mode 100644 index 00000000000..a9e065320c8 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C @@ -0,0 +1,38 @@ +// PR c++/109876 +// { dg-do compile { target c++11 } } + +using size_t = decltype(sizeof 0); + +namespace std { +template struct initializer_list { + const int *_M_array; + size_t _M_len; + constexpr size_t size() const { return _M_len; } +}; +} // namespace std + +constexpr std::initializer_list gnum{2}; + +template struct Array {}; +template void g() +{ + static constexpr std::initializer_list num{2}; + static_assert(num.size(), ""); + Array ctx; + + constexpr Array<1> num1{}; +} + +template +struct Foo +{ + static constexpr std::initializer_list num = { 1, 2 }; + static_assert(num.size(), ""); + Array ctx; +}; + +void +f (Foo<5>) +{ + g<0>(); +} diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C new file mode 100644 index 00000000000..58be046fd36 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C @@ -0,0 +1,25 @@ +// PR c++/109876 +// { dg-do compile { target c++17 } } + +struct Foo {}; +template struct X {}; + +void g() +{ + static constexpr Foo foo; + X x; +} + +template +void f() +{ + static constexpr Foo foo; + X x; +} + +void +h () +{ + f<0>(); + f<1>(); +} diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C new file mode 100644 index 00000000000..5a9a96ba60a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C @@ -0,0 +1,25 @@ +// PR c++/109876 +// { dg-do compile { target c++17 } } + +struct Foo {}; +template struct X {}; + +void g() +{ + static constexpr Foo foo{}; + X x; +} + +template +void f() +{ + static constexpr Foo foo{}; + X x; +} + +void +h () +{ + f<0>(); + f<1>(); +} base-commit: 834f34947b20b18696487fc5d2bccab5ea720351 -- 2.41.0