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[2603:7000:9500:2e39::1db4]) by smtp.gmail.com with ESMTPSA id o8-20020ac841c8000000b00398313f286dsm9771924qtm.40.2022.10.12.09.27.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Oct 2022 09:27:36 -0700 (PDT) Date: Wed, 12 Oct 2022 12:27:34 -0400 From: Marek Polacek To: Jason Merrill Cc: GCC Patches Subject: [PATCH v2] c++: ICE with VEC_INIT_EXPR and defarg [PR106925] Message-ID: References: <20221011200003.695682-1-polacek@redhat.com> <778ca670-6623-77f9-e941-51302007da64@redhat.com> MIME-Version: 1.0 In-Reply-To: <778ca670-6623-77f9-e941-51302007da64@redhat.com> User-Agent: Mutt/2.2.7 (2022-08-07) 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=-12.4 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,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 Tue, Oct 11, 2022 at 04:28:11PM -0400, Jason Merrill wrote: > On 10/11/22 16:00, Marek Polacek wrote: > > Since r12-8066, in cxx_eval_vec_init we perform expand_vec_init_expr > > while processing the default argument in this test. > > Hmm, why are we calling cxx_eval_vec_init during parsing of the default > argument? In particular, any expansion that depends on the enclosing > function context should be deferred until the default arg is used by a call. I think this is part of the semantic constraints checking [dcl.fct.default]/5 talks about, as in, this doesn't compile even though the default argument is not executed: struct S { S() = delete; }; void foo (S = S()) { } In the test below we parse '= MyVector<1>()' and end up calling mark_used on the implicit "constexpr MyVector<1>::MyVector() noexcept ()" ctor. mark_used calls maybe_instantiate_noexcept. Since the ctor has a DEFERRED_NOEXCEPT, we have to figure out if the ctor should be noexcept or not using get_defaulted_eh_spec. That means walking the members of MyVector. Thus we reach /* Core 1351: If the field has an NSDMI that could throw, the default constructor is noexcept(false). */ and call get_nsdmi on 'data'. There we digest its initializer which is {}. massage_init_elt calls digest_init_r on the {} and produces TARGET_EXPR >>> and the subsequent fold_non_dependent_init leads to cxx_eval_vec_init -> expand_vec_init_expr. I think this is all correct except that the fold_non_dependent_init is somewhat questionable to me; do we really have to fold in order to say if the NSDMI init can throw? Sure, we need to digest the {}, maybe the field's ctors can throw, but I don't know about the folding. > But it's certainly true that the "function_body" test is wrong in this > situation; you might move the c_f_d test into the calculation of that > variable. The patch is OK with that change, but please also answer my > question above. I like that. Before I go ahead and apply, please let me know if the answer above is satisfying. -- >8 -- Since r12-8066, in cxx_eval_vec_init we perform expand_vec_init_expr while processing the default argument in this test. At this point start_preparsed_function hasn't yet set current_function_decl. expand_vec_init_expr then leads to maybe_splice_retval_cleanup which checks DECL_CONSTRUCTOR_P (current_function_decl) without checking that c_f_d is non-null first. It seems correct that c_f_d is null here, so it seems to me that maybe_splice_retval_cleanup should check c_f_d as in the following patch. PR c++/106925 gcc/cp/ChangeLog: * except.cc (maybe_splice_retval_cleanup): Check current_function_decl. Make the bool const. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/initlist-defarg3.C: New test. --- gcc/cp/except.cc | 7 +++++-- gcc/testsuite/g++.dg/cpp0x/initlist-defarg3.C | 13 +++++++++++++ 2 files changed, 18 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/initlist-defarg3.C diff --git a/gcc/cp/except.cc b/gcc/cp/except.cc index b8a85ed0572..a9114a5f7a5 100644 --- a/gcc/cp/except.cc +++ b/gcc/cp/except.cc @@ -1322,9 +1322,12 @@ maybe_splice_retval_cleanup (tree compound_stmt) { /* If we need a cleanup for the return value, add it in at the same level as pushdecl_outermost_localscope. And also in try blocks. */ - bool function_body + const bool function_body = (current_binding_level->level_chain - && current_binding_level->level_chain->kind == sk_function_parms); + && current_binding_level->level_chain->kind == sk_function_parms + /* When we're processing a default argument, c_f_d may not have been + set. */ + && current_function_decl); if ((function_body || current_binding_level->kind == sk_try) && !DECL_CONSTRUCTOR_P (current_function_decl) diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist-defarg3.C b/gcc/testsuite/g++.dg/cpp0x/initlist-defarg3.C new file mode 100644 index 00000000000..5c3e886b306 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/initlist-defarg3.C @@ -0,0 +1,13 @@ +// PR c++/106925 +// { dg-do compile { target c++11 } } + +struct Foo; +template struct __array_traits { typedef Foo _Type[_Nm]; }; +template struct array { + typename __array_traits<_Nm>::_Type _M_elems; +}; +template struct MyVector { array data{}; }; +struct Foo { + float a{0}; +}; +void foo(MyVector<1> = MyVector<1>()); base-commit: fbf423309e103b54f7c9d39b2f7870b9bedfe9d2 -- 2.37.3