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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id q27-20020a37f71b000000b006cec8001bf4sm973223qkj.26.2022.12.22.13.33.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 Dec 2022 13:33:04 -0800 (PST) Message-ID: <3104f611-2ac9-5a79-583d-957f2a8ac8e5@redhat.com> Date: Thu, 22 Dec 2022 16:33:03 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH] c++: get_nsdmi in template context [PR108116] To: Patrick Palka Cc: gcc-patches@gcc.gnu.org References: <20221221145254.389983-1-ppalka@redhat.com> <9f0509b3-abd3-2d26-2264-183cc1cf4b11@idea> From: Jason Merrill In-Reply-To: <9f0509b3-abd3-2d26-2264-183cc1cf4b11@idea> 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=-13.0 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_NONE,RCVD_IN_MSPIKE_H2,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 12/22/22 11:31, Patrick Palka wrote: > On Wed, 21 Dec 2022, Jason Merrill wrote: > >> On 12/21/22 09:52, Patrick Palka wrote: >>> Here during ahead of time checking of C{}, we indirectly call get_nsdmi >>> for C::m from finish_compound_literal, which in turn calls >>> break_out_target_exprs for C::m's (non-templated) initializer, during >>> which we end up building a call to A::~A and checking expr_noexcept_p >>> for it (from build_vec_delete_1). But this is all done with >>> processing_template_decl set, so the built A::~A call is templated >>> (whose form r12-6897-gdec8d0e5fa00ceb2 recently changed) which >>> expr_noexcept_p doesn't expect and we crash. >>> >>> In r10-6183-g20afdcd3698275 we fixed a similar issue by guarding a >>> expr_noexcept_p call with !processing_template_decl, which works here >>> too. But it seems to me since the initializer we obtain in get_nsdmi is >>> always non-templated, it should be calling break_out_target_exprs with >>> processing_template_decl cleared since otherwise the function might end >>> up mixing templated and non-templated trees. >>> >>> I'm not sure about this though, perhaps this is not the best fix here. >>> Alternatively, when processing_template_decl we could make get_nsdmi >>> avoid calling break_out_target_exprs at all or something. Additionally, >>> perhaps break_out_target_exprs should be a no-op more generally when >>> processing_template_decl since we shouldn't see any TARGET_EXPRs inside >>> a template? >> >> Hmm. >> >> Any time we would call break_out_target_exprs we're dealing with non-dependent >> expressions; if we're in a template, we're building up an initializer or a >> call that we'll soon throw away, just for the purpose of checking or type >> computation. >> >> Furthermore, as you say, the argument is always a non-template tree, whether >> in get_nsdmi or convert_default_arg. So having processing_template_decl >> cleared would be correct. >> >> I don't think we can get away with not calling break_out_target_exprs at all >> in a template; if nothing else, we would lose immediate invocation expansion. >> However, we could probably skip the bot_manip tree walk, which should avoid >> the problem. >> >> Either way we end up returning non-template trees, as we do now, and callers >> have to deal with transient CONSTRUCTORs containing such (as we do in >> massage_init_elt). > > Ah I see, makes sense. > >> >> Does convert_default_arg not run into the same problem, e.g. when calling >> >> void g(B = {0}); > > In practice it seems not, because we don't call convert_default_arg > when processing_template_decl is set (verified with an assert to > that effect). In build_over_call for example we exit early when > processing_template_decl is set, and return a templated CALL_EXPR > that doesn't include default arguments at all. A consequence of > this is that we don't reject ahead of time a call that would use > an ill-formed dependent default argument, e.g. > > template > void g(B = T{0}); > > template > void f() { > g(); > } > > since the default argument instantiation would be the responsibility > of convert_default_arg. > > Thinking hypothetically here, if we do in the future want to include default > arguments in the templated form of a CALL_EXPR, We definitely do not want to; the templated form should be as close as possible to the source. We might want to perform non-dependent conversions to get any errors (such as this one) before throwing away the result. Which would be parallel to what we currently do in calling get_nsdmi, and would want the same behavior. > [snip] > shall we go with the original approach to clear > processing_template_decl directly from get_nsdmi? OK, but then we should also checking_assert !processing_template_decl in b_o_t_e. Jason >> ? >> >>> Bootstrapped and regtested on x86_64-pc-linux-gnu. >>> >>> PR c++/108116 >>> >>> gcc/cp/ChangeLog: >>> >>> * init.cc (get_nsdmi): Clear processing_template_decl before >>> processing the non-templated initializer. >>> >>> gcc/testsuite/ChangeLog: >>> >>> * g++.dg/cpp0x/nsdmi-template24.C: New test. >>> --- >>> gcc/cp/init.cc | 8 ++++++- >>> gcc/testsuite/g++.dg/cpp0x/nsdmi-template24.C | 22 +++++++++++++++++++ >>> 2 files changed, 29 insertions(+), 1 deletion(-) >>> create mode 100644 gcc/testsuite/g++.dg/cpp0x/nsdmi-template24.C >>> >>> diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc >>> index 73e6547c076..c4345ebdaea 100644 >>> --- a/gcc/cp/init.cc >>> +++ b/gcc/cp/init.cc >>> @@ -561,7 +561,8 @@ perform_target_ctor (tree init) >>> return init; >>> } >>> -/* Return the non-static data initializer for FIELD_DECL MEMBER. */ >>> +/* Return the non-static data initializer for FIELD_DECL MEMBER. >>> + The initializer returned is always non-templated. */ >>> static GTY((cache)) decl_tree_cache_map *nsdmi_inst; >>> @@ -670,6 +671,11 @@ get_nsdmi (tree member, bool in_ctor, tsubst_flags_t >>> complain) >>> current_class_ptr = build_address (current_class_ref); >>> } >>> + /* Since INIT is always non-templated clear processing_template_decl >>> + before processing it so that we don't interleave templated and >>> + non-templated trees. */ >>> + processing_template_decl_sentinel ptds; >>> + >>> /* Strip redundant TARGET_EXPR so we don't need to remap it, and >>> so the aggregate init code below will see a CONSTRUCTOR. */ >>> bool simple_target = (init && SIMPLE_TARGET_EXPR_P (init)); >>> diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi-template24.C >>> b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template24.C >>> new file mode 100644 >>> index 00000000000..202c67d7321 >>> --- /dev/null >>> +++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template24.C >>> @@ -0,0 +1,22 @@ >>> +// PR c++/108116 >>> +// { dg-do compile { target c++11 } } >>> + >>> +#include >>> + >>> +struct A { >>> + A(int); >>> + ~A(); >>> +}; >>> + >>> +struct B { >>> + B(std::initializer_list); >>> +}; >>> + >>> +struct C { >>> + B m{0}; >>> +}; >>> + >>> +template >>> +void f() { >>> + C c = C{}; >>> +}; >> >> >