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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id bj42-20020a05620a192a00b006bb82221013sm1071399qkb.0.2022.12.22.14.03.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 Dec 2022 14:03:26 -0800 (PST) Message-ID: <1c8d0290-8a99-5519-26e5-26424fa96cff@redhat.com> Date: Thu, 22 Dec 2022 17:03:25 -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> <3104f611-2ac9-5a79-583d-957f2a8ac8e5@redhat.com> <4383deb5-17f8-eff5-1e5f-e05995b6b5d5@idea> From: Jason Merrill In-Reply-To: <4383deb5-17f8-eff5-1e5f-e05995b6b5d5@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 16:41, Patrick Palka wrote: > On Thu, 22 Dec 2022, Jason Merrill wrote: > >> 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. > > Ah, sounds good. > >> >> 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. > > *nod* > >> >>> [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. > > Unfortunately we'd trigger that assert from maybe_constant_value, which > potentially calls b_o_t_e with processing_template_decl set. maybe_constant_value could also clear processing_template_decl; entries in cv_cache are non-templated. >>>>> 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{}; >>>>> +}; >>>> >>>> >>> >> >> >