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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id i1-20020ac84881000000b003a7ec97c882sm2164008qtq.6.2022.12.23.08.04.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 23 Dec 2022 08:04:37 -0800 (PST) Message-ID: <66eed465-287f-20fc-eb51-c78b26639177@redhat.com> Date: Fri, 23 Dec 2022 11:04:36 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 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> <1c8d0290-8a99-5519-26e5-26424fa96cff@redhat.com> <7af2c937-12ce-61ee-5fdc-6059aca07a2b@idea> From: Jason Merrill In-Reply-To: <7af2c937-12ce-61ee-5fdc-6059aca07a2b@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 12/23/22 10:48, Patrick Palka wrote: > On Thu, 22 Dec 2022, Patrick Palka wrote: > >> On Thu, 22 Dec 2022, Jason Merrill wrote: >> >>> 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. >> >> Aha! I'll try that. > > How does this look? Bootstrapped and regtested on x86_64-pc-linux-gnu. OK. > -- >8 -- > > Subject: [PATCH] c++: get_nsdmi in template context [PR108116] > > 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 build a call to A::~A and check 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 was recently > changed by r12-6897-gdec8d0e5fa00ceb2) which expr_noexcept_p doesn't > expect, and we crash. > > This patch fixes this by clearing processing_template_decl before > the call to break_out_target_exprs from get_nsdmi. And since it more > generally seems we shouldn't be seeing (or producing) non-templated > trees from break_out_target_exprs, this patch also adds an assert to > that effect. > > PR c++/108116 > > gcc/cp/ChangeLog: > > * constexpr.cc (maybe_constant_value): Clear > processing_template_decl before calling break_out_target_exprs. > * init.cc (get_nsdmi): Likewise. > * tree.cc (break_out_target_exprs): Assert processing_template_decl > is cleared. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp0x/nsdmi-template24.C: New test. > --- > gcc/cp/constexpr.cc | 4 ++++ > gcc/cp/init.cc | 4 ++++ > gcc/cp/tree.cc | 4 ++++ > gcc/testsuite/g++.dg/cpp0x/nsdmi-template24.C | 22 +++++++++++++++++++ > 4 files changed, 34 insertions(+) > create mode 100644 gcc/testsuite/g++.dg/cpp0x/nsdmi-template24.C > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc > index d99c49bdbe2..414af7a6d4c 100644 > --- a/gcc/cp/constexpr.cc > +++ b/gcc/cp/constexpr.cc > @@ -8507,6 +8507,10 @@ maybe_constant_value (tree t, tree decl /* = NULL_TREE */, > r = *cached; > if (r != t) > { > + /* Clear processing_template_decl for sake of break_out_target_exprs; > + entries in the cv_cache are non-templated. */ > + processing_template_decl_sentinel ptds; > + > r = break_out_target_exprs (r, /*clear_loc*/true); > protected_set_expr_location (r, EXPR_LOCATION (t)); > } > diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc > index 73e6547c076..b49a7ca9169 100644 > --- a/gcc/cp/init.cc > +++ b/gcc/cp/init.cc > @@ -670,6 +670,10 @@ get_nsdmi (tree member, bool in_ctor, tsubst_flags_t complain) > current_class_ptr = build_address (current_class_ref); > } > > + /* Clear processing_template_decl for sake of break_out_target_exprs; > + INIT is always non-templated. */ > + 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/cp/tree.cc b/gcc/cp/tree.cc > index 33bde16f128..faf01616f87 100644 > --- a/gcc/cp/tree.cc > +++ b/gcc/cp/tree.cc > @@ -3342,6 +3342,10 @@ break_out_target_exprs (tree t, bool clear_location /* = false */) > static int target_remap_count; > static splay_tree target_remap; > > + /* We shouldn't be called on templated trees, nor do we want to > + produce them. */ > + gcc_checking_assert (!processing_template_decl); > + > if (!target_remap_count++) > target_remap = splay_tree_new (splay_tree_compare_pointers, > /*splay_tree_delete_key_fn=*/NULL, > 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{}; > +};