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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id bp13-20020a05620a458d00b006fefa5f7fc9sm1042068qkb.134.2022.12.22.14.41.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Dec 2022 14:41:12 -0800 (PST) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Thu, 22 Dec 2022 17:41:11 -0500 (EST) To: Jason Merrill cc: Patrick Palka , gcc-patches@gcc.gnu.org Subject: Re: [PATCH] c++: get_nsdmi in template context [PR108116] In-Reply-To: <1c8d0290-8a99-5519-26e5-26424fa96cff@redhat.com> Message-ID: 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> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-13.9 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_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 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. > > > > > > > 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{}; > > > > > > +}; > > > > > > > > > > > > > > > > > > > > > > > >