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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id q27-20020a37f71b000000b006cec8001bf4sm2403225qkj.26.2022.12.23.07.48.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Dec 2022 07:48:34 -0800 (PST) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Fri, 23 Dec 2022 10:48:33 -0500 (EST) To: Patrick Palka cc: Jason Merrill , gcc-patches@gcc.gnu.org Subject: Re: [PATCH] c++: get_nsdmi in template context [PR108116] In-Reply-To: Message-ID: <7af2c937-12ce-61ee-5fdc-6059aca07a2b@idea> 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, 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. -- >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{}; +}; -- 2.39.0.95.g7c2ef319c5