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[130.44.146.16]) by smtp.gmail.com with ESMTPSA id j3-20020a05620a146300b00767660afed5sm3891269qkl.99.2023.07.25.13.24.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Jul 2023 13:24:41 -0700 (PDT) Message-ID: Date: Tue, 25 Jul 2023 16:24:39 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH] c++: fix ICE with is_really_empty_class [PR110106] To: Marek Polacek Cc: Patrick Palka , GCC Patches References: <20230718211458.858343-1-polacek@redhat.com> <7007162f-c356-cbde-575e-1cbbd545323d@idea> <03d798a6-0951-1d11-5ae4-476e85f5636e@redhat.com> <197c642a-a916-5be4-fe9e-2f0710333c92@redhat.com> From: Jason Merrill In-Reply-To: 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=-12.6 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_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE 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 7/25/23 15:59, Marek Polacek wrote: > On Fri, Jul 21, 2023 at 01:44:17PM -0400, Jason Merrill wrote: >> On 7/20/23 17:58, Marek Polacek wrote: >>> On Thu, Jul 20, 2023 at 03:51:32PM -0400, Marek Polacek wrote: >>>> On Thu, Jul 20, 2023 at 02:37:07PM -0400, Jason Merrill wrote: >>>>> On 7/20/23 14:13, Marek Polacek wrote: >>>>>> On Wed, Jul 19, 2023 at 10:11:27AM -0400, Patrick Palka wrote: >>>>>>> On Tue, 18 Jul 2023, Marek Polacek via Gcc-patches wrote: >>>>>>> >>>>>>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk and branches? >>>>>>> >>>>>>> Looks reasonable to me. >>>>>> >>>>>> Thanks. >>>>>>> Though I wonder if we could also fix this by not checking potentiality >>>>>>> at all in this case? The problematic call to is_rvalue_constant_expression >>>>>>> happens from cp_parser_constant_expression with 'allow_non_constant' != 0 >>>>>>> and with 'non_constant_p' being a dummy out argument that comes from >>>>>>> cp_parser_functional_cast, so the result of is_rvalue_constant_expression >>>>>>> is effectively unused in this case, and we should be able to safely elide >>>>>>> it when 'allow_non_constant && non_constant_p == nullptr'. >>>>>> >>>>>> Sounds plausible. I think my patch could be applied first since it >>>>>> removes a tiny bit of code, then I can hopefully remove the flag below, >>>>>> then maybe go back and optimize the call to is_rvalue_constant_expression. >>>>>> Does that sound sensible? >>>>>> >>>>>>> Relatedly, ISTM the member cp_parser::non_integral_constant_expression_p >>>>>>> is also effectively unused and could be removed? >>>>>> >>>>>> It looks that way. Seems it's only used in cp_parser_constant_expression: >>>>>> 10806 if (allow_non_constant_p) >>>>>> 10807 *non_constant_p = parser->non_integral_constant_expression_p; >>>>>> but that could be easily replaced by a local var. I'd be happy to see if >>>>>> we can actually do away with it. (I wonder why it was introduced and when >>>>>> it actually stopped being useful.) >>>>> >>>>> It was for the C++98 notion of constant-expression, which was more of a >>>>> parser-level notion, and has been supplanted by the C++11 version. I'm >>>>> happy to remove it, and therefore remove the is_rvalue_constant_expression >>>>> call. >>>> >>>> Wonderful. I'll do that next. >>> >>> I found a use of parser->non_integral_constant_expression_p: >>> finish_id_expression_1 can set it to true which then makes >>> a difference in cp_parser_constant_expression in C++98. In >>> cp_parser_constant_expression we set n_i_c_e_p to false, call >>> cp_parser_assignment_expression in which finish_id_expression_1 >>> sets n_i_c_e_p to true, then back in cp_parser_constant_expression >>> we skip the cxx11 block, and set *non_constant_p to true. If I >>> remove n_i_c_e_p, we lose that. This can be seen in init/array60.C. >> >> Sure, we would need to use the C++11 code for C++98 mode, which is likely >> fine but is more uncertain. >> >> It's probably simpler to just ignore n_i_c_e_p for C++11 and up, along with >> Patrick's suggestion of allowing null non_constant_p with true >> allow_non_constant_p. > > Something like this, then? I see that cp_parser_initializer_clause et al > offer further opportunities (because they sometimes use a dummy too) but > this should be a good start. Looks good. Please do update the other callers as well, while you're looking at this. > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > -- >8 -- > It's pointless to call *_rvalue_constant_expression when we're not using > the result. Also apply some drive-by cleanups. > > gcc/cp/ChangeLog: > > * parser.cc (cp_parser_constant_expression): Allow non_constant_p to be > nullptr even when allow_non_constant_p is true. Don't call > _rvalue_constant_expression when not necessary. Move local variable > declarations closer to their first use. > (cp_parser_static_assert): Don't pass a dummy down to > cp_parser_constant_expression. > --- > gcc/cp/parser.cc | 24 +++++++++++------------- > 1 file changed, 11 insertions(+), 13 deletions(-) > > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc > index 5e2b5cba57e..efaa806f107 100644 > --- a/gcc/cp/parser.cc > +++ b/gcc/cp/parser.cc > @@ -10734,11 +10734,6 @@ cp_parser_constant_expression (cp_parser* parser, > bool *non_constant_p /* = NULL */, > bool strict_p /* = false */) > { > - bool saved_integral_constant_expression_p; > - bool saved_allow_non_integral_constant_expression_p; > - bool saved_non_integral_constant_expression_p; > - cp_expr expression; > - > /* It might seem that we could simply parse the > conditional-expression, and then check to see if it were > TREE_CONSTANT. However, an expression that is TREE_CONSTANT is > @@ -10757,10 +10752,12 @@ cp_parser_constant_expression (cp_parser* parser, > will fold this operation to an INTEGER_CST for `3'. */ > > /* Save the old settings. */ > - saved_integral_constant_expression_p = parser->integral_constant_expression_p; > - saved_allow_non_integral_constant_expression_p > + bool saved_integral_constant_expression_p > + = parser->integral_constant_expression_p; > + bool saved_allow_non_integral_constant_expression_p > = parser->allow_non_integral_constant_expression_p; > - saved_non_integral_constant_expression_p = parser->non_integral_constant_expression_p; > + bool saved_non_integral_constant_expression_p > + = parser->non_integral_constant_expression_p; > /* We are now parsing a constant-expression. */ > parser->integral_constant_expression_p = true; > parser->allow_non_integral_constant_expression_p > @@ -10780,6 +10777,7 @@ cp_parser_constant_expression (cp_parser* parser, > For example, cp_parser_initializer_clauses uses this function to > determine whether a particular assignment-expression is in fact > constant. */ > + cp_expr expression; > if (strict_p) > expression = cp_parser_conditional_expression (parser); > else > @@ -10789,7 +10787,8 @@ cp_parser_constant_expression (cp_parser* parser, > = saved_integral_constant_expression_p; > parser->allow_non_integral_constant_expression_p > = saved_allow_non_integral_constant_expression_p; > - if (cxx_dialect >= cxx11) > + if (cxx_dialect >= cxx11 > + && (!allow_non_constant_p || non_constant_p)) > { > /* Require an rvalue constant expression here; that's what our > callers expect. Reference constant expressions are handled > @@ -10803,7 +10802,7 @@ cp_parser_constant_expression (cp_parser* parser, > if (!is_const && !allow_non_constant_p) > require_rvalue_constant_expression (decay); > } > - if (allow_non_constant_p) > + if (allow_non_constant_p && non_constant_p) > *non_constant_p = parser->non_integral_constant_expression_p; > parser->non_integral_constant_expression_p > = saved_non_integral_constant_expression_p; > @@ -16400,12 +16399,11 @@ cp_parser_linkage_specification (cp_parser* parser, tree prefix_attr) > If MEMBER_P, this static_assert is a class member. */ > > static void > -cp_parser_static_assert(cp_parser *parser, bool member_p) > +cp_parser_static_assert (cp_parser *parser, bool member_p) > { > cp_expr condition; > location_t token_loc; > tree message; > - bool dummy; > > /* Peek at the `static_assert' token so we can keep track of exactly > where the static assertion started. */ > @@ -16430,7 +16428,7 @@ cp_parser_static_assert(cp_parser *parser, bool member_p) > condition = > cp_parser_constant_expression (parser, > /*allow_non_constant_p=*/true, > - /*non_constant_p=*/&dummy); > + /*non_constant_p=*/nullptr); > > if (cp_lexer_peek_token (parser->lexer)->type == CPP_CLOSE_PAREN) > { > > base-commit: 6e424febfbcb27c21a7fe3a137e614765f9cf9d2