{"id":2230497,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2230497/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/tencent_6643D30414E51F9CE20CC76E6C2C65AB3D05@qq.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/1.1/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null},"msgid":"","date":"2026-04-29T19:22:49","name":"[v5] c++, contracts: fix testsuite basic.contract.eval.p8 failed","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"bf3440b2f66edf7e7c27accbe0a24b9568d180e0","submitter":{"id":89506,"url":"http://patchwork.ozlabs.org/api/1.1/people/89506/?format=json","name":"yxj-github-437","email":"2457369732@qq.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/tencent_6643D30414E51F9CE20CC76E6C2C65AB3D05@qq.com/mbox/","series":[{"id":502139,"url":"http://patchwork.ozlabs.org/api/1.1/series/502139/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=502139","date":"2026-04-29T19:22:49","name":"[v5] c++, contracts: fix testsuite basic.contract.eval.p8 failed","version":5,"mbox":"http://patchwork.ozlabs.org/series/502139/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2230497/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2230497/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=qq.com header.i=@qq.com header.a=rsa-sha256\n header.s=s201512 header.b=H+Ndphtf;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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If this is supposed to improve the test in\n>>> [basic.contract.eval]/8, then I don't see how, since with this patch\n>>> we emit the error twice:\n>>>\n>>> q.C:3:3: error: contract condition is not constant\n>>> 3 | contract_assert((++const_cast(i), true));\n>>> | ^~~~~~~~~~~~~~~\n>>> q.C:3:3: error: contract condition is not constant\n>>>\n>>> instead of just once as before. That doesn't seem like an improvement.\n>>\n>> Yes, the patch was wrong.The reason for the test case failure may be that\n>> constexpr_call did not cache contract violation information.\n>> The new patch as following.\n>>\n>> ----------------8<-----------------\n>>\n>> I noticed that the following code passed.\n>>\n>> 1 | consteval void foo( auto x ) pre( false ) { return x; }\n>> 2 |\n>> 3 | static_assert (foo( 1 ) == 1, \"\");\n>> 4 |\n>> 5 | int main() {\n>> 6 | foo( 1 );\n>> 7 | }\n>>\n>> However, the code has a contract violation.\n>> In constexpr_call, the result will be cached, but not cache the\n>> existence of contract violations.\n>>\n>> gcc/cp/ChangeLog:\n>> * constexpr.cc (cxx_eval_constant_expression): cache failed or\n>> no constant contract statement\n>\n> I think it would be simpler to set cacheable to false if there are\n> contract violations.\n\nIt's great! The change is very small.\nAnd I notice that:\n\nbasic.contract.eval.p8.C: In function 'int main()':\nbasic.contract.eval.p8.C:8:30: error: contract predicate is false in constant expression\n 8 | consteval void foo( auto x ) pre( false ) {}\n | ^~~~~~~~~~~~\nbasic.contract.eval.p8.C:11:6: error: call to consteval function 'foo(42)' is not a constant expression\n 11 | foo( 42 ); // { dg-error {call to consteval function 'foo\\(42\\)' is not a constant expression} }\n | ~~~^~~~~~\nbasic.contract.eval.p8.C:8:30: error: contract predicate is false in constant expression\n 8 | consteval void foo( auto x ) pre( false ) {}\n | ^~~~~~~~~~~~\n\nThe error report abort contract violations appeared twice. It's expected?\nIf it only needs to be reported once, consider adding the following code in the function `check_for_failed_contracts`.\n\n if (!ctx->quiet)\n return error;\n\nHow abort it?\n\n----------------8<-----------------\n\nI noticed that the following code passed.\n\n1 | consteval void foo( auto x ) pre( false ) { return x; }\n2 |\n3 | static_assert (foo( 1 ) == 1, \"\");\n4 |\n5 | int main() {\n6 | foo( 1 );\n7 | }\n\nHowever, the code has contract violations.\nIn constexpr_call, a result with contract violations should\nnot be cached.\n\ngcc/cp/ChangeLog:\n\t* constexpr.cc (cxx_eval_constant_expression): donot cache\n\tresult with contract violation.\ngcc/testsuite/ChangeLog:\n\t* g++.dg/contracts/cpp26/basic.contract.eval.p8-3.C: New\n---\n gcc/cp/constexpr.cc | 4 ++++\n .../contracts/cpp26/basic.contract.eval.p8-3.C | 15 +++++++++++++++\n 2 files changed, 19 insertions(+)\n create mode 100644 gcc/testsuite/g++.dg/contracts/cpp26/basic.contract.eval.p8-3.C\n\n--\n2.43.0","diff":"diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc\nindex a593b66dd41..efb7a42014b 100644\n--- a/gcc/cp/constexpr.cc\n+++ b/gcc/cp/constexpr.cc\n@@ -4639,6 +4639,10 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,\n \t /* Only cache a permitted result of a constant expression. */\n \t if (cacheable && !reduced_constant_expression_p (result))\n \t cacheable = false;\n+\n+\t /* Only cache a result without contract violations */\n+\t if (cacheable && ctx->global->contract_statement)\n+\t cacheable = false;\n \t}\n else\n \t/* Couldn't get a function copy to evaluate. */\ndiff --git a/gcc/testsuite/g++.dg/contracts/cpp26/basic.contract.eval.p8-3.C b/gcc/testsuite/g++.dg/contracts/cpp26/basic.contract.eval.p8-3.C\nnew file mode 100644\nindex 00000000000..869d7dc35e6\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/contracts/cpp26/basic.contract.eval.p8-3.C\n@@ -0,0 +1,15 @@\n+// basic.contract.eval/p8\n+// If a contract violation occurs in a context that is manifestly\n+// constant-evaluated ([expr.const]), and the evaluation semantic is a\n+// terminating semantic, the program is ill-formed.\n+// { dg-do compile { target c++23 } }\n+// { dg-additional-options \"-fcontracts \" }\n+\n+consteval auto foo( auto x ) pre( false ) { return x; }\n+// { dg-error {contract predicate is false in constant expression} \"\" { target *-*-* } .-1 }\n+\n+static_assert(foo( 42 ) == 42, \"\");\n+\n+int main() {\n+ foo( 42 ); // { dg-error {call to consteval function 'foo\\(42\\)' is not a constant expression} }\n+}\n","prefixes":["v5"]}