Hi! The following testcase fails due to ODR warnings starting with the r16-3233 change (P2115R0 PR120503 implementation).
The problem is that for C++20 we mangle differently the anonymous union at the class scope from C++17, in C++17 the unnamed enumeration that has an enumerator as a name for linkage purposes before it is counted as TYPE_UNNAMED_P in nested_anon_class_index, but for C++20 it is not, therefore the ODR warning. While the term defined in https://eel.is/c++draft/dcl.enum#12.sentence-2 is defined for all enum types, its only use in https://eel.is/c++draft/basic.link#4.5 is solely for enumeration types at namespace scope, changing anything for those at class scope or block scope has undesirable ABI consequences. Fixed thusly, bootstrapped/regtested on x86_64-linux, ok for trunk? Or shall I change the function name too or add TYPE_NAMESPACE_SCOPE_P checks next to the enum_with_enumerator_for_linkage_p calls? 2025-12-01 Jakub Jelinek <[email protected]> PR c++/122905 * decl.cc (enum_with_enumerator_for_linkage_p): Only return true for namespace scope types. * g++.dg/lto/pr122905.h: New file. * g++.dg/lto/pr122905_0.C: New test. * g++.dg/lto/pr122905_1.C: New test. --- gcc/cp/decl.cc.jj 2025-11-29 12:40:36.124343863 +0100 +++ gcc/cp/decl.cc 2025-11-29 13:26:00.076837722 +0100 @@ -18754,7 +18754,7 @@ start_enum (tree name, tree enumtype, tr } /* Returns true if TYPE is an enum that uses an enumerator name for - linkage purposes. */ + linkage purposes at namespace scope. */ bool enum_with_enumerator_for_linkage_p (tree type) @@ -18762,7 +18762,8 @@ enum_with_enumerator_for_linkage_p (tree return (cxx_dialect >= cxx20 && UNSCOPED_ENUM_P (type) && TYPE_ANON_P (type) - && TYPE_VALUES (type)); + && TYPE_VALUES (type) + && TYPE_NAMESPACE_SCOPE_P (type)); } /* After processing and defining all the values of an enumeration type, --- gcc/testsuite/g++.dg/lto/pr122905.h.jj 2025-11-29 13:21:33.734480975 +0100 +++ gcc/testsuite/g++.dg/lto/pr122905.h 2025-11-29 13:19:27.037689730 +0100 @@ -0,0 +1,9 @@ +struct A { + typedef char *B; + struct C { C (B x) {} }; + C c; + enum { D = 15 }; + union { char e[16]; }; + A (const char *x) : c {e} {} +}; +A foo (); --- gcc/testsuite/g++.dg/lto/pr122905_0.C.jj 2025-11-29 13:21:36.455433539 +0100 +++ gcc/testsuite/g++.dg/lto/pr122905_0.C 2025-11-29 13:25:05.606787318 +0100 @@ -0,0 +1,16 @@ +/* PR c++/122905 */ +/* { dg-lto-do link } */ +/* { dg-lto-options { { -O2 -flto -std=c++20 } } } */ + +#include "pr122905.h" + +A +foo () +{ + return "foo"; +} + +int +main () +{ +} --- gcc/testsuite/g++.dg/lto/pr122905_1.C.jj 2025-11-29 13:21:39.259384657 +0100 +++ gcc/testsuite/g++.dg/lto/pr122905_1.C 2025-11-29 13:25:20.765523054 +0100 @@ -0,0 +1,5 @@ +// { dg-options "-O2 -flto -std=c++17" } + +#include "pr122905.h" + +volatile auto v = foo (); Jakub
