https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106599
Bug ID: 106599 Summary: Wrong copy elision in delegating to copy-constructor Product: gcc Version: 12.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: fchelnokov at gmail dot com Target Milestone: --- The following program should be valid: ``` struct A { int v = 0; constexpr A() = default; constexpr A(const A&) : v(1) {} constexpr A(int) : A(A()) {} }; static_assert( A(2).v == 1 ); ``` and is accepted by Clang but not GCC. Online demo: https://gcc.godbolt.org/z/zKoqq3rKW Clang is probably correct here, because http://eel.is/c++draft/class.base.init#7 says: The expression-list or braced-init-list in a mem-initializer is used to initialize the designated subobject (or, in the case of a delegating constructor, the complete class object) according to the initialization rules of [dcl.init] for direct-initialization. So we should use the rules for direct-initialization and http://eel.is/c++draft/dcl.init#general-16.6.2 says: Otherwise, if the initialization is direct-initialization, or if it is copy-initialization where the cv-unqualified version of the source type is the same class as, or a derived class of, the class of the destination, constructors are considered. The applicable constructors are enumerated ([over.match.ctor]), and the best one is chosen through overload resolution ([over.match]). So we need to consider the constructors, and select A(const A&) : v(1)