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)
