[Bug c++/108324] New: Temporary not bound to reference in default member initializer destroyed early from parenthesized expression-list initialization of aggregate

[Bug c++/108324] New: Temporary not bound to reference in default member initializer destroyed early from parenthesized expression-list initialization of aggregate

[hstong at ca dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108324

            Bug ID: 108324
           Summary: Temporary not bound to reference in default member
                    initializer destroyed early from parenthesized
                    expression-list initialization of aggregate
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: rejects-valid, wrong-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hstong at ca dot ibm.com
  Target Milestone: ---

While the lifetime-extension rules for temporaries bound to a reference member
differ between braced and parenthesized aggregate initialization, the
full-expression associated with default member initializers used in the
aggregate initialization are the same in both cases ([intro.execution]).

It seems GCC thinks that the parenthesized expression-list case causes
destruction of temporaries from the default member initializer at an earlier
point than in the braced initialization case.

ICC does not have this problem (at least when doing constant expression
evaluation).

Online compiler link: https://godbolt.org/z/aPhffr7xT

### SOURCE (<stdin>):
struct A {
  constexpr A(int x) : x(x) {}
  constexpr ~A() { x = 13; }
  int x;
  constexpr A &ref() { return *this; }
};
struct B {
  const A *ap = &A(42).ref();
};
constexpr int f() { return B{}.ap->x; }
constexpr int g() { return B().ap->x; }

extern char q[f()];
extern char q[42];
extern char k[g()];
extern char k[42];


### COMPILER INVOCATION COMMAND:
g++ -fsyntax-only -std=c++2b -xc++ -


### ACTUAL OUTPUT:
<stdin>:15:16: error: size of array 'k' is not an integral constant-expression
<stdin>:16:13: error: conflicting declaration 'char k [42]'
<stdin>:15:13: note: previous declaration as 'char k [1]'


### EXPECTED OUTPUT:
(Clean compile)


### COMPILER VERSION INFO (g++ -v):
Using built-in specs.
COLLECT_GCC=/opt/wandbox/gcc-head/bin/g++
COLLECT_LTO_WRAPPER=/opt/wandbox/gcc-head/libexec/gcc/x86_64-pc-linux-gnu/13.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../source/configure --prefix=/opt/wandbox/gcc-head
--enable-languages=c,c++ --disable-multilib --without-ppl --without-cloog-ppl
--enable-checking=release --disable-nls --enable-lto
LDFLAGS=-Wl,-rpath,/opt/wandbox/gcc-head/lib,-rpath,/opt/wandbox/gcc-head/lib64,-rpath,/opt/wandbox/gcc-head/lib32
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.0.0 20230106 (experimental) (GCC)

[Bug c++/108324] Temporary not bound to reference in default member initializer destroyed early from parenthesized expression-list initialization of aggregate

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108324

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
MSVC rejects it for the same reason as GCC:

<source>(15): error C2131: expression did not evaluate to a constant
<source>(11): note: a non-constant (sub-)expression was encountered
<source>(16): error C2369: 'k': redefinition; different subscripts
<source>(15): note: see declaration of 'k'

Note clang rejects both array definitions thinking it is a VLA ....