[Bug libstdc++/110493] New: 'is not a constant expression' for function-local static std::initializer_list<std::string> with fsanitize=undefined

[Bug libstdc++/110493] New: 'is not a constant expression' for function-local static std::initializer_list<std::string> with fsanitize=undefined

[ed at catmur dot uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110493

            Bug ID: 110493
           Summary: 'is not a constant expression' for function-local
                    static std::initializer_list<std::string> with
                    fsanitize=undefined
           Product: gcc
           Version: 12.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ed at catmur dot uk
  Target Milestone: ---

Since 12.3.0, under -fsanitize=undefined -std=c++20:

#include <initializer_list>
#include <string>
void f() {
    static auto a = {std::string()};
}

error: '(((const std::__cxx11::basic_string<char>*)(& <temporary>)) != 0)' is
not a constant expression

Clearly this is an instance of bug 71962, but this is in fairly unexceptional
code and could make ubsan unusable; it's not obvious that this code should have
anything to do with constant evaluation.

Since it only appears in a point release I would hope it might be possible to
fix in library for this specific case, within <initializer_list>?

[Bug libstdc++/110493] 'is not a constant expression' for function-local static std::initializer_list<std::string> with fsanitize=undefined

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110493

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
std::string::string is a constexpr in C++20 ...

*** This bug has been marked as a duplicate of bug 71962 ***

[Bug libstdc++/110493] 'is not a constant expression' for function-local static std::initializer_list<std::string> with fsanitize=undefined

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110493

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|DUPLICATE                   |---
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=107079
             Status|RESOLVED                    |UNCONFIRMED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually let's reopen this ...

[Bug c++/110493] 'is not a constant expression' for function-local static std::initializer_list<std::string> with fsanitize=undefined

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110493

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|libstdc++                   |c++

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note it was not libstdc++ that changed but the front-end (PR 107079  ).

[Bug c++/110493] 'is not a constant expression' for function-local static std::initializer_list<std::string> with fsanitize=undefined

[ed at catmur dot uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110493

--- Comment #4 from Ed Catmur <ed at catmur dot uk> ---
Ah, thanks. So a workaround is something like:

void f() { static auto a = {((bool*)&(int const&)0, std::string())}; }

That's not too bad, then.