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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/114580] New: Bogus warning on if constexpr
Date: Thu, 04 Apr 2024 10:02:04 +0000
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X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114580

            Bug ID: 114580
           Summary: Bogus warning on if constexpr
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

#include <type_traits>

template <typename T>
void foo ()
{
  if constexpr ((T) std::is_constant_evaluated ())
    ;
}

void
bar ()
{
  foo <bool> ();
}

emits bogus warning with -std=3Dc++17 -Wall.
Once it (incorrectly) warns about
warning: =E2=80=98std::is_constant_evaluated=E2=80=99 always evaluates to f=
alse in a
non-=E2=80=98constexpr=E2=80=99 function [-Wtautological-compare]
and once it correctly warns about
warning: =E2=80=98std::is_constant_evaluated=E2=80=99 always evaluates to t=
rue in =E2=80=98if
constexpr=E2=80=99 [-Wtautological-compare]
on the same line.  In reality, std::is_constant_evaluated () here always
evaluates to true, never to false.=