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Subject: [Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C  -std=gnu++20 
 (test for errors)
Date: Thu, 24 Mar 2022 12:21:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104620

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Reduced testcase for -std=3Dc++23
consteval int foo (int x) { return x; }
consteval int bar () { return 2; }

template <typename T>
constexpr int
qux (int x)
{
  int r =3D 0;
  if consteval
    {
      r +=3D 2 * bar ();
    }
  else
    {
      r +=3D foo (8 * x); // { dg-error "is not a constant expression" }
    }
  if ! consteval
    {
      r +=3D foo (32 * x);// { dg-error "is not a constant expression" }
    }
  if consteval
    {
      r +=3D 32 * bar ();
    }
  return r;
}

The intent of the testcase was to test whether we catch at least some of the
non-dependent consteval calls already during template parsing and so regard=
less
of whether we actually instantiate them or not.
Worst case it will be diagnosed during instantiation, sure.
But x is not type nor value dependent and neither is 8 * x nor 32 * x.
And make_args_non_dependent calls build_non_dependent_arg which will not wr=
ap
say x or 8, but does wrap x * 8 even when both arguments have integral type=
s.
So, either build_non_dependent_arg should be made smarter and not wrap even
simple arithmetics etc. where no C++ template-ish trees appear inside of it=
 and
everything is like in normal non-template-ish code, or we should reconsider
the r12-7264 case because clearly often we can handle NON_DEPENDENT_EXPR ju=
st
fine.=