Re: [pushed] c++: __integer_pack with class argument [PR111357]

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Sep 12, 2023 at 01:34:43PM -0400, Marek Polacek via Gcc-patches wrote:
> On Tue, Sep 12, 2023 at 01:27:44PM -0400, Jason Merrill via Gcc-patches wrote:
> > Tested x86_64-pc-linux-gnu, applying to trunk.
> > 
> > -- 8< --
> > 
> > The argument might not already be an integer.
> > 
> > 	PR c++/111357
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* pt.cc (expand_integer_pack): Convert argument to int.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* g++.dg/ext/integer-pack7.C: New test.
> > ---
> >  gcc/cp/pt.cc                             |  2 ++
> >  gcc/testsuite/g++.dg/ext/integer-pack7.C | 38 ++++++++++++++++++++++++
> >  2 files changed, 40 insertions(+)
> >  create mode 100644 gcc/testsuite/g++.dg/ext/integer-pack7.C
> > 
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index 838179d5fe3..b583c11eb99 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -3793,6 +3793,8 @@ expand_integer_pack (tree call, tree args, tsubst_flags_t complain,
> >      }
> >    else
> >      {
> > +      hi = perform_implicit_conversion_flags (integer_type_node, hi, complain,
> > +					      LOOKUP_IMPLICIT);
> 
> FWIW, we have perform_implicit_conversion for this.

Is it correct to convert exactly to integer_type_node though?
Consider
#include <utility>

using std::integer_sequence;
using std::make_integer_sequence;

template<long... V>
void g(integer_sequence<long,V...>)
{}

template<typename ...T>
struct c1
{
  static constexpr int value = 1;
  constexpr operator int() { return value; } 
  constexpr operator long() { return value + 1; }
};
template<typename T>
struct R
{
	using S = make_integer_sequence<long,c1<T>{}>;

	R() noexcept(noexcept(g(S())))
	{}
};
int main()
{
        R<int>();
}
Shouldn't that invoke c1<T>{}.operator long() rather than operator int()?
I thought the conversion was supposed to be done a few lines earlier,
instead of doing
          CALL_EXPR_ARG (call, 0) = hi;
do
          CALL_EXPR_ARG (call, 0)
	    = perform_implicit_conversion_flags (TREE_TYPE (ohi), hi,
						 complain, LOOKUP_IMPLICIT);
or tsubst that TREE_TYPE (ohi) as well?  I.e. convert to type of the
template parameter.

	Jakub