[Bug c++/94489] New: ICE: unexpected expression ‘std::min’ of kind overload

[Bug c++/94489] New: ICE: unexpected expression ‘std::min’ of kind overload

[bisqwit at iki dot fi]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94489

            Bug ID: 94489
           Summary: ICE: unexpected expression ‘std::min’ of kind overload
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bisqwit at iki dot fi
  Target Milestone: ---

On GCC 9.3.0:

$ g++-9 test5.cc -std=c++2a -g -fconcepts
test5.cc: In instantiation of ‘auto Mul(const T&, const T2&) [with T =
std::array<float, 2>; T2 = std::array<float, 2>]’:
test5.cc:33:62:   required from here
test5.cc:28:117: internal compiler error: unexpected expression ‘std::min’ of
kind overload
   28 |                  return typename arith_result<T,T2>::type {
std::plus<void>(std::get<P>(vec), std::get<P>(val)) ... };
      |                                                                        
                                            ^
0x7f78e300ce0a __libc_start_main
        ../csu/libc-start.c:308

On 10.0.1 20200324 (experimental) [master revision
596c90d3559:023579257f5:906b3eb9df6c577d3f6e9c3ea5c9d7e4d1e90536]:

$ g++-10 test5.cc -std=c++20 -g
test5.cc: In instantiation of ‘auto Mul(const T&, const T2&) [with T =
std::array<float, 2>; T2 = std::array<float, 2>]’:
test5.cc:33:62:   required from here
test5.cc:28:117: internal compiler error: unexpected expression ‘std::min’ of
kind overload
   28 |                  return typename arith_result<T,T2>::type {
std::plus<void>(std::get<P>(vec), std::get<P>(val)) ... };
      |                                                                        
                                            ^
0x63d82b cxx_eval_constant_expression
        ../../src/gcc/cp/constexpr.c:6301
0x637ded cxx_eval_call_expression
        ../../src/gcc/cp/constexpr.c:2055
0x63ad65 cxx_eval_constant_expression
        ../../src/gcc/cp/constexpr.c:5483
0x63ccc2 cxx_eval_indirect_ref
        ../../src/gcc/cp/constexpr.c:4213
0x63ccc2 cxx_eval_constant_expression
        ../../src/gcc/cp/constexpr.c:5704
0x63dbe0 cxx_eval_outermost_constant_expr
        ../../src/gcc/cp/constexpr.c:6502
0x63e5ec cxx_constant_value(tree_node*, tree_node*)
        ../../src/gcc/cp/constexpr.c:6659
0x733823 expand_integer_pack
        ../../src/gcc/cp/pt.c:3751
0x733823 expand_builtin_pack_call
        ../../src/gcc/cp/pt.c:3790
0x733823 tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*)
        ../../src/gcc/cp/pt.c:12714
0x735561 tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
        ../../src/gcc/cp/pt.c:13078
0x73a678 tsubst_argument_pack(tree_node*, tree_node*, int, tree_node*)
        ../../src/gcc/cp/pt.c:13040
0x735534 tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
        ../../src/gcc/cp/pt.c:13090
0x7356e5 tsubst_aggr_type
        ../../src/gcc/cp/pt.c:13295
0x72c6f4 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
        ../../src/gcc/cp/pt.c:20100
0x7304e4 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
        ../../src/gcc/cp/pt.c:15745
0x7304e4 tsubst(tree_node*, tree_node*, int, tree_node*)
        ../../src/gcc/cp/pt.c:15745
0x735466 tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
        ../../src/gcc/cp/pt.c:13092
0x7356e5 tsubst_aggr_type
        ../../src/gcc/cp/pt.c:13295
0x7307fe tsubst(tree_node*, tree_node*, int, tree_node*)
        ../../src/gcc/cp/pt.c:15633

Code is listed below.

    #include <array>
    #include <tuple>
    #include <functional>

    template<typename T, std::size_t MinSz = 1, std::size_t MaxSz =
~std::size_t{}>
    concept IsTuple = requires(T t) { {std::get<0>(t) };} and
(std::tuple_size_v<std::remove_cvref_t<T>>-MinSz) <= (MaxSz-MinSz);

    template<IsTuple T, IsTuple T2,
             std::size_t dim =
std::min(std::tuple_size_v<T>,std::tuple_size_v<T2>),
             class seq = decltype(std::make_index_sequence<dim>{})>
    struct arith_result
    {
        template<std::size_t... I>
        static auto t(std::index_sequence<I...>)
            -> std::tuple<std::common_type_t<std::tuple_element_t<I,T>,
std::tuple_element_t<I,T2>>...>;

        template<std::size_t... I>
        static auto a(std::index_sequence<I...>)
            -> std::array<std::common_type_t<std::tuple_element_t<I,T>...,
std::tuple_element_t<I,T2>...>, dim>;

        using type = std::conditional_t<requires(T t){t[0]; },
decltype(a(seq{})), decltype(t(seq{}))>;
    };

    template<typename T = std::array<float,3>, typename T2 = T>
    auto Mul(const T& vec, const T2& val)
    {
        return [&]<std::size_t... P>(std::index_sequence<P...>) {
                 return typename arith_result<T,T2>::type {
std::plus<void>(std::get<P>(vec), std::get<P>(val)) ... };
            }
(std::make_index_sequence<std::min(std::tuple_size_v<std::remove_cvref_t<decltype(vec)>>,
                                                
std::tuple_size_v<std::remove_cvref_t<decltype(val)>>)>{});
    }

    auto x = Mul(std::array<float,2>{}, std::array<float,2>{});

[Bug c++/94489] ICE: unexpected expression ‘std::min’ of kind overload

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94489

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-04-06
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r9-6542-gf869f40780836d17 with -fconcepts, without it started with
r10-3735-gcb57504a55015891.

[Bug c++/94489] ICE: unexpected expression ‘std::min’ of kind overload

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94489

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org
           Keywords|ice-on-valid-code           |ice-on-invalid-code,
                   |                            |needs-reduction

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Doesn't seem like valid code; clang++ trunk also rejects it:
94489.C:28:61: error: no matching constructor for initialization of
'std::plus<void>'

I think the fix should be

--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -3748,6 +3748,7 @@ expand_integer_pack (tree call, tree args, tsubst_flags_t
complain,
     }
   else
     {
+      hi = instantiate_non_dependent_expr_sfinae (hi, complain);
       hi = cxx_constant_value (hi);
       int len = valid_constant_size_p (hi) ? tree_to_shwi (hi) : -1;


but it'd be nice to have a reduced version.

[Bug c++/94489] ICE: unexpected expression ‘std::min’ of kind overload

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94489

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Likely still invalid, but it compiles without errors with the patch above.

template <typename, unsigned> struct S { };
template <typename T, unsigned N> using U = S<T, __integer_pack(N)...>;
template <typename T> constexpr long g(T) { return 1l; }
template<typename T, typename TT = U<T, g(T{})>> struct X { };

template<typename T>
auto foo(T)
{
  []<unsigned>() {
      foo(1);
      X<T> x;
  };
}

[Bug c++/94489] ICE: unexpected expression ‘std::min’ of kind overload

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94489

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #2)
> Doesn't seem like valid code; clang++ trunk also rejects it:
> 94489.C:28:61: error: no matching constructor for initialization of
> 'std::plus<void>'
> 
> I think the fix should be
> 
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -3748,6 +3748,7 @@ expand_integer_pack (tree call, tree args,
> tsubst_flags_t complain,
>      }
>    else
>      {
> +      hi = instantiate_non_dependent_expr_sfinae (hi, complain);
>        hi = cxx_constant_value (hi);
>        int len = valid_constant_size_p (hi) ? tree_to_shwi (hi) : -1;
>  
> 
> but it'd be nice to have a reduced version.

This is not a complete fix because this one ICEs even with that:

template <typename, int...> struct b;
template <typename T, T... d> using e = b<T, __integer_pack(d)...>;
template <unsigned d> using f = e<unsigned, d>;
template <typename T> constexpr long g(T) { return 1l; }
struct array { };
template <typename> constexpr unsigned h{};
template<typename T, long dim = g(h<T>), class X = decltype(f<dim>{})> struct k
{ int n; };

template<typename T, typename U>
auto m(T t, U)
{
  [t] <unsigned> () {
      m(array{}, array{});
      return k<T, 1>::n;
  };
}

[Bug c++/94489] ICE: unexpected expression ‘std::min’ of kind overload

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94489

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
If we change std::plus<void> to std::plus<void>{} in order to make the testcase
valid, then we accept ever since the PR94490 fix.

The comment #4 testcase can be further reduced to:

template<int...> struct A;
template<int... Ns> A<__integer_pack(Ns)...>* f();

int main() {
  f<5, 6>();
}

This seems invalid indeed, how should we even expand __integer_pack(Ns)... when
Ns itself is a pack?