[Bug c++/99968] New: [11 Regression] ICE on remove_const_t<incomplete enum type> in requires-expression

["redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99968

            Bug ID: 99968
           Summary: [11 Regression] ICE on remove_const_t<incomplete enum
                    type> in requires-expression
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

template<typename T> struct remove_const { using type = T; };
template<typename T> struct remove_const<const T> { using type = T; };
template<typename T> using remove_const_t = typename remove_const<T>::type;

template<typename T>
constexpr inline bool is_enum_v = __is_enum(T);

template<typename T>
struct is_scoped_enum
{
  static constexpr bool value = false;
};

template<typename T>
requires is_enum_v<T> && requires (remove_const_t<T> t) { t = t; }
struct is_scoped_enum<T>
{
  static constexpr bool value = !requires (T t, int i) { i = t; };
};

template<typename T>
constexpr inline bool is_scoped_enum_v = is_scoped_enum<T>::value;

void f()
{
  enum E { e0 = is_enum_v<E>, e1 = is_scoped_enum_v<E> };
  static_assert( e0 );
  static_assert( ! e1 );
}

Compiled with -std=gnu++20:

e.C: In instantiation of 'struct remove_const<f()::E>':
e.C:3:28:   required by substitution of 'template<class T> using remove_const_t
= typename remove_const::type [with T = f()::E]'
e.C:15:26:   required by substitution of 'template<class T>  requires
(is_enum_v<T>) && requires(typename remove_const<T>::type t) {t = t;} struct
is_scoped_enum<T> [with T = f()::E]'
e.C:22:61:   required from 'constexpr const bool is_scoped_enum_v<f()::E>'
e.C:26:36:   required from here
e.C:1:29: error: enum value type is not 'INTEGER_TYPE' nor convertible to the
enum
    1 | template<typename T> struct remove_const { using type = T; };
      |                             ^~~~~~~~~~~~
 <const_decl 0x7fcf7f625070 e0
    type <boolean_type 0x7fcf7f4c1b28 bool public unsigned type_6 QI
        size <integer_cst 0x7fcf7f4a3fa8 constant 8>
        unit-size <integer_cst 0x7fcf7f4a3fc0 constant 1>
        align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0x7fcf7f4c1b28 precision:1 min <integer_cst 0x7fcf7f4c4210 0> max <integer_cst
0x7fcf7f4c4240 1>>
    readonly constant VOID e.C:26:12
    align:1 warn_if_not_align:0 context <enumeral_type 0x7fcf7f61cf18 E>
initial <integer_cst 0x7fcf7f4c4240 1> chain <type_decl 0x7fcf7f61f7b8 E>>
 <identifier_node 0x7fcf7f61b900 e0 normal local bindings <(nil)>>
 <enumeral_type 0x7fcf7f61cf18 E type_6 VOID
    align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0x7fcf7f61cf18 precision:0
    values <tree_list 0x7fcf7f61de88
        purpose <identifier_node 0x7fcf7f61b900 e0
            normal local bindings <(nil)>>
        value <const_decl 0x7fcf7f625070 e0 type <boolean_type 0x7fcf7f4c1b28
bool>
            readonly constant VOID e.C:26:12
            align:1 warn_if_not_align:0 context <enumeral_type 0x7fcf7f61cf18
E> initial <integer_cst 0x7fcf7f4c4240 1> chain <type_decl 0x7fcf7f61f7b8 E>>>
context <function_decl 0x7fcf7f608d00 f>
    chain <type_decl 0x7fcf7f61f7b8 E>>
e.C:1:29: internal compiler error: 'verify_type' failed
0x1385d10 verify_type(tree_node const*)
        /home/jwakely/src/gcc/gcc/gcc/tree.c:14926
0xcdd13d gen_type_die_with_usage
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25731
0xcdeaa6 gen_type_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25962
0xcdf01c modified_type_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:13727
0xce29f1 add_type_attribute
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:21910
0xcf78da gen_typedef_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25638
0xcf78da gen_typedef_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25572
0xcd9f8a gen_decl_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:26604
0xcdc18d gen_member_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25415
0xcdc18d gen_struct_or_union_type_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25511
0xcdc18d gen_tagged_type_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25712
0xcdd42a gen_tagged_type_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25666
0xcdd42a gen_type_die_with_usage
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25907
0xcdeaa6 gen_type_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:25962
0xcd9a52 gen_decl_die
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:26601
0xcdac53 dwarf2out_decl
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:27156
0xcdb1e1 dwarf2out_type_decl
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:26874
0xcdb1e1 dwarf2out_type_decl
        /home/jwakely/src/gcc/gcc/gcc/dwarf2out.c:26869
0xfc7994 rest_of_type_compilation(tree_node*, int)
        /home/jwakely/src/gcc/gcc/gcc/passes.c:339
0x8fdc63 finish_struct_1(tree_node*)
        /home/jwakely/src/gcc/gcc/gcc/cp/class.c:7548
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