[Bug c++/114706] New: ICE - std::bit_cast in consteval function involving union

["cuzdav at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114706

            Bug ID: 114706
           Summary: ICE - std::bit_cast in consteval function involving
                    union
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cuzdav at gmail dot com
  Target Milestone: ---

ICE in a consteval function bit_casting an array of unions.  The code isn't
valid due to the union, but the compiler is not handling it properly (since
gcc11...trunk).  Reduced to the following program:

CODE

    #include <bit>
    union U { int u; };
    consteval void f() {
        U result[]{0, 0};   
        auto x = std::bit_cast<long>(result);
    }
    int main() { f(); }

LIVE:
https://godbolt.org/z/Y943bc5zK


OUTPUT

/opt/compiler-explorer/gcc-trunk-20240412/include/c++/14.0.1/bit:94:33:
internal compiler error: in native_encode_initializer, at fold-const.cc:8468
   94 |       return __builtin_bit_cast(_To, __from);
      |                                 ^~~
0x267826c internal_error(char const*, ...)
        ???:0
0xa58c63 fancy_abort(char const*, int, char const*)
        ???:0
0xfa0eaf native_encode_initializer(tree_node*, unsigned char*, int, int,
unsigned char*)
        ???:0
0xacf0f0 maybe_constant_value(tree_node*, tree_node*, mce_value)
        ???:0
0xd3a75f store_init_value(tree_node*, tree_node*, vec<tree_node*, va_gc,
vl_embed>**, int)
        ???:0
0xb474fe cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int,
cp_decomp*)
        ???:0
0xc5c81a c_parse_file()
        ???:0
0xdb1489 c_common_parse_file()
        ???:0
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