[Bug c++/83918] New: [c++17, regression from 7.2] ICE on constexpr eval of datatype involving function and variadic template

[dimitri.gorokhovik at free dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83918

            Bug ID: 83918
           Summary: [c++17, regression from 7.2] ICE on constexpr eval of
                    datatype involving function and variadic template
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dimitri.gorokhovik at free dot fr
  Target Milestone: ---

Hi,

The following code below compiles with GCC 7.2 (Ubuntu 7.2.0-8ubuntu3) but
provokes the crash (probably segfault) of gcc (GCC) 8.0.1 20180117
(experimental) (r256776).

I honestly tried to look for duplicates in Bugzilla, but it feels like not the
right moment ;-(


========================================================================

constexpr unsigned f (unsigned a, unsigned b) { return a > b ? a : b; }


template <typename a, typename b> struct mult_width;

template <auto ...> struct list;

template <auto a, auto ... as, auto b, auto ... bs>
struct mult_width <list <a, as...>, list <b, bs...>>
{
        enum : unsigned 
        {
                h = f (sizeof (a), sizeof (b)),
                t = mult_width <list <as...>, list <bs...>>::width,
                width = f (h, t)
        };
};

template <>
struct mult_width <list <>, list <>>
{
        enum : unsigned { width = 0 };
};


constexpr static const auto w { mult_width <list <1,2,3,4,5,6,7,8,9>, list
<9,8,7,6,5,4,3,2,1>>::width };
static_assert (w == sizeof (int));

==========================================================================

Backtrace:

Compilation started at Wed Jan 17 20:20:33

/home/user/gcc-trunk/dist/bin/g++ -std=c++17  -c bug-1.cpp -o bug-1
bug-1.cpp:17:18: internal compiler error: Segmentation fault
   width = f (h, t)
                  ^
0xe76e3f crash_signal
        ../../srcdir/gcc/toplev.c:325
0x82209c potential_constant_expression_1
        ../../srcdir/gcc/cp/constexpr.c:5386
0x821f8d potential_constant_expression_1
        ../../srcdir/gcc/cp/constexpr.c:5323
0x8dc487 cp_parser_constant_expression
        ../../srcdir/gcc/cp/parser.c:9736
0x8f340e cp_parser_enumerator_definition
        ../../srcdir/gcc/cp/parser.c:18343
0x8f340e cp_parser_enumerator_list
        ../../srcdir/gcc/cp/parser.c:18283
0x8f340e cp_parser_enum_specifier
        ../../srcdir/gcc/cp/parser.c:18210
0x8f340e cp_parser_type_specifier
        ../../srcdir/gcc/cp/parser.c:16670
0x900086 cp_parser_decl_specifier_seq
        ../../srcdir/gcc/cp/parser.c:13559
0x8efc66 cp_parser_member_declaration
        ../../srcdir/gcc/cp/parser.c:23443
0x8f0d4a cp_parser_member_specification_opt
        ../../srcdir/gcc/cp/parser.c:23298
0x8f0d4a cp_parser_class_specifier_1
        ../../srcdir/gcc/cp/parser.c:22440
0x8f2d89 cp_parser_class_specifier
        ../../srcdir/gcc/cp/parser.c:22692
0x8f2d89 cp_parser_type_specifier
        ../../srcdir/gcc/cp/parser.c:16698
0x900086 cp_parser_decl_specifier_seq
        ../../srcdir/gcc/cp/parser.c:13559
0x904eb5 cp_parser_single_declaration
        ../../srcdir/gcc/cp/parser.c:27001
0x90523c cp_parser_template_declaration_after_parameters
        ../../srcdir/gcc/cp/parser.c:26693
0x905afc cp_parser_explicit_template_declaration
        ../../srcdir/gcc/cp/parser.c:26930
0x905afc cp_parser_template_declaration_after_export
        ../../srcdir/gcc/cp/parser.c:26949
0x90af09 cp_parser_declaration
        ../../srcdir/gcc/cp/parser.c:12661
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.

Compilation exited abnormally with code 1 at Wed Jan 17 20:20:33