[Bug c++/83205] New: ICE on structured binding with ill-formed negative std::tuple_size<T>::value

["jcemmett1 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83205

            Bug ID: 83205
           Summary: ICE on structured binding with ill-formed negative
                    std::tuple_size<T>::value
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jcemmett1 at gmail dot com
  Target Milestone: ---

The following ill-formed code results in an ICE with GCC 8. Needs only
-std=c++17.

=====
struct Foo { int i; };

namespace std {
    template <typename T> struct tuple_size;

    template <> struct tuple_size<Foo> {
        static constexpr int value = -1;
    };
}

int main()
{
    auto [i] = Foo{};
}
=====

Output: 

GNU C++17 (GCC-Explorer-Build) version 8.0.0 20171128 (experimental)
(x86_64-linux-gnu)
        compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR
version 3.1.4, MPC version 1.0.3, isl version isl-0.18-GMP
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: 6355e9ef8f7b704fe373fdf166e4fd6e
<source>: In function 'int main()':
14 : <source>:14:20: internal compiler error: in tree_to_uhwi, at tree.c:6643
     auto [i] = Foo{};
                    ^
mmap: Cannot allocate memory
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler exited with result code 1

Godbolt link: https://godbolt.org/g/NJ6fLG