[Bug c++/98930] New: ICE when using function local static constexpr variable at runtime

["matthieum.147192 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98930

            Bug ID: 98930
           Summary: ICE when using function local static constexpr
                    variable at runtime
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: matthieum.147192 at gmail dot com
  Target Milestone: ---

The following code crashes gcc trunk (11.0) and produces a linker error on
prior versions -- from 7.2 to 10.2.1 -- from -O0 to -O3.

Link to compiler explorer: https://godbolt.org/z/qox73Y



Self-sufficient code snippet:

template <char const* format>
class Source {
public:
    explicit Source() noexcept {
        asm volatile("" : : "r,m"(format) : "memory");
    }

    int index() const noexcept { return 0; }
};

template <typename T>
T impl() {
    static constexpr const char FORMAT_[] = "Hello, {}!";
    static Source<FORMAT_> const SOURCE{};

    return SOURCE.index();
}

int main() {
    return impl<int>();
}



GCC trunk crash:

<source>: In instantiation of 'Source<format>::Source() [with const char*
format = (& FORMAT_)]':
<source>:4:14:   required from here
<source>:4:14: internal compiler error: in discriminator_for_local_entity, at
cp/mangle.c:1949
    4 |     explicit Source() noexcept {
      |              ^~~~~~
0x1ce5ce9 internal_error(char const*, ...)
        ???:0
0x6b6f1b fancy_abort(char const*, int, char const*)
        ???:0
0x812f3b mangle_decl(tree_node*)
        ???:0
0x135b052 decl_assembler_name(tree_node*)
        ???:0
0x138e478 assign_assembler_name_if_needed(tree_node*)
        ???:0
0xb48015 cgraph_node::analyze()
        ???:0
0xb4c6dd symbol_table::finalize_compilation_unit()
        ???:0



GCC 10.2 linker error:

/opt/compiler-explorer/gcc-10.2.0/bin/../lib/gcc/x86_64-linux-gnu/10.2.0/../../../../x86_64-linux-gnu/bin/ld:
/tmp/cc6YCcxH.o: in function `_ZN6SourceIXadL_ZZ4implIT_ES1_vE7FORMAT_EEEC1Ev':
/home/ce/<source>:5: undefined reference to `_ZZ4implIT_ES0_vE7FORMAT_'
collect2: error: ld returned 1 exit status



Other compilers: ICE on Clang 11.0, Works on Clang (trunk).



In the same area (local static constexpr) I found 2 bug reports:

- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95686
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98288 (which I reported)


Regards.