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From: "nshead at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/114954] New: [modules] ICE in write_class_def with
 templated union type
Date: Mon, 06 May 2024 00:53:19 +0000
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X-Bugzilla-Version: 15.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114954

            Bug ID: 114954
           Summary: [modules] ICE in write_class_def with templated union
                    type
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nshead at gcc dot gnu.org
            Blocks: 103524
  Target Milestone: ---

The following sample crashes on trunk:

  export module main;

  template <int N>
  union U {
  private:
    char a[N + 1];
    int b;
  };

  U<4> p;

With 'g++ -fmodules-ts -S main.cpp':
~/ice/main.cpp:1:8: internal compiler error: in write_class_def, at
cp/module.cc:12118
    1 | export module main;
      |        ^~~~~~
0x1010c67 write_class_def
        ../../gcc/gcc/cp/module.cc:12118
0x1014d91 write_definition
        ../../gcc/gcc/cp/module.cc:12731
0x101880e depset::hash::find_dependencies(module_state*)
        ../../gcc/gcc/cp/module.cc:13640
0x1026a62 module_state::write_begin(elf_out*, cpp_reader*,
module_state_config&, unsigned int&)
        ../../gcc/gcc/cp/module.cc:18253
0x102e39f finish_module_processing(cpp_reader*)
        ../../gcc/gcc/cp/module.cc:20693
0xf50556 c_parse_final_cleanups()
        ../../gcc/gcc/cp/decl2.cc:5393
0x131e75f c_common_parse_file()
        ../../gcc/gcc/c-family/c-opts.cc:1329

The assertion that fails is

  /* Every class but __as_base has a type-specific.  */
  gcc_checking_assert (!TYPE_LANG_SPECIFIC (type) =3D=3D IS_FAKE_BASE_TYPE =
(type));

The issue looks to be that a union `__as_base` type doesn't satisfy the
'IS_FAKE_BASE_TYPE', which only applies to RECORD_TYPEs.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103524
[Bug 103524] [meta-bug] modules issue=