[Bug c++/126223] [15/16/17 Regression] Compiler fails with message "internal compiler error: Segmentation fault"

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126223

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |15.3.0, 16.1.0
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |14.4.0, 15.2.0
   Last reconfirmed|                            |2026-07-31
     Ever confirmed|0                           |1
   Target Milestone|---                         |15.4
                 CC|                            |ppalka at gcc dot gnu.org
           Keywords|                            |ice-on-valid-code
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=120499
            Summary|Compiler fails with message |[15/16/17 Regression]
                   |"internal compiler error:   |Compiler fails with message
                   |Segmentation fault"         |"internal compiler error:
                   |                            |Segmentation fault"

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Confirmed, seems to have started with r16-3353 which has been backported to
15.3.

$ cat 126223_a.C
module;
#include <compare>
export module a;

struct A {
    int x;
    std::strong_ordering operator<=>(const A&) const;
};

export struct B {
    A a;
    int y;

    friend auto operator<=>(const B&, const B&) = default;
};

$ cat 126223_b.C
#include <compare>
import a;

bool useB() {
    auto b1 = B{.a = {.x = 1}, .y = 2};
    auto b2 = B{.a = {.x = 1}, .y = 3};
    return b1 < b2;
}

$ g++ -fmodules 126223_{a.C,b.C}
In module a, imported at 126223_b.C:2:
126223_a.C:14:17: internal compiler error: in mangle_module, at
cp/module.cc:16805
   14 |     friend auto operator<=>(const B&, const B&) = default;
      |                 ^~~~~~~~