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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/108566] ICE: tree check: expected tree that contains 'decl
 with visibility' structure, have 'field_decl' in write_unqualified_name with
 anonymous struct inside an anonymous union
Date: Fri, 27 Jan 2023 03:29:38 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108566

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note this is using a GCC extension so this might not be as important.
clang mangles the symbol as:
_Z5dummyIXtl8wrapper1IdEtlNS1_Ut_Edi9RightNametlNS2_Ut_ELd405ec00000000000E=
EEEEEvv

Which does demangle to:
void dummy<wrapper1<double>{wrapper1<double>::{unnamed
type#1}{.RightName=3D{unnamed type#1}::{unnamed
type#1}{(double)[405ec00000000000]}}}>()


If you change it to:
```
template<typename T>
struct wrapper1 {
  union {
    struct {
      double hh;
      double hh1;
    };
  };
};

template<auto tparam> void dummy(){}

void uses() {
  dummy<wrapper1<double>{123.0, 123.0}>();
}

```
clang mangles the symbol as:
_Z5dummyIXtl8wrapper1IdEtlNS1_Ut_Edi2hhtlNS2_Ut_ELd405ec00000000000ELd405ec=
00000000000EEEEEEvv

Which demangles as:
void dummy<wrapper1<double>{wrapper1<double>::{unnamed type#1}{.hh=3D{unnam=
ed
type#1}::{unnamed type#1}{(double)[405ec00000000000],
(double)[405ec00000000000]}}}>()

But takes the name of the struct from the first field ...
Which might be what GCC is trying to do but it fails.


Here is a more complex test (wrapper1 does not need to be a template to get=
 the
crash):
struct wrapper1 {
  union {
    struct {
       union {
      double hh;
      double hh1;
      };
    };
  };
};

template<auto tparam> void dummy(){}

void uses() {
  dummy<wrapper1{123.0}>();
}

clang's mangled named:
_Z5dummyIXtl8wrapper1tlNS0_Ut_Edi2hhtlNS1_Ut_EtlNS2_Ut_Edi2hhLd405ec0000000=
0000EEEEEEEvv

Which demangles as:
void dummy<wrapper1{wrapper1::{unnamed type#1}{.hh=3D{unnamed type#1}::{unn=
amed
type#1}{wrapper1::{unnamed type#1}::{unnamed
type#1}{.hh=3D((double)[405ec00000000000])}}}}>()

Notice the use of the first field's name.=