[Bug c++/126623] New: c++filt cannot unmangle _ZTSZZ1XIEEUlNS_EE_EUlS_E_

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D126623

            Bug ID: 126623
           Summary: c++filt cannot unmangle _ZTSZZ1XIEEUlNS_EE_EUlS_E_
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tapplencourt at anl dot gov
  Target Milestone: ---

Hi,

Sorry if it's not the correct place to report a `libiberty` bug.=20

In short `libiberty` (tested with upstream
`5ff1facfba558514eae0efaeb70adb91b6c32a5f`) cannot un-mangle
`_ZTSZZ1XIEEUlNS_EE_EUlS_E_` where `llvm::demangle` have no problem to do so
and produce `typeinfo name for X<>::'lambda'(X)::'lambda'(X)`.

I'm not an expert of Itanimun mangling, so I don't know if this mangling is
even correct, and I was not able to make `g++` generate this mangled name.=
=20
But `llvm` generate it (I was not able to make a simple reproducer... so you
will need to take my word for it, sorry) , and we need demangle name genera=
ted
by llvm-based compiled (sadly?).


```
applenco@aurora-uan-0009:~/project/tmp> c++filt _ZTSZZ1XIEEUlNS_EE_EUlS_E_
_ZTSZZ1XIEEUlNS_EE_EUlS_E_
applenco@aurora-uan-0009:~/project/tmp> c++filt_llvm
'_ZTSZZ1XIEEUlNS_EE_EUlS_E_'  # Using ` llvm::demangle`=20
typeinfo name for X<>::'lambda'(X)::'lambda'(X)
```

Maybe related too #93035=