https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95677
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to liusujian from comment #2)
> (In reply to Richard Biener from comment #1)
> > It's more likely the GENERIC / cgraph output by the C++ frontend is not
> > correct
> > and works by accident without LTO. Initial symbol table:
> >
> > Initial Symbol table:
> >
> > int {anonymous}::xx/3 (int {anonymous}::xx) @0x7f615d2d8180
> > Type: variable
> > Visibility: external
> > References:
> > Referring: _ZN12_GLOBAL__N_13fooEv/0 (write)
> > Availability: not-ready
> > Varpool flags:
> > main/2 (int main()) @0x7f615d421168
> > Type: function definition analyzed
> > Visibility: force_output no_reorder public
> > Aux: @0x37a5000
> > References: int {anonymous}::xx/1 (write)
> > Referring:
> > Function flags: body
> > Called by:
> > Calls:
> > int {anonymous}::xx/1 (int {anonymous}::xx) @0x7f615d2d8100
> > Type: variable definition analyzed
> > Visibility: force_output no_reorder
> > Aux: @0x7f615d421168
> > References:
> > Referring: main/2 (write)
> > Availability: not-ready
> > Varpool flags: initialized
> > _ZN12_GLOBAL__N_13fooEv/0 (void {anonymous}::foo()) @0x7f615d421000
> > Type: function definition analyzed
> > Visibility: force_output no_reorder
> > Aux: @0x7f615d2d8100
> > References: int {anonymous}::xx/3 (write)
> > Referring:
> > Function flags: body
> > Called by:
> > Calls:
> >
> > where you can see there are actually two 'xx' objects and the C++ FE
> > takes it up to the linker/assembler to resolve them. But the symtab
> > code does not include such "resolving" step.
>
>
> In other words, C++ is currently unable to deal with this scenario ? Or any
> other problems cause the error?
The C++ frontend creates two distinct objects for 'xx' (thus it does not know
they refer to the same object). Not sure if it is possible to exploit this
fact to create a testcase that shows this fact even without LTO. I guess
using constexpr and fail to constexpr evaluate a function using constexpr
'xx'? Not sure if there can be a "extern" constexpr though ;)
As said the testcase "works" without LTO because both instances mangle
to the same symbol name so the assembler/linker figure they _are_ the same
object. Just the C++ frontend doesn't know within this TU.
