Help in tracking down unusual apparent 5.2.0 LTO issue

[Markus Trippelsdorf]

On 2016.03.17 at 16:04 +0000, Matt Godbolt wrote:
> Hi again,
> 
> I managed to get GCC5.2.0 building against binutils 2.26:
> 
> $ ~/.fighome/runtime/gcc/5.2.0-2/bin/ld.gold --version
> GNU gold (DRW-internal-build 2.26.20160125) 1.11
> 
> Sadly the problem remains:
> 
> Dump of assembler code for function std::_List_node<std::function<void ()>
> >::~_List_node():
>    0x0000000000762240 <+0>: push   %rbp
>    0x0000000000762241 <+1>: mov    %rsp,%rbp
>    0x0000000000762244 <+4>: sub    $0x10,%rsp
>    0x0000000000762248 <+8>: mov    %rdi,-0x8(%rbp)
>    0x000000000076224c <+12>: mov    -0x8(%rbp),%rax
>    0x0000000000762250 <+16>: add    $0x10,%rax
>    0x0000000000762254 <+20>: mov    %rax,%rdi
>    0x0000000000762257 <+23>: callq  0x0
>    0x000000000076225c <+28>: nop
>    0x000000000076225d <+29>: leaveq
>    0x000000000076225e <+30>: retq
> End of assembler dump.
> 
> Any thoughts on what flags I might give to gold to try and track this down?
> I tried -Wl,--debug,all and there didn't seem to be all that much debug
> information.

Before digging into gold I would rule out other possible issues first:

- Are both projects using the same libstdc++ ABI? There was a new
  implementation of std::list for gcc-5. See:
  http://gcc.gnu.org/gcc-5/changes.html#libstdcxx

- Are there any one-definition-rule issues? Or any other possible
  undefined behavior? Try building everything with -fsanitize=undefined
  and see if anything pops up.

If nothing helps then please try again to come up with a testcase and
open a http://sourceware.org/bugzilla/ gold bug.

-- 
Markus