[llvm-dev] LTO in LLVM3.8

[Matt Godbolt via llvm-dev]

In the linked bug, the issue is that symbols defined in multiple places
(LTO and non-LTO) are provided by the linker plugin (which in GCC's case
marks the symbols as private).  The error appears to be a difference in
which symbol gold or ld picks as canonical. I don't think it's the same as
the issue you're seeing (unless you're mixing LTO and non-LTO files).

I'd guess likely the 'ar' et al needs to be the llvm-ar. I have no
experience with LTO in llvm, but with GCC unless one uses the "right" ar,
then often LTO information is lost in the archive.

On Tue, Apr 5, 2016 at 8:43 AM Daniil Troshkov via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> you can also try to find exactly revision number (using binary search
> through revisions and using comments in suspicious commits) and try to ask
> author directly... at least it will be additional info...
>
> On Tue, Apr 5, 2016 at 4:28 AM, Below, Daniel via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi all,
>>
>>
>> I've been playing around with LLVM and LTO trying to compile some
>> open-source projects.
>>
>>
>> Prior to the 3.8 release I had been using r250630 (if I remember
>> correctly) and I was able to successfully build GamePlay (
>> https://github.com/gameplay3d/GamePlay).
>>
>> Sadly, since upgrading to 3.8 I am getting weird link-time-errors (error:
>> undefined reference to 'XYZ::~XYZ').
>>
>>
>> It appears that these destructors are all virtual (although I cannot
>> guarantee this does not break for non-virtual destructors too). The project
>> generates an archive file which is then linked against to generate a few
>> sample applications. During this linking phase, the above error (undefined
>> reference to 'XYZ::~XYZ') appears.
>>
>>
>>
>> I have upgraded the gold-linker, and I have tried using the current trunk
>> of LLVM - both did not help. After three days of trying to debug this, I
>> have run out of ideas.
>>
>>
>> Is this a known bug? I have found an issue on the gnu/binutils bugtracker
>> that sounds similar (
>> https://lists.gnu.org/archive/html/bug-binutils/2016-03/msg00235.html -
>> bugged symbol resolution of weak symbols), although in my case compilation
>> is aborted because of said errors.
>>
>>
>> Have there been any undocumented changes to LTO in 3.8 I should be aware
>> of? Is there maybe a specific gold-linker version I have to use or should I
>> use llvm-ar/nm now, instead of the ar/nm provided by binutils (which have
>> worked for me before 3.8)?
>>
>>
>> Any help is greatly appreciated,
>>
>>
>> Daniel
>>
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>> llvm-dev at lists.llvm.org
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>>
>>
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