[llvm-dev] New warnings when building trunk with GCC 9

[David Blaikie via llvm-dev]

Fair point made on that thread - that this is a DR, so technically the
std::move is pessimizing even in C++11 mode. Richard: Any thoughts on
generalizing the warning to cover these cases even in C++11 mode?

On Sat, Sep 15, 2018 at 2:37 AM Dávid Bolvanský <david.bolvansky at gmail.com>
wrote:

> There is a new discussion related to -Wredundant-move warning on GCC
> bugzilla.
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87300
>
> pi 14. 9. 2018 o 9:53 David Blaikie <dblaikie at gmail.com> napísal(a):
>
>>
>>
>> On Fri, Sep 14, 2018 at 12:48 AM Stephan Bergmann <sbergman at redhat.com>
>> wrote:
>>
>>> On 13/09/2018 18:22, David Blaikie via llvm-dev wrote:
>>> > On Thu, Sep 13, 2018 at 12:13 AM Dávid Bolvanský via llvm-dev
>>> > <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>> >
>>>  /home/davidbolvansky/trunk/llvm/unittests/ExecutionEngine/Orc/CompileOnDemandLayerTest.cpp:79:40:
>>>
>>> >       required from here
>>> >
>>>  /home/davidbolvansky/trunk/llvm/include/llvm/ExecutionEngine/Orc/CompileOnDemandLayer.h:314:29:
>>> >     warning: redundant move in return statement [-Wredundant-move]
>>> >     314 |         return std::move(Err);
>>>
>>> Note that the move (into the implicit JITSymbol(Error) ctor) is only
>>> redundant if the compiler implements a fix for
>>> <http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1579>
>>> "Return by converting move constructor".  (But not sure whether the LLVM
>>> compiler baselines imply that, anyway.
>>
>>
>> Looks like that was accepted for C++14, not 11. So I don't believe it's
>> valid to remove the std::move in C++11 code. (& I believe Clang's warning
>> correctly diagnoses this only in the right language versions) - so we
>> probably want to disable the buggy GCC warning here, then.
>>
>>
>>> In LibreOffice it forced me to
>>> introduce ugly #ifs, to not have to disable that warning outright,
>>> <
>>> https://cgit.freedesktop.org/libreoffice/core/commit/?id=dc06c8f4989fc28d0c31ebd333e53dfe0e0f5f66>
>>>
>>> "-Werror=redundant-move (GCC 9), take two".)
>>>
>>
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