llvm dev - Sep 2018 - [cfe-dev] New warnings when building trunk with GCC 9

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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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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Yes, we should produce this warning in C++11 mode too. (I could be
misrecalling, but I think the rationale for the current behaviour is based
on historical GCC behaviour.)

On Sun, 16 Sep 2018, 10:04 David Blaikie via cfe-dev, <
cfe-dev at lists.llvm.org> wrote:
> 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".)
>>>>
>>> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
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