[llvm-dev] [cfe-dev] New warnings when building trunk with GCC 9 (original) (raw)

Richard Smith via llvm-dev llvm-dev at lists.llvm.org
Sun Sep 16 10:40:47 PDT 2018

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/showbug.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/cwgdefects.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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