VisualStudio 15.7.x compilation error in /W4 /WX

[christophe-calmejane]

Using just released v5.0, I've got some compilation errors using VS15.7.x compiler when /W4 and /WX flags are set: "Unreachable code"

I've a workaround that consists of disabling this warning before including fmt, but it's not very "clean". Maybe there is a way to fix this warning (or to add the pragma push/disable/pop) directly in fmt headers.

This simple code (compiled in release) cause a compilation error with /W4 /WX:
#include <fmt/format.h> int main(int, char**) { fmt::format("Test"); return 0; }

The current fix for this is (win32 only)
#pragma warning(push) #pragma warning(disable:4702) #include <fmt/format.h> #pragma warning(pop)

Haven't tested on clang/gcc yet.

[eliaskosunen]

Plenty of warnings are fixed on #736

[vitaut]

Could you post the full warning message? I don't have access to a Windows machine and the warning doesn't reproduce on godbolt: https://godbolt.org/g/c67EiY

[christophe-calmejane]

1>test.cpp
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): error C2220: warning treated as error - no 'object' file generated
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\core.h(744): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(1267): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(2004): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(2048): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(2062): warning C4702: unreachable code
1>c:\dev\test\fmtlib\include\fmt\format.h(2066): warning C4702: unreachable code
1>Done building project "Test.vcxproj" -- FAILED.

This is using commitID 5386f1d (release branch)

[mwinterb]

Does this occur with the optimizer disabled? If not, when the optimizer is on, are you also compiling with link time code generation enabled?

…

On Wed, May 23, 2018, 00:00 Christophe Calmejane ***@***.***> wrote: 1>test.cpp 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): error C2220: warning treated as error - no 'object' file generated 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1672): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1648): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\core.h(744): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(1267): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(2004): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(2048): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(2062): warning C4702: unreachable code 1>c:\dev\test\fmtlib\include\fmt\format.h(2066): warning C4702: unreachable code 1>Done building project "Test.vcxproj" -- FAILED. This is using commitID 5386f1d <5386f1d> (release branch) — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#748 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABCB733r-xEb2RltnKHYpbGDN_q_8etVks5t1Qj8gaJpZM4UI63e> .

[christophe-calmejane]

Optimizer is not disabled, it happens only in a Release build. Debug build is fine.
I'm just using a cmake file as simple as this to create the project, run cmake and compile:

cmake_minimum_required(VERSION 3.5)
project(test LANGUAGES C CXX VERSION 1.0.0.0)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
add_subdirectory(fmtlib)
add_executable(Test test.cpp)
target_link_libraries(Test PRIVATE fmt-header-only)

[mwinterb]

Ah, header-only, that's probably why I haven't encountered it. What's likely happening is the optimizer is seeing through the on_error abstractions, seeing that they always throw, and reporting that the return statements are unreachable. (Just to be needlessly clear on my part.) It's probably reasonable for fmt to suppress that warning in header only mode. I think the same problem would occur with LTCG/WPO, but I'm unaware if Microsoft provides a way to introspect optimization levels at compile time. I don't see anything in #736 to explicitly address this case, but it is well past my bedtime, so I may have missed it.

…

On Wed, May 23, 2018, 00:22 Christophe Calmejane ***@***.***> wrote: Optimizer is not disabled, it happens only in a Release build. Debug build is fine. I'm just using a cmake file as simple as this to create the project, run cmake and compile: cmake_minimum_required(VERSION 3.5) project(test LANGUAGES C CXX VERSION 1.0.0.0) set(CMAKE_CXX_STANDARD 17) set(CMAKE_CXX_STANDARD_REQUIRED TRUE) add_subdirectory(fmtlib) add_executable(Test test.cpp) target_link_libraries(Test PRIVATE fmt-header-only) — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#748 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABCB76cj9YTMIRKDbY3D-lUbf2JU376Sks5t1Q5TgaJpZM4UI63e> .

[christophe-calmejane]

Yeah sorry I should have pasted the cmake source before :)
Like I said, right now I've to disable the warnings (win32 only) before including fmt, so if it can be done directly in the header it would be better for everyone.
Ty (and gn)

[Remotion]

Can we simple use such code to disable unreachable code warning ?

#if _MSC_VER && !defined(__clang__) && !defined(__INTEL_COMPILER)
#pragma warning( push )
#pragma warning( disable: 4702 ) // unreachable code
#endif

#if _MSC_VER && !defined(__clang__) && !defined(__INTEL_COMPILER)
#pragma warning( pop )
#endif // warning 4702 is back

[christophe-calmejane]

It's what I'm doing before including fmt (except I don't care about excluding vs_clang or intel, but the idea is here).

[vitaut]

@christophe-calmejane what's the complete list of command-line options passed to cl (in addition to /W4 /WX)? Maybe I could repro it on godbolt after all.

[christophe-calmejane]

C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.14.26428\bin\HostX86\x86\CL.exe /c /IC:\test\fmtlib\include /nologo /W4 /WX /diagnostics:classic /O2 /Ob2 /Oy- /D WIN32 /D _WINDOWS /D NDEBUG /D FMT_HEADER_ONLY=1 /D "CMAKE_INTDIR="Release"" /D _MBCS /Gm- /EHsc /MD /GS /fp:precise /Zc:wchar_t /Zc:forScope /Zc:inline /GR /std:c++17 /Fo"Test.dir\Release\" /Fd"Test.dir\Release\vc141.pdb" /Gd /TP /analyze- /FC /errorReport:queue C:\test\test.cpp

[vitaut]

Should be fixed in f8d5220, thanks for reporting.

[vitaut]

Had to temporarily revert part of the fix because of some MSVC issue, but will bring it back.

[vitaut]

On further inspection, it turned out that the above commit doesn't solve the issue, reopening.

[vitaut]

Here goes a proper fix: 252f11f