[CMake] Link Time Code Generation (LTGC) by default, for Release configurations of Visual Studio projects?

[Niels Dekker]

Thank you for your encouraging replies, Johannes and Cristian.

In the meantime I created "default" Visual C++ projects on Visual Studio 
2008, Visual Studio 2010, Visual Studio 2013, Visual Studio 2015 and 
Visual Studio 2017 (from within the IDE, without using CMake). It 
appears that each of these Visual Studio versions hast Link Time Code 
Generation by default, for Release configurations.

I don't have access to a machine with Visual Studio 2005. Can someone 
tell me whether this version also has Link Time Code Generation by 
default, for Release configurations?

Kind regards, Niels


On 2018-01-25 14:54, Mueller-Roemer, Johannes Sebastian wrote:
> This would be a great feature! Currently I override my release flags
> by setting CMAKE_<LANG>_FLAGS_RELEASE_INIT and
> CMAKE_<TYPE>_LINKER_FLAGS_RELEASE_INIT in a
> CMAKE_USER_MAKE_RULES_OVERRIDE script. Direct support for /GL and
> /LTCG in CMake would be great. Fewer target specifics to worry
> about…
> 
> 
> FROM: Cristian Adam
> SENT: Wednesday, January 24, 2018 21:42
> TO: Niels Dekker
> CC: cmake <cmake at cmake.org>
> SUBJECT: Re: [CMake] Link Time Code Generation (LTGC) by default, for
> Release configurations of Visual Studio projects?
> 
> Hi,
> 
> I had a quick check to see if CMake 3.10 for which compilers it has
> support for Interprocedural Optimization  (IPO, or LTCG as known on
> Visual C++).
> 
> Modules/Compiler had only for GNU, CLANG and PGI the following:
> 
> set(_CMAKE_${lang}_IPO_MAY_BE_SUPPORTED_BY_COMPILER YES)
> 
> QNX with QCC didn't have it set to YES even though nowdays QNX comes
> with GCC 5.4.0 on QNX 7.0, which should be just fine.
> 
> It would be nice if CMake would have support for IPO on Visual C++.
> 
> The steps would be to set the right variables into
> Modules/Compiler/MSVC-CXX.cmake, change the CheckIPOSupported
> module, change some flags in some places,update tests, documentation,
> and so on.
> 
> Shouldn't be hard to add this feature.
> 
> Cheers,
> 
> Cristian.
> 
> On Wed, Jan 24, 2018 at 9:06 PM, Niels Dekker wrote:
> 
>> When a Visual C++ project is created within Visual Studio (by File
>> menu, New, Project...), it has Link Time Code Generation (LTGC) by
>> default, for its Release configurations: Compiler option /GL and
>> linker option /LTCG. However, when the Visual C++ project is
>> generated by CMake, it does not have LTGC, by default. LTCG looks
>> like a very useful feature to me. I think it's worth enabling the
>> feature by default, for Release configurations. What do you think?
>> 
>> Some details:
>> 
>> I created a "dummy" Visual C++ project in Visual Studio 2017
>> (Version 15.5.4), by File menu, New, Project..., and I also
>> generated one by CMake (version 3.10.2), using a very minimal
>> CMakeLists.txt
>> 
>> The Visual C++ project created by Visual Studio 2017 has the
>> following compile options, by default, for Release (x64):
>> 
>> /permissive- /GS /GL /W3 /Gy /Zc:wchar_t /Zi /Gm- /O2 /sdl
>> /Fd"x64\Release\vc141.pdb" /Zc:inline /fp:precise /D "_MBCS"
>> /errorReport:prompt /WX- /Zc:forScope /Gd /Oi /MD /Fa"x64\Release\"
>> /EHsc /nologo /Fo"x64\Release\" /Fp"x64\Release\MyVS2015Project.pch"
>> /diagnostics:classic
>> 
>> And the following linker options:
>> 
>> 
> /OUT:"F:\X\Src\MyProject\MyVS2015Project\x64\Release\MyVS2015Project.exe"
>> /MANIFEST /LTCG:incremental /NXCOMPAT
>> 
> /PDB:"F:\X\Src\MyProject\MyVS2015Project\x64\Release\MyVS2015Project.pdb"
>> /DYNAMICBASE "kernel32.lib" "user32.lib" "gdi32.lib" "winspool.lib"
>> "comdlg32.lib" "advapi32.lib" "shell32.lib" "ole32.lib"
>> "oleaut32.lib" "uuid.lib" "odbc32.lib" "odbccp32.lib" /DEBUG:FULL
>> /MACHINE:X64 /OPT:REF
>> 
> /PGD:"F:\X\Src\MyProject\MyVS2015Project\x64\Release\MyVS2015Project.pgd"
>> /MANIFESTUAC:"level='asInvoker' uiAccess='false'"
>> 
> /ManifestFile:"x64\Release\MyVS2015Project.exe.intermediate.manifest"
>> /OPT:ICF /ERRORREPORT:PROMPT /NOLOGO /TLBID:1
>> 
>> The vcxproj file created by Visual Studio has
>> "<WholeProgramOptimization>true</WholeProgramOptimization>" for its
>> Release configurations.
>> 
>> The Visual C++ project generated by CMake (Generator: Visual Studio
>> 15 2017 Win64) has the following compile options, for its Release
>> configuration:
>> 
>> /GS /TP /W3 /Zc:wchar_t /Gm- /O2 /Ob2
>> /Fd"MyExecutable.dir\Release\vc141.pdb" /Zc:inline /fp:precise /D
>> "WIN32" /D "_WINDOWS" /D "NDEBUG" /D "CMAKE_INTDIR=\"Release\"" /D
>> "_MBCS" /errorReport:prompt /WX- /Zc:forScope /GR /Gd /MD
>> /Fa"Release/" /EHsc /nologo /Fo"MyExecutable.dir\Release\"
>> /Fp"MyExecutable.dir\Release\MyExecutable.pch" /diagnostics:classic
>> 
>> And the following linker options:
>> 
>> /OUT:"F:\X\Bin\vc141-64\MyProject\Release\MyExecutable.exe"
>> /MANIFEST /NXCOMPAT
>> /PDB:"F:/X/Bin/vc141-64/MyProject/Release/MyExecutable.pdb"
>> /DYNAMICBASE "kernel32.lib" "user32.lib" "gdi32.lib" "winspool.lib"
>> "shell32.lib" "ole32.lib" "oleaut32.lib" "uuid.lib" "comdlg32.lib"
>> "advapi32.lib"
>> /IMPLIB:"F:/X/Bin/vc141-64/MyProject/Release/MyExecutable.lib"
>> /MACHINE:X64 /INCREMENTAL:NO
>> /PGD:"F:\X\Bin\vc141-64\MyProject\Release\MyExecutable.pgd"
>> /SUBSYSTEM:CONSOLE /MANIFESTUAC:"level='asInvoker' uiAccess='false'"
>> /ManifestFile:"MyExecutable.dir\Release\MyExecutable.exe.int
>> [1]ermediate.manifest" /ERRORREPORT:PROMPT /NOLOGO /TLBID:1
>> 
>> The vcxproj file generated by CMake does not have a
>> "<WholeProgramOptimization>" tag.
>> 
>> I hope you can consider adding LTCG to Release configurations of
>> Visual C++ projects generated by CMake, by default.
>> 
>> Kind regards, Niels

-- 
Niels Dekker
Scientific programmer
LKEB, Leiden University Medical Center