Git failed when build on /std:c++latest + MSVC on windows

[QuellaZhang]

Hi All,

We (the Microsoft C++ team) use the Git project as a part of our "Real World Code" tests. In our latest version, Git failed when build under /std:c++latest option like below error, I just want to confirm if the flag '/Gm' is very necessary for the project? This will not compatable with 'std:c++latest' any more in future.

Failures:
cl : Command line warning D9035 : option 'Gm' has been deprecated and will be removed in a future release
cl : Command line error D8016 : '/Gm' and '/std:c++latest' command-line options are incompatible

[dscho]

Hi @QuellaZhang, pleasure to meet you!

AFAIU /Gm makes it faster to re-build incrementally, right? If so, it would be nice to keep using that feature. Are there better/other options we should use?

[dscho]

And: could you describe which revision of Git you are compiling, and using what method (make MSVC=1 vs Visual Studio)?

[cdacamar]

/Gm is a very old attempt to make incremental compiling faster. In newer versions of msvc it is not compatible with much of the way the compiler works anymore and hasn't been actively maintained in several years.

As of 15.9 the feature has been deprecated with the intent of complete removal. The preferred option for incremental builds is still incremental link. Additionally, if incremental builds are still a concern investigating C++ modules would also be worth investigation.

[dscho]

@cdacamar thanks. I still would like to know how you build Git, as I am unable to find any mention of the Gm flag in the source code.

[cdacamar]

All we do is checkout the vs/master branch and invoke msbuild on the top-level .sln file: git.sln. So if there are references in any .vcxproj file it should be removed. Here's one example: https://github.com/git-for-windows/git/blob/vs/master/git/git.vcxproj#L69