[cfe-users] MSVC always trying to rebuild project while using clang-cl (LLVM-vs2014 toolset)

[Zachary Turner via cfe-users]

Fwiw, the new extension only supports vs2017, so you may need to upgrade.
If you can’t upgrade, set your project compile options to C7 Compatible
Debug Info (/Z7). That will also fix it
On Thu, Sep 6, 2018 at 6:41 AM Hans Wennborg <hans at chromium.org> wrote:

> This is the problem described in
> https://bugs.llvm.org/show_bug.cgi?id=36140
>
> Have you tried using the new VS extension?
>
> https://marketplace.visualstudio.com/items?itemName=LLVMExtensions.llvm-toolchain
> It should not have this problem.
>
>  - Hans
>
> On Mon, Sep 3, 2018 at 12:34 PM, Aleksei via cfe-users
> <cfe-users at lists.llvm.org> wrote:
> > Hello everyone,
> >
> >
> >
> > I don’t know if I’ve found a bug in clang-cl using Visual Studio 2015, or
> > it’s a quite normal behavior… It would be nice if someone clarify it and
> > (better) fix something in clang-cl, because the current behavior is IMHO
> > very confusing.
> >
> >
> >
> > Background: Visual Studio 2015, version 14.0.25431.01 Update 3, LLVM
> version
> > 6.0.1 for win64
> >
> >
> >
> > So, the problem is MSVC (under some condition) would always require to
> > rebuild a project that has to be built with LLVM-vs2014 toolset, even if
> > it’d just finished last rebuild.
> >
> >
> >
> > The root cause of it in the absence of a file, that is specified under
> > “Configuration Properties / C/C++ / Output Files / Program Database File
> > Name” (typically, it’s filled with macro
> > “$(IntDir)vc$(PlatformToolsetVersion).pdb” that expands to something
> similar
> > to “x64\Debug\vc140.pdb”). I might be wrong in general case, but in my
> case
> > this file is not generated by clang-cl at all during build process, it’s
> > generated only by VC’s native compiler. So, should one delete it
> > intentionally during manual cleanup or by an accident, MSVC would start
> to
> > always require a full project rebuild before each run/debug.
> >
> >
> >
> > It’s very easy to reproduce the problem: create a new Win32 console
> project
> > in MSVC, then immediately change the toolset used to build the project to
> > LLVM-vs2015 and then build the project (don’t build the project with
> native
> > compiler before this step). Then run it and notice that MSVC would
> require
> > the project to be rebuild.
> >
> > Now, if one to switch back the toolset to VC’s native, build the project
> (to
> > produce corresponding .pdb file), then switch the toolset to LLVM again
> and
> > then build it and after that run it – MSVC would start the program
> > immediately.
> >
> >
> >
> > If the .pdb file is not required to run/debug a project, I guess it
> would be
> > much better if clang-cl to emit some kind of warning/information during
> > compilation about that fact. I’ve just wasted about 3-4 hours to find out
> > why VC requires project rebuilding all the time…
> >
> >
> >
> > Thanks.
> >
> >
> >
> > Sincerely,
> >
> > Aleksei
> >
> >
> >
> >
> >
> >
> > _______________________________________________
> > cfe-users mailing list
> > cfe-users at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
> >
>
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