llvm dev - Oct 2019 - How to Switch to Static Runtime and Enable C++ Exceptions?

Hi Osman,

You can’t enable the static CRT through the command-line. You would need to
apply this patch: https://reviews.llvm.org/D55056
(although it doesn’t work with lldb)

Alex.
________________________________
De : llvm-dev <llvm-dev-bounces at lists.llvm.org> de la part de Osman
Zakir via llvm-dev <llvm-dev at lists.llvm.org>
Envoyé : 28 octobre 2019 07:47:43
À : llvm-dev at lists.llvm.org <llvm-dev at lists.llvm.org>
Objet : Re: [llvm-dev] How to Switch to Static Runtime and Enable C++
Exceptions?

I ran this command "cmake -S../llvm -G"Visual Studio 16 2019"
-Thost=x64 -DCMAKE_INSTALL_PREFIX=../install -DCMAKE_BUILD_TYPE=Release
-DCMAKE_MSVC_RUNTIME_LIBRARY=MT -DCMAKE_CXX_FLAGS="/permissive- /EHsc
/std:c++17 /O2 /MT /D_SILENCE_ALL_CXX_DEPRECATION_WARNINGS"
-DLLVM_ENABLE_RTTI=On -DLLVM_ENABLE_EH=ON -DCMAKE_CXX_STANDARD=17
-DPYTHON_HOME=C:/Users/Osman/AppData/Local/Programs/Python/Python38
-DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld;lldb;libcxx;libcxxabi"".
But I still get "Using Release VC++ CRT: MD", and also the CMake
warning: "CMake Warning at utils/benchmark/CMakeLists.txt:244 (message):
  Using std::regex with exceptions disabled is not fully supported".

Please help.
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Okay, thanks.  So how do I apply the patch?
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I would really like to know about how to apply the patch for making MSVC-built
LLVM executables lighter.  But aside from that, I also want to know what LLVM
does to CMake's default setting of /EHsc.  I want to keep that setting on,
but I can't figure out how.  Any help is appreciated.  Thanks in advance. 
P.S. The CMAKE_CXX_FLAGS variable isn't helping at all, otherwise I
wouldn't be asking this.
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On Mon, Oct 28, 2019 at 5:11 AM Alexandre Ganea via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> You can’t enable the static CRT through the command-line. You would need
> to apply this patch: https://reviews.llvm.org/D55056
> (although it doesn’t work with lldb)
>
Are you sure? I would expect `cmake -DLLVM_USE_CRT_RELEASE=MT` to use the
static CRT.

I think Zach is correct, Osman can use -DLLVM_ENABLE_EH=ON, and it will
enable exceptions.

You're still getting a warning from the benchmark library because
LLVM's cmake forcibly disables benchmark library exceptions here:
https://github.com/llvm/llvm-project/blob/2724d9e/llvm/CMakeLists.txt#L1094
That's probably a bug, it should probably be dependent on LLVM_ENABLE_EH.
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Yes you’re right, -DLLVM_USE_CRT_RELEASE=MT works indeed! Although the “Visual
Studio” cmake generators are multi-config, so you end up with
-DCMAKE_BUILD_TYPE=Release  being ignored, which means that if you want to make
things right, you would need to also set the other –DLLVM_USE_CRT_XXX values as
well, to avoid surprises when switching targets inside VS. For those
multi-config generators, reintroducing -DLLVM_USE_CRT would be nice, maybe.

De : Reid Kleckner <rnk at google.com>
Envoyé : October 28, 2019 4:13 PM
À : Alexandre Ganea <alexandre.ganea at ubisoft.com>
Cc : Osman Zakir <osmanzakir90 at hotmail.com>; llvm-dev <llvm-dev at
lists.llvm.org>
Objet : Re: [llvm-dev] How to Switch to Static Runtime and Enable C++
Exceptions?

On Mon, Oct 28, 2019 at 5:11 AM Alexandre Ganea via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
You can’t enable the static CRT through the command-line. You would need to
apply this patch: https://reviews.llvm.org/D55056
(although it doesn’t work with lldb)

Are you sure? I would expect `cmake -DLLVM_USE_CRT_RELEASE=MT` to use the static
CRT.

I think Zach is correct, Osman can use -DLLVM_ENABLE_EH=ON, and it will enable
exceptions.

You're still getting a warning from the benchmark library because LLVM's
cmake forcibly disables benchmark library exceptions here:
https://github.com/llvm/llvm-project/blob/2724d9e/llvm/CMakeLists.txt#L1094
That's probably a bug, it should probably be dependent on LLVM_ENABLE_EH.
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