Subject: Re: [boost] [clang][preprocessor] Testing of clang emualting the VC++ preprocessor on Windows
From: degski (degski_at_[hidden])
Date: 2016-03-31 10:27:16
Hi,
Is there a (simple) git command-line that gives me a complete "develop"
boost source distribution clone, so I could give it a try?
Thanks in advance,
degski
On 31 March 2016 at 14:28, Edward Diener <eldiener_at_[hidden]> wrote:
> On 3/30/2016 5:05 PM, Edward Diener wrote:
>
>> I have made local changes in the Boost preprocessor config.hpp on the
>> 'develop' branch to have clang's emulation of the non-standard VC++
>> preprocessor act like the VC++ preprocessor as far as Boost PP is
>> concerned. Boost PP has a large number of workarounds for VC++ without
>> which Boost PP preprocessor code would not work when compiling using any
>> version of VC++.
>>
>> I have tested the usual compilers extensively to make sure they are
>> unaffected by these changes as well as the normal clang-linux
>> implementation. Everything remains the same for these compilers with my
>> changes so I am assured the changes will not affect any other compiler
>> implementation.
>>
>> I was able to test both clang-3.8 and the latest build of clang, which
>> is clang-3.9, by invoking clang-cl. My user-config.jam file for these
>> entries looks like:
>>
>> using clang-win : 3.8 : SomePath/clang-cl : <compatibility>vc12
>> using clang-win : 3.9 : SomePath/clang-cl : <compatibility>vc14
>>
>> By passing toolset=clang-win-3.8 or toolset=clang-win-3.9 I was able to
>> successfully test these implementations against the Boost PP test code.
>>
>> There are quite a few failures in this clang emulation of the VC++
>> preprocessor when tested against the preprocessor test code. In fact
>> testing clang emulation of VC++ preprocessor when I don't treat clang as
>> VC++ in Boost PP, but as its normal C++ standard conforming
>> preprocessor, still fails a few cases but far less than when clang is
>> treated as VC++ in Boost PP. Needless to say when invoking clang-linux,
>> which tests the normal clang implementation whether on Windows or Linux,
>> there are no failures in the Boost PP tests.
>>
>> I am perfectly willing to push my changes to 'develop' for the
>> preprocessor. The changes are essentially just in the Boost PP
>> config.hpp file, which sets macros which control the compiler
>> workarounds in Boost PP. As I have previously stated I am not personally
>> willing to try to figure out or report to clang why their VC++
>> preprocessor emulation in Boost PP is failing, but others who are
>> interested can do so if they wish. My personal reasons for this is that
>> I think it is a very bad thing to attempt to replicate an already flawed
>> C++ preprocessor in another compiler in general code. I also have spent
>> enough time working with the VC++ preprocessor trying to find
>> workarounds for its non-standard behavior that I do not want to do so
>> for another preprocessor which attempts to be non-standard.
>>
>> I posted this to alert others to my plans to update Boost PP on
>> 'develop' with this change, in case anybody is greatly opposed to it or
>> wants to discuss it further. The change will not affect any other
>> compiler but clang in VC++ preprocessor emulation mode. Unless I hear
>> objections etc. I plan to push my update within the next day although I
>> will wait awhile for any replies to this post.
>>
>
> I pushed my update to Boost PP on 'develop' so anybody using clang
> targeting VC++ for Windows can try it out. It is possible that the clang
> emulating the non-standard VC++ preprocessor errors I see when running the
> preprocessor tests with clang-win toolset are few but are being propagated
> in many different cases. However I don't even think there is a way to see,
> for anybody interested, how clang is expanding macros in its VC++ emulation
> as opposed to normal clang-linux where macro expansion is shown when clang
> preprocessor erros are detected.
>
> Note on clang targeting on Windows:
>
> The LLVM 3.8 binary distribution of clang for Windows defaults to
> clang/clang++ targeting VC++, while all previous LLVM binary distributions
> of clang for Windows defaulted to clang/clang++ targeting mingw(-64)/gcc.
>
> The clang-cl executable always targets VC++ AFAIK. When you build from
> source using VC++ on Windows then clang/clang++ targets VC++ by default and
> when you build from source using mingw(-64)/gcc on Windows then
> clang/clang++ targets mingw(-64)/gcc by default.
>
> You can always change the targeting of clang through the use of the
> clang/clang++ '-target' option. It's details are poorly documented at
> http://clang.llvm.org/docs/CrossCompilation.html#target-triple. I chided
> clang developers about this incomplete documentation but without effect.
>
> I was given the targets '-target i686-pc-windows-gnu' and '-target
> x86_64-pc-windows-gnu' as a way of targeting mingw(-64)/gcc for 32-bit and
> 64-bit clang/clang++ versions respectively, both of which I have tested and
> do work. I believe the equivalent targets for 32-bit and 64-bit versions of
> clang/clang++ targeting VC++ are '-target=i686-pc-windows-msvc' and
> '-target=x86_64-pc-windows-msvc' respectively but I have not tried these
> out.
>
>
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