Re: [boost] Regression testing Clang/LLVM with VC14.

Subject: Re: [boost] Regression testing Clang/LLVM with VC14.
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2016-04-09 03:19:58

On 9 Apr 2016 at 8:32, degski wrote:

> Sergey suggested I'd run regression tests, in the "other thread". I was
> hesitant at first, mostly due to the luke warm reception.

It's only apparently a luke warm reception due to the volume from 
those with various axes to grind about winclang's historical 
decisions. I very much doubt if the majority here isn't very excited 
about an officially Microsoft supported clang built into Visual 
Studio, and the fact we finally can write fully standards conforming 
C++ 14 (sans preprocessor) for the MSVC target.

All it requires is someone to raise the target on the Boost 
regression testing infrastructure and that should bring eyeballs to 
any compatibility problems. I thank you for investing the effort to 
make this happen.

> This was a test-run (testing the testing), with VC14U2. Assuming the above
> can get sorted, I would in reality like to test Clang/LLVM (with VC14U2). I
> would like to ask (Niall Douglas in particular, I guess) what the suggested
> parameters to run.py should be for this combo.

I am afraid I don't know. I have ... fairly eccentric views regarding 
Boost in that I'd like my libraries into Boost, but to otherwise have 
no mandatory dependencies on Boost whatsoever. To that end, I make 
very little use of Boost anything, especially recently with the post 
peer review AFIO v2 rewrite which only requires Bjarne's GSL as a 
mandatory dependency.

(gsl-lite is actually the variant I use, Microsoft GSL is a bit 
heavy. span<T> is amazing, AFIO v2's design is utterly based on 
span<T> and wouldn't be possible without).

> Should I target clang.exe or clang-cl.exe, develop or master. What about
> Clang/C2?

I can say much more useful about this. I would test BOTH because they 
are quite different in behaviour once you get into using them in 
anger. As a general hand waving sweeping generalisation, LLVM clang 
3.8 targeting MSVC is the superior tool relative to C2 clang 3.7. 
It's more stable, it generates better code, it doesn't ICE anything 
like as much. It does not, however, generate much useful debug info, 
only line numbers whereas C2 clang generates mostly accurate debug 
info.

I wouldn't bother with LLVM clang before 3.8 for the MSVC target. 
Previous versions ICEd a lot when you have RTTI and exceptions turned 
on.

Finally, be aware that --analyze works perfectly on winclang, and it 
will find quite a few problems that Microsoft's /analyze does not.

> How to reduce disk-space usage? 

Look into the /Z7 debug flag for MSVC. Generates only line number 
debug info, it's vastly smaller than /Zi.

If Boost is turning on /ZI (capital i), then it ought to change to 
/Zi (small i) as the Edit and Continue feature is excessive on disc 
space.

Finally passing pch=off to b2.exe might help reduce disk space, but 
slow builds.

Good luck and best speed with your efforts.

Niall

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