[llvm] r234343 - Enable W4 warnings by default for MSVC builds

[Aaron Ballman]

Since AlignOf is part of our support headers, I would slightly prefer
if we could fix it there. As an experiment, I put in the proper
#pragma incantation around the declaration of AlignmentCalcImpl<T> in
AlignOf.h, and it resolved *all* of the warnings.

#pragma warning(push)
#pragma warning(disable : 4324)
template <typename T>
struct AlignmentCalcImpl {
  char x;
  T t;
private:
  AlignmentCalcImpl() {} // Never instantiate.
};
#pragma warning(pop)


While the #pragma dance is ugly (and would need to be abstracted away
via macros), it may be worth it since this is a support header (and we
cannot fix the padding issue because that's the whole point to that
structure). How do others feel?

~Aaron

On Thu, Apr 16, 2015 at 10:49 AM, Yaron Keren <yaron.keren at gmail.com> wrote:
> /W3 was probably cached from the previous build.
>
> So should we disable C4324 or fix (how?) the AlignOf?
>
>
> 2015-04-16 17:34 GMT+03:00 Aaron Ballman <aaron at aaronballman.com>:
>>
>> It seems that in order to trigger this, you have to have done a clean
>> cmake build, as I am now seeing the same warnings you are.
>>
>> ~Aaron
>>
>> On Thu, Apr 16, 2015 at 10:16 AM, Aaron Ballman <aaron at aaronballman.com>
>> wrote:
>> > On Thu, Apr 16, 2015 at 10:03 AM, Yaron Keren <yaron.keren at gmail.com>
>> > wrote:
>> >> It is same in the IDE and command line, Release or Debug (unthreaded),
>> >> 32
>> >> bit.
>> >> The warning is:
>> >>
>> >>   PPMacroExpansion.cpp
>> >> c:\llvm\include\llvm/Support/AlignOf.h(25): warning C4324:
>> >> 'llvm::AlignmentCalcImpl<T>' : structure was padded due to
>> >> __declspec(align()) [c:\llvm\msvc\tools\clang\lib\Lex\clangLex.vcxproj]
>> >>           with
>> >>           [
>> >>               T=clang::SrcMgr::ContentCache
>> >>           ] (c:\llvm\tools\clang\lib\Lex\PPCaching.cpp)
>> >>           c:\llvm\include\llvm/Support/AlignOf.h(40) : see reference to
>> >> class template instantiation 'llvm::AlignmentC
>> >>   alcImpl<T>' being compiled
>> >>           with
>> >>           [
>> >>               T=clang::SrcMgr::ContentCache
>> >>           ]
>> >>           c:\llvm\tools\clang\include\clang/Basic/SourceManager.h(225)
>> >> : see
>> >> reference to class template instantiation
>> >>    'llvm::AlignOf<clang::SrcMgr::ContentCache>' being compiled
>> >>
>> >> referring to SourceManager.h(225):
>> >>
>> >>   static_assert(llvm::AlignOf<ContentCache>::Alignment >= 8,
>> >>                 "ContentCache must be 8-byte aligned.");
>> >>
>> >> And appears whenever SourceManager.h is included, a lot.
>> >>
>> >> The compiler is Microsoft Visual Studio Ultimate 2013,  Version
>> >> 12.0.31101.00 Update 4.
>> >>
>> >> I'll try threaded build now.
>> >
>> > I will do a clean rebuild from scratch; I wonder if the reason I'm not
>> > seeing anything is because of some caching somewhere. Thank you!
>> >
>> > ~Aaron
>
>