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

Mon Apr 13 12:00:40 PDT 2015

http://www.cmake.org/Bug/view.php?id=14149

This is a bug on the CMake side that is asking how to remove /EHsc.  Not
really related to  the issue here, but you can see that this user had the
same conclusion: That CMake is initializinag CMAKE_CXX_FLAGS by default to
containa  few values, one of which is /W3.

If you're not seeing the issue, the only thing I can think of is that it's
because you have a cached value for LLVM_ENABLE_WARNINGS that is causing
/W4 to not be added to the command line.  Look in your build.ninja or run
ninja -v to see the actual command line being invoked.  I'm guessing it
contains /W3 but not /W4

On Mon, Apr 13, 2015 at 11:56 AM Zachary Turner <zturner at google.com> wrote:

> No, CMake itself initializes CMAKE_CXX_FLAGS to include /W3.  By default,
> if you do nothing, CMAKE_CXX_FLAGS will have /W3.  You can verify this by
> printing the value of CMAKE_CXX_FLAGS in the first line of
> llvm/CMakeLists.txt
>
> On Mon, Apr 13, 2015 at 11:55 AM Kaylor, Andrew <andrew.kaylor at intel.com>
> wrote:
>
>> I'm not sure I understand.  Are you saying this problem only happens if
>> you have CMAKE_CXX_FLAGS defined to include W3?
>>
>> I don't have CMAKE_CXX_FLAGS defined on my system and my version of CMake
>> (3.0.1) isn't defining it on its own, which would explain why I'm not
>> seeing the problem.  I guess your patch to strip W3 if it's there is OK,
>> though it should probably also look for W1 and W2.
>>
>> On the other hand, if there isn't some non-user reason that W3 would be
>> part of CMAKE_CXX_FLAGS I would say this fall under the "don't do that"
>> category of fix.
>>
>> -Andy
>>
>> -----Original Message-----
>> From: aaron.ballman at gmail.com [mailto:aaron.ballman at gmail.com] On Behalf
>> Of Aaron Ballman
>> Sent: Monday, April 13, 2015 11:44 AM
>> To: Zachary Turner
>> Cc: Kaylor, Andrew; llvm-commits at cs.uiuc.edu
>> Subject: Re: [llvm] r234343 - Enable W4 warnings by default for MSVC
>> builds
>>
>> When I do that, the first line of output shows /W3:
>>
>>
>> E:\llvm\x64>"D:\Program Files (x86)\Microsoft Visual Studio
>> 12.0\VC\vcvarsall.bat" amd64
>>
>> E:\llvm\x64>cmake -G "Visual Studio 12" ..\llvm CMAKE_CXX_FLAGS =
>> /DWIN32 /D_WINDOWS /W3 /GR /EHsc ....
>>
>> ~Aaron
>>
>> On Mon, Apr 13, 2015 at 2:37 PM, Zachary Turner <zturner at google.com>
>> wrote:
>> > Also what version of CMake are you using?  Maybe it's an issue with
>> > CMake >= 3.0?  Try putting the following line at the top of your
>> > CMakeLists.txt
>> >
>> > message("CMAKE_CXX_FLAGS = ${CMAKE_CXX_FLAGS}")
>> >
>> > If you don't see /W3 in there, you won't hit the problem.
>> >
>> > On Mon, Apr 13, 2015 at 11:36 AM Zachary Turner <zturner at google.com>
>> wrote:
>> >>
>> >> Just realized maybe 2012 was a typo.  Are you actually still using
>> 2012?
>> >> I thought support was dropped.
>> >>
>> >> On Mon, Apr 13, 2015 at 11:33 AM Aaron Ballman
>> >> <aaron at aaronballman.com>
>> >> wrote:
>> >>>
>> >>> I do not get the warnings when building x64 or x86 on Windows 7,
>> >>> MSVC 2012, debug build. This is when building LLVM, Clang, lld, and
>> >>> clang tools extra
>> >>>
>> >>> ~Aaron
>> >>>
>> >>> On Mon, Apr 13, 2015 at 2:22 PM, Zachary Turner <zturner at google.com>
>> >>> wrote:
>> >>> > I'm building x64.  Can you try that?  Run "vcvarsall amd64" before
>> >>> > building LLVM
>> >>> >
>> >>> > On Mon, Apr 13, 2015 at 11:21 AM Kaylor, Andrew
>> >>> > <andrew.kaylor at intel.com>
>> >>> > wrote:
>> >>> >>
>> >>> >> I haven’t seen that.  I’m not seeing any warnings right now.
>> >>> >>
>> >>> >>
>> >>> >>
>> >>> >> From: Zachary Turner [mailto:zturner at google.com]
>> >>> >> Sent: Monday, April 13, 2015 11:17 AM
>> >>> >> To: Kaylor, Andrew; llvm-commits at cs.uiuc.edu
>> >>> >> Subject: Re: [llvm] r234343 - Enable W4 warnings by default for
>> >>> >> MSVC builds
>> >>> >>
>> >>> >>
>> >>> >>
>> >>> >> Hi Andy, this is causing a huge slew of warning spam.  Is this
>> >>> >> expected?
>> >>> >> CMake passes /W3 by default, so  every single translation unit I
>> >>> >> compile gives me the following warning:
>> >>> >>
>> >>> >>
>> >>> >>
>> >>> >> cl : Command line warning D9025 : overriding '/W3' with '/W4'
>> >>> >>
>> >>> >>
>> >>> >>
>> >>> >> Furthermore, since this is a command line warning and not a
>> >>> >> compiler warning, it cannot be suppressed.  Unless you have any
>> >>> >> better ideas on how to address this, I think this should be
>> >>> >> reverted.
>> >>> >>
>> >>> >>
>> >>> >>
>> >>> >> On Tue, Apr 7, 2015 at 12:07 PM Andrew Kaylor
>> >>> >> <andrew.kaylor at intel.com>
>> >>> >> wrote:
>> >>> >>
>> >>> >> Author: akaylor
>> >>> >> Date: Tue Apr  7 14:01:01 2015
>> >>> >> New Revision: 234343
>> >>> >>
>> >>> >> URL: http://llvm.org/viewvc/llvm-project?rev=234343&view=rev
>> >>> >> Log:
>> >>> >> Enable W4 warnings by default for MSVC builds
>> >>> >>
>> >>> >> Modified:
>> >>> >>     llvm/trunk/CMakeLists.txt
>> >>> >>
>> >>> >> Modified: llvm/trunk/CMakeLists.txt
>> >>> >> URL:
>> >>> >>
>> >>> >> http://llvm.org/viewvc/llvm-project/llvm/trunk/CMakeLists.txt?rev
>> >>> >> =234343&r1=234342&r2=234343&view=diff
>> >>> >>
>> >>> >>
>> >>> >> =================================================================
>> >>> >> =============
>> >>> >> --- llvm/trunk/CMakeLists.txt (original)
>> >>> >> +++ llvm/trunk/CMakeLists.txt Tue Apr  7 14:01:01 2015
>> >>> >> @@ -233,14 +233,7 @@ list(REMOVE_DUPLICATES LLVM_TARGETS_TO_B
>> >>> >>  include(AddLLVMDefinitions)
>> >>> >>
>> >>> >>  option(LLVM_ENABLE_PIC "Build Position-Independent Code" ON)
>> >>> >> -
>> >>> >> -# MSVC has a gazillion warnings with this.
>> >>> >> -if( MSVC )
>> >>> >> -  option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." OFF)
>> >>> >> -else()
>> >>> >> -  option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
>> >>> >> -endif()
>> >>> >> -
>> >>> >> +option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
>> >>> >>  option(LLVM_ENABLE_MODULES "Compile with C++ modules enabled."
>> >>> >> OFF)  option(LLVM_ENABLE_CXX1Y "Compile with C++1y enabled." OFF)
>> >>> >> option(LLVM_ENABLE_LIBCXX "Use libc++ if available." OFF)
>> >>> >>
>> >>> >>
>> >>> >> _______________________________________________
>> >>> >> llvm-commits mailing list
>> >>> >> llvm-commits at cs.uiuc.edu
>> >>> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>> >>> >
>> >>> >
>> >>> > _______________________________________________
>> >>> > llvm-commits mailing list
>> >>> > llvm-commits at cs.uiuc.edu
>> >>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>> >>> >
>>
>
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