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

NAKAMURA Takumi geek4civic at gmail.com
Wed Apr 15 05:13:17 PDT 2015 

It'd be good idea for published headers to be W4-clean, even if they
were ugly for us.

2015-04-15 21:10 GMT+09:00 Aaron Ballman <aaron at aaronballman.com>:
> On Wed, Apr 15, 2015 at 3:49 AM, Yaron Keren <yaron.keren at gmail.com> wrote:
>> Hi,
>>
>> Now with real /W4 in effect, there are new warnings
>>
>>  lib\support\Windows/TimeValue.inc(48): warning C4189: 'Error' : local
>> variable is initialized but not referenced
>
> Thank you for fixing this one!
>
>>
>>  lib\transforms\utils\lcssa.cpp(345): warning C4718: 'verifyLoop' :
>> recursive call has no side effects, deleting
>
> I think this one has pointed out a possible issue, but likely a benign
> one. It looks like the point to that recursive call was the assert,
> but the code was commit with the assert commented out in r200067.
>
>>
>> and tons of :
>>
>>  include\llvm/Support/AlignOf.h(25): warning C4324:
>> 'llvm::AlignmentCalcImpl<T>' : structure was padded due to
>> __declspec(align())
>
> I think this warning can be globally disabled, but it might be nice to
> selectively enable it for headers we expose to the C API?
>
> ~Aaron
>
>>
>> I fixed the first warning in r234982 but not sure if the other warnings
>> should be disabled or the code fixed.
>>
>> Yaron
>>
>>
>> 2015-04-14 2:46 GMT+03:00 Zachary Turner <zturner at google.com>:
>>>
>>> Will commit the patch to strip /W3 tomorrow morning if there's no further
>>> objections.
>>>
>>> On Mon, Apr 13, 2015 at 12:25 PM Aaron Ballman <aaron at aaronballman.com>
>>> wrote:
>>>>
>>>> On Mon, Apr 13, 2015 at 3:21 PM, Zachary Turner <zturner at google.com>
>>>> wrote:
>>>> > I think I figured all this out (mostly).  Basically it only happens
>>>> > with
>>>> > Ninja.  Ninja doesn't know what command line options actually mean, it
>>>> > just
>>>> > makes a big list of them and passes them through for each file.  The
>>>> > Visual
>>>> > Studio generator has to know, because to make a meaningful Visual
>>>> > Studio
>>>> > project it has to generate XML with semantic tags like
>>>> > <WarningLevel>Level4</WarningLevel>.  So I think what happens is the
>>>> > Visual
>>>> > Studio generator seems /W3 then later sees /W4 and only generates one
>>>> > tag in
>>>> > the vcxproj (I confirmed that even in my case where /W3 and /W4 are
>>>> > part of
>>>> > CMAKE_CXX_FLAGS, Only a single <WarningLevel>Level4</WarningLevel> goes
>>>> > into
>>>> > the vcxproj.
>>>> >
>>>> > There's still the question of why your CMAKE_CXX_FLAGS doesn't contain
>>>> > anything, and I'm not sure about that.  But I don't think it matters
>>>> > much,
>>>> > because you would be seeing the same behavior with Visual Studio either
>>>> > way
>>>> > (namely, that it would work).
>>>> >
>>>> > On the other hand, ninja just appends commands line and passes them all
>>>> > through without knowing what they mean, so it can't be made smart
>>>> > enough to
>>>> > know that /W3 and /W4 should be collapsed.  You can verify that running
>>>> > "cl
>>>> > /W3 /W4 foo.cpp" will reproduce the error, for example.
>>>> >
>>>> > The patch I included earlier removes /W3 from the command line, but
>>>> > only if
>>>> > it's about to append /W4.  I think this should cover everything?  Aaron
>>>> > raised a question on IRC about what happens if the user manually
>>>> > specifies a
>>>> > warning level on the command line.  I don't have a good answer to that,
>>>> > other than to say that if you manually write
>>>> > CMAKE_CXX_FLAGS:STRING="/W2" or
>>>> > something at CMake time, the current patch is already messed up as it
>>>> > will
>>>> > then append /W4 which in the best could would overwrite your /W2
>>>> > setting,
>>>> > and in the worst case would give the warnings I'm seeing here.  So I
>>>> > feel
>>>> > like we should just be able to ignore this case, and if it becomes an
>>>> > issue
>>>> > for someone in the future, we can add something like
>>>> > -DMSVC_WARNING_LEVEL
>>>> > which will allow us a better means to be able to override the /W4 with
>>>> > something else.
>>>>
>>>> If we're not regressing behavior with the patch you posted, then I
>>>> think that patch is good. We definitely don't want a ton of warnings
>>>> with Ninja.
>>>>
>>>> ~Aaron
>>>>
>>>> >
>>>> > On Mon, Apr 13, 2015 at 12:11 PM Kaylor, Andrew
>>>> > <andrew.kaylor at intel.com>
>>>> > wrote:
>>>> >>
>>>> >> I’m not set up for Ninja, so I get this:
>>>> >>
>>>> >>
>>>> >>
>>>> >> CMake Error: CMake was unable to find a build program corresponding to
>>>> >> "Ninja".
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >> But really I don’t know how much time it’s worth spending to figure
>>>> >> out
>>>> >> why it isn’t happening to me.  It is happening to you so we need to
>>>> >> fix it.
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >> From: Zachary Turner [mailto:zturner at google.com]
>>>> >> Sent: Monday, April 13, 2015 12:02 PM
>>>> >>
>>>> >>
>>>> >> To: Kaylor, Andrew; Aaron Ballman
>>>> >> Cc: llvm-commits at cs.uiuc.edu
>>>> >> Subject: Re: [llvm] r234343 - Enable W4 warnings by default for MSVC
>>>> >> builds
>>>> >>
>>>> >>
>>>> >>
>>>> >> Can you try the ninja generator?  First run "vcvarsall amd64", then
>>>> >> just
>>>> >> run "cmake -G Ninja f:\users\akaylor\llvm-s\llvm".  That's the only
>>>> >> difference I can see in what we're doing.
>>>> >>
>>>> >>
>>>> >>
>>>> >> On Mon, Apr 13, 2015 at 12:00 PM Kaylor, Andrew
>>>> >> <andrew.kaylor at intel.com>
>>>> >> wrote:
>>>> >>
>>>> >> I added the line you suggested to CMakeLists.txt, and this is what I
>>>> >> see:
>>>> >>
>>>> >>
>>>> >>
>>>> >> f:\users\akaylor\llvm-s\test>cmake -G "Visual Studio 12 2013 Win64"
>>>> >> f:\users\akaylor\llvm-s\llvm
>>>> >>
>>>> >> CMAKE_CXX_FLAGS =
>>>> >>
>>>> >> -- No build type selected, default to Debug
>>>> >>
>>>> >> -- The C compiler identification is MSVC 18.0.31101.0
>>>> >>
>>>> >> …
>>>> >>
>>>> >>
>>>> >>
>>>> >> Also, the /W3 flag isn’t being used during my build.
>>>> >>
>>>> >>
>>>> >>
>>>> >> -Andy
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >> From: Zachary Turner [mailto:zturner at google.com]
>>>> >> Sent: Monday, April 13, 2015 11:57 AM
>>>> >> To: Kaylor, Andrew; Aaron Ballman
>>>> >> Cc: llvm-commits at cs.uiuc.edu
>>>> >>
>>>> >>
>>>> >> Subject: Re: [llvm] r234343 - Enable W4 warnings by default for MSVC
>>>> >> builds
>>>> >>
>>>> >>
>>>> >>
>>>> >> 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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>>

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