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

Aaron Ballman aaron at aaronballman.com
Wed Apr 15 05:10:39 PDT 2015 

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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