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

Wed Apr 15 00:49:32 PDT 2015

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

 lib\transforms\utils\lcssa.cpp(345): warning C4718: 'verifyLoop' :
recursive call has no side effects, deleting

and tons of :

 include\llvm/Support/AlignOf.h(25): warning C4324:
'llvm::AlignmentCalcImpl<T>' : structure was padded due to
__declspec(align())

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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