[llvm] r234343 - Enable W4 warnings by default for MSVC builds
Zachary Turner
zturner at google.com
Mon Apr 13 16:46:12 PDT 2015
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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