[llvm-dev] Miscellaneous warnings in code using Visual Studio

Tue Jan 12 09:42:03 PST 2021

On Tue, Jan 12, 2021 at 12:37 PM David Blaikie <dblaikie at gmail.com> wrote:
>
>
>
> On Tue, Jan 12, 2021 at 9:34 AM Aaron Ballman <aaron at aaronballman.com> wrote:
>>
>> On Tue, Jan 12, 2021 at 12:17 PM David Blaikie via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> >
>> > If they prove to be good cleanup/improvements to the code in general - but we don't try too hard to be -Werror clean on every compiler, mostly just self-hosted clang.
>>
>> This doesn't match my understanding -- we have a documented CMake
>> option that controls -Werror and I think we've always tried to be
>> -Werror clean with Clang, GCC, and MSVC builds before to support that
>> build configuration.
>
>
> Certainly I don't think we've ever outright rejected any path forward for avoiding a warning from any supported compiler (either by changing the code or suppressing the warning in the LLVM build in general) - though I don't think practically speaking we try very hard to keep all the supported compiler versions (not just brands, but the full supported version range of each) -Werror clean - about the cleanest would be a selfhost build, there are many buildbots/etc that check that is -Werror clean.

My recollection is that we only require the selfhost build to be
-Werror clean (with a bot configured to test that) but that we strive
to be -Werror clean when it won't introduce unwanted changes to the
code (in which case, we're happier to disable the warning within
CMake). So I think we may be saying the same things with different
words, but maybe we have a different definition of "try very hard"
here. :-)

~Aaron

>
>>
>>
>> > The line is fuzzy - if a warning isn't /too/ bad (ie: doesn't require extreme contortions to the code to address the warning) then fixing instances seems ok. If it's unhelpful (eg: a warning has a high false positive rate and/or clang's equivalent warning is more nuanced and avoids the need to touch false positives) we may disable warnings in LLVM. (this doesn't address the issue of warnings in LLVM's public headers - not every downstream consumer of LLVM is going to disable the same set of warnings, so sometimes it's necessary to do some warning cleanup even for undesirable warnings)
>>
>> I agree that we don't want large amounts of code churn for warnings
>> that are typically off by default in our default cmake configuration
>> (or could be made off by default if they're sufficiently low quality),
>> but I think this situation is different. I think these new warnings
>> were recently introduced and are ones we would typically fix with an
>> NFC patch.
>>
>> ~Aaron
>>
>> >
>> > On Tue, Jan 12, 2021 at 9:14 AM Paul C. Anagnostopoulos via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> >>
>> >> When I build on Windows 7 with Visual Studio, I get various warnings that were ignored until I recently set
>> >>
>> >> LLVM_ENABLE_WERROR:BOOL=ON
>> >>
>> >> One example is shown below. Should I take the time to hunt these down and fix them?
>> >>
>> >>
>> >> **********************************************************************
>> >> ** Visual Studio 2019 Developer Command Prompt v16.8.1
>> >> ** Copyright (c) 2020 Microsoft Corporation
>> >> **********************************************************************
>> >>
>> >> D:\LLVM\build>build-targets.bat
>> >>         1 file(s) copied.
>> >> [363/1578] Building CXX object lib\CodeGen\...LLVMGlobalISel.dir\MachineIRBuilder.cpp.obj
>> >> FAILED: lib/CodeGen/GlobalISel/CMakeFiles/LLVMGlobalISel.dir/MachineIRBuilder.cpp.obj
>> >> C:\PROGRA~2\MIB055~1\2019\COMMUN~1\VC\Tools\MSVC\1428~1.293\bin\Hostx86\x86\cl.exe  /nolog
>> >> o /TP -DGTEST_HAS_RTTI=0 -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS
>> >> -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_FILE_OFFSET_BITS=64 -D_HAS_EXCEPTI
>> >> ONS=0 -D_LARGEFILE_SOURCE -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE
>> >> -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Ilib\CodeGen\Global
>> >> ISel -IC:\LLVM\llvm-project\llvm\lib\CodeGen\GlobalISel -Iinclude -IC:\LLVM\llvm-project\l
>> >> lvm\include /DWIN32 /D_WINDOWS   /WX /Zc:inline /Zc:__cplusplus /Zc:strictStrings /Oi /Zc:
>> >> rvalueCast /bigobj /W4 -wd4141 -wd4146 -wd4244 -wd4267 -wd4291 -wd4351 -wd4456 -wd4457 -wd
>> >> 4458 -wd4459 -wd4503 -wd4624 -wd4722 -wd4100 -wd4127 -wd4512 -wd4505 -wd4610 -wd4510 -wd47
>> >> 02 -wd4245 -wd4706 -wd4310 -wd4701 -wd4703 -wd4389 -wd4611 -wd4805 -wd4204 -wd4577 -wd4091
>> >>  -wd4592 -wd4319 -wd4709 -wd4324 -w14062 -we4238 /MDd /Zi /Ob0 /Od /RTC1  /EHs-c- /GR- -st
>> >> d:c++14 /showIncludes /Folib\CodeGen\GlobalISel\CMakeFiles\LLVMGlobalISel.dir\MachineIRBui
>> >> lder.cpp.obj /Fdlib\CodeGen\GlobalISel\CMakeFiles\LLVMGlobalISel.dir\LLVMGlobalISel.pdb /F
>> >> S -c C:\LLVM\llvm-project\llvm\lib\CodeGen\GlobalISel\MachineIRBuilder.cpp
>> >> C:\LLVM\llvm-project\llvm\lib\CodeGen\GlobalISel\MachineIRBuilder.cpp(657): error C2220: t
>> >> he following warning is treated as an error
>> >> C:\LLVM\llvm-project\llvm\lib\CodeGen\GlobalISel\MachineIRBuilder.cpp(657): warning C4018:
>> >>  '>=': signed/unsigned mismatch
>> >> [366/1578] Building CXX object lib\CodeGen\...CMakeFiles\LLVMGlobalISel.dir\Utils.cpp.obj
>> >> ninja: build stopped: subcommand failed.
>> >>
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>> >
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