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

Tue Jan 12 09:33:52 PST 2021

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.

> 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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