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

Tue Jan 12 09:36:55 PST 2021

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.

>
> > 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.
> >>
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
> > _______________________________________________
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>
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