[PATCH] D42762: Rewrite the VS Integration Scripts

[Hans Wennborg via llvm-commits]

I'd still like to understand how msbuild.exe is running the build to
expect vc140.pdb to be written, and why we're outputing the .pdb file
in the wrong place. Or is vc140.pdb some additional pdb that's
supposed to get output on the side?

I don't like the idea of the vs integration rewriting flags. What
about users not using msbuild but cmake? Should cmake start rewriting
flags for clang-cl too?

On Fri, Feb 2, 2018 at 5:49 PM, Zachary Turner <zturner at google.com> wrote:
> That’s why we unset the option in msbuild, so it no longer expects that. The
> current solution makes it behave exactly as if /Z7 had been chosen in the
> UI. Having the compiler write a type server pdb seems like an enormous
> amount of work, and writing a 0 byte file seems odd.
>
> On Fri, Feb 2, 2018 at 8:46 AM Hans Wennborg <hans at chromium.org> wrote:
>>
>> But if the build system invokes the compiler + linker, expects to end
>> up with vc140.pdb but instead ends up with foo.pdb, maybe the compiler
>> + linker is not interpreting the flags passed from the build system
>> correctly.
>>
>> On Fri, Feb 2, 2018 at 5:44 PM, Zachary Turner <zturner at google.com> wrote:
>> > Also, since this is a build system issue and not a compiler issue, it
>> > seems
>> > intuitive to me to deal with it at the build system level
>> > On Fri, Feb 2, 2018 at 8:42 AM Zachary Turner <zturner at google.com>
>> > wrote:
>> >>
>> >> It’s a compiler generated pdb, /Zi means “all compiler processes should
>> >> write to the same pdb”, whereas /Z7 means “put the debug info in the
>> >> object
>> >> files instead”. If the user does a clean build the file will get
>> >> deleted and
>> >> there won’t even be anything to touch. The file name comes from another
>> >> flag
>> >> (/Fo or /Fd, can’t remember) which msbuild defaults to vc$(ToolsetName)
>> >> On Fri, Feb 2, 2018 at 8:36 AM Hans Wennborg <hans at chromium.org> wrote:
>> >>>
>> >>> Yes, but I'd like to understand exactly why. Where does the name
>> >>> vc140.pdb come from? What is supposed to go into this file? Maybe
>> >>> clang-cl should touch it when invoked with /Zi?
>> >>>
>> >>> On Fri, Feb 2, 2018 at 5:32 PM, Zachary Turner <zturner at google.com>
>> >>> wrote:
>> >>> > Symptom: when /Zi is selected, VS always rebuilds all source files,
>> >>> > even if
>> >>> > just 1 (possibly even none) have changed.
>> >>> >
>> >>> > Fix: Change /Zi to /Z7 in the UI
>> >>> >
>> >>> > More details here: https://bugs.llvm.org/show_bug.cgi?id=36140
>> >>> >
>> >>> > On Fri, Feb 2, 2018 at 8:12 AM Hans Wennborg <hans at chromium.org>
>> >>> > wrote:
>> >>> >>
>> >>> >> On Fri, Feb 2, 2018 at 4:40 PM, Zachary Turner <zturner at google.com>
>> >>> >> wrote:
>> >>> >> >
>> >>> >> > On Fri, Feb 2, 2018 at 6:23 AM Hans Wennborg <hans at chromium.org>
>> >>> >> > wrote:
>> >>> >> >>
>> >>> >> >> (Your reply didn't go to Phabricator, so re-adding folks
>> >>> >> >> subscribed
>> >>> >> >> there.)
>> >>> >> >>
>> >>> >> >> On Thu, Feb 1, 2018 at 9:08 PM, Zachary Turner via llvm-commits
>> >>> >> >> <llvm-commits at lists.llvm.org> wrote:
>> >>> >> >> > I'm kind of imagining this world where we have one VS
>> >>> >> >> > Integration
>> >>> >> >> > that
>> >>> >> >> > works
>> >>> >> >> > no matter what version of LLVM you have.  The nice thing about
>> >>> >> >> > this
>> >>> >> >> > is
>> >>> >> >> > that
>> >>> >> >> > it allows it to work with hermetic toolchains, older versions
>> >>> >> >> > of
>> >>> >> >> > LLVM
>> >>> >> >> > that
>> >>> >> >> > may already be installed on a user's machine, local dev builds
>> >>> >> >> > of
>> >>> >> >> > LLVM,
>> >>> >> >> > etc.
>> >>> >> >>
>> >>> >> >> I'm on board with this. It seems useful especially for the case
>> >>> >> >> where
>> >>> >> >> the developer may have multiple LLVM toolchains installed and
>> >>> >> >> want
>> >>> >> >> to
>> >>> >> >> point at a specific one. It would be nice if we could still
>> >>> >> >> trigger
>> >>> >> >> the installation of the toolset when installing the LLVM
>> >>> >> >> toolchain
>> >>> >> >> though.
>> >>> >> >>
>> >>> >> >> But for the integration to work regardless of LLVM version, I
>> >>> >> >> don't
>> >>> >> >> think the integration can bake in assumptions about what flags
>> >>> >> >> clang-cl supports and re-map them etc. The set of flags
>> >>> >> >> supported
>> >>> >> >> by
>> >>> >> >> clang-cl and how they're handled changes frequently.
>> >>> >> >>
>> >>> >> >> I like the idea of a VS integration that's LLVM-version
>> >>> >> >> independent
>> >>> >> >> --
>> >>> >> >> the current one is almost that except for the baked in version
>> >>> >> >> number
>> >>> >> >> -- but for it to work, I think it has to be really simple,
>> >>> >> >> basically
>> >>> >> >> just pointing MSVC at clang-cl.exe and nothing more.
>> >>> >> >
>> >>> >> > I’ve already mentioned at least one case whereas this is
>> >>> >> > impossible
>> >>> >> > (/Zi
>> >>> >> > vs
>> >>> >> > /Z7), and given that there are thousands of lines of msbuild
>> >>> >> > logic
>> >>> >> > that
>> >>> >> > are
>> >>> >> > running and processing these options before they make it to
>> >>> >> > clang-cl,
>> >>> >> > I’m
>> >>> >> > certain there are more that we don’t yet know about.
>> >>> >>
>> >>> >> I'd like to understand the /Zi vs /Z7 thing better. Can you ELI5
>> >>> >> the
>> >>> >> problem?
>> >>> >>
>> >>> >>
>> >>> >> >
>> >>> >> > Simple is nice, I don’t disagree with that, but not at the
>> >>> >> > expense
>> >>> >> > of
>> >>> >> > user
>> >>> >> > experience.  i still don’t think there’s any maintenance issues
>> >>> >> > here
>> >>> >> > though.
>> >>> >> > I think the current version here could probably sit for 5+ years
>> >>> >> > and
>> >>> >> > never
>> >>> >> > need to be touched, continuing to work both with future VS
>> >>> >> > versions
>> >>> >> > and
>> >>> >> > future clang-cl versions unmodified.
>> >>> >> >
>> >>> >> >
>> >>> >> >>
>> >>> >> >>
>> >>> >> >> > The only maintenance burden I can think of is one where we
>> >>> >> >> > remove
>> >>> >> >> > or
>> >>> >> >> > add
>> >>> >> >> > flags in clang-cl, which doesn't happen very often, if ever.
>> >>> >> >>
>> >>> >> >> It puzzles me that you think we rarely or ever change the flags
>> >>> >> >> clang-cl supports or how they're handled. In my experience, the
>> >>> >> >> flags
>> >>> >> >> change every release.
>> >>> >> >>
>> >>> >> >> >  Any flag that
>> >>> >> >> > is added to MSVC doesn't require any action from us.
>> >>> >> >>
>> >>> >> >> Depends on the flag, no?
>> >>> >> >
>> >>> >> > Not really.  Any flag that msvc adds, assuming we don’t update
>> >>> >> > this
>> >>> >> > file,
>> >>> >> > gets passed through to clang-cl which is what you’re proposing i
>> >>> >> > do
>> >>> >> > with
>> >>> >> > all
>> >>> >> > options anyway.
>> >>> >> >
>> >>> >> >
>> >>> >> >>
>> >>> >> >>
>> >>> >> >> > I plan to expose a UI for optimizations and warning, so I
>> >>> >> >> > could
>> >>> >> >> > see a
>> >>> >> >> > maintenace burden when we add new -W or -f flags that are not
>> >>> >> >> > exposed
>> >>> >> >> > to
>> >>> >> >> > the
>> >>> >> >> > UI.  But those can still be specified via additional compiler
>> >>> >> >> > flags.
>> >>> >> >> > And
>> >>> >> >> > the maintenance burden is actually less than coupling it to
>> >>> >> >> > the
>> >>> >> >> > installed
>> >>> >> >> > toolchain because we can do it at our leisure, rather than
>> >>> >> >> > being
>> >>> >> >> > pressed
>> >>> >> >> > to
>> >>> >> >> > get it done by a release.
>> >>> >> >>
>> >>> >> >> But you're saying that the toolset should be independent of the
>> >>> >> >> LLVM
>> >>> >> >> version? If we add a -Wfoobar flag in Clang x.y.z and want to
>> >>> >> >> expose
>> >>> >> >> that in your UI, that UI then needs to be conditional on what
>> >>> >> >> version
>> >>> >> >> of Clang it's targeting. Same thing if we remove -Wquux in
>> >>> >> >> another
>> >>> >> >> Clang version. This sounds like a maintenance nightmare to me.
>> >>> >> >
>> >>> >> > If we do nothing, any added -W options are still available via
>> >>> >> > Additional
>> >>> >> > Compiler Flags.   So as with all the other custom logic in the
>> >>> >> > msbuild
>> >>> >> > files, we’re still not obligated to maintain that, and it will
>> >>> >> > still
>> >>> >> > continue to work fine
>> >>> >> >
>> >>> >> > For options that we remove, sure, we should update the file.  One
>> >>> >> > way to
>> >>> >> > handle this would be to add a new version of clang-cl.xml every
>> >>> >> > release,
>> >>> >> > and
>> >>> >> > conditionally include the proper xml file.  How frequently do we
>> >>> >> > remove
>> >>> >> > warnings though?  Doing so would cause people’s builds to break
>> >>> >> > because
>> >>> >> > they’d be passing unrecognized options, so I suspect it’s almost
>> >>> >> > never.
>> >>> >> >
>> >>> >> > Of all the things though, this is the one that I think it’s most
>> >>> >> > important
>> >>> >> > to accept the maintenance burden of.  This is the difference
>> >>> >> > between
>> >>> >> > “we
>> >>> >> > put
>> >>> >> > the minimum amount of work possible into getting this working so
>> >>> >> > we
>> >>> >> > could do
>> >>> >> > other things” and “we care about this, we made it as easy as
>> >>> >> > possible to
>> >>> >> > use, we designed it with VS users in mind”.  As someone who used
>> >>> >> > VS
>> >>> >> > through
>> >>> >> > the UI exclusively for over 15 years, there’s going to be a huge
>> >>> >> > difference
>> >>> >> > between providing this feature and not providing it.
>> >>> >> >
>> >>> >> > I *still* don’t see the maintenance burden as being high though.
>> >>> >> > We
>> >>> >> > can
>> >>> >> > release a new clang-cl.xml like every 2-3 years and it would take
>> >>> >> > all of
>> >>> >> > 30
>> >>> >> > minutes to put it together and get it on the marketplace.
>> >>> >> >
>> >>> >> >
>> >>> >> >
>> >>> >> >>
>> >>> >> >>
>> >>> >> >>
>> >>> >> >> > One thing I could maybe do to lower the maintenance burden a
>> >>> >> >> > little
>> >>> >> >> > is
>> >>> >> >> > to
>> >>> >> >> > try to have some better logic for detecting the clang version.
>> >>> >> >> > We
>> >>> >> >> > were
>> >>> >> >> > already using the registry before anyway to find the installed
>> >>> >> >> > LLVM,
>> >>> >> >> > maybe
>> >>> >> >> > there's a way for me to just figure out the version without
>> >>> >> >> > the
>> >>> >> >> > additional
>> >>> >> >> > registry value.  I'll have to look into that though.
>> >>> >> >> >
>> >>> >> >> >
>> >>> >> >> >
>> >>> >> >> > On Thu, Feb 1, 2018 at 11:09 AM Zachary Turner
>> >>> >> >> > <zturner at google.com>
>> >>> >> >> > wrote:
>> >>> >> >> >>
>> >>> >> >> >> On Thu, Feb 1, 2018 at 10:48 AM Hans Wennborg via Phabricator
>> >>> >> >> >> <reviews at reviews.llvm.org> wrote:
>> >>> >> >> >>>
>> >>> >> >> >>> hans added inline comments.
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>> ================
>> >>> >> >> >>> Comment at: llvm/tools/msbuild/Clang.Cpp.Common.props:41
>> >>> >> >> >>> +
>> >>> >> >> >>> +    <!-- The registry key may not be set if it's an old
>> >>> >> >> >>> installer,
>> >>> >> >> >>> try
>> >>> >> >> >>> the newest version that exists -->
>> >>> >> >> >>> +    <LLVMVersion Condition="'$(LLVMVersion)' == '' and
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>> Exists('$(LLVMInstallDir)\lib\clang\7.0.0')">7.0.0</LLVMVersion>
>> >>> >> >> >>> ----------------
>> >>> >> >> >>> zturner wrote:
>> >>> >> >> >>> > hans wrote:
>> >>> >> >> >>> > > As I mentioned before, separating the toolset config
>> >>> >> >> >>> > > from
>> >>> >> >> >>> > > the
>> >>> >> >> >>> > > actual
>> >>> >> >> >>> > > toolchain installation makes me a little nervous.
>> >>> >> >> >>> > >
>> >>> >> >> >>> > > But if we're doing it, the version checks below should
>> >>> >> >> >>> > > probably
>> >>> >> >> >>> > > include the .1 versions too, i.e. at least 5.0.1 and
>> >>> >> >> >>> > > 6.0.1.
>> >>> >> >> >>> > Unless we're going to release the full thing including the
>> >>> >> >> >>> > compiler,
>> >>> >> >> >>> > linker, etc through the marketplace I don't see an
>> >>> >> >> >>> > alternative.
>> >>> >> >> >>> > In
>> >>> >> >> >>> > any
>> >>> >> >> >>> > case, I actually think this it's preferable this way.
>> >>> >> >> >>> > There's
>> >>> >> >> >>> > nothing
>> >>> >> >> >>> > really about the two that benefits from having them
>> >>> >> >> >>> > coupled
>> >>> >> >> >>> > together, as far
>> >>> >> >> >>> > as I can see.   I'm willing to be convinced though, if we
>> >>> >> >> >>> > can
>> >>> >> >> >>> > figure
>> >>> >> >> >>> > out how
>> >>> >> >> >>> > to to do it so that we can still ship it on the
>> >>> >> >> >>> > marketplace.
>> >>> >> >> >>> "There's nothing really about the two that benefits from
>> >>> >> >> >>> having
>> >>> >> >> >>> them
>> >>> >> >> >>> coupled together,"
>> >>> >> >> >>>
>> >>> >> >> >>> The toolset needs to know at least where to find the
>> >>> >> >> >>> toolchain
>> >>> >> >> >>> and
>> >>> >> >> >>> how
>> >>> >> >> >>> to
>> >>> >> >> >>> invoke it. If we decouple them, there needs to be an
>> >>> >> >> >>> interface
>> >>> >> >> >>> between
>> >>> >> >> >>> them
>> >>> >> >> >>> that can't change: in this case the LLVM path and version
>> >>> >> >> >>> number in
>> >>> >> >> >>> the
>> >>> >> >> >>> registry.
>> >>> >> >> >>
>> >>> >> >> >> Has that ever changed?  Doesn’t seem too onerous, using the
>> >>> >> >> >> registry
>> >>> >> >> >> is
>> >>> >> >> >> the windows way anyway, if anything this feels like the
>> >>> >> >> >> proper
>> >>> >> >> >> way.
>> >>> >> >> >>
>> >>> >> >> >>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>> But at the same time you're baking in all this logic in the
>> >>> >> >> >>> toolset
>> >>> >> >> >>> about
>> >>> >> >> >>> how to invoke the toolchain, what flags are supported, etc.
>> >>> >> >> >>> Those
>> >>> >> >> >>> things are
>> >>> >> >> >>> strongly dependent on the toolchain, which in this
>> >>> >> >> >>> de-coupled
>> >>> >> >> >>> world
>> >>> >> >> >>> seems
>> >>> >> >> >>> problematic. It seems like you're actually making the
>> >>> >> >> >>> coupling
>> >>> >> >> >>> tighter
>> >>> >> >> >>> in
>> >>> >> >> >>> that way, except you still want to ship the two parts
>> >>> >> >> >>> separately.
>> >>> >> >> >>>
>> >>> >> >> >>> Are there restrictions in the marketplace about how big a
>> >>> >> >> >>> vsix
>> >>> >> >> >>> can
>> >>> >> >> >>> be?
>> >>> >> >> >>> Because if not, I think we could just package up
>> >>> >> >> >>> clang+headers+runtime
>> >>> >> >> >>> into
>> >>> >> >> >>> a vsix and ship the whole thing, and maybe that would be the
>> >>> >> >> >>> best
>> >>> >> >> >>> thing.
>> >>> >> >> >>
>> >>> >> >> >> An installer is very large though, and even if it’s allowed
>> >>> >> >> >> it’s
>> >>> >> >> >> kind
>> >>> >> >> >> of
>> >>> >> >> >> obnoxious to have to download a large amount of stuff if only
>> >>> >> >> >> one
>> >>> >> >> >> thing
>> >>> >> >> >> changes.  Being able to push changes to the Integration
>> >>> >> >> >> independently
>> >>> >> >> >> of an
>> >>> >> >> >> llvm release seems like a feature to me.
>> >>> >> >> >>
>> >>> >> >> >>  coupling it would also make it more difficult to use a
>> >>> >> >> >> custom
>> >>> >> >> >> built
>> >>> >> >> >> llvm
>> >>> >> >> >> toolchain, i can just change a registry setting right now and
>> >>> >> >> >> it’s
>> >>> >> >> >> good
>> >>> >> >> >> to
>> >>> >> >> >> go.  Even the builtin VS toolchains use the registry to
>> >>> >> >> >> locate
>> >>> >> >> >> paths,
>> >>> >> >> >> and we
>> >>> >> >> >> were already reading the registry before this anyway
>> >>> >> >> >>
>> >>> >> >> >>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>> Or we could just stick to the current installer version and
>> >>> >> >> >>> make it
>> >>> >> >> >>> a
>> >>> >> >> >>> little smarter about finding VS2017. Maybe instead of the
>> >>> >> >> >>> batch
>> >>> >> >> >>> files
>> >>> >> >> >>> we
>> >>> >> >> >>> write an actual program that finds the installation and
>> >>> >> >> >>> copies
>> >>> >> >> >>> the
>> >>> >> >> >>> files.
>> >>> >> >> >>
>> >>> >> >> >> I definitely think vsix is the way to go.  I’d hate to stick
>> >>> >> >> >> with
>> >>> >> >> >> batch
>> >>> >> >> >> files and not use the proper method of having an extension.
>> >>> >> >> >> It’s
>> >>> >> >> >> also
>> >>> >> >> >> more
>> >>> >> >> >> discoverable as an extension on the marketplace.
>> >>> >> >> >>
>> >>> >> >> >>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>> ================
>> >>> >> >> >>> Comment at: llvm/tools/msbuild/LLVM.props:8
>> >>> >> >> >>> +    <!-- Friendly names added to the PlatformToolset in the
>> >>> >> >> >>> property
>> >>> >> >> >>> pages. -->
>> >>> >> >> >>> +    <_PlatformToolsetFriendlyNameFor_llvm
>> >>> >> >> >>> Condition="'$(_PlatformToolsetFriendlyNameFor_llvm)' ==
>> >>> >> >> >>> ''">Clang
>> >>> >> >> >>> for
>> >>> >> >> >>> Windows</_PlatformToolsetFriendlyNameFor_llvm>
>> >>> >> >> >>> +  </PropertyGroup>
>> >>> >> >> >>> ----------------
>> >>> >> >> >>> zturner wrote:
>> >>> >> >> >>> > hans wrote:
>> >>> >> >> >>> > > Hmm, we previously intentionally called the toolset
>> >>> >> >> >>> > > "LLVM"
>> >>> >> >> >>> > > with
>> >>> >> >> >>> > > the
>> >>> >> >> >>> > > thinking that it would eventually include lld and
>> >>> >> >> >>> > > designated
>> >>> >> >> >>> > > the
>> >>> >> >> >>> > > complete
>> >>> >> >> >>> > > llvm toolchain, not just Clang. And is the "for Windows"
>> >>> >> >> >>> > > part
>> >>> >> >> >>> > > necessary?
>> >>> >> >> >>> > Do you think there's any value in having a toolset that
>> >>> >> >> >>> > does
>> >>> >> >> >>> > Clang+Link
>> >>> >> >> >>> > and a second one that does Clang+LLD?  Or do you think we
>> >>> >> >> >>> > should
>> >>> >> >> >>> > stick with
>> >>> >> >> >>> > only a single one?  I can change the name to LLVM though.
>> >>> >> >> >>> The best would be to only have one, but where the user could
>> >>> >> >> >>> select
>> >>> >> >> >>> between the two linkers, I think.
>> >>> >> >> >>
>> >>> >> >> >> Yea.  Can try that in a followup, may be tricky though
>> >>> >> >> >>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>> ================
>> >>> >> >> >>> Comment at: llvm/tools/msbuild/Toolset.targets:38
>> >>> >> >> >>> +
>> >>> >> >> >>> +    <!-- Warn if Fiber Safe Optimizations are enabled, and
>> >>> >> >> >>> then
>> >>> >> >> >>> ignore
>> >>> >> >> >>> them. -->
>> >>> >> >> >>> +    <Warning
>> >>> >> >> >>> Condition="'%(ClCompile.EnableFiberSafeOptimizations)'
>> >>> >> >> >>> ==
>> >>> >> >> >>> 'true'"
>> >>> >> >> >>> ----------------
>> >>> >> >> >>> zturner wrote:
>> >>> >> >> >>> > hans wrote:
>> >>> >> >> >>> > > This seems to duplicate a lot of logic from clang-cl.
>> >>> >> >> >>> > > It's
>> >>> >> >> >>> > > nice
>> >>> >> >> >>> > > to
>> >>> >> >> >>> > > provide a good UI for the user, but maintaining this
>> >>> >> >> >>> > > seems
>> >>> >> >> >>> > > a
>> >>> >> >> >>> > > lot
>> >>> >> >> >>> > > of work.
>> >>> >> >> >>> > > Are you not concerned that this will rot?
>> >>> >> >> >>> > I don't think it will.  Maybe I'm being overly optimistic
>> >>> >> >> >>> > here,
>> >>> >> >> >>> > but
>> >>> >> >> >>> > the
>> >>> >> >> >>> > only case we would ever need to maintain this again is if
>> >>> >> >> >>> > we
>> >>> >> >> >>> > started
>> >>> >> >> >>> > supporting these options.  Fiber Safe Optimizations, for
>> >>> >> >> >>> > example,
>> >>> >> >> >>> > I'm pretty
>> >>> >> >> >>> > sure we will never support.  If MSVC ever removes the
>> >>> >> >> >>> > option,
>> >>> >> >> >>> > for
>> >>> >> >> >>> > example,
>> >>> >> >> >>> > we can do nothing and continue to work.
>> >>> >> >> >>> >
>> >>> >> >> >>> > We could also just silently ignore them and just pass the
>> >>> >> >> >>> > option
>> >>> >> >> >>> > through to clang-cl, but these are pretty unusual options
>> >>> >> >> >>> > with
>> >>> >> >> >>> > pretty
>> >>> >> >> >>> > specialized use cases, so I feel like if I had gone out of
>> >>> >> >> >>> > my
>> >>> >> >> >>> > way
>> >>> >> >> >>> > to
>> >>> >> >> >>> > enable
>> >>> >> >> >>> > such a strange option I would want to know if the compiler
>> >>> >> >> >>> > was
>> >>> >> >> >>> > not
>> >>> >> >> >>> > going to
>> >>> >> >> >>> > respect it.
>> >>> >> >> >>> I feel pretty strongly that we should handle this clang-cl
>> >>> >> >> >>> side. If
>> >>> >> >> >>> a
>> >>> >> >> >>> flag is not supported, either we should ignore it, or if
>> >>> >> >> >>> it's
>> >>> >> >> >>> something the
>> >>> >> >> >>> user would want to know about us not supporting, we should
>> >>> >> >> >>> warn.
>> >>> >> >> >>> That's what
>> >>> >> >> >>> clang-cl tries to do currently, and if there are flags we
>> >>> >> >> >>> don't
>> >>> >> >> >>> get
>> >>> >> >> >>> right,
>> >>> >> >> >>> we should fix it.
>> >>> >> >> >>>
>> >>> >> >> >>> And we do move flags from the unsupported to supported
>> >>> >> >> >>> category
>> >>> >> >> >>> now
>> >>> >> >> >>> and
>> >>> >> >> >>> then, so the "only case we would ever need to maintain this
>> >>> >> >> >>> again
>> >>> >> >> >>> is
>> >>> >> >> >>> if we
>> >>> >> >> >>> started supporting these options" scenario is real.
>> >>> >> >> >>
>> >>> >> >> >> It’s not a matter of clang-cl doing it right or wrong, it’s
>> >>> >> >> >> that
>> >>> >> >> >> there
>> >>> >> >> >> are
>> >>> >> >> >> other moving parts before it even gets to clang-cl.
>> >>> >> >> >> Specifically,
>> >>> >> >> >> MSBuild.
>> >>> >> >> >> We’ve already seen one example of how  just letting clang-cl
>> >>> >> >> >> do
>> >>> >> >> >> its
>> >>> >> >> >> thing is
>> >>> >> >> >> insufficient, and nothing we can ever do in clang-cl can fix
>> >>> >> >> >> that.
>> >>> >> >> >> Given
>> >>> >> >> >> that it’s required sometimes, and that doing it for all
>> >>> >> >> >> options
>> >>> >> >> >> doesn’t
>> >>> >> >> >> increase our maintenance burden, i think it makes sense to do
>> >>> >> >> >> it
>> >>> >> >> >> everywhere
>> >>> >> >> >> and never have to deal with msbuild issues again.
>> >>> >> >> >>
>> >>> >> >> >>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>> ================
>> >>> >> >> >>> Comment at: llvm/tools/msbuild/Toolset.targets:46
>> >>> >> >> >>> +             File="@(ClCompile)(0,0)"
>> >>> >> >> >>> +             Text="clang-cl does not support MSVC Link Time
>> >>> >> >> >>> Optimization.  Disable this option in compatibility settings
>> >>> >> >> >>> to
>> >>> >> >> >>> silence this
>> >>> >> >> >>> warning."/>
>> >>> >> >> >>> +
>> >>> >> >> >>> ----------------
>> >>> >> >> >>> zturner wrote:
>> >>> >> >> >>> > hans wrote:
>> >>> >> >> >>> > > But maybe we want clang-cl to map this to -flto one day.
>> >>> >> >> >>> > > Now we
>> >>> >> >> >>> > > need
>> >>> >> >> >>> > > to update two places. And with the toolset/toolchain
>> >>> >> >> >>> > > install
>> >>> >> >> >>> > > split, the two
>> >>> >> >> >>> > > places may be installed separately :-/
>> >>> >> >> >>> > That's even better then.  All we have to do is change this
>> >>> >> >> >>> > xml,
>> >>> >> >> >>> > push
>> >>> >> >> >>> > a
>> >>> >> >> >>> > new build to the market place, and the VS UI will update
>> >>> >> >> >>> > their
>> >>> >> >> >>> > extension for
>> >>> >> >> >>> > them.
>> >>> >> >> >>> >
>> >>> >> >> >>> > Note that we could do the mapping at the MSBuild level, in
>> >>> >> >> >>> > this
>> >>> >> >> >>> > file
>> >>> >> >> >>> > down below where we have an `ItemGroup`.  Just add a line
>> >>> >> >> >>> > that
>> >>> >> >> >>> > says
>> >>> >> >> >>> > `<AdditionalOptions
>> >>> >> >> >>> > Condition="%(ClCompile.WholeProgramOptimization)' ==
>> >>> >> >> >>> > 'true'>-flto=thin
>> >>> >> >> >>> > %(AdditionalOptions)</AdditionalOptions>`
>> >>> >> >> >>> >
>> >>> >> >> >>> > and we can do this without touching clang.
>> >>> >> >> >>> But the toolset is decoupled from the toolchain in your
>> >>> >> >> >>> proposal.
>> >>> >> >> >>>
>> >>> >> >> >>> Not only would we need to update both clang-cl and this
>> >>> >> >> >>> file,
>> >>> >> >> >>> but
>> >>> >> >> >>> this
>> >>> >> >> >>> file would need to handle clang-cl versions both before and
>> >>> >> >> >>> after.
>> >>> >> >> >>
>> >>> >> >> >> We wouldn’t have to update clang-cl.  We could map ltcg to
>> >>> >> >> >> -flto=thin
>> >>> >> >> >> in
>> >>> >> >> >> the extension and it would automatically work with the
>> >>> >> >> >> installed
>> >>> >> >> >> toolchain.
>> >>> >> >> >>
>> >>> >> >> >>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>> ================
>> >>> >> >> >>> Comment at: llvm/tools/msbuild/Toolset.targets:83
>> >>> >> >> >>> +
>> >>> >> >> >>> +    <!-- Warn if XML Documentation is generated, and then
>> >>> >> >> >>> ignore
>> >>> >> >> >>> it.
>> >>> >> >> >>> -->
>> >>> >> >> >>> +    <Warning
>> >>> >> >> >>> Condition="'%(ClCompile.GenerateXMLDocumentationFiles)'
>> >>> >> >> >>> ==
>> >>> >> >> >>> 'true'"
>> >>> >> >> >>> ----------------
>> >>> >> >> >>> zturner wrote:
>> >>> >> >> >>> > hans wrote:
>> >>> >> >> >>> > > Keeping up with all these flags seems like a huge amount
>> >>> >> >> >>> > > of
>> >>> >> >> >>> > > work.
>> >>> >> >> >>> > > Why
>> >>> >> >> >>> > > not just let clang-cl ignore it?
>> >>> >> >> >>> > See the large comment at the top of the file.  For some
>> >>> >> >> >>> > options,
>> >>> >> >> >>> > we
>> >>> >> >> >>> > could probably get by with this.  Maybe even this one, I
>> >>> >> >> >>> > debated
>> >>> >> >> >>> > on
>> >>> >> >> >>> > this
>> >>> >> >> >>> > particular one.
>> >>> >> >> >>> >
>> >>> >> >> >>> > My bar was "If the option fundamentally changes
>> >>> >> >> >>> > assumptions
>> >>> >> >> >>> > about
>> >>> >> >> >>> > the
>> >>> >> >> >>> > way code could be compiled, we should generate an error.
>> >>> >> >> >>> > If
>> >>> >> >> >>> > it
>> >>> >> >> >>> > changes the
>> >>> >> >> >>> > behavior of the language in a way we don't support,
>> >>> >> >> >>> > changes
>> >>> >> >> >>> > the
>> >>> >> >> >>> > way
>> >>> >> >> >>> > we
>> >>> >> >> >>> > generate code in a meaningful way, or causes specialized
>> >>> >> >> >>> > output
>> >>> >> >> >>> > files to be
>> >>> >> >> >>> > written, warn, and if it's an option we ignore then drop
>> >>> >> >> >>> > it"
>> >>> >> >> >>> >
>> >>> >> >> >>> > The last category there we could probably just pass
>> >>> >> >> >>> > through
>> >>> >> >> >>> > in
>> >>> >> >> >>> > some
>> >>> >> >> >>> > cases, but in that comment I also mentioned a case where
>> >>> >> >> >>> > setting
>> >>> >> >> >>> > an
>> >>> >> >> >>> > option
>> >>> >> >> >>> > that clang-cl ignores impacts MSBuild's ability to figure
>> >>> >> >> >>> > out
>> >>> >> >> >>> > dependencies
>> >>> >> >> >>> > and ends up causing a full rebuild every time even when
>> >>> >> >> >>> > nothing
>> >>> >> >> >>> > changed.
>> >>> >> >> >>> >
>> >>> >> >> >>> > We can scour the entire cl build tasks and try to discover
>> >>> >> >> >>> > if
>> >>> >> >> >>> > any
>> >>> >> >> >>> > other
>> >>> >> >> >>> > ones have unintended consequences, but I think it's easier
>> >>> >> >> >>> > to
>> >>> >> >> >>> > just
>> >>> >> >> >>> > turn them
>> >>> >> >> >>> > off at the MSBuild level.  And as a side benefit, the user
>> >>> >> >> >>> > gets
>> >>> >> >> >>> > shorter
>> >>> >> >> >>> > command lines, which is always nice.
>> >>> >> >> >>> >
>> >>> >> >> >>> > As for maintenance, this all looks like zero-maintenance
>> >>> >> >> >>> > code
>> >>> >> >> >>> > to
>> >>> >> >> >>> > me.
>> >>> >> >> >>> > Did you have an example in mind of where we'd need to
>> >>> >> >> >>> > update
>> >>> >> >> >>> > this?
>> >>> >> >> >>> > Whether
>> >>> >> >> >>> > it be a new VS version, or VS dropping support for one of
>> >>> >> >> >>> > these
>> >>> >> >> >>> > options or
>> >>> >> >> >>> > deprecating them, I don't think we'd have to do anything.
>> >>> >> >> >>> The maintenance would come from when clang-cl changes how it
>> >>> >> >> >>> handles
>> >>> >> >> >>> some
>> >>> >> >> >>> option, or when VS adds new options.
>> >>> >> >> >>
>> >>> >> >> >> But these are all really obscure options that we will
>> >>> >> >> >> probably
>> >>> >> >> >> never
>> >>> >> >> >> touch.  When vc adds new options we’re not obligated to
>> >>> >> >> >> update
>> >>> >> >> >> this
>> >>> >> >> >> file
>> >>> >> >> >> either.
>> >>> >> >> >>
>> >>> >> >> >>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>>
>> >>> >> >> >>> ================
>> >>> >> >> >>> Comment at: llvm/tools/msbuild/install.bat:10
>> >>> >> >> >>> +REM Older versions of VS would look for these files in the
>> >>> >> >> >>> Program
>> >>> >> >> >>> Files\MSBuild directory
>> >>> >> >> >>> +REM but with VS2017 it seems to look for these directly in
>> >>> >> >> >>> the
>> >>> >> >> >>> Visual
>> >>> >> >> >>> Studio instance.
>> >>> >> >> >>> +REM This means we'll need to do a little extra work to
>> >>> >> >> >>> properly
>> >>> >> >> >>> detect
>> >>> >> >> >>> all the various
>> >>> >> >> >>> ----------------
>> >>> >> >> >>> zturner wrote:
>> >>> >> >> >>> > hans wrote:
>> >>> >> >> >>> > > Don't we want to support at least 2015 too?
>> >>> >> >> >>> > Mentioned in the other review, but the install.bat file
>> >>> >> >> >>> > shouldn't
>> >>> >> >> >>> > really be used anymore except for during development.  The
>> >>> >> >> >>> > VSIX
>> >>> >> >> >>> > supports
>> >>> >> >> >>> > both 2015 and 2017 (I tested it in both and confirmed it
>> >>> >> >> >>> > works)
>> >>> >> >> >>> Hmm, but then we should delete it, or at least take it out
>> >>> >> >> >>> of
>> >>> >> >> >>> the
>> >>> >> >> >>> installer, and we need a replacement. As it is now, if we
>> >>> >> >> >>> land
>> >>> >> >> >>> this,
>> >>> >> >> >>> it
>> >>> >> >> >>> breaks the installer for versions before 2017.
>> >>> >> >> >>
>> >>> >> >> >>
>> >>> >> >> >> I thought i took it out of the installer, but maybe I missed
>> >>> >> >> >> something.
>> >>> >> >> >> We still need it for dev purposes because it allows us to
>> >>> >> >> >> overwrite
>> >>> >> >> >> the
>> >>> >> >> >> existing installed version with new files
>> >>> >> >> >
>> >>> >> >> >
>> >>> >> >> > _______________________________________________
>> >>> >> >> > llvm-commits mailing list
>> >>> >> >> > llvm-commits at lists.llvm.org
>> >>> >> >> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>> >>> >> >> >