[PATCH] D42762: Rewrite the VS Integration Scripts

Fri Feb 2 08:12:02 PST 2018

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
>> >
>> >
>> > _______________________________________________
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>> >