[PATCH] D42762: Rewrite the VS Integration Scripts

[Zachary Turner via llvm-commits]

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
> >>> >> >> >
>
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