[PATCH] D42762: Rewrite the VS Integration Scripts

[Zachary Turner via llvm-commits]

It’s an additional pdb, which the linker then uses as an input. The linker
still writes the final pdb. The msbuild task that actually invokes cl.exe
is implemented in a dll, so we can only observe its effects.

I’m not sure how cmake is implemented, but this is really a build system
issue of inputs, outputs, and dependencies. If cmake does have issues,
patching cmake seems like the appropriate solution.
On Fri, Feb 2, 2018 at 8:54 AM Hans Wennborg <hans at chromium.org> wrote:

> 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
> >> >>> >> >> >
>
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