llvm dev - Feb 2017 - [RFC] Queries for LLVM version

So Mehdi,
you're not in favour of providing this functionality then? Or just not in
favour of that use case?

On Wed, Feb 8, 2017 at 10:18 AM, Mehdi Amini <mehdi.amini at apple.com>
wrote:
>
> > On Feb 7, 2017, at 5:44 PM, Timothy Arceri via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > On Wed, 2017-02-08 at 00:12 +0100, Nemanja Ivanovic wrote:
> >> I am certainly willing to write up a patch to do this. I was
hoping
> >> to get a few more responses/buy-in from the community.
> >> And honestly, I'd be interested to know if this can be
back-ported to
> >> at least 4.0 if it gets accepted.
> >
> > My *possible* use case is for identifying the version of llvm used to
> > compile shaders for AMD gpus. This information would be used with an
> > on-disk cache of compiled shaders allowing old cache items to be
> > ignored if llvm is upgraded.
> >
> > One downside of this is there is no way to know if distros backport
> > fixes to llvm. If the version is not bumped then the a buggy cached
> > shader would continue to be used even after the distro makes the fix.
>
> This is exactly why we don’t use this kind of versioning: it is
> fragile/unreliable.
>
> —
> Mehdi
>
>
> >
> >
> >>
> >> Now that I see that there's more interest in this than just my
own,
> >> I'll put up a patch on Phabricator.
> >
> > Cool, thanks!
> >
> >>
> >> On Wed, Feb 8, 2017 at 12:04 AM, Timothy Arceri via llvm-dev
<llvm-de
> >> v at lists.llvm.org> wrote:
> >>> On 01/26/2017 12:45 AM, Nemanja Ivanovic via llvm-dev wrote:
> >>>> This has actually come up in the context of a JIT, but I
think
> >>> that
> >>>> having the functionality in general could be useful.
> >>>>
> >>>> Currently, there does not appear to be an API in LLVM to
query
> >>> for
> >>>> LLVM version information. In the particular context where
this
> >>> came
> >>>> up, LLVM is used as a shared library and various
functionality
> >>> (and
> >>>> bug fixes) used by the JIT is available in various LLVM
versions.
> >>> So
> >>>> it would be quite convenient to be able to dynamically
determine
> >>> the
> >>>> version that happens to be loaded.
> >>>>
> >>>> Honestly, I am not completely clear on what the best place
for
> >>>> something like this would be, but it appears that the
following
> >>> seems
> >>>> like a natural choice:
> >>>>
> >>>> llvm::VersionPrinter in lib/Support/CommandLine.cpp
already
> >>> queries
> >>>> this data so it might make sense for it to expose the
following
> >>> API's
> >>>> (as part of VersionPrinter, accessed through the
instance):
> >>>> llvm::cl::getVersionMajor()
> >>>> llvm::cl::getVersionMinor()
> >>>> llvm::cl::getVersionPatch()
> >>>
> >>> Hi,
> >>>
> >>> I'm also interested in querying this at runtime. Has there
been any
> >>> patches submitted for this yet?
> >>>
> >>> Thanks,
> >>> Tim
> >>> _______________________________________________
> >>> LLVM Developers mailing list
> >>> llvm-dev at lists.llvm.org
> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >>>
> >>
> >>
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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> On Feb 8, 2017, at 7:51 AM, Nemanja Ivanovic <nemanja.i.ibm at
gmail.com> wrote:
> 
> So Mehdi,
> you're not in favour of providing this functionality then?
I’m not against the functionality, but I’m not sure the API is the right one for
the use-case.
> Or just not in favour of that use case?
The use-case (object cache) makes perfect sense, but I wouldn’t use this API.
I’d like use a `const char *getLLVMVersion()` API that would be documented as
returning an opaque string representing the LLVM version.
The reason to return an opaque string is to prevent (not encourage…) users to
parse it. It could return something like “LLVM 4.0.0svn(r12345)”.
Using this as part of your cache key makes it more robust to switching a given
version of the compiler.

But ultimately, if I had to build such a caching system*, I’d likely do it
upstream in LLVM and design the API to such that it would “just work” for my
shader driver and could be maintained/improved by the community and reused by
other users.

* https://github.com/llvm-mirror/llvm/blob/master/lib/LTO/Caching.cpp
https://github.com/llvm-mirror/llvm/blob/master/include/llvm/Support/CachePruning.h

— 
Mehdi

> 
> On Wed, Feb 8, 2017 at 10:18 AM, Mehdi Amini <mehdi.amini at apple.com
<mailto:mehdi.amini at apple.com>> wrote:
> 
> > On Feb 7, 2017, at 5:44 PM, Timothy Arceri via llvm-dev <llvm-dev
at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> >
> > On Wed, 2017-02-08 at 00:12 +0100, Nemanja Ivanovic wrote:
> >> I am certainly willing to write up a patch to do this. I was
hoping
> >> to get a few more responses/buy-in from the community.
> >> And honestly, I'd be interested to know if this can be
back-ported to
> >> at least 4.0 if it gets accepted.
> >
> > My *possible* use case is for identifying the version of llvm used to
> > compile shaders for AMD gpus. This information would be used with an
> > on-disk cache of compiled shaders allowing old cache items to be
> > ignored if llvm is upgraded.
> >
> > One downside of this is there is no way to know if distros backport
> > fixes to llvm. If the version is not bumped then the a buggy cached
> > shader would continue to be used even after the distro makes the fix.
> 
> This is exactly why we don’t use this kind of versioning: it is
fragile/unreliable.
> 
> —
> Mehdi
> 
> 
> >
> >
> >>
> >> Now that I see that there's more interest in this than just my
own,
> >> I'll put up a patch on Phabricator.
> >
> > Cool, thanks!
> >
> >>
> >> On Wed, Feb 8, 2017 at 12:04 AM, Timothy Arceri via llvm-dev
<llvm-de
> >> v at lists.llvm.org <mailto:v at lists.llvm.org>> wrote:
> >>> On 01/26/2017 12:45 AM, Nemanja Ivanovic via llvm-dev wrote:
> >>>> This has actually come up in the context of a JIT, but I
think
> >>> that
> >>>> having the functionality in general could be useful.
> >>>>
> >>>> Currently, there does not appear to be an API in LLVM to
query
> >>> for
> >>>> LLVM version information. In the particular context where
this
> >>> came
> >>>> up, LLVM is used as a shared library and various
functionality
> >>> (and
> >>>> bug fixes) used by the JIT is available in various LLVM
versions.
> >>> So
> >>>> it would be quite convenient to be able to dynamically
determine
> >>> the
> >>>> version that happens to be loaded.
> >>>>
> >>>> Honestly, I am not completely clear on what the best place
for
> >>>> something like this would be, but it appears that the
following
> >>> seems
> >>>> like a natural choice:
> >>>>
> >>>> llvm::VersionPrinter in lib/Support/CommandLine.cpp
already
> >>> queries
> >>>> this data so it might make sense for it to expose the
following
> >>> API's
> >>>> (as part of VersionPrinter, accessed through the
instance):
> >>>> llvm::cl::getVersionMajor()
> >>>> llvm::cl::getVersionMinor()
> >>>> llvm::cl::getVersionPatch()
> >>>
> >>> Hi,
> >>>
> >>> I'm also interested in querying this at runtime. Has there
been any
> >>> patches submitted for this yet?
> >>>
> >>> Thanks,
> >>> Tim
> >>> _______________________________________________
> >>> LLVM Developers mailing list
> >>> llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> >>>
> >>
> >>
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> 
> 
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Would it make sense to:

   1. Provide the integer Major/Minor/Patch API's for use cases where the
   user wants to check that the loaded version is at least some version that
   contains a fix they're after
   2. Provide a string API for the caching use case you outlined


On Wed, Feb 8, 2017 at 3:56 PM, Mehdi Amini <mehdi.amini at apple.com>
wrote:
>
> On Feb 8, 2017, at 7:51 AM, Nemanja Ivanovic <nemanja.i.ibm at
gmail.com>
> wrote:
>
> So Mehdi,
> you're not in favour of providing this functionality then?
>
>
> I’m not against the functionality, but I’m not sure the API is the right
> one for the use-case.
>
> Or just not in favour of that use case?
>
>
> The use-case (object cache) makes perfect sense, but I wouldn’t use this
> API.
> I’d like use a `const char *getLLVMVersion()` API that would be documented
> as returning an opaque string representing the LLVM version.
> The reason to return an opaque string is to prevent (not encourage…) users
> to parse it. It could return something like “LLVM 4.0.0svn(r12345)”.
> Using this as part of your cache key makes it more robust to switching a
> given version of the compiler.
>
> But ultimately, if I had to build such a caching system*, I’d likely do it
> upstream in LLVM and design the API to such that it would “just work” for
> my shader driver and could be maintained/improved by the community and
> reused by other users.
>
> * https://github.com/llvm-mirror/llvm/blob/master/lib/LTO/Caching.cpp
> https://github.com/llvm-mirror/llvm/blob/master/include/llvm/Support/
> CachePruning.h
>
> —
> Mehdi
>
>
>
> On Wed, Feb 8, 2017 at 10:18 AM, Mehdi Amini <mehdi.amini at
apple.com>
> wrote:
>
>>
>> > On Feb 7, 2017, at 5:44 PM, Timothy Arceri via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>> >
>> > On Wed, 2017-02-08 at 00:12 +0100, Nemanja Ivanovic wrote:
>> >> I am certainly willing to write up a patch to do this. I was
hoping
>> >> to get a few more responses/buy-in from the community.
>> >> And honestly, I'd be interested to know if this can be
back-ported to
>> >> at least 4.0 if it gets accepted.
>> >
>> > My *possible* use case is for identifying the version of llvm used
to
>> > compile shaders for AMD gpus. This information would be used with
an
>> > on-disk cache of compiled shaders allowing old cache items to be
>> > ignored if llvm is upgraded.
>> >
>> > One downside of this is there is no way to know if distros
backport
>> > fixes to llvm. If the version is not bumped then the a buggy
cached
>> > shader would continue to be used even after the distro makes the
fix.
>>
>> This is exactly why we don’t use this kind of versioning: it is
>> fragile/unreliable.
>>
>> —
>> Mehdi
>>
>>
>> >
>> >
>> >>
>> >> Now that I see that there's more interest in this than
just my own,
>> >> I'll put up a patch on Phabricator.
>> >
>> > Cool, thanks!
>> >
>> >>
>> >> On Wed, Feb 8, 2017 at 12:04 AM, Timothy Arceri via llvm-dev
<llvm-de
>> >> v at lists.llvm.org> wrote:
>> >>> On 01/26/2017 12:45 AM, Nemanja Ivanovic via llvm-dev
wrote:
>> >>>> This has actually come up in the context of a JIT, but
I think
>> >>> that
>> >>>> having the functionality in general could be useful.
>> >>>>
>> >>>> Currently, there does not appear to be an API in LLVM
to query
>> >>> for
>> >>>> LLVM version information. In the particular context
where this
>> >>> came
>> >>>> up, LLVM is used as a shared library and various
functionality
>> >>> (and
>> >>>> bug fixes) used by the JIT is available in various
LLVM versions.
>> >>> So
>> >>>> it would be quite convenient to be able to dynamically
determine
>> >>> the
>> >>>> version that happens to be loaded.
>> >>>>
>> >>>> Honestly, I am not completely clear on what the best
place for
>> >>>> something like this would be, but it appears that the
following
>> >>> seems
>> >>>> like a natural choice:
>> >>>>
>> >>>> llvm::VersionPrinter in lib/Support/CommandLine.cpp
already
>> >>> queries
>> >>>> this data so it might make sense for it to expose the
following
>> >>> API's
>> >>>> (as part of VersionPrinter, accessed through the
instance):
>> >>>> llvm::cl::getVersionMajor()
>> >>>> llvm::cl::getVersionMinor()
>> >>>> llvm::cl::getVersionPatch()
>> >>>
>> >>> Hi,
>> >>>
>> >>> I'm also interested in querying this at runtime. Has
there been any
>> >>> patches submitted for this yet?
>> >>>
>> >>> Thanks,
>> >>> Tim
>> >>> _______________________________________________
>> >>> LLVM Developers mailing list
>> >>> llvm-dev at lists.llvm.org
>> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>>
>> >>
>> >>
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
>
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