llvm dev - May 2015 - [LLVMdev] libiomp, not libgomp as default library linked with -fopenmp

On Fri, May 1, 2015 at 1:57 PM, Chandler Carruth <chandlerc at google.com>
wrote:
> On Fri, May 1, 2015 at 10:46 AM Jack Howarth <
> howarth.mailing.lists at gmail.com> wrote:
>
>> On Thu, Apr 30, 2015 at 5:51 PM, Chandler Carruth <chandlerc at
google.com>
>> wrote:
>>
>>> On Thu, Apr 30, 2015 at 6:52 AM Andrey Bokhanko <
>>> andreybokhanko at gmail.com> wrote:
>>>
>>>> All,
>>>>
>>>> I'd like to resurrect the discussion on replacing libgomp
with libiomp
>>>> as the default OpenMP runtime library linked with -fopenmp.
>>>>
>>>
>>> Just for the record, I'm really excited to see this. =]
>>>
>>>
>>>> We are very close to getting *full* OpenMP 3.1 specification
supported
>>>> in clang (only one (!) clause is not implemented yet, and the
patch is
>>>> already sent for review today: http://reviews.llvm.org/D9370).
This
>>>> implementation generates Intel API library calls; thus, it
can't be used
>>>> with libgomp and it is simply logical to link a compatible
runtime
>>>> (libiomp) instead.
>>>>
>>>
>>> Is there no way to support libgomp here as well? I don't say
this to
>>> hold up changing the defaults in any way, just curious. =]
>>>
>>> Also, for the record, I'm really excited to see the progress
here as
>>> well.
>>>
>>>
>>>> Chandler?
>>>>
>>>
>>> Hi! ;]
>>>
>>> I totally agree, I think things are way better now. I generally
support
>>> the direction. I think there are a few things I'd suggest we do
as part of
>>> the process, but I think these are really small and just about
"how" we
>>> switch.
>>>
>>> 1) I completely agree with the comments some others have made about
us
>>> needing to make it clear that this isn't some Intel-only thing,
its the
>>> LLVM OpenMP runtime. Some suggestions that I think would make sense
to help
>>> here:
>>> - I agree with finding some non-Intel folks to add as explicit code
>>> owners. I don't know who has been sufficiently involved, but if
Hal makes
>>> sense, awesome.
>>> - Clearly updating the readme and such would be appropriate.
>>> - I suspect we should change the name of the installed library.
>>> 'libiomp' is pretty clearly the Intel library. We could
continue in the
>>> grand tradition of LLVM naming conventions and use
'libllomp'? Of course,
>>> we should install symlinks under the name 'libiomp' if
needed for existing
>>> users to not be broken.
>>> - Any other changes?
>>>
>>>
>> Is this naming issue so serious that it will be blocker for the current
>> patches to enabled the openmp build from within llvm/projects?
Can't we
>> just proceed with the current library name until the top-level openmp
build
>> infrastructure added and the switch of the default for -fopenmp to
libiomp5
>> is made. It seems more sensible to stabilize the openmp support first
and
>> then revisit the naming issue in a couple of weeks.
>>
>
> For me, I would prefer that the default switch for -fopenmp be towards the
> new name.
>
> I freely admit this is a non-technical thing, I just think it helps send
> the correct message.
>
> Also, as I said, I'm very sympathetic to the desire to support existing
> users of the existing name. I think we should at least either make it
> configurable or install symlinks under the old name... I actually think we
> should probably do *both*.
>

To be done simultaneously or can we stage them so that the name change is
checked in *after* we stabilize the overall build and switch-over to
openmp? I would hate to see things delayed over this when we have ages to
switch the name before the 3.7 release. Also, might you not want to take
that time for a more in-depth discussion about any changes related to so
versioning? Do we expect to always just be able to use the same shared
library name or will we have to explicitly version it for possible ABI
changes later on. If we expect the existing ABI to never change but only
see additions to the ABI as OpenMP 4.0 support is added, I guess that isn't
an issue. Perhaps such issues should be digested for awhile before jumping
to a shared library name change.
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+1

The longer one has to explicitly mention "libiomp5" in compiler
options, the better chances for this name to firmly stuck (in readmes,
howtows, tests / performance measurements, etc, etc)

Andrey


On Fri, May 1, 2015 at 9:16 PM, Jack Howarth
<howarth.mailing.lists at gmail.com> wrote:
>
>
> On Fri, May 1, 2015 at 1:57 PM, Chandler Carruth <chandlerc at
google.com>
> wrote:
>>
>> On Fri, May 1, 2015 at 10:46 AM Jack Howarth
>> <howarth.mailing.lists at gmail.com> wrote:
>>>
>>> On Thu, Apr 30, 2015 at 5:51 PM, Chandler Carruth <chandlerc at
google.com>
>>> wrote:
>>>>
>>>> On Thu, Apr 30, 2015 at 6:52 AM Andrey Bokhanko
>>>> <andreybokhanko at gmail.com> wrote:
>>>>>
>>>>> All,
>>>>>
>>>>> I'd like to resurrect the discussion on replacing
libgomp with libiomp
>>>>> as the default OpenMP runtime library linked with -fopenmp.
>>>>
>>>>
>>>> Just for the record, I'm really excited to see this. =]
>>>>
>>>>>
>>>>> We are very close to getting *full* OpenMP 3.1
specification supported
>>>>> in clang (only one (!) clause is not implemented yet, and
the patch is
>>>>> already sent for review today:
http://reviews.llvm.org/D9370). This
>>>>> implementation generates Intel API library calls; thus, it
can't be used
>>>>> with libgomp and it is simply logical to link a compatible
runtime (libiomp)
>>>>> instead.
>>>>
>>>>
>>>> Is there no way to support libgomp here as well? I don't
say this to
>>>> hold up changing the defaults in any way, just curious. =]
>>>>
>>>> Also, for the record, I'm really excited to see the
progress here as
>>>> well.
>>>>
>>>>>
>>>>> Chandler?
>>>>
>>>>
>>>> Hi! ;]
>>>>
>>>> I totally agree, I think things are way better now. I generally
support
>>>> the direction. I think there are a few things I'd suggest
we do as part of
>>>> the process, but I think these are really small and just about
"how" we
>>>> switch.
>>>>
>>>> 1) I completely agree with the comments some others have made
about us
>>>> needing to make it clear that this isn't some Intel-only
thing, its the LLVM
>>>> OpenMP runtime. Some suggestions that I think would make sense
to help here:
>>>> - I agree with finding some non-Intel folks to add as explicit
code
>>>> owners. I don't know who has been sufficiently involved,
but if Hal makes
>>>> sense, awesome.
>>>> - Clearly updating the readme and such would be appropriate.
>>>> - I suspect we should change the name of the installed library.
>>>> 'libiomp' is pretty clearly the Intel library. We could
continue in the
>>>> grand tradition of LLVM naming conventions and use
'libllomp'? Of course, we
>>>> should install symlinks under the name 'libiomp' if
needed for existing
>>>> users to not be broken.
>>>> - Any other changes?
>>>>
>>>
>>> Is this naming issue so serious that it will be blocker for the
current
>>> patches to enabled the openmp build from within llvm/projects?
Can't we just
>>> proceed with the current library name until the top-level openmp
build
>>> infrastructure added and the switch of the default for -fopenmp to
libiomp5
>>> is made. It seems more sensible to stabilize the openmp support
first and
>>> then revisit the naming issue in a couple of weeks.
>>
>>
>> For me, I would prefer that the default switch for -fopenmp be towards
the
>> new name.
>>
>> I freely admit this is a non-technical thing, I just think it helps
send
>> the correct message.
>>
>> Also, as I said, I'm very sympathetic to the desire to support
existing
>> users of the existing name. I think we should at least either make it
>> configurable or install symlinks under the old name... I actually think
we
>> should probably do *both*.
>
>
>
> To be done simultaneously or can we stage them so that the name change is
> checked in *after* we stabilize the overall build and switch-over to
openmp?
> I would hate to see things delayed over this when we have ages to switch
the
> name before the 3.7 release. Also, might you not want to take that time for
> a more in-depth discussion about any changes related to so versioning? Do
we
> expect to always just be able to use the same shared library name or will
we
> have to explicitly version it for possible ABI changes later on. If we
> expect the existing ABI to never change but only see additions to the ABI
as
> OpenMP 4.0 support is added, I guess that isn't an issue. Perhaps such
> issues should be digested for awhile before jumping to a shared library
name
> change.
>

On Sat, May 2, 2015 at 4:22 PM, Andrey Bokhanko <andreybokhanko at
gmail.com>
wrote:
> +1
>
> The longer one has to explicitly mention "libiomp5" in compiler
> options, the better chances for this name to firmly stuck (in readmes,
> howtows, tests / performance measurements, etc, etc)
>
> Andrey
>
>
Andrey,
     The only thing I don't like about the libiomp5 name is the the 5. It
really should have been libiomp.5.dylib. Otherwise, when and if the ABI
changes after the initial release, you would have to switch the library
name to libiomp6 rather just bumping the so version to libiomp.6.dylib. I
worry that embedding the so version into the file name might complicate
doing configure/cmake checks for symbols in the shared library as the root
library name will keep changing over time.
                Jack

> On Fri, May 1, 2015 at 9:16 PM, Jack Howarth
> <howarth.mailing.lists at gmail.com> wrote:
> >
> >
> > On Fri, May 1, 2015 at 1:57 PM, Chandler Carruth <chandlerc at
google.com>
> > wrote:
> >>
> >> On Fri, May 1, 2015 at 10:46 AM Jack Howarth
> >> <howarth.mailing.lists at gmail.com> wrote:
> >>>
> >>> On Thu, Apr 30, 2015 at 5:51 PM, Chandler Carruth <
> chandlerc at google.com>
> >>> wrote:
> >>>>
> >>>> On Thu, Apr 30, 2015 at 6:52 AM Andrey Bokhanko
> >>>> <andreybokhanko at gmail.com> wrote:
> >>>>>
> >>>>> All,
> >>>>>
> >>>>> I'd like to resurrect the discussion on replacing
libgomp with
> libiomp
> >>>>> as the default OpenMP runtime library linked with
-fopenmp.
> >>>>
> >>>>
> >>>> Just for the record, I'm really excited to see this.
=]
> >>>>
> >>>>>
> >>>>> We are very close to getting *full* OpenMP 3.1
specification
> supported
> >>>>> in clang (only one (!) clause is not implemented yet,
and the patch
> is
> >>>>> already sent for review today:
http://reviews.llvm.org/D9370). This
> >>>>> implementation generates Intel API library calls;
thus, it can't be
> used
> >>>>> with libgomp and it is simply logical to link a
compatible runtime
> (libiomp)
> >>>>> instead.
> >>>>
> >>>>
> >>>> Is there no way to support libgomp here as well? I
don't say this to
> >>>> hold up changing the defaults in any way, just curious. =]
> >>>>
> >>>> Also, for the record, I'm really excited to see the
progress here as
> >>>> well.
> >>>>
> >>>>>
> >>>>> Chandler?
> >>>>
> >>>>
> >>>> Hi! ;]
> >>>>
> >>>> I totally agree, I think things are way better now. I
generally
> support
> >>>> the direction. I think there are a few things I'd
suggest we do as
> part of
> >>>> the process, but I think these are really small and just
about "how"
> we
> >>>> switch.
> >>>>
> >>>> 1) I completely agree with the comments some others have
made about us
> >>>> needing to make it clear that this isn't some
Intel-only thing, its
> the LLVM
> >>>> OpenMP runtime. Some suggestions that I think would make
sense to
> help here:
> >>>> - I agree with finding some non-Intel folks to add as
explicit code
> >>>> owners. I don't know who has been sufficiently
involved, but if Hal
> makes
> >>>> sense, awesome.
> >>>> - Clearly updating the readme and such would be
appropriate.
> >>>> - I suspect we should change the name of the installed
library.
> >>>> 'libiomp' is pretty clearly the Intel library. We
could continue in
> the
> >>>> grand tradition of LLVM naming conventions and use
'libllomp'? Of
> course, we
> >>>> should install symlinks under the name 'libiomp'
if needed for
> existing
> >>>> users to not be broken.
> >>>> - Any other changes?
> >>>>
> >>>
> >>> Is this naming issue so serious that it will be blocker for
the current
> >>> patches to enabled the openmp build from within llvm/projects?
Can't
> we just
> >>> proceed with the current library name until the top-level
openmp build
> >>> infrastructure added and the switch of the default for
-fopenmp to
> libiomp5
> >>> is made. It seems more sensible to stabilize the openmp
support first
> and
> >>> then revisit the naming issue in a couple of weeks.
> >>
> >>
> >> For me, I would prefer that the default switch for -fopenmp be
towards
> the
> >> new name.
> >>
> >> I freely admit this is a non-technical thing, I just think it
helps send
> >> the correct message.
> >>
> >> Also, as I said, I'm very sympathetic to the desire to support
existing
> >> users of the existing name. I think we should at least either make
it
> >> configurable or install symlinks under the old name... I actually
think
> we
> >> should probably do *both*.
> >
> >
> >
> > To be done simultaneously or can we stage them so that the name change
is
> > checked in *after* we stabilize the overall build and switch-over to
> openmp?
> > I would hate to see things delayed over this when we have ages to
switch
> the
> > name before the 3.7 release. Also, might you not want to take that
time
> for
> > a more in-depth discussion about any changes related to so versioning?
> Do we
> > expect to always just be able to use the same shared library name or
> will we
> > have to explicitly version it for possible ABI changes later on. If we
> > expect the existing ABI to never change but only see additions to the
> ABI as
> > OpenMP 4.0 support is added, I guess that isn't an issue. Perhaps
such
> > issues should be digested for awhile before jumping to a shared
library
> name
> > change.
> >
>
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