llvm dev - May 2017 - Should we split llvm Support and ADT?

I thought we already did write tablegen output to temporary files like
X86GenAsmWriter1.inc.tmp first and then diffed them with the real .inc file
and conditionally copied.

~Craig

On Sat, May 27, 2017 at 11:02 AM, David Blaikie via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
>
> On Fri, May 26, 2017 at 8:06 PM Zachary Turner via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> It would be better, because a debug tablegen is slower than an
optimized
>> tablegen, but it's still slow and it doesn't address the
problem that
>> tablegen runs *at all* when it doesn't really need to. I think if
tablegen
>> wasn't running all the time we could incremental builds down from
15
>> minutes (and that's on my really powerful machine) to under 5,
which seemed
>> like a big productivity boost averaged out over all users x time
>>
>
> Is that 10 minutes of running tablegen, though? I think this touches on
> Hal's comment:
> "Maybe we should use a diff-and-update approach (I thought, however,
that
> we already did that)."
>
> In that the 10 minutes is presumably from timestamp-based invalidation
> chaining down from running tablegen, to then rebuilding everything that
> depends on tablegen's output.
>
> That could be addressed by either the build system or tablegen writing
> output to a temporary file, comparing the temp to the current file, and not
> modifying the current file if they're the same - thus not invalidating
> everything down the chain that depends on the tablegen output (not sure if
> that's actually enough to convince a build system not to rebuild other
> things - but worth a shot). This is a bit of a hackaround what the build
> system itself could/should be doing, but in the absence of a content based
> invalidation scheme - addressing this one particularly critical point in
> LLVM's build seems like it could be worth such a workaround. (this
would
> speed up the build for even the times when tablegen's real dependencies
> change - add a new function to ArrayRef, or STLExtras, etc... and tablegen
> runs, but it doesn't cascade to everything else).
>
> (plus, opt build of tablegen, so that conclusion can be reached more
> quickly)
>
> As Hal also mentioned, I'd be OK with this if there's a good
logical
> division that can be taken more than "whatever is/isn't used in
tablegen".
>
>
>>
>> We've got a lot of random stuff in Support, not all really related
and
>> not all relevant to every project. It seems like we should be able to
do
>> better.
>> On Fri, May 26, 2017 at 6:48 PM Hal Finkel <hfinkel at anl.gov>
wrote:
>>
>>>
>>> On 05/26/2017 07:59 PM, Zachary Turner wrote:
>>>
>>> It's that TableGen depends on Support, so if you change one
file in
>>> support, support gets recompiled into a new static archive, which
triggers
>>> a rerun of tablegen on all the tablegen inputs, which is extremely
slow.
>>>
>>>
>>> I thought that we had a "build an optimized tablegen even in
debug mode"
>>> setting to work around this problem. Would that avoid this problem?
>>>
>>>
>>>  -Hal
>>>
>>>
>>>
>>> On Fri, May 26, 2017 at 5:56 PM Hal Finkel <hfinkel at
anl.gov> wrote:
>>>
>>>>
>>>>
>>>> On 05/26/2017 07:47 PM, Zachary Turner via llvm-dev wrote:
>>>>
>>>> Changing a header file somewhere and having to spend 10 minutes
waiting
>>>> for a build leads to a lot of wasted developer time.
>>>>
>>>> The real culprit here is tablegen.  Can we split support and
ADT into
>>>> two - the parts that tablegen depends on and the parts that it
doesn't?
>>>>
>>>>
>>>> What's the actual problem here? Is it that TableGen
regenerates
>>>> different files and so we then need to rebuild all dependencies
of those
>>>> files? Maybe we should use a diff-and-update approach (I
thought, however,
>>>> that we already did that).
>>>>
>>>>  -Hal
>>>>
>>>>
>>>> From what I can gather, Tablegen currently depends on these
headers and
>>>> all of their transitive dependencies.
>>>>
>>>> #include "llvm/Support/Casting.h"
>>>> #include "llvm/Support/CommandLine.h"
>>>> #include "llvm/Support/Compiler.h"
>>>> #include "llvm/Support/DataTypes.h"
>>>> #include "llvm/Support/Debug.h"
>>>> #include "llvm/Support/Error.h"
>>>> #include "llvm/Support/ErrorHandling.h"
>>>> #include "llvm/Support/Format.h"
>>>> #include "llvm/Support/FormattedStream.h"
>>>> #include "llvm/Support/LEB128.h"
>>>> #include "llvm/Support/LowLevelTypeImpl.h"
>>>> #include "llvm/Support/ManagedStatic.h"
>>>> #include "llvm/Support/MathExtras.h"
>>>> #include "llvm/Support/MemoryBuffer.h"
>>>> #include "llvm/Support/PrettyStackTrace.h"
>>>> #include "llvm/Support/Regex.h"
>>>> #include "llvm/Support/SMLoc.h"
>>>> #include "llvm/Support/ScopedPrinter.h"
>>>> #include "llvm/Support/Signals.h"
>>>> #include "llvm/Support/SourceMgr.h"
>>>> #include "llvm/Support/raw_ostream.h"
>>>>
>>>> #include "llvm/ADT/APInt.h"
>>>> #include "llvm/ADT/ArrayRef.h"
>>>> #include "llvm/ADT/BitVector.h"
>>>> #include "llvm/ADT/CachedHashString.h"
>>>> #include "llvm/ADT/DenseSet.h"
>>>> #include "llvm/ADT/IndexedMap.h"
>>>> #include "llvm/ADT/IntEqClasses.h"
>>>> #include "llvm/ADT/MapVector.h"
>>>> #include "llvm/ADT/Optional.h"
>>>> #include "llvm/ADT/PointerUnion.h"
>>>> #include "llvm/ADT/STLExtras.h"
>>>> #include "llvm/ADT/SetVector.h"
>>>> #include "llvm/ADT/SmallPtrSet.h"
>>>> #include "llvm/ADT/SmallSet.h"
>>>> #include "llvm/ADT/SmallVector.h"
>>>> #include "llvm/ADT/SparseBitVector.h"
>>>> #include "llvm/ADT/Statistic.h"
>>>> #include "llvm/ADT/StringExtras.h"
>>>> #include "llvm/ADT/StringMap.h"
>>>> #include "llvm/ADT/StringRef.h"
>>>> #include "llvm/ADT/StringSet.h"
>>>> #include "llvm/ADT/StringSwitch.h"
>>>> #include "llvm/ADT/TinyPtrVector.h"
>>>> #include "llvm/ADT/Twine.h"
>>>>
>>>>
>>>> Is this something worth putting effort into?  If so, I
volunteer.
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing listllvm-dev at
lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>>
>>>> --
>>>> Hal Finkel
>>>> Lead, Compiler Technology and Programming Languages
>>>> Leadership Computing Facility
>>>> Argonne National Laboratory
>>>>
>>>>
>>> --
>>> Hal Finkel
>>> Lead, Compiler Technology and Programming Languages
>>> Leadership Computing Facility
>>> Argonne National Laboratory
>>>
>>> _______________________________________________
>> 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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Maybe we do and build systems aren't respecting/noticing this? I'm not
sure.

On Sat, May 27, 2017 at 12:50 PM Craig Topper <craig.topper at gmail.com>
wrote:
> I thought we already did write tablegen output to temporary files like
> X86GenAsmWriter1.inc.tmp first and then diffed them with the real .inc file
> and conditionally copied.
>
> ~Craig
>
> On Sat, May 27, 2017 at 11:02 AM, David Blaikie via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>>
>>
>> On Fri, May 26, 2017 at 8:06 PM Zachary Turner via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> It would be better, because a debug tablegen is slower than an
optimized
>>> tablegen, but it's still slow and it doesn't address the
problem that
>>> tablegen runs *at all* when it doesn't really need to. I think
if tablegen
>>> wasn't running all the time we could incremental builds down
from 15
>>> minutes (and that's on my really powerful machine) to under 5,
which seemed
>>> like a big productivity boost averaged out over all users x time
>>>
>>
>> Is that 10 minutes of running tablegen, though? I think this touches on
>> Hal's comment:
>> "Maybe we should use a diff-and-update approach (I thought,
however,
>> that we already did that)."
>>
>> In that the 10 minutes is presumably from timestamp-based invalidation
>> chaining down from running tablegen, to then rebuilding everything that
>> depends on tablegen's output.
>>
>> That could be addressed by either the build system or tablegen writing
>> output to a temporary file, comparing the temp to the current file, and
not
>> modifying the current file if they're the same - thus not
invalidating
>> everything down the chain that depends on the tablegen output (not sure
if
>> that's actually enough to convince a build system not to rebuild
other
>> things - but worth a shot). This is a bit of a hackaround what the
build
>> system itself could/should be doing, but in the absence of a content
based
>> invalidation scheme - addressing this one particularly critical point
in
>> LLVM's build seems like it could be worth such a workaround. (this
would
>> speed up the build for even the times when tablegen's real
dependencies
>> change - add a new function to ArrayRef, or STLExtras, etc... and
tablegen
>> runs, but it doesn't cascade to everything else).
>>
>> (plus, opt build of tablegen, so that conclusion can be reached more
>> quickly)
>>
>> As Hal also mentioned, I'd be OK with this if there's a good
logical
>> division that can be taken more than "whatever is/isn't used
in tablegen".
>>
>>
>>>
>>> We've got a lot of random stuff in Support, not all really
related and
>>> not all relevant to every project. It seems like we should be able
to do
>>> better.
>>> On Fri, May 26, 2017 at 6:48 PM Hal Finkel <hfinkel at
anl.gov> wrote:
>>>
>>>>
>>>> On 05/26/2017 07:59 PM, Zachary Turner wrote:
>>>>
>>>> It's that TableGen depends on Support, so if you change one
file in
>>>> support, support gets recompiled into a new static archive,
which triggers
>>>> a rerun of tablegen on all the tablegen inputs, which is
extremely slow.
>>>>
>>>>
>>>> I thought that we had a "build an optimized tablegen even
in debug
>>>> mode" setting to work around this problem. Would that
avoid this problem?
>>>>
>>>>
>>>>  -Hal
>>>>
>>>>
>>>>
>>>> On Fri, May 26, 2017 at 5:56 PM Hal Finkel <hfinkel at
anl.gov> wrote:
>>>>
>>>>>
>>>>>
>>>>> On 05/26/2017 07:47 PM, Zachary Turner via llvm-dev wrote:
>>>>>
>>>>> Changing a header file somewhere and having to spend 10
minutes
>>>>> waiting for a build leads to a lot of wasted developer
time.
>>>>>
>>>>> The real culprit here is tablegen.  Can we split support
and ADT into
>>>>> two - the parts that tablegen depends on and the parts that
it doesn't?
>>>>>
>>>>>
>>>>> What's the actual problem here? Is it that TableGen
regenerates
>>>>> different files and so we then need to rebuild all
dependencies of those
>>>>> files? Maybe we should use a diff-and-update approach (I
thought, however,
>>>>> that we already did that).
>>>>>
>>>>>  -Hal
>>>>>
>>>>>
>>>>> From what I can gather, Tablegen currently depends on these
headers
>>>>> and all of their transitive dependencies.
>>>>>
>>>>> #include "llvm/Support/Casting.h"
>>>>> #include "llvm/Support/CommandLine.h"
>>>>> #include "llvm/Support/Compiler.h"
>>>>> #include "llvm/Support/DataTypes.h"
>>>>> #include "llvm/Support/Debug.h"
>>>>> #include "llvm/Support/Error.h"
>>>>> #include "llvm/Support/ErrorHandling.h"
>>>>> #include "llvm/Support/Format.h"
>>>>> #include "llvm/Support/FormattedStream.h"
>>>>> #include "llvm/Support/LEB128.h"
>>>>> #include "llvm/Support/LowLevelTypeImpl.h"
>>>>> #include "llvm/Support/ManagedStatic.h"
>>>>> #include "llvm/Support/MathExtras.h"
>>>>> #include "llvm/Support/MemoryBuffer.h"
>>>>> #include "llvm/Support/PrettyStackTrace.h"
>>>>> #include "llvm/Support/Regex.h"
>>>>> #include "llvm/Support/SMLoc.h"
>>>>> #include "llvm/Support/ScopedPrinter.h"
>>>>> #include "llvm/Support/Signals.h"
>>>>> #include "llvm/Support/SourceMgr.h"
>>>>> #include "llvm/Support/raw_ostream.h"
>>>>>
>>>>> #include "llvm/ADT/APInt.h"
>>>>> #include "llvm/ADT/ArrayRef.h"
>>>>> #include "llvm/ADT/BitVector.h"
>>>>> #include "llvm/ADT/CachedHashString.h"
>>>>> #include "llvm/ADT/DenseSet.h"
>>>>> #include "llvm/ADT/IndexedMap.h"
>>>>> #include "llvm/ADT/IntEqClasses.h"
>>>>> #include "llvm/ADT/MapVector.h"
>>>>> #include "llvm/ADT/Optional.h"
>>>>> #include "llvm/ADT/PointerUnion.h"
>>>>> #include "llvm/ADT/STLExtras.h"
>>>>> #include "llvm/ADT/SetVector.h"
>>>>> #include "llvm/ADT/SmallPtrSet.h"
>>>>> #include "llvm/ADT/SmallSet.h"
>>>>> #include "llvm/ADT/SmallVector.h"
>>>>> #include "llvm/ADT/SparseBitVector.h"
>>>>> #include "llvm/ADT/Statistic.h"
>>>>> #include "llvm/ADT/StringExtras.h"
>>>>> #include "llvm/ADT/StringMap.h"
>>>>> #include "llvm/ADT/StringRef.h"
>>>>> #include "llvm/ADT/StringSet.h"
>>>>> #include "llvm/ADT/StringSwitch.h"
>>>>> #include "llvm/ADT/TinyPtrVector.h"
>>>>> #include "llvm/ADT/Twine.h"
>>>>>
>>>>>
>>>>> Is this something worth putting effort into?  If so, I
volunteer.
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> LLVM Developers mailing listllvm-dev at
lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>
>>>>>
>>>>> --
>>>>> Hal Finkel
>>>>> Lead, Compiler Technology and Programming Languages
>>>>> Leadership Computing Facility
>>>>> Argonne National Laboratory
>>>>>
>>>>>
>>>> --
>>>> Hal Finkel
>>>> Lead, Compiler Technology and Programming Languages
>>>> Leadership Computing Facility
>>>> Argonne National Laboratory
>>>>
>>>> _______________________________________________
>>> 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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I think there are logical ways of splitting, but taken individually they
would be rather small. For example, threading support, i/o related support,
file system support.

At the same time, when you look at support there's kind of some glaringly
obvious differences in how "low level" the various things are.
Compiler.h
is pretty low level. Dwarf.h, not so much. It's hard to really quantify
this, but I could certainly imagine introducing something even more low
level than Support, perhaps with a name like Base
On Sat, May 27, 2017 at 12:55 PM David Blaikie <dblaikie at gmail.com>
wrote:
> Maybe we do and build systems aren't respecting/noticing this? I'm
not
> sure.
>
> On Sat, May 27, 2017 at 12:50 PM Craig Topper <craig.topper at
gmail.com>
> wrote:
>
>> I thought we already did write tablegen output to temporary files like
>> X86GenAsmWriter1.inc.tmp first and then diffed them with the real .inc
file
>> and conditionally copied.
>>
>> ~Craig
>>
>> On Sat, May 27, 2017 at 11:02 AM, David Blaikie via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>>
>>>
>>> On Fri, May 26, 2017 at 8:06 PM Zachary Turner via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> It would be better, because a debug tablegen is slower than an
>>>> optimized tablegen, but it's still slow and it doesn't
address the problem
>>>> that tablegen runs *at all* when it doesn't really need to.
I think if
>>>> tablegen wasn't running all the time we could incremental
builds down from
>>>> 15 minutes (and that's on my really powerful machine) to
under 5, which
>>>> seemed like a big productivity boost averaged out over all
users x time
>>>>
>>>
>>> Is that 10 minutes of running tablegen, though? I think this
touches on
>>> Hal's comment:
>>> "Maybe we should use a diff-and-update approach (I thought,
however,
>>> that we already did that)."
>>>
>>> In that the 10 minutes is presumably from timestamp-based
invalidation
>>> chaining down from running tablegen, to then rebuilding everything
that
>>> depends on tablegen's output.
>>>
>>> That could be addressed by either the build system or tablegen
writing
>>> output to a temporary file, comparing the temp to the current file,
and not
>>> modifying the current file if they're the same - thus not
invalidating
>>> everything down the chain that depends on the tablegen output (not
sure if
>>> that's actually enough to convince a build system not to
rebuild other
>>> things - but worth a shot). This is a bit of a hackaround what the
build
>>> system itself could/should be doing, but in the absence of a
content based
>>> invalidation scheme - addressing this one particularly critical
point in
>>> LLVM's build seems like it could be worth such a workaround.
(this would
>>> speed up the build for even the times when tablegen's real
dependencies
>>> change - add a new function to ArrayRef, or STLExtras, etc... and
tablegen
>>> runs, but it doesn't cascade to everything else).
>>>
>>> (plus, opt build of tablegen, so that conclusion can be reached
more
>>> quickly)
>>>
>>> As Hal also mentioned, I'd be OK with this if there's a
good logical
>>> division that can be taken more than "whatever is/isn't
used in tablegen".
>>>
>>>
>>>>
>>>> We've got a lot of random stuff in Support, not all really
related and
>>>> not all relevant to every project. It seems like we should be
able to do
>>>> better.
>>>> On Fri, May 26, 2017 at 6:48 PM Hal Finkel <hfinkel at
anl.gov> wrote:
>>>>
>>>>>
>>>>> On 05/26/2017 07:59 PM, Zachary Turner wrote:
>>>>>
>>>>> It's that TableGen depends on Support, so if you change
one file in
>>>>> support, support gets recompiled into a new static archive,
which triggers
>>>>> a rerun of tablegen on all the tablegen inputs, which is
extremely slow.
>>>>>
>>>>>
>>>>> I thought that we had a "build an optimized tablegen
even in debug
>>>>> mode" setting to work around this problem. Would that
avoid this problem?
>>>>>
>>>>>
>>>>>  -Hal
>>>>>
>>>>>
>>>>>
>>>>> On Fri, May 26, 2017 at 5:56 PM Hal Finkel <hfinkel at
anl.gov> wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>> On 05/26/2017 07:47 PM, Zachary Turner via llvm-dev
wrote:
>>>>>>
>>>>>> Changing a header file somewhere and having to spend 10
minutes
>>>>>> waiting for a build leads to a lot of wasted developer
time.
>>>>>>
>>>>>> The real culprit here is tablegen.  Can we split
support and ADT into
>>>>>> two - the parts that tablegen depends on and the parts
that it doesn't?
>>>>>>
>>>>>>
>>>>>> What's the actual problem here? Is it that TableGen
regenerates
>>>>>> different files and so we then need to rebuild all
dependencies of those
>>>>>> files? Maybe we should use a diff-and-update approach
(I thought, however,
>>>>>> that we already did that).
>>>>>>
>>>>>>  -Hal
>>>>>>
>>>>>>
>>>>>> From what I can gather, Tablegen currently depends on
these headers
>>>>>> and all of their transitive dependencies.
>>>>>>
>>>>>> #include "llvm/Support/Casting.h"
>>>>>> #include "llvm/Support/CommandLine.h"
>>>>>> #include "llvm/Support/Compiler.h"
>>>>>> #include "llvm/Support/DataTypes.h"
>>>>>> #include "llvm/Support/Debug.h"
>>>>>> #include "llvm/Support/Error.h"
>>>>>> #include "llvm/Support/ErrorHandling.h"
>>>>>> #include "llvm/Support/Format.h"
>>>>>> #include "llvm/Support/FormattedStream.h"
>>>>>> #include "llvm/Support/LEB128.h"
>>>>>> #include "llvm/Support/LowLevelTypeImpl.h"
>>>>>> #include "llvm/Support/ManagedStatic.h"
>>>>>> #include "llvm/Support/MathExtras.h"
>>>>>> #include "llvm/Support/MemoryBuffer.h"
>>>>>> #include "llvm/Support/PrettyStackTrace.h"
>>>>>> #include "llvm/Support/Regex.h"
>>>>>> #include "llvm/Support/SMLoc.h"
>>>>>> #include "llvm/Support/ScopedPrinter.h"
>>>>>> #include "llvm/Support/Signals.h"
>>>>>> #include "llvm/Support/SourceMgr.h"
>>>>>> #include "llvm/Support/raw_ostream.h"
>>>>>>
>>>>>> #include "llvm/ADT/APInt.h"
>>>>>> #include "llvm/ADT/ArrayRef.h"
>>>>>> #include "llvm/ADT/BitVector.h"
>>>>>> #include "llvm/ADT/CachedHashString.h"
>>>>>> #include "llvm/ADT/DenseSet.h"
>>>>>> #include "llvm/ADT/IndexedMap.h"
>>>>>> #include "llvm/ADT/IntEqClasses.h"
>>>>>> #include "llvm/ADT/MapVector.h"
>>>>>> #include "llvm/ADT/Optional.h"
>>>>>> #include "llvm/ADT/PointerUnion.h"
>>>>>> #include "llvm/ADT/STLExtras.h"
>>>>>> #include "llvm/ADT/SetVector.h"
>>>>>> #include "llvm/ADT/SmallPtrSet.h"
>>>>>> #include "llvm/ADT/SmallSet.h"
>>>>>> #include "llvm/ADT/SmallVector.h"
>>>>>> #include "llvm/ADT/SparseBitVector.h"
>>>>>> #include "llvm/ADT/Statistic.h"
>>>>>> #include "llvm/ADT/StringExtras.h"
>>>>>> #include "llvm/ADT/StringMap.h"
>>>>>> #include "llvm/ADT/StringRef.h"
>>>>>> #include "llvm/ADT/StringSet.h"
>>>>>> #include "llvm/ADT/StringSwitch.h"
>>>>>> #include "llvm/ADT/TinyPtrVector.h"
>>>>>> #include "llvm/ADT/Twine.h"
>>>>>>
>>>>>>
>>>>>> Is this something worth putting effort into?  If so, I
volunteer.
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing listllvm-dev at
lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Hal Finkel
>>>>>> Lead, Compiler Technology and Programming Languages
>>>>>> Leadership Computing Facility
>>>>>> Argonne National Laboratory
>>>>>>
>>>>>>
>>>>> --
>>>>> Hal Finkel
>>>>> Lead, Compiler Technology and Programming Languages
>>>>> Leadership Computing Facility
>>>>> Argonne National Laboratory
>>>>>
>>>>> _______________________________________________
>>>> 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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In my experience the buildsystem works fine in combination with tablegen (at
least this aspect of it). The real problem here is that tablegen is just slow.
Some of the X86 tables take indeed

Last time I looked at it tablegen had still room to optimize the way it resolves
class hierarchies and the variables within which it did basically one at a time,
so it needed to traverse the hierarchies again for each variables.
> On May 27, 2017, at 12:54 PM, David Blaikie via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Maybe we do and build systems aren't respecting/noticing this? I'm
not sure.
> 
> On Sat, May 27, 2017 at 12:50 PM Craig Topper <craig.topper at gmail.com
<mailto:craig.topper at gmail.com>> wrote:
> I thought we already did write tablegen output to temporary files like
X86GenAsmWriter1.inc.tmp first and then diffed them with the real .inc file and
conditionally copied.
> 
> ~Craig
> 
> On Sat, May 27, 2017 at 11:02 AM, David Blaikie via llvm-dev <llvm-dev
at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> 
> 
> On Fri, May 26, 2017 at 8:06 PM Zachary Turner via llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> It would be better, because a debug tablegen is slower than an optimized
tablegen, but it's still slow and it doesn't address the problem that
tablegen runs *at all* when it doesn't really need to. I think if tablegen
wasn't running all the time we could incremental builds down from 15 minutes
(and that's on my really powerful machine) to under 5, which seemed like a
big productivity boost averaged out over all users x time
> 
> Is that 10 minutes of running tablegen, though? I think this touches on
Hal's comment:
> "Maybe we should use a diff-and-update approach (I thought, however,
that we already did that)."
> 
> In that the 10 minutes is presumably from timestamp-based invalidation
chaining down from running tablegen, to then rebuilding everything that depends
on tablegen's output.
> 
> That could be addressed by either the build system or tablegen writing
output to a temporary file, comparing the temp to the current file, and not
modifying the current file if they're the same - thus not invalidating
everything down the chain that depends on the tablegen output (not sure if
that's actually enough to convince a build system not to rebuild other
things - but worth a shot). This is a bit of a hackaround what the build system
itself could/should be doing, but in the absence of a content based invalidation
scheme - addressing this one particularly critical point in LLVM's build
seems like it could be worth such a workaround. (this would speed up the build
for even the times when tablegen's real dependencies change - add a new
function to ArrayRef, or STLExtras, etc... and tablegen runs, but it doesn't
cascade to everything else).
> 
> (plus, opt build of tablegen, so that conclusion can be reached more
quickly)
> 
> As Hal also mentioned, I'd be OK with this if there's a good
logical division that can be taken more than "whatever is/isn't used in
tablegen".
>  
> 
> We've got a lot of random stuff in Support, not all really related and
not all relevant to every project. It seems like we should be able to do better.
> On Fri, May 26, 2017 at 6:48 PM Hal Finkel <hfinkel at anl.gov
<mailto:hfinkel at anl.gov>> wrote:
> 
> On 05/26/2017 07:59 PM, Zachary Turner wrote:
>> It's that TableGen depends on Support, so if you change one file in
support, support gets recompiled into a new static archive, which triggers a
rerun of tablegen on all the tablegen inputs, which is extremely slow.
> 
> I thought that we had a "build an optimized tablegen even in debug
mode" setting to work around this problem. Would that avoid this problem?
> 
> 
>  -Hal
> 
> 
>> 
>> On Fri, May 26, 2017 at 5:56 PM Hal Finkel <hfinkel at anl.gov
<mailto:hfinkel at anl.gov>> wrote:
>> 
>> 
>> On 05/26/2017 07:47 PM, Zachary Turner via llvm-dev wrote:
>>> Changing a header file somewhere and having to spend 10 minutes
waiting for a build leads to a lot of wasted developer time.
>>> 
>>> The real culprit here is tablegen.  Can we split support and ADT
into two - the parts that tablegen depends on and the parts that it doesn't?
>> 
>> What's the actual problem here? Is it that TableGen regenerates
different files and so we then need to rebuild all dependencies of those files?
Maybe we should use a diff-and-update approach (I thought, however, that we
already did that).
>> 
>>  -Hal
>> 
>>> 
>>> From what I can gather, Tablegen currently depends on these headers
and all of their transitive dependencies.
>>> 
>>> #include "llvm/Support/Casting.h"
>>> #include "llvm/Support/CommandLine.h"
>>> #include "llvm/Support/Compiler.h"
>>> #include "llvm/Support/DataTypes.h"
>>> #include "llvm/Support/Debug.h"
>>> #include "llvm/Support/Error.h"
>>> #include "llvm/Support/ErrorHandling.h"
>>> #include "llvm/Support/Format.h"
>>> #include "llvm/Support/FormattedStream.h"
>>> #include "llvm/Support/LEB128.h"
>>> #include "llvm/Support/LowLevelTypeImpl.h"
>>> #include "llvm/Support/ManagedStatic.h"
>>> #include "llvm/Support/MathExtras.h"
>>> #include "llvm/Support/MemoryBuffer.h"
>>> #include "llvm/Support/PrettyStackTrace.h"
>>> #include "llvm/Support/Regex.h"
>>> #include "llvm/Support/SMLoc.h"
>>> #include "llvm/Support/ScopedPrinter.h"
>>> #include "llvm/Support/Signals.h"
>>> #include "llvm/Support/SourceMgr.h"
>>> #include "llvm/Support/raw_ostream.h"
>>> 
>>> #include "llvm/ADT/APInt.h"
>>> #include "llvm/ADT/ArrayRef.h"
>>> #include "llvm/ADT/BitVector.h"
>>> #include "llvm/ADT/CachedHashString.h"
>>> #include "llvm/ADT/DenseSet.h"
>>> #include "llvm/ADT/IndexedMap.h"
>>> #include "llvm/ADT/IntEqClasses.h"
>>> #include "llvm/ADT/MapVector.h"
>>> #include "llvm/ADT/Optional.h"
>>> #include "llvm/ADT/PointerUnion.h"
>>> #include "llvm/ADT/STLExtras.h"
>>> #include "llvm/ADT/SetVector.h"
>>> #include "llvm/ADT/SmallPtrSet.h"
>>> #include "llvm/ADT/SmallSet.h"
>>> #include "llvm/ADT/SmallVector.h"
>>> #include "llvm/ADT/SparseBitVector.h"
>>> #include "llvm/ADT/Statistic.h"
>>> #include "llvm/ADT/StringExtras.h"
>>> #include "llvm/ADT/StringMap.h"
>>> #include "llvm/ADT/StringRef.h"
>>> #include "llvm/ADT/StringSet.h"
>>> #include "llvm/ADT/StringSwitch.h"
>>> #include "llvm/ADT/TinyPtrVector.h"
>>> #include "llvm/ADT/Twine.h"
>>> 
>>> 
>>> Is this something worth putting effort into?  If so, I volunteer.
>>> 
>>> 
>>> 
>> 
>>> _______________________________________________
>>> 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>
>> 
>> 
>>  -- 
>> Hal Finkel
>> Lead, Compiler Technology and Programming Languages
>> Leadership Computing Facility
>> Argonne National Laboratory
> 
> -- 
> Hal Finkel
> Lead, Compiler Technology and Programming Languages
> Leadership Computing Facility
> Argonne National Laboratory
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> 
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