[llvm-dev] Should we split llvm Support and ADT?

[Hal Finkel via llvm-dev]

On 05/26/2017 10:06 PM, Zachary Turner 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
>
> 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.

That certainly makes sense. I wonder, however, if we could have a more 
principled decomposition (instead of just "What's used by TableGen" vs. 
"What's not used by TableGen").

  -Hal

> 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
>>
>>         -- 
>>         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
>

-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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