[LLVMdev] [Polly] Summary of some expensive compiler passes, especially PollyDependence

[Tobias Grosser]

On 08/08/2013 07:45 PM, Star Tan wrote:
> At 2013-08-09 10:20:46,"Tobias Grosser" <tobias at grosser.es> wrote:>On 08/08/2013 06:27 PM, Star Tan wrote:
>>>   At 2013-08-08 22:28:33,"Tobias Grosser" <tobias at grosser.es> wrote:
>>>>   On 08/08/2013 01:29 AM, Star Tan wrote:
>>>>>   Hi all,
>>>>>
>>>>>
>>>>>   I have summarized the top 10 compiler passes for Polly when compiling LLVM test-ssuite. Results can be viewed on:
>>>>>         https://gist.github.com/tanstar/581bcea1e4e03498f935/raw/f6a4ec4e8565f7a7bbdb924cd59fcf145caac039/Polly-top10
>>>>>
>>>>>
>>>>>   Based on the comparison between "clang -O3" and "polly -O3" listed on:
>>>>>         http://188.40.87.11:8000/db_default/v4/nts/18?compare_to=14&baseline=14
>>>>
>>>>   Please compare against clang -O3 -load LLVMPolly.so, otherwise
>>>>   especially the compile time of the small binaries includes the overhead
>>>>   of loading the Polly shared object file.
>>>
>>>   In fact, the compile-time overhead of loading Polly shared object file is very small (usually less than 1%). Their overhead can be viewed on:
>>>        http://188.40.87.11:8000/db_default/v4/nts/15?compare_to=14&baseline=14
>>
>> I see. Still, I think we should eliminate to remove another source of noise.
>
> Got it.  The comparison between Polly and "clang -O3 -load LLVMPolly.so" can be viewed on:
>     http://188.40.87.11:8000/db_default/v4/nts/18?compare_to=15&baseline=15

I see.

>>>>>   diff --git a/lib/Analysis/Dependences.cpp b/lib/Analysis/Dependences.cpp index 9f918f3..39c3fb6 100644 --- a/lib/Analysis/Dependences.cpp +++ b/lib/Analysis/Dependences.cpp @@ -95,6 +95,10 @@ void Dependences::calculateDependences(Scop &S) { collectInfo(S, &Read, &Write, &MayWrite, &Schedule); + Read = isl_union_map_coalesce(Read); + Write = isl_union_map_coalesce(Write); + MayWrite = isl_union_map_coalesce(MayWrite); + DEBUG(dbgs() << "Read: " << Read << "\n"
>>>>
>>>>   This patch is unreadable in the mail. However, the one you submitted
>>>>   looked good and was committed.
>>>>
>>>>>   With this patch file, we can reduce the compile-time percentage of PollyDependence from 98.5% to 15.3%. Unfortunately, the compile-time percentage of PollyDependence for benchmarks, such as "nestedloop", is still very high.
>>>>
>>>>   It would be good to get an up-to-date comparison with the latest patch
>>>>   having gone into Polly.
>>>
>>>   Yes, you can view the comparison on:
>>>        http://188.40.87.11:8000/db_default/v4/nts/26?compare_to=25&baseline=25
>>
>> I am slightly confused. What are we comparing here? It seems we compare
>> a PollyScopInfo run with a PollyDependences run (same source code?) and
>> the Dependences run shows compile time speedup over ScopInfo? This is
>> surprising.
>
> In fact, there are three runs:
>
> pollyOpt (run id = 18): the baseline of Polly
> pollyScopInfo (run id = 25): Polly with the ScopInfo patch r187728 that split start value from SCEVAddRecExpr
> pollyDependence (run id = 26): Polly with both ScopInfo patch r187728 and PollyDependence patch r187981 that simplify the Read/Write/MayWrite before feeding them into ISL.
>
> As a result, I compare pollyDependence (run id = 26) with pollyScopInfo (run id = 25) to see the impact of our ScopDependence patch r187981.  Their only difference is the ScopDependence patch file.

I see. I did not realize that all those runs have been performed with 
'-O3 -polly'. Now it makes sense.

If you happen to not use the tester machine right now, it would be 
interesting to schedule runs that give us the current state of Polly 
performance. Meaning pollyBasic, pollyNoGen, pollyNoOpt and pollyOpt for 
the latest version of Polly.

Cheers,
Tobi