Marcello Maggioni
2011-Nov-21 11:44 UTC
[LLVMdev] How to make Polly ignore some non-affine memory accesses
2011/11/21 Tobias Grosser <tobias at grosser.es>:> On 11/20/2011 04:36 PM, Marcello Maggioni wrote: >> >> Sorry for the noobish question, but what kind of subscripts generate a >> SCEVCouldNotCompute from the SCEV engine? >> I tried for a while but I wasn't able to trigger that > > Hi Marcello, > > the SCEV returns SCEVCouldNotCompute in case it cannot analyze an expression > or if the analysis would be to complicated. I am currently > not sure if this may actually happen when calling getSCEV(), because > getSCEV() could just return a SCEVUnknown referencing the Value itself. > Maybe SCEVCouldNotCompute is just generated by functions like > SE->getBackedgeTakenCount()? > > In case you cannot generate a test case that yields to this, I don't think > there is a need to try more. Even without such a test case the patch should > be OK. > > Cheers > Tobi >Ok, thanks, I'll try other test cases to check if everything is ok, better being sure. About SCOPs with a "bitcast instruction" inside them I see that ScopDetection discards those. What problems can cause bitcasts to the Scop? Is it related to aliasing? Marcello
Tobias Grosser
2011-Nov-21 11:55 UTC
[LLVMdev] How to make Polly ignore some non-affine memory accesses
On 11/21/2011 03:44 AM, Marcello Maggioni wrote:> 2011/11/21 Tobias Grosser<tobias at grosser.es>: >> On 11/20/2011 04:36 PM, Marcello Maggioni wrote: >>> >>> Sorry for the noobish question, but what kind of subscripts generate a >>> SCEVCouldNotCompute from the SCEV engine? >>> I tried for a while but I wasn't able to trigger that >> >> Hi Marcello, >> >> the SCEV returns SCEVCouldNotCompute in case it cannot analyze an expression >> or if the analysis would be to complicated. I am currently >> not sure if this may actually happen when calling getSCEV(), because >> getSCEV() could just return a SCEVUnknown referencing the Value itself. >> Maybe SCEVCouldNotCompute is just generated by functions like >> SE->getBackedgeTakenCount()? >> >> In case you cannot generate a test case that yields to this, I don't think >> there is a need to try more. Even without such a test case the patch should >> be OK. >> >> Cheers >> Tobi >> > > Ok, thanks, I'll try other test cases to check if everything is ok, > better being sure. > > About SCOPs with a "bitcast instruction" inside them I see that > ScopDetection discards those. > What problems can cause bitcasts to the Scop? Is it related to aliasing?I don't know. At the moment I wrote the scop detection I was not sure that they don't cause any problems, so I conservatively discarded them. Meanwhile I actually believe the don't introduce any problems and could be allowed. However, before changing this, I would like to set up a nightly tester that ensures the llvm test suite is compiled correctly. This would allow us to understand if the support for this construct introduces any regressions. Cheers Tobi
Tobias Grosser
2011-Dec-04 10:42 UTC
[LLVMdev] How to make Polly ignore some non-affine memory accesses
On 11/21/2011 12:44 PM, Marcello Maggioni wrote:> 2011/11/21 Tobias Grosser<tobias at grosser.es>: >> On 11/20/2011 04:36 PM, Marcello Maggioni wrote: >>> >>> Sorry for the noobish question, but what kind of subscripts generate a >>> SCEVCouldNotCompute from the SCEV engine? >>> I tried for a while but I wasn't able to trigger that >> >> Hi Marcello, >> >> the SCEV returns SCEVCouldNotCompute in case it cannot analyze an expression >> or if the analysis would be to complicated. I am currently >> not sure if this may actually happen when calling getSCEV(), because >> getSCEV() could just return a SCEVUnknown referencing the Value itself. >> Maybe SCEVCouldNotCompute is just generated by functions like >> SE->getBackedgeTakenCount()? >> >> In case you cannot generate a test case that yields to this, I don't think >> there is a need to try more. Even without such a test case the patch should >> be OK. >> >> Cheers >> Tobi >> > > Ok, thanks, I'll try other test cases to check if everything is ok, > better being sure.Hi Marcello, any news here? I would love to commit your patch. Do you happen to have a final version ready? Cheers Tobi
Marcello Maggioni
2011-Dec-15 14:41 UTC
[LLVMdev] How to make Polly ignore some non-affine memory accesses
Hi, sorry for the late response. I've been away for a week and after that probably I missed your email (considering the high amount of mails that come from LLVMDev :p ) Anyway, now it's just a matter of checking the code , I'm finalizing a test and after that (a couple of days) I'll post the patch hoping everything is ok :) Thank you Marcello 2011/12/4 Tobias Grosser <tobias at grosser.es>:> On 11/21/2011 12:44 PM, Marcello Maggioni wrote: >> >> 2011/11/21 Tobias Grosser<tobias at grosser.es>: >>> >>> On 11/20/2011 04:36 PM, Marcello Maggioni wrote: >>>> >>>> >>>> Sorry for the noobish question, but what kind of subscripts generate a >>>> SCEVCouldNotCompute from the SCEV engine? >>>> I tried for a while but I wasn't able to trigger that >>> >>> >>> Hi Marcello, >>> >>> the SCEV returns SCEVCouldNotCompute in case it cannot analyze an >>> expression >>> or if the analysis would be to complicated. I am currently >>> not sure if this may actually happen when calling getSCEV(), because >>> getSCEV() could just return a SCEVUnknown referencing the Value itself. >>> Maybe SCEVCouldNotCompute is just generated by functions like >>> SE->getBackedgeTakenCount()? >>> >>> In case you cannot generate a test case that yields to this, I don't >>> think >>> there is a need to try more. Even without such a test case the patch >>> should >>> be OK. >>> >>> Cheers >>> Tobi >>> >> >> Ok, thanks, I'll try other test cases to check if everything is ok, >> better being sure. > > > Hi Marcello, > > any news here? I would love to commit your patch. Do you happen to have a > final version ready? > > Cheers > Tobi >
Marcello Maggioni
2011-Dec-20 15:39 UTC
[LLVMdev] How to make Polly ignore some non-affine memory accesses
Perfect! :) Thank you for all the help! Marcello 2011/12/20 Tobias Grosser <tobias at grosser.es>:> On 12/19/2011 05:45 PM, Marcello Maggioni wrote: >> >> Hi, here the latest version of the patch. >> >> Sorry for the wait :) > > > Thanks a lot. The patch looked good. I added some last style changes, but > nothing big (80 columns violation and adding an early exit). > > I pushed the change out to Polly. > > Cheers > Tobi
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