search for: delinearisation

...TERNAL] Re: [llvm-dev] Delinearization validity checks in DependenceAnalysis Hello Interestingly, the example you provide works for me so long as either it's a 32bit target, or the array bounds (n and m) are changed to unsigned. For a bit of history, DA used to have a different delinearisation method based on geps, but it was known to be invalid in same cases and was eventually removed. There was no delinearisation for a while until these checks were fixed, enough to be correct, but not as powerful as they could be. I believe Pollys delinearisation is much more powerful, and can version...

...ecks in >             DependenceAnalysis > > > > Hello > > Interestingly, the example you provide works for me so long as either it's > a 32bit target, or the array bounds (n and m) are changed to unsigned. > > For a bit of history, DA used to have a different delinearisation method > based on geps, but it was known to be invalid in same cases and was > eventually removed. There was no delinearisation for a while until these > checks were fixed, enough to be correct, but not as powerful as they could > be. I believe Pollys delinearisation is much more powerf...

Hi all, I have been looking at the `DependenceAnalysis` pass in `llvm/include/llvm/Analysis/DependenceAnalysis.h`. In order for this analysis to produce accurate dependence vectors for multi-dimensional arrays in nested loops, it needs to "delinearize" array element accesses to recover the subscripts in each dimension of the array. I believe that the current implementation of

Hello Yes, I agree that the SCEV cannot be simplified. Is my understanding correct that it is passed to a function like "isKnownNegative"? Which could still be able to prove is always true. The delinearisation may be valid, depending on exactly how you define delinearisation (under what conditions it should be giving results). It would be invalid for DA to return a dependency of [0 >] though. The code is perfectly valid from the C or llvm-ir specifications and we can't change the meaning of it jus...

...it. > As we are speaking about modifying the lib, here are two things I would like to modify/add in it: - Replacing depedency expressions from direction vector to a polyhedral representation. The representation can then be easily converted to DV for those who only care about them. - Supporting delinearisation.

...d implementing the logic for isa, cast and dyn_cast. - Provide some constructors to build a dependence type from a less precise one. This does not scale well with the number of type to maintain. But as long as there is few types (3 so far) this is maintainable. > >> >> - Supporting delinearisation. > > >I think this should be a separate pass. I agree. It should be an analysis pass queried by the dependence analysis as a fall back whenever all the dependence tests from the other indexes were non-conclusive. --Matthieu