[LLVMdev] How to make Polly ignore some non-affine memory accesses

[Tobias Grosser]

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