[llvm] [DA] Replace delinearization for fixed size array (PR #161822)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

> > Removing `getIndexExpressionsFromGEP` is a bit tricky since Polly also uses it...
> 
> I can take care of that. The work there is that 49 tests assume GEP delinierization

Great, thanks. The function corresponding to `getIndexExpressionsFromGEP` would be `findFixedSizeArrayDimensions`, which I previously added to eliminate array size estimation based on GEP.
JFYI about `findFixedSizeArrayDimensions`: I'm not familiar with the details of Polly, but this function is fairly minimal and may not be sufficient for Polly's use cases. As far as I can tell, it doesn't handle triangular loops well. Additionally, cases where loop ranges depend on the induction variables of outer loops likely won't work either.

https://github.com/llvm/llvm-project/pull/161822