Note the llvm/lib/Analysis/Delinearization.cpp recommends
See also llvm/lib/Analysis/DependenceAnalysis.cpp w/r the GEP operator.
Also note this 2015 paper:
On recovering multi-dimensional arrays in Polly
Tobias Grosser, Sebastian Pop, J. Ramanujam, P. Sadayappan
Impact2015 at HiPEAC, Amsterdam, The Netherlands
Slides & Paper: Impact 2015
Delinearization is useful, particularly when the code has been hand linearized,
as is often the case for C/C++. Nonetheless, information may be lost by lowering
multidimenional array references early. Consider:
float A[n1][n2], B[n2];
for (i = 0; i < ni; ++i)
for (j = 0; j < nj; ++j)
A[ix[i]][j] += B[j];
Even in C, the compiler may assume 0 <= j < n2.
In Fortran this is beyond dispute. But after linearization,
even with delinearization, the fact that nj <= n2 is not
known at compile time. If the subscripts to A where
interchange the situation is even worse, as 0 <= ix[i] < n2
is expensive to verify.
So delinearization provide a benefit w/r hand linearized subscripts,
while analysis of actual multidimensional references is best
done prior to linearization - before information is lost.