[SCEV] Assume parameters coming from function calls contain IVs

[SCEV] Assume parameters coming from function calls contain IVs

The optimistic delinearization implemented in LLVM detects array sizes by
looking for non-linear products between parameters and induction variables.
In OpenCL code, such products often look like:

  A[get_global_id(0) * N + get_global_id(1)]

Hence, the IV is hidden in the get_global_id() call and consequently
delinearization would fail as no induction variable is available that helps
us to identify N as array size parameter.

We now use a very simple heuristic to change this. We assume that each parameter
that comes directly from a function call is a hidden induction variable. As
a result, we can delinearize the access above to:

  A[get_global_id(0)][get_global_id(1]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304073 91177308-0d34-0410-b5e6-96231b3b80d8